Materials

Open AccessEditor’s ChoiceArticle

Mechanistic Study of Fast Performance Decay of PtCu Alloy-based Catalyst Layers for Polymer Electrolyte Fuel Cells through Electrochemical Impedance Spectroscopy

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Materials 2023, 16(9), 3544; https://doi.org/10.3390/ma16093544 - 05 May 2023

Viewed by 577

Abstract

In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during [...] Read more.

In the past, platinum–copper catalysts have proven to be highly active for the oxygen reduction reaction (ORR), but transferring the high activities measured in thin-film rotating disk electrodes (TF-RDEs) to high-performing membrane electrode assemblies (MEAs) has proven difficult due to stability issues during operation. High initial performance can be achieved. However, fast performance decay on a timescale of 24 h is induced by repeated voltage load steps with H₂/air supplied. This performance decay is accelerated if high relative humidity (>60% RH) is set for a prolonged time and low voltages are applied during polarization. The reasons and possible solutions for this issue have been investigated by means of electrochemical impedance spectroscopy and distribution of relaxation time analysis (EIS–DRT). The affected electrochemical sub-processes have been identified by comparing the PtCu electrocatalyst with commercial Pt/C benchmark materials in homemade catalyst-coated membranes (CCMs). The proton transport resistance (R_pt) increased by a factor of ~2 compared to the benchmark materials. These results provide important insight into the challenges encountered with the de-alloyed PtCu/KB electrocatalyst during cell break-in and operation. This provides a basis for improvements in the catalysts’ design and break-in procedures for the highly attractive PtCu/KB catalyst system. Full article

(This article belongs to the Special Issue Novel Materials for Green Hydrogen Production, Energy Conversion, and Fuel Cell Applications)

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Open AccessEditor’s ChoiceArticle

Understanding Chloride Diffusion Coefficient in Cementitious Materials

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Zhiyuan Xu

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Guang Ye

Materials 2023, 16(9), 3464; https://doi.org/10.3390/ma16093464 - 29 Apr 2023

Viewed by 504

Abstract

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination [...] Read more.

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. Full article

(This article belongs to the Collection Concrete and Building Materials)

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Open AccessEditor’s ChoiceArticle

GAM: General Auxetic Metamaterial with Tunable 3D Auxetic Behavior Using the Same Unit Cell Boundary Connectivity

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Ismael Ben-Yelun

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Guillermo Gómez-Carano

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Francisco J. San Millán

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Miguel Ángel Sanz

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Francisco Javier Montáns

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Luis Saucedo-Mora

Materials 2023, 16(9), 3473; https://doi.org/10.3390/ma16093473 - 29 Apr 2023

Viewed by 584

Abstract

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the [...] Read more.

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the effect, (2) coupling and combining auxetic metamaterials with non-auxetic materials due to boundary compatibility, (3) obtaining the same auxetic behavior in all directions in the transverse plane, and (4) adapting the regular geometry to the component design boundary and shape. The goal of this paper is to present a novel, recently patented tunable 3D metamaterial created to reproduce a wide spectrum of 3D auxetic and non-auxetic Poisson’s ratios and Young’s moduli. This wide range is obtained using the same basic unit cell geometry and boundary connections with neighboring cells, facilitating designs using functionally graded metamaterials as only the connectivity and position of the cell’s internal nodes are modified. Based on simple spatial triangularization, the metamaterial is easily scalable and better accommodates spatial curvatures or boundaries by changing the locations of nodes and lengths of bars. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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Open AccessEditor’s ChoiceArticle

CFD–PBM Simulation for Continuous Hydrothermal Flow Synthesis of Zirconia Nanoparticles in a Confined Impinging Jet Reactor

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Qingyun Li

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Zihua Wang

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Xuezhong Wang

Materials 2023, 16(9), 3421; https://doi.org/10.3390/ma16093421 - 27 Apr 2023

Viewed by 489

Abstract

Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and [...] Read more.

Computational fluid dynamics (CFD) and population balance models (PBM) were coupled together for the first time to simulate the synthesis of zirconia nanoparticles in a continuous hydrothermal flow synthesis (CHFS) system with a self-designed confined impinging jet mixing (CJM) reactor. The hydrodynamic and thermodynamic behaviors within the CJM reactor strongly influenced the formation of the ZrO₂ nanoparticles. Crucial parameters, such as velocities, temperatures, mixing conditions, and reaction rates, were analyzed under various supercritical conditions. Temperature and velocity measurements as functions of distance were also investigated. Normal particle size distribution (PSD) patterns were observed in all cases. The mean particle sizes in this study were calculated and compared using PBM aggregation analysis. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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Open AccessEditor’s ChoiceReview

Synthesis Methods and Optical Sensing Applications of Plasmonic Metal Nanoparticles Made from Rhodium, Platinum, Gold, or Silver

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Elizaveta Demishkevich

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Materials 2023, 16(9), 3342; https://doi.org/10.3390/ma16093342 - 24 Apr 2023

Viewed by 664

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The purpose of this paper is to provide an in-depth review of plasmonic metal nanoparticles made from rhodium, platinum, gold, or silver. We describe fundamental concepts, synthesis methods, and optical sensing applications of these nanoparticles. Plasmonic metal nanoparticles have received a lot of [...] Read more.

The purpose of this paper is to provide an in-depth review of plasmonic metal nanoparticles made from rhodium, platinum, gold, or silver. We describe fundamental concepts, synthesis methods, and optical sensing applications of these nanoparticles. Plasmonic metal nanoparticles have received a lot of interest due to various applications, such as optical sensors, single-molecule detection, single-cell detection, pathogen detection, environmental contaminant monitoring, cancer diagnostics, biomedicine, and food and health safety monitoring. They provide a promising platform for highly sensitive detection of various analytes. Due to strongly localized optical fields in the hot-spot region near metal nanoparticles, they have the potential for plasmon-enhanced optical sensing applications, including metal-enhanced fluorescence (MEF), surface-enhanced Raman scattering (SERS), and biomedical imaging. We explain the plasmonic enhancement through electromagnetic theory and confirm it with finite-difference time-domain numerical simulations. Moreover, we examine how the localized surface plasmon resonance effects of gold and silver nanoparticles have been utilized for the detection and biosensing of various analytes. Specifically, we discuss the syntheses and applications of rhodium and platinum nanoparticles for the UV plasmonics such as UV-MEF and UV-SERS. Finally, we provide an overview of chemical, physical, and green methods for synthesizing these nanoparticles. We hope that this paper will promote further interest in the optical sensing applications of plasmonic metal nanoparticles in the UV and visible ranges. Full article

(This article belongs to the Special Issue Advances in Metal-Based Nanoparticles)

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Open AccessEditor’s ChoiceArticle

Ferroelectricity and Oxide Reliability of Stacked Hafnium–Zirconium Oxide Devices

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Materials 2023, 16(9), 3306; https://doi.org/10.3390/ma16093306 - 23 Apr 2023

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In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked [...] Read more.

In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked HfZrO films not only exhibited excellent ferroelectricity but also demonstrated a high performance on reliability. The optimized condition of the 45% Zr proportion exhibited a robust ferroelectric polarization value of 32.57 μC/cm², and a polarization current with a peak value of 159.98 μA. Besides this, the ferroelectric stacked HfZrO also demonstrated good reliability with a ten-year lifetime under >−2 V constant voltage stress. Therefore, the appropriate modulation of zirconium proportion in stacked HfZrO showed great promise for integrating in high-performance ferroelectric memory. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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Open AccessEditor’s ChoiceArticle

Influence of Calcination Temperature and Amount of Low-Grade Clay Replacement on Mitigation of the Alkali–Silica Reaction

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Daria Jóźwiak-Niedźwiedzka

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Materials 2023, 16(8), 3210; https://doi.org/10.3390/ma16083210 - 19 Apr 2023

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Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al₂O₃ content equal to 26% and SiO₂—58% was used. The calcination temperatures were as follows: 650 °C, [...] Read more.

Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al₂O₃ content equal to 26% and SiO₂—58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na₂O_eq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay. Full article

(This article belongs to the Special Issue Building Materials Engineering and Innovative Sustainable Materials)

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Open AccessEditor’s ChoiceReview

Principles and Applications of Resonance Energy Transfer Involving Noble Metallic Nanoparticles

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Materials 2023, 16(8), 3083; https://doi.org/10.3390/ma16083083 - 13 Apr 2023

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Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, [...] Read more.

Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Laser Micro/Nanostructuring and Synthesis of Micro/Nanomaterials)

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Open AccessEditor’s ChoiceArticle

Band Gaps and Optical Properties of RENiO₃ upon Strain: Combining First-Principles Calculations and Machine Learning

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Xuchang Tang

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Zhaokai Luo

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Yuanyuan Cui

Materials 2023, 16(8), 3070; https://doi.org/10.3390/ma16083070 - 13 Apr 2023

Viewed by 582

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Rare earth nickel-based perovskite oxides (RENiO₃) have been widely studied over recent decades because of their unique properties. In the synthesis of RENiO₃ thin films, a lattice mismatch frequently exists between the substrates and the thin films, [...] Read more.

Rare earth nickel-based perovskite oxides (RENiO₃) have been widely studied over recent decades because of their unique properties. In the synthesis of RENiO₃ thin films, a lattice mismatch frequently exists between the substrates and the thin films, which may affect the optical properties of RENiO₃. In this paper, the first-principles calculations were employed to study the electronic and optical properties of RENiO₃ under strain. The results showed that with the increase in tensile strength, the band gap generally shows a widening trend. For optical properties, the absorption coefficients increase with the enhancement of photon energies in the far-infrared range. The compressive strain increases the light absorption, while the tensile strain suppresses it. For the reflectivity spectrum in the far-infrared range, a minimum reflectivity displays around the photon energy of 0.3 eV. The tensile strain enhances the reflectivity in the range of 0.05–0.3 eV, whereas it decreases it when the photon energies are larger than 0.3 eV. Furthermore, machine learning algorithms were applied and found that the planar epitaxial strain, electronegativity, volume of supercells, and rare earth element ion radius play key roles in the band gaps. Photon energy, electronegativity, band gap, the ionic radius of the rare earth element, and the tolerance factor are key parameters significantly influencing the optical properties. Full article

(This article belongs to the Section Materials Simulation and Design)

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Open AccessEditor’s ChoiceArticle

Adsorption Tuning of Polarity and Magnetism in AgCr₂S₄ Monolayer

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Materials 2023, 16(8), 3058; https://doi.org/10.3390/ma16083058 - 12 Apr 2023

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As a recent successfully exfoliated non-van der Waals layered material, AgCrS₂ has received a lot of attention. Motivated by its structure-related magnetic and ferroelectric behavior, a theoretical study on its exfoliated monolayer AgCr₂S₄ has been carried out in the [...] Read more.

As a recent successfully exfoliated non-van der Waals layered material, AgCrS₂ has received a lot of attention. Motivated by its structure-related magnetic and ferroelectric behavior, a theoretical study on its exfoliated monolayer AgCr₂S₄ has been carried out in the present work. Based on density functional theory, the ground state and magnetic order of monolayer AgCr₂S₄ have been determined. The centrosymmetry emerges upon two-dimensional confinement and thus eliminates the bulk polarity. Moreover, two-dimensional ferromagnetism appears in the CrS₂ layer of AgCr₂S₄ and can persist up to room temperature. The surface adsorption has also been taken into consideration, which shows a nonmonotonic effect on the ionic conductivity through ion displacement of the interlayer Ag, but has little impact on the layered magnetic structure. Full article

(This article belongs to the Special Issue First-Principles Calculations of 2D Magnetic Materials)

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Open AccessEditor’s ChoiceArticle

On the Springback and Load in Three-Point Air Bending of the AW-2024 Aluminium Alloy Sheet with AW-1050A Aluminium Cladding

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Stanisław Kut

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Grzegorz Pasowicz

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Feliks Stachowicz

Materials 2023, 16(8), 2945; https://doi.org/10.3390/ma16082945 - 07 Apr 2023

Viewed by 589

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This article presents the results of an analysis of the bending load characteristics and the springback phenomenon occurring during three-point bending of 1.0 and 2.0 mm thick AW-2024 aluminium alloy sheets with rolled AW-1050A cladding. A new proprietary equation was proposed for determining [...] Read more.

This article presents the results of an analysis of the bending load characteristics and the springback phenomenon occurring during three-point bending of 1.0 and 2.0 mm thick AW-2024 aluminium alloy sheets with rolled AW-1050A cladding. A new proprietary equation was proposed for determining the bending angle as a function of deflection, which takes into account the influence of the tool radius and the sheet thickness. The experimentally determined springback and bending load characteristics were compared with the results of numerical modelling using different models: Model I, a 2D model for a plane deformation state, disregarding the material properties of the clad layers; Model II, a 2D model for a plane deformation state, taking into account the material properties of the cladding layers; Model III, a 3D shell model with the Huber–von Mises isotropic plasticity condition; Model IV, a 3D shell model with the Hill anisotropic plasticity condition; and Model V, a 3D shell model with the Barlat anisotropic plasticity condition. The effectiveness of these five tested FEM models in predicting the bending load and springback characteristics was demonstrated. Model II was the most effective in predicting bending load, while Model III was the most effective in predicting the amount of springback after bending. Full article

(This article belongs to the Special Issue Technologies for Joining and Forming Thin-Walled Structures in the Construction of Transportation Vehicles)

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Open AccessEditor’s ChoiceArticle

The Influence of Mg-Impurities in Raw Materials on the Synthesis of Rankinite Clinker and the Strength of Mortar Hardening in CO₂ Environment

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Raimundas Siauciunas

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Edita Prichockiene

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Zenonas Valancius

Materials 2023, 16(7), 2930; https://doi.org/10.3390/ma16072930 - 06 Apr 2023

Viewed by 635

Abstract

The idea of this work is to reduce the negative effect of ordinary Portland cement (OPC) manufacture on the environment by decreasing clinker production temperature and developing an alternative rankinite binder that hardens in the CO₂ atmosphere. The common OPC raw materials, [...] Read more.

The idea of this work is to reduce the negative effect of ordinary Portland cement (OPC) manufacture on the environment by decreasing clinker production temperature and developing an alternative rankinite binder that hardens in the CO₂ atmosphere. The common OPC raw materials, limestone and mica clay, if they contain a higher MgO content, have been found to be unsuitable for the synthesis of CO₂-curing low-lime binders. X-ray diffraction analysis (ex-situ and in-situ in the temperature range of 25–1150 °C) showed that akermanite Ca₂Mg(Si₂O₇) begins to form at a temperature of 900 °C. According to Rietveld refinement, the interlayer distances of the resulting curve are more accurately described by the compound, which contains intercalated Fe²⁺ and Al³⁺ ions and has the chemical formula Ca₂(MgO_0.495·FeO_0.202·AlO_0.303)·(FeO_0.248·AlO·Si_1.536·O₇). Stoichiometric calculations showed that FeO and Al₂O₃ have replaced about half of the MgO content in the akermanite structure. All this means that only ~4 wt% MgO content in the raw materials determines that ~60 wt% calcium magnesium silicates are formed in the synthesis product. Moreover, it was found that the formed akermanite practically does not react with CO₂. Within 24 h of interaction with 99.9 wt% of CO₂ gas (15 bar), the intensity of the akermanite peaks does not practically change at 25 °C; no changes are observed at 45 °C, either, which means that the chemical reaction does not take place. As a result, the compressive strength of the samples compressed from the synthesized product and CEN Standard sand EN 196-1 (1:3), and hardened at 15 bar CO₂, 45 °C for 24 h, was only 14.45 MPa, while the analogous samples made from OPC clinker obtained from the same raw materials yielded 67.5 MPa. Full article

(This article belongs to the Special Issue Advances in Sustainable Civil Engineering Materials)

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Open AccessEditor’s ChoiceArticle

Negative Magnetoresistance in Hopping Regime of Lightly Doped Thermoelectric SnSe

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Materials 2023, 16(7), 2863; https://doi.org/10.3390/ma16072863 - 04 Apr 2023

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Semiconducting SnSe, an analog of black phosphorus, recently attracted great scientific interest due to a disputed report of a large thermoelectric figure of merit, which has not been reproduced subsequently. Here we concentrate on the low-temperature ground state. To gain a better understanding [...] Read more.

Semiconducting SnSe, an analog of black phosphorus, recently attracted great scientific interest due to a disputed report of a large thermoelectric figure of merit, which has not been reproduced subsequently. Here we concentrate on the low-temperature ground state. To gain a better understanding of the system, we present magneto-transport properties in high-quality single crystals of as-grown, lightly doped SnSe down to liquid helium temperatures. We show that SnSe behaves as a p-type doped semiconductor in the vicinity of a metal-insulator transition. Electronic transport at the lowest temperatures is dominated by the hopping mechanism. Negative magnetoresistance at low fields is well described by antilocalization, while positive magnetoresistance at higher fields is consistent with the shrinkage of localized impurity wavefunctions. At higher temperatures, a dilute metallic regime is realized where elusive T² and B² resistivity dependence is observed, posing a challenge to theoretical comprehension of the underlying physical mechanism. Full article

(This article belongs to the Special Issue New Insights into Metal–Insulator Transitions)

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Open AccessEditor’s ChoiceArticle

A Bond-Based Peridynamic Model with Matrix Plasticity for Impact Damage Analysis of Composite Materials

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Materials 2023, 16(7), 2884; https://doi.org/10.3390/ma16072884 - 04 Apr 2023

Viewed by 490

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The prediction of damage and failure to fiber-reinforced polymer composites in extreme environments, particularly when subjected to impact loading, is a crucial issue for the application and design of protective structures. In this paper, based on the prototype microelastic brittle (PMB) model and [...] Read more.

The prediction of damage and failure to fiber-reinforced polymer composites in extreme environments, particularly when subjected to impact loading, is a crucial issue for the application and design of protective structures. In this paper, based on the prototype microelastic brittle (PMB) model and the LaRC05 composite materials failure model, we proposed a bond-based peridynamic (BB-PD) model with the introduction of plastic hardening of the resin matrix for fiber-reinforced polymer composites. The PD constitutive relationships of the matrix bond and interlayer bond under compressive loading are considered to include two stages of linear elasticity and plastic hardening, according to the stress–strain relationship of the resin matrix in the LaRC05 failure model. The proposed PD model is employed to simulate the damage behaviors of laminated composites subjected to impact loading. The corresponding ballistic impact tests of composite laminates were carried out to observe their damage behaviors. The PD prediction results are in good agreement with the ballistic experimental results, which can verify the correctness and accuracy of the PD model developed in this study in describing the impact damage behaviors of composite materials. In addition, the characteristics and degree of damage in composite laminates are analyzed and discussed based on this PD model. The difference in the impact resistance of composite laminates with different stacking sequences is also studied using the numerical simulation results. Full article

(This article belongs to the Special Issue Computational Fracture and Damage Modeling of Engineered Materials)

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Open AccessEditor’s ChoiceReview

Semiconductor Characterization by Terahertz Excitation Spectroscopy

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Arūnas Krotkus

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Ignas Nevinskas

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Ričardas Norkus

Materials 2023, 16(7), 2859; https://doi.org/10.3390/ma16072859 - 03 Apr 2023

Viewed by 635

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Surfaces of semiconducting materials excited by femtosecond laser pulses emit electromagnetic waves in the terahertz (THz) frequency range, which by definition is the 0.1–10 THz region. The nature of terahertz radiation pulses is, in the majority of cases, explained by the appearance of [...] Read more.

Surfaces of semiconducting materials excited by femtosecond laser pulses emit electromagnetic waves in the terahertz (THz) frequency range, which by definition is the 0.1–10 THz region. The nature of terahertz radiation pulses is, in the majority of cases, explained by the appearance of ultrafast photocurrents. THz pulse duration is comparable with the photocarrier momentum relaxation time, thus such hot-carrier effects as the velocity overshoot, ballistic carrier motion, and optical carrier alignment must be taken into consideration when explaining experimental observations of terahertz emission. Novel commercially available tools such as optical parametric amplifiers that are capable of generating femtosecond optical pulses within a wide spectral range allow performing new unique experiments. By exciting semiconductor surfaces with various photon energies, it is possible to look into the ultrafast processes taking place at different electron energy levels of the investigated materials. The experimental technique known as the THz excitation spectroscopy (TES) can be used as a contactless method to study the band structure and investigate the ultrafast processes of various technologically important materials. A recent decade of investigations with the THz excitation spectroscopy method is reviewed in this article. TES experiments performed on the common bulk A3B5 compounds such as the wide-gap GaAs, and narrow-gap InAs and InSb, as well as Ge, Te, GaSe and other bulk semiconductors are reviewed. Finally, the results obtained by this non-contact technique on low-dimensional materials such as ultrathin mono-elemental Bi films, InAs, InGaAs, and GaAs nanowires are also presented. Full article

(This article belongs to the Special Issue Laser and Plasma Technologies in Materials Science: Physics and Applications)

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Open AccessEditor’s ChoiceReview

Recent Advances of Indium Oxide-Based Catalysts for CO₂ Hydrogenation to Methanol: Experimental and Theoretical

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Materials 2023, 16(7), 2803; https://doi.org/10.3390/ma16072803 - 31 Mar 2023

Viewed by 1138

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Methanol synthesis from the hydrogenation of carbon dioxide (CO₂) with green H₂ has been proven as a promising method for CO₂ utilization. Among the various catalysts, indium oxide (In₂O₃)-based catalysts received tremendous research interest due [...] Read more.

Methanol synthesis from the hydrogenation of carbon dioxide (CO₂) with green H₂ has been proven as a promising method for CO₂ utilization. Among the various catalysts, indium oxide (In₂O₃)-based catalysts received tremendous research interest due to the excellent methanol selectivity with appreciable CO₂ conversion. Herein, the recent experimental and theoretical studies on In₂O₃-based catalysts for thermochemical CO₂ hydrogenation to methanol were systematically reviewed. It can be found that a variety of steps, such as the synthesis method and pretreatment conditions, were taken to promote the formation of oxygen vacancies on the In₂O₃ surface, which can inhibit side reactions to ensure the highly selective conversion of CO₂ into methanol. The catalytic mechanism involving the formate pathway or carboxyl pathway over In₂O₃ was comprehensively explored by kinetic studies, in situ and ex situ characterizations, and density functional theory calculations, mostly demonstrating that the formate pathway was extremely significant for methanol production. Additionally, based on the cognition of the In₂O₃ active site and the reaction path of CO₂ hydrogenation over In₂O₃, strategies were adopted to improve the catalytic performance, including (i) metal doping to enhance the adsorption and dissociation of hydrogen, improve the ability of hydrogen spillover, and form a special metal-In₂O₃ interface, and (ii) hybrid with other metal oxides to improve the dispersion of In₂O₃, enhance CO₂ adsorption capacity, and stabilize the key intermediates. Lastly, some suggestions in future research were proposed to enhance the catalytic activity of In₂O₃-based catalysts for methanol production. The present review is helpful for researchers to have an explicit version of the research status of In₂O₃-based catalysts for CO₂ hydrogenation to methanol and the design direction of next-generation catalysts. Full article

(This article belongs to the Special Issue Nanocatalysts for CO₂ Utilization)

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Open AccessEditor’s ChoiceArticle

Heat Transfer Analysis of Warm Guss Asphalt Concrete for Mini-Trench Overlaying

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Materials 2023, 16(7), 2808; https://doi.org/10.3390/ma16072808 - 31 Mar 2023

Viewed by 506

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Conventional hot mix asphalt overlaying on trench infrastructure typically necessitates extended cooling times for further works and can have adverse effects on buried components, such as electricity cables and hot water pipes. Therefore, this research aims to investigate the use of warm guss [...] Read more.

Conventional hot mix asphalt overlaying on trench infrastructure typically necessitates extended cooling times for further works and can have adverse effects on buried components, such as electricity cables and hot water pipes. Therefore, this research aims to investigate the use of warm guss mastic asphalt (at an installation temperature of 160 °C) as an overlaying material for mini-trenches, which can reduce the cooling time required for traffic opening and improve the efficiency of the construction process. This research involved two stages: first, lab testing and related research results were used to generate the thermal conductivity and specific heat necessary for simulation work. Second, a finite element model analysis was conducted to evaluate the thermal transmission of the overlaying surface and the buried conduit based on the summer pavement temperature distribution through the Korean Pavement Research Program. Afterward, the field test bed was constructed to verify the simulation. The results indicate that the optimal thickness of the overlaying material and the concrete covering should be designed to ensure thermal durability and meet traffic opening requirements. The overlaying depth of the mini trench using warm mix guss mastic asphalt should be less than 100 mm to meet with the traffic opening time, while the thickness of the concrete covering should be designed to be more than 100 mm to ensure thermal durability. Additionally, the findings suggest that the application of warm guss asphalt could reduce the opening time by 30 min to 1 h and 25 min compared to conventional hot guss asphalt materials. When the pavement surface temperature for the traffic opening is controlled at 50 °C, the asphalt mixture requires at least 2 h to 5 h to meet the cooling criteria for traffic opening, respectively. Overall, this research confirms the potential benefits and optimal use of warm guss mastic asphalt in the construction process of mini-trenches. Full article

(This article belongs to the Special Issue Sustainable Asphalt Pavements: Materials, Design Methods, and Characterization Techniques (Second Volume))

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Open AccessEditor’s ChoiceReview

Sol–Gel Photonic Glasses: From Material to Application

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Alessandro Carpentiero

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Materials 2023, 16(7), 2724; https://doi.org/10.3390/ma16072724 - 29 Mar 2023

Viewed by 848

Abstract

In this review, we present a short overview of the development of sol–gel glasses for application in the field of photonics, with a focus on some of the most interesting results obtained by our group and collaborators in that area. Our main attention [...] Read more.

In this review, we present a short overview of the development of sol–gel glasses for application in the field of photonics, with a focus on some of the most interesting results obtained by our group and collaborators in that area. Our main attention is devoted to silicate glasses of different compositions, which are characterized by specific optical and spectroscopic properties for various applications, ranging from luminescent systems to light-confining structures and memristors. In particular, the roles of rare-earth doping, matrix composition, the densification process and the fabrication protocol on the structural, optical and spectroscopic properties of the developed photonic systems are discussed through appropriate examples. Some achievements in the fabrication of oxide sol–gel optical waveguides and of micro- and nanostructures for the confinement of light are also briefly discussed. Full article

(This article belongs to the Special Issue Glassy Materials: From Preparation to Application)

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Open AccessEditor’s ChoiceArticle

Study on Perforation Behavior of PTFE/Al Reactive Material Composite Jet Impacting Steel Target

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Materials 2023, 16(7), 2715; https://doi.org/10.3390/ma16072715 - 29 Mar 2023

Viewed by 452

Abstract

To study the penetration and cratering effect of reactive material composite jets, a series of experiments are carried out for the shaped charge (SC) with different composite liners damaging steel targets. The inner layer of composite liners is metal and the outer one [...] Read more.

To study the penetration and cratering effect of reactive material composite jets, a series of experiments are carried out for the shaped charge (SC) with different composite liners damaging steel targets. The inner layer of composite liners is metal and the outer one is a polytetrafluoroethylene/aluminum (PTFE/Al) reactive material. Copper (Cu), titanium (Ti) and Al inner liners are used in this paper. The reactive material liner is composed of 73.5 wt.% PTFE and 26.5 wt.% Al powder through mass-matched ratios. Reactive material composite liners are prepared through machining, cold pressing and a sintering process. The SC mainly consists of a case, a composite liner, high-energy explosive and an initiator. The steel target is steel 45#, with a thickness of 66 mm. A standoff of 1.0 CD (charge diameter) is selected to conduct the penetration experiments. The experimental results show that when the inner layer of the composite liner is composed of Ti and Al, the hole diameters on the steel target formed by the reactive material composite jet are significantly larger than that of the inner Cu liner. By introducing the initiation delay time (τ) and detonation-like reaction model of PTFE/Al reactive materials, an integrated numerical simulation algorithm of the penetration and detonation-like effects of reactive material composite jets is realized. Numerical simulations demonstrate that the initial penetration holes on the steel targets are enlarged under the detonation-like effects of PTFE/Al reactive materials, and the simulated perforation sizes are in good agreement with the experimental results. Full article

(This article belongs to the Special Issue Dynamic Mechanical Analysis of Energetic Materials)

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Open AccessEditor’s ChoiceArticle

Multifunctional TiO₂ Nanotube-Matrix Composites with Enhanced Photocatalysis and Lithium-Ion Storage Performances

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Mengmeng Zhang

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Hui Li

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Chunrui Wang

Materials 2023, 16(7), 2716; https://doi.org/10.3390/ma16072716 - 29 Mar 2023

Viewed by 432

Abstract

As a multifunctional material, TiO₂ shows excellent performance in catalytic degradation and lithium-ion storage. However, high electron-hole pair recombination, poor conductivity, and low theoretical capacity severely limit the practical application of TiO₂. Herein, TiO₂ nanotube (TiO₂ NT) with [...] Read more.

As a multifunctional material, TiO₂ shows excellent performance in catalytic degradation and lithium-ion storage. However, high electron-hole pair recombination, poor conductivity, and low theoretical capacity severely limit the practical application of TiO₂. Herein, TiO₂ nanotube (TiO₂ NT) with a novel double-layer honeycomb structure were prepared by two-step electrochemical anodization. Honeycombed TiO₂ NT arrays possess clean top surfaces and a long-range ordering, which greatly facilitates the preparation of high-performance binary and ternary materials. A binary TiO₂ nanotube@Au nanoparticle (TiO₂ NT@Au NP) composite accompanied by appropriately concentrated and uniformly distributed gold particles was prepared in this work. Interestingly, the TiO₂ nanotube@Au nanoparticle (TiO₂ NT@Au NP) composites not only showed the excellent catalytic degradation effect of methylene blue, but also demonstrated large lithium-ion storage capacity (310.6 μAh cm⁻², 1.6 times of pristine TiO₂ NT). Based on the realization of the controllable fabrication of binary TiO₂ nanotube@MoS₂ nanosheet (TiO₂ NT@MoS₂ NS) composite, ternary TiO₂ nanotube@MoS₂ nanosheet@Au nanoparticle (TiO₂ NT@MoS₂ NS@Au NP) composite with abundant defects and highly ordered structure was also innovatively designed and fabricated. As expected, the TiO₂ NT@MoS₂ NS@Au NP anode exhibits extremely high initial discharge specific capacity (487.4 μAh cm⁻², 2.6 times of pristine TiO₂ NT) and excellent capacity retention (81.0%). Full article

(This article belongs to the Special Issue Advanced Nanomaterials and Mechanistic Studies for Energy Electrocatalysis)

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Open AccessEditor’s ChoiceArticle

Vibration and Bandgap Behavior of Sandwich Pyramid Lattice Core Plate with Resonant Rings

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Chengfei Li

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Zhaobo Chen

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Yinghou Jiao

Materials 2023, 16(7), 2730; https://doi.org/10.3390/ma16072730 - 29 Mar 2023

Cited by 4 | Viewed by 441

Abstract

The vibration suppression performance of the pyramid lattice core sandwich plates is receiving increasing attention and needs further investigation for technical upgrading of potential engineering applications. Inspired by the localized resonant mechanism of the acoustic metamaterials and considering the integrity of the lattice [...] Read more.

The vibration suppression performance of the pyramid lattice core sandwich plates is receiving increasing attention and needs further investigation for technical upgrading of potential engineering applications. Inspired by the localized resonant mechanism of the acoustic metamaterials and considering the integrity of the lattice sandwich plate, we reshaped a sandwich pyramid lattice core with resonant rings (SPLCRR). Finite element (FE) models are built up for the calculations of the dispersion curves and vibration transmission. The validity of the bandgap of the SPLCRR and remarkable vibration suppression are verified by experimental observations and the numerical methods. Furthermore, the effects of geometric parameters, material parameters and period parameters on the bandgaps of the SPLCRR are systematically investigated, which offers a deeper understanding of the underlying mechanism of bandgap and helps the SPLCRR structure meet the technological update requirements of practical engineering design. Full article

(This article belongs to the Section Mechanics of Materials)

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Open AccessEditor’s ChoiceReview

The Characteristic Microstructures and Properties of Steel-Based Alloy via Additive Manufacturing

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Materials 2023, 16(7), 2696; https://doi.org/10.3390/ma16072696 - 28 Mar 2023

Viewed by 649

Abstract

Differing from metal alloys produced by conventional techniques, metallic products prepared by additive manufacturing experience distinct solidification thermal histories and solid−state phase transformation processes, resulting in unique microstructures and superior performance. This review starts with commonly used additive manufacturing techniques in steel−based alloy [...] Read more.

Differing from metal alloys produced by conventional techniques, metallic products prepared by additive manufacturing experience distinct solidification thermal histories and solid−state phase transformation processes, resulting in unique microstructures and superior performance. This review starts with commonly used additive manufacturing techniques in steel−based alloy and then some typical microstructures produced by metal additive manufacturing technologies with different components and processes are summarized, including porosity, dislocation cells, dendrite structures, residual stress, element segregation, etc. The characteristic microstructures may exert a significant influence on the properties of additively manufactured products, and thus it is important to tune the components and additive manufacturing process parameters to achieve the desired microstructures. Finally, the future development and prospects of additive manufacturing technology in steel are discussed. Full article

(This article belongs to the Special Issue Advances in the Experimentation and Numerical Modeling of Material Joining Processes)

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Open AccessEditor’s ChoiceReview

Progress and Perspective of Glass-Ceramic Solid-State Electrolytes for Lithium Batteries

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Materials 2023, 16(7), 2655; https://doi.org/10.3390/ma16072655 - 27 Mar 2023

Viewed by 760

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The all-solid-state lithium battery (ASSLIB) is one of the key points of future lithium battery technology development. Because solid-state electrolytes (SSEs) have higher safety performance than liquid electrolytes, and they can promote the application of Li-metal anodes to endow batteries with higher energy [...] Read more.

The all-solid-state lithium battery (ASSLIB) is one of the key points of future lithium battery technology development. Because solid-state electrolytes (SSEs) have higher safety performance than liquid electrolytes, and they can promote the application of Li-metal anodes to endow batteries with higher energy density. Glass-ceramic SSEs with excellent ionic conductivity and mechanical strength are one of the main focuses of SSE research. In this review paper, we discuss recent advances in the synthesis and characterization of glass-ceramic SSEs. Additionally, some discussions on the interface problems commonly found in glass-ceramic SSEs and their solutions are provided. At the end of this review, some drawbacks of glass-ceramic SSEs are summarized, and future development directions are prospected. We hope that this review paper can help the development of glass-ceramic solid-state electrolytes. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Superionic Conductive Glass and Ceramics)

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Open AccessEditor’s ChoiceArticle

Effective and Efficient Porous CeO₂ Adsorbent for Acid Orange 7 Adsorption

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Materials 2023, 16(7), 2650; https://doi.org/10.3390/ma16072650 - 27 Mar 2023

Viewed by 664

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A porous CeO₂ was synthesized following the addition of guanidine carbonate to a Ce³⁺ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO₂, including the [...] Read more.

A porous CeO₂ was synthesized following the addition of guanidine carbonate to a Ce³⁺ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO₂, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template−free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco−friendly raw materials. The porous CeO₂ possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO₂] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption–desorption equilibrium between the porous CeO₂ adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO₂ could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template−free hydrothermal strategy was developed to enable the design of CeO₂−based catalysts or catalyst carriers. Full article

(This article belongs to the Special Issue Recent Progress in Advanced Adsorption Materials)

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Open AccessEditor’s ChoiceArticle

Laser Emission Spectroscopy of Graphene Oxide Deposited on 316 Steel and Ti6Al4V Titanium Alloy Suitable for Orthopedics

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Barbara Nasiłowska

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Wojciech Skrzeczanowski

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Aneta Bombalska

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Zdzisław Bogdanowicz

Materials 2023, 16(7), 2574; https://doi.org/10.3390/ma16072574 - 24 Mar 2023

Cited by 1 | Viewed by 593

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This paper presents the results of an analysis of carbon (in the form of graphene oxide) deposited on the surface of threads made from stainless steel 316 and titanium alloy Ti6Al4V used in orthopedics using Laser Induced Breakdown Spectroscopy (LIBS). The aim of [...] Read more.

This paper presents the results of an analysis of carbon (in the form of graphene oxide) deposited on the surface of threads made from stainless steel 316 and titanium alloy Ti6Al4V used in orthopedics using Laser Induced Breakdown Spectroscopy (LIBS). The aim of the article is to indicate the possibility of using the LIBS spectra for the study of thin layers, including graphene derivatives and other elements. Stratigraphic measurements allowed the detection of differences in the spectra peaks of individual elements, not only in the surface layer itself and in the native material, but also in the intermediate layer connecting the two layers. Due to the clear difference in the outline of the spectrum of graphene oxide and the spectrum of the native material of the samples analyzed, a clear incorporation of carbon atoms into the surface layer was observed. A factor analysis was performed, which confirmed the incorporation of graphene oxide into the surface layer of the native material of the elements examined. Full article

(This article belongs to the Special Issue Material Surfaces and Interactions: Structure, Properties, Processes and Applications)

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Open AccessEditor’s ChoiceArticle

Enhanced Mechanical and Corrosion Properties via Annealing Treatment on the Hot-Rolled Ti-Zr-Mo Alloy

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Materials 2023, 16(7), 2597; https://doi.org/10.3390/ma16072597 - 24 Mar 2023

Viewed by 379

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In this work, the Ti-20Zr-15Mo alloy in its hot-rolled state was annealed in different phase zones, and the effects of the annealing treatment on the phase composition, organization, mechanical and corrosion resistance properties of the alloy were systematically investigated. The results showed that [...] Read more.

In this work, the Ti-20Zr-15Mo alloy in its hot-rolled state was annealed in different phase zones, and the effects of the annealing treatment on the phase composition, organization, mechanical and corrosion resistance properties of the alloy were systematically investigated. The results showed that the original β grains of the alloy had all recrystallized to form the β equiaxial grains when annealed at 800 °C, and the grains had been significantly refined. This allowed the alloy to reach a tensile strength of 1000 MPa, a maximum of 28% after stretching, and a significant increase in plasticity. Also, due to the single beta phase, there was no galvanic corrosion, making the alloy annealed at 800 °C have the best corrosion resistance. Full article

(This article belongs to the Section Mechanics of Materials)

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Open AccessEditor’s ChoiceArticle

Black Liquor and Wood Char-Derived Nitrogen-Doped Carbon Materials for Supercapacitors

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Loreta Tamasauskaite-Tamasiunaite

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Vitalija Jasulaitiene

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Gediminas Niaura

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Audrius Drabavicius

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Mari Juel

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Luis Colmenares-Rausseo

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Ivar Kruusenberg

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Kätlin Kaare

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Eugenijus Norkus

Materials 2023, 16(7), 2551; https://doi.org/10.3390/ma16072551 - 23 Mar 2023

Viewed by 487

Abstract

Herein, we present a synthesis route for high-efficiency nitrogen-doped carbon materials using kraft pulping residue, black liquor, and wood charcoal as carbon sources. The synthesized nitrogen-doped carbon materials, based on black liquor and its mixture with wood charcoal, exhibited high specific surface areas [...] Read more.

Herein, we present a synthesis route for high-efficiency nitrogen-doped carbon materials using kraft pulping residue, black liquor, and wood charcoal as carbon sources. The synthesized nitrogen-doped carbon materials, based on black liquor and its mixture with wood charcoal, exhibited high specific surface areas (SSAs) of 2481 and 2690 m² g⁻¹, respectively, as well as a high volume of mesopores with an average size of 2.9–4.6 nm. The nitrogen content was approximately 3–4 at% in the synthesized nitrogen-doped carbon materials. A specific capacitance of approximately 81–142 F g⁻¹ was achieved in a 1 M Na₂SO₄ aqueous solution at a current density of 0.2 A g⁻¹. In addition, the specific capacitance retention was 99% after 1000 cycles, indicating good electrochemical stability. Full article

(This article belongs to the Special Issue Nanostructured Materials for Electrochemical Energy Storage)

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Open AccessEditor’s ChoiceArticle

PCL and DMSO₂ Composites for Bio-Scaffold Materials

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Materials 2023, 16(6), 2481; https://doi.org/10.3390/ma16062481 - 21 Mar 2023

Viewed by 997

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Polycaprolactone (PCL) has been one of the most popular biomaterials in tissue engineering due to its relatively low melting temperature, excellent thermal stability, and cost-effectiveness. However, its low cell attraction, low elastic modulus, and long-term degradation time have limited its application in a [...] Read more.

Polycaprolactone (PCL) has been one of the most popular biomaterials in tissue engineering due to its relatively low melting temperature, excellent thermal stability, and cost-effectiveness. However, its low cell attraction, low elastic modulus, and long-term degradation time have limited its application in a wide range of scaffold studies. Dimethyl sulfone (DMSO₂) is a stable and non-hazardous organosulfur compound with low viscosity and high surface tension. PCL and DMSO₂ composites may overcome the limitations of PCL as a biomaterial and tailor the properties of biocomposites. In this study, PCL and DMSO₂ composites were investigated as a new bio-scaffold material to increase hydrophilicity and mechanical properties and tailor degradation properties in vitro. PCL and DMSO₂ were physically mixed with 10, 20, and 30 wt% of DMSO₂ to evaluate thermal, hydrophilicity, mechanical, and degradation properties of the composites. The water contact angle of the composites for hydrophilicity decreased by 15.5% compared to pure PCL. The experimental results showed that the mechanical and degradation properties of PCL and DMSO₂ were better than those of pure PCL, and the properties can be tuned by regulating DMSO2 concentration in the PCL matrix. The elastic modulus of the composite with 30 wt% of DMSO2 showed 532 MPa, and its degradation time was 18 times faster than that of PCL. Full article

(This article belongs to the Section Biomaterials)

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Open AccessEditor’s ChoiceReview

3D Construction Printing Standing for Sustainability and Circularity: Material-Level Opportunities

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Mariana Fonseca

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Ana Mafalda Matos

Materials 2023, 16(6), 2458; https://doi.org/10.3390/ma16062458 - 20 Mar 2023

Viewed by 1482

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Three-dimensional Cementitious materials Printing (3DCP) is a cutting-edge technology for the construction industry. Three-dimensional printed buildings have shown that a well-developed automated technology can foster valuable benefits, such as a freeform architectural design without formworks and reduced human intervention. However, scalability, commercialization and [...] Read more.

Three-dimensional Cementitious materials Printing (3DCP) is a cutting-edge technology for the construction industry. Three-dimensional printed buildings have shown that a well-developed automated technology can foster valuable benefits, such as a freeform architectural design without formworks and reduced human intervention. However, scalability, commercialization and sustainability of the 3DPC technology remain critical issues. The current work presents the ecological fragility, challenges and opportunities inherent in decreasing the 3DCP environmental footprint at a material level (cementitious materials and aggregates). The very demanding performance of printable mixtures, namely in a fresh state, requires high dosages of cement and supplementary cementitious materials (SCM). Besides the heavy carbon footprint of cement production, the standard SCM availability might be an issue, especially in the longer term. One exciting option to decrease the embodied CO₂ of 3DCP is, for example, to incorporate alternative and locally available SCM as partial cement replacements. Those alternative SCM can be wastes or by-products from industries or agriculture, with no added value. Moreover, the partial replacement of natural aggregate can also bring advantages for natural resource preservation. This work has highlighted the enormous potential of 3DCP to contribute to reducing the dependence on Portland cement and to manage the current colossal wastes and by-products with no added value, shifting to a Circular Economy. Though LCA analysis, mixture design revealed a critical parameter in the environmental impact of 3DCP elements or buildings. Even though cement significantly affects the LCA of 3DCP, it is crucial to achieving adequate fresh properties and rheology. From the literature survey, mixtures formulated with alternative SCM (wastes or by-products) are still restricted to rice husk ash, Municipal Solid Waste ashes and recycled powder from construction and demolition wastes. Natural aggregate replacement research has been focused on recycled fine sand, mine tailing, copper tailing, iron tailing, ornamental stone waste, recycled glass, crumb rubber, rubber powder and granules, recycled PET bottles and steel slag. However, flowability loss and mechanical strength decrease are still critical. Research efforts are needed to find low-carbon cement replacements and mix-design optimization, leading to a more sustainable and circular 3DCP while ensuring the final product performance. Full article

(This article belongs to the Special Issue Sustainability and Applications of Materials in Civil Engineering and Building)

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Open AccessEditor’s ChoiceArticle

Study of Viscoelastic Properties of Graphene Foams Using Dynamic Mechanical Analysis and Coarse-Grained Molecular Dynamics Simulations

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Materials 2023, 16(6), 2457; https://doi.org/10.3390/ma16062457 - 20 Mar 2023

Viewed by 857

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As a promising nano-porous material for energy dissipation, the viscoelastic properties of three-dimensional (3D) graphene foams (GrFs) are investigated by combining a dynamic mechanical analysis (DMA) and coarse-grained molecular dynamic (CGMD) simulations. The effects of the different factors, such as the density of [...] Read more.

As a promising nano-porous material for energy dissipation, the viscoelastic properties of three-dimensional (3D) graphene foams (GrFs) are investigated by combining a dynamic mechanical analysis (DMA) and coarse-grained molecular dynamic (CGMD) simulations. The effects of the different factors, such as the density of the GrFs, temperature, loading frequency, oscillatory amplitude, the pre-strain on the storage and loss modulus of the GrFs as well as the micro-mechanical mechanisms are mainly focused upon. Not only the storage modulus but also the loss modulus are found to be independent of the temperature and the frequency. The storage modulus can be weakened slightly by bond-breaking with an increasing loading amplitude. Furthermore, the tensile/compressive pre-strain and density of the GrFs can be used to effectively tune the viscoelastic properties of the GrFs. These results should be helpful not only for understanding the mechanical mechanism of GrFs but also for optimal designs of advanced damping materials. Full article

(This article belongs to the Special Issue New Advances in Characterization of Cellular Materials)

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Open AccessEditor’s ChoiceArticle

Influence of Surface Chemistry of Fiber and Lignocellulosic Materials on Adhesion Properties with Polybutylene Succinate at Nanoscale

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Véronique Aguié-Béghin

Materials 2023, 16(6), 2440; https://doi.org/10.3390/ma16062440 - 18 Mar 2023

Cited by 5 | Viewed by 706

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The production of bio-based composites with enhanced characteristics constitutes a strategic action to minimize the use of fossil fuel resources. The mechanical performances of these materials are related to the specific properties of their components, as well as to the quality of the [...] Read more.

The production of bio-based composites with enhanced characteristics constitutes a strategic action to minimize the use of fossil fuel resources. The mechanical performances of these materials are related to the specific properties of their components, as well as to the quality of the interface between the matrix and the fibers. In a previous research study, it was shown that the polarity of the matrix played a key role in the mechanisms of fiber breakage during processing, as well as on the final properties of the composite. However, some key questions remained unanswered, and new investigations were necessary to improve the knowledge of the interactions between a lignocellulosic material and a polar matrix. In this work, for the first time, atomic force microscopy based on force spectroscopy measurements was carried out using functionalized tips to characterize the intermolecular interactions at the single molecule level, taking place between poly(butylene succinate) and four different plant fibers. The efficiency of the tip functionalization was checked out by scanning electron microscopy and energy-dispersive X-ray spectroscopy, whereas the fibers chemistry was characterized by Fourier-transform infrared spectroscopy. Larger interactions at the nanoscale level were found between the matrix and hypolignified fibers compared to lignified ones, as in control experiments on single lignocellulosic polymer films. These results could significantly aid in the design of the most appropriate composite composition depending on its final use. Full article

(This article belongs to the Special Issue Advances in the Circularity of Polymeric and Composite Materials)

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Open AccessEditor’s ChoiceArticle

CALPHAD-Based Modelling of the Temperature–Composition–Structure Relationship during Physical Vapor Deposition of Mg-Ca Thin Films

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Materials 2023, 16(6), 2417; https://doi.org/10.3390/ma16062417 - 17 Mar 2023

Viewed by 544

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The temperature-dependent composition and phase formation during the physical vapor deposition (PVD) of Mg-Ca thin films is modeled using a CALPHAD-based approach. Considering the Mg and Ca sublimation fluxes calculated based on the vapor pressure obtained by employing thermochemical equilibrium calculations, the experimentally [...] Read more.

The temperature-dependent composition and phase formation during the physical vapor deposition (PVD) of Mg-Ca thin films is modeled using a CALPHAD-based approach. Considering the Mg and Ca sublimation fluxes calculated based on the vapor pressure obtained by employing thermochemical equilibrium calculations, the experimentally observed synthesis-temperature trends in the thin-film composition and phase formation were reproduced. The model is a significant step towards understanding how synthesis parameters control composition and, therefore, phase formation in the PVD of metals with high vapor pressures. Full article

(This article belongs to the Special Issue Sputter Deposition/Physical Vapor Deposition (PVD) Materials and Processes)

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Open AccessEditor’s ChoiceArticle

Influence of Antibacterial Coating and Mechanical and Chemical Treatment on the Surface Properties of PA12 Parts Manufactured with SLS and MJF Techniques in the Context of Medical Applications

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Anna Bazan

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Paweł Turek

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Andrzej Zakręcki

Materials 2023, 16(6), 2405; https://doi.org/10.3390/ma16062405 - 17 Mar 2023

Cited by 1 | Viewed by 714

Abstract

Additive manufacturing (AM) is a rapidly growing branch of manufacturing techniques used, among others, in the medical industry. New machines and materials and additional processing methods are improved or developed. Due to the dynamic development of post-processing and its relative novelty, it has [...] Read more.

Additive manufacturing (AM) is a rapidly growing branch of manufacturing techniques used, among others, in the medical industry. New machines and materials and additional processing methods are improved or developed. Due to the dynamic development of post-processing and its relative novelty, it has not yet been widely described in the literature. This study focuses on the surface topography (parameters Sa, Sz, Sdq, Sds, Str, Sdr) of biocompatible polyamide 12 (PA12) samples made by selective laser sintering (SLS) and multi jet fusion (MJF). The surfaces of the samples were modified by commercial methods: four types of smoothing treatments (two mechanical and two chemical), and two antibacterial coatings. The smoothing treatment decreased the values of all analyzed topography parameters. On average, the Sa of the SLS samples was 33% higher than that of the MJF samples. After mechanical treatment, Sa decreased by 42% and after chemical treatment by 80%. The reduction in Sdq and Sdr is reflected in a higher surface gloss. One antibacterial coating did not significantly modify the surface topography. The other coating had a smoothing effect on the surface. The results of the study can help in the development of manufacturing methodologies for parts made of PA12, e.g., in the medical industry. Full article

(This article belongs to the Special Issue Biocompatible Materials Investigated with Optical Methods)

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Open AccessEditor’s ChoiceArticle

The Influence of Cellulose Nanocrystal Characteristics on Regenerative Silk Composite Fiber Properties

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Hak Jeon Kim

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Won Jun Lee

Materials 2023, 16(6), 2323; https://doi.org/10.3390/ma16062323 - 14 Mar 2023

Viewed by 495

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Cellulose nanocrystals (CNCs), obtained from natural resources, possess great potential as a bioderived reinforcement for natural-fiber-reinforced composites (NFRPs) due to their superior crystallinity and high aspect ratio. To elucidate the specific parameters of CNCs that significantly affect their mechanical performance, various CNCs were [...] Read more.

Cellulose nanocrystals (CNCs), obtained from natural resources, possess great potential as a bioderived reinforcement for natural-fiber-reinforced composites (NFRPs) due to their superior crystallinity and high aspect ratio. To elucidate the specific parameters of CNCs that significantly affect their mechanical performance, various CNCs were investigated to fabricate high-performance nanocomposite fibers together with regenerated silk fibroin (RSF). We confirmed that the high aspect ratio (~9) of the CNCs was the critical factor to increase the tensile strength and stiffness rather than the crystallinity. At a 1 vol% of CNCs, the strength and stiffness reached ~300 MPa and 10.5 GPa, respectively, which was attributed not only to a stable dispersion but also to alignment. This approach has the potential to evaluate the parameters of natural reinforcement and may also be useful in constructing high-performance NFRPs. Full article

(This article belongs to the Special Issue Advances in Nanostructured Materials - Volume 2)

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Open AccessEditor’s ChoiceArticle

Spherical Attapulgite/Silica Aerogels Fabricated via Different Drying Methods with Excellent Adsorption Performance

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Materials 2023, 16(6), 2292; https://doi.org/10.3390/ma16062292 - 13 Mar 2023

Viewed by 1017

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Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO₂) gels were initially prepared [...] Read more.

Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO₂) gels were initially prepared by easily scalable sol-gel dripping methods and then dried to aerogels with three drying techniques, namely, supercritical CO₂ drying (SCD), freeze-drying (FD), and ambient pressure drying (APD). The effect of the drying techniques and heat-treated temperature on the physical characteristic, morphological properties, microstructure, and chemical structure of the spherical ATP/SiO₂ aerogels were investigated. The macroscopic morphology of the spherical ATP/SiO₂ aerogels was homogeneous and integrated without local cracking. The average pore diameter and specific surface area of the spherical ATP/SiO₂ aerogels prepared by the three drying techniques were in the range of 6.8–8.6 nm and 218.5–267.4 m²/g, respectively. The heat treatment temperature had a significant effect on the pore structure and the wetting properties of the aerogels. The 600 °C heat-treated aerogels were subjected to adsorption tests in methylene blue (MB) solution (60 mg/g, 100 mL), which exhibited a great adsorption capacity of 102.50 mg/g. Therefore, the resulting spherical ATP/SiO₂ aerogels possessed multipath preparation and exhibited an efficient adsorption performance, with the potential to be applied as an adsorbent for dye wastewater. Full article

(This article belongs to the Special Issue Advances in Porous Materials: Synthesis, Characterisations and Applications)

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Open AccessEditor’s ChoiceReview

Recent Advances on PEO-PCL Block and Graft Copolymers as Nanocarriers for Drug Delivery Applications

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Materials 2023, 16(6), 2298; https://doi.org/10.3390/ma16062298 - 13 Mar 2023

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Abstract

Poly(ethylene oxide)-poly(ε-caprolactone) (PEO-PCL) is a family of block (or graft) copolymers with several biomedical applications. These types of copolymers are well-known for their good biocompatibility and biodegradability properties, being ideal for biomedical applications and for the formation of a variety of nanosystems intended [...] Read more.

Poly(ethylene oxide)-poly(ε-caprolactone) (PEO-PCL) is a family of block (or graft) copolymers with several biomedical applications. These types of copolymers are well-known for their good biocompatibility and biodegradability properties, being ideal for biomedical applications and for the formation of a variety of nanosystems intended for controlled drug release. The aim of this review is to present the applications and the properties of different nanocarriers derived from PEO-PCL block and graft copolymers. Micelles, polymeric nanoparticles, drug conjugates, nanocapsules, and hybrid polymer-lipid nanoparticles, such as hybrid liposomes, are the main categories of PEO-PCL based nanocarriers loaded with different active ingredients. The advantages and the limitations in preclinical studies are also discussed in depth. PEO-PCL based nanocarriers could be the next generation of delivery systems with fast clinical translation. Finally, current challenges and future perspectives of the PEO-PCL based nanocarriers are highlighted. Full article

(This article belongs to the Special Issue Drug Delivery: Recent Developments and Future Prospects)

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Open AccessEditor’s ChoiceArticle

Bi-Functionalized Transferrin@MoS₂-PEG Nanosheets for Improving Cellular Uptake in HepG2 Cells

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Materials 2023, 16(6), 2277; https://doi.org/10.3390/ma16062277 - 12 Mar 2023

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Abstract

Pre-coating with a protein corona on the surface of nanomaterials (NMs) is an important strategy for reducing non-specific serum protein absorption while maintaining targeting specificity. Here, we present lipoic acid-terminated polyethylene glycol and transferrin bi-functionalized MoS₂ nanosheets (Tf@MoS₂-PEG NSs) as [...] Read more.

Pre-coating with a protein corona on the surface of nanomaterials (NMs) is an important strategy for reducing non-specific serum protein absorption while maintaining targeting specificity. Here, we present lipoic acid-terminated polyethylene glycol and transferrin bi-functionalized MoS₂ nanosheets (Tf@MoS₂-PEG NSs) as a feasible approach to enhance cellular uptake. Tf@MoS₂-PEG NSs can maintain good dispersion stability in cell culture medium and effectively protect MoS₂ NSs from oxidation in ambient aqueous conditions. Competitive adsorption experiments indicate that transferrin was more prone to bind MoS₂ NSs than bovine serum albumin (BSA). It is noteworthy that single HepG2 cell uptake of Tf@MoS₂-PEG presented a heterogeneous distribution pattern, and the cellular uptake amount spanned a broader range (from 0.4 fg to 2.4 fg). Comparatively, the intracellular Mo masses in HepG2 cells treated with BSA@MoS₂-PEG and MoS₂-PEG showed narrower distribution, indicating homogeneous uptake in the single HepG2 cells. Over 5% of HepG2 cells presented uptake of the Tf@MoS₂-PEG over 1.2 fg of Mo, about three-fold that of BSA@MoS₂-PEG (0.4 fg of Mo). Overall, this work suggests that Tf coating enhances the cellular uptake of MoS₂ NSs and is a promising strategy for improving the intracellular uptake efficiency of cancer cells. Full article

(This article belongs to the Special Issue Recent Development of Surface Chemistry of Nanomaterials)

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Open AccessEditor’s ChoiceArticle

Raman Characterization of the In-Plane Stress Tensor of Gallium Nitride

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Materials 2023, 16(6), 2255; https://doi.org/10.3390/ma16062255 - 10 Mar 2023

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Abstract

Experimental characterization of the in-plane stress tensor is a basic requirement for the development of GaN strain engineering. In this work, a theoretical model of stress characterization for GaN using polarized micro-Raman spectroscopy was developed based on elasticity theory and lattice dynamics. Compared [...] Read more.

Experimental characterization of the in-plane stress tensor is a basic requirement for the development of GaN strain engineering. In this work, a theoretical model of stress characterization for GaN using polarized micro-Raman spectroscopy was developed based on elasticity theory and lattice dynamics. Compared with other works, the presented model can give the quantitative relationship between all components of the in-plane stress tensor and the measured Raman shift. The model was verified by a calibration experiment under step-by-step uniaxial compression. By combining the stress characterization model with the expanding cavity model, the in-plane residual stress component field around Berkovich indentation on the (0001) plane GaN was achieved. The experimental results show that the distributions of the stress components, which significantly differed from the distribution of the Raman shift, were closely related to the GaN crystal structure and exhibited a gradient along each crystal direction. Full article

(This article belongs to the Special Issue Experimental Mechanics of Micro-Nano Scale Spectroscopy)

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