Surfaces, Volume 6, Issue 3 (September 2023) – 9 articles

Porous carbon is an emerging material for the capture of CO₂ from point sources of emissions due to its high structural, mechanical, and chemical stability, along with reusability advantages. Currently, research efforts are mainly focused on high- or medium-pressure adsorption, rather than low-pressure or DAC (direct air capture) conditions. Highly porous and functionalized carbon, containing heteroatoms (N, O, etc.), is synthesized using different activation synthesis routes, such as hard template, soft template, and chemical activation, to achieve high CO₂ capture efficiency at various temperatures and pressure ranges. Fundamental pore formation mechanisms with different activation routes have been evaluated and explored. Higher porosity alone can be ineffective without the presence of proper saturated diffusion pathways for CO₂ transfer. Therefore, it is imperative to emphasize more rational multi-hierarchical macro-/meso-/micro-/super-/ultra-pore design strategies to achieve a higher utilization efficiency of these pores. Moreover, the present research primarily focuses on powder-based hierarchical porous carbon materials, which may reduce the efficiency of the capture performance when shaping the powder into pellets or fixed-bed shapes for applications considered. Therefore, it is imperative to develop a synthesis strategy for pelletized porous carbon and to explore its mechanistic synthesis route and potential for CO₂ capture. Full article

Bacterial adhesion and biofilm formation on the surface of titanium implants are the main causes of implant-associated infection. An antibacterial coating on the implant surface can reduce the risk of biofilm formation. The aim of this study was to investigate the bactericidal effects of a van-comycin-loaded polymer coated on an implant surface. For this purpose, poly(N-isopropylacrylamide) (PNIPAAm) was first synthesized as a homopolymer or by co-polymerization with acrylamide (PNIPAAm-AAm) at a 5% weight ratio. Then, thin and uniform polymer coatings were prepared using the spin coating technique. The degree of surface hydro-philicity of the polymer coatings was evaluated by measuring the water contact angle (CA). For the antibacterial tests, the polymer-coated surfaces were loaded with vancomycin. The tests were performed in three conditions: on a glass surface (control), on a PNIPAAm-AAm-coated surface, and on a PNIPAAm-AAm-coated surface loaded with vancomycin. The death rates of the bacteria in contact with the coated surfaces were evaluated at different temperatures with fluorescence microscopy. A scanning electron microscopy (SEM) analysis of cross sections of the polymer coatings revealed a uniform thin film of approximately 200 nm in thickness. The water contact angle analysis performed at different temperatures revealed that the polymer-coated surfaces were more hydrophobic (CAs ranging between 53° and 63°) than the uncoated glass surface (CA ranging between 15° and 35°). The bacterial death rate, measured at 40 °C or while continuously switching the temperature between 37 °C and 40 °C, was higher in the presence of the surface coated with vancomycin-loaded PNIPAAm-AAm than when using the other surfaces (p-value ≤ 0.001). The vancomycin-loaded polymer coating evaluated in this study exhibited effective antibacterial properties when the polymer reached the phase transition temperature. Full article

The mechanism of the vapor–gas deposition of vinyltrimethoxysilane (VS) and ethylene glycol (EG) from azeotropic solutions is investigated, which allows a reduction of the evaporation temperature of the components of working mixtures. The need for such studies is associated with the development of a new direction in the technology of vapor–gas deposition of polymer coatings. Methods have been developed for monitoring the chemical composition of working solutions in evaporators using optical spectroscopy, which makes it possible to calculate the partial pressures of vapor-phase components. Based on these studies, compositions of working solutions are proposed that allow the equalization of the partial pressures of the components of working mixtures with a large difference in the boiling point. With the aid of vapor–gas deposition, siloxane coatings on low-carbon steel were obtained, the protective properties of which exceeded the treatment with volatile inhibitors of the adsorption type by two to three orders of magnitude. A new method of vapor–gas deposition of non-volatile powder inhibitors on metals is proposed. Chemical compositions of siloxane coatings were determined using XPS, and mechanisms of interaction of VS with the polymerization promoters ethylene glycol and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) were proposed. Full article

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 10⁶ A/m²); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported. Full article

The development of biodegradable Zn-based alloys for implants that effectively mimic the functionality of native bone throughout the healing process is a multifaceted challenge; this is particularly evident in the task of achieving appropriate corrosion rates. This work explores the incorporation of 0.5wt.%Mn into a Zn−1wt.%Mg alloy, with focus on the relationship between corrosion behavior and microstructure. Electrochemical corrosion tests were carried out in a 0.06 M NaCl solution using as-solidified samples with two distinct microstructural length scales. Mn addition was found to induce significant electrochemical active behavior. Localized corrosion was predominant in interdendritic regions, with the ternary alloy exhibiting a higher susceptibility. For both alloys, the coarsening of the microstructure promoted a slight inclination to accelerate the corrosion rates in both biodegradable Zn alloys. The corrosion rate showed an increase of about nine-times with Mn addition for coarser eutectic spacings, while for finer ones, the increase was by about 22 times. Full article

We measured spectra of low energy electrons emitted in the interaction of singly charged Ne⁺ ions with the Mg surface at incident ion energies ranging from 50 eV to 4 keV. The study examines issues related to the excitation of both the surface and the bulk plasmons of the target. We will also focus on the dynamics of the production of the singlet Ne2p⁴(¹D)3s² and triplet Ne2p⁴(³P)3s² autoionizing states of projectiles scattered in a vacuum. The threshold behavior of the autoionization lines show that double excitation occurs simultaneously in a single scattering. The predominant excitation of the triplet state indicates the importance of charge rearrangement and the electron correlation effects during the collisional excitation. Full article

A flexible chitin nanofiber (ChNF) film with a thin fiber morphology, named, scaled-down (SD)-ChNF film, was previously found to be formed via successive partial deacetylation of the parent self-assembled ChNFs, cationization/dispersion via electrostatic repulsion in aqueous acetic acid, and suction filtration/drying. In this study, acetylation of a SD-ChNF film using acetic anhydride in pyridine was carried out to improve the mechanical properties. The FT-IR spectra of the acetylated SD-ChNF films suggested that acetylation progressed from the surface to the interior of the films with the increasing amounts of pyridine and elevating temperatures. The degrees of acetylation (DA) strongly affected the chitin crystallinity and surface morphology of the acetylated SD-ChNF films. Tensile testing of the acetylated SD-ChNF films indicated that the mechanical properties were improved by adjusting the DA values of the films. For example, the acetylated SD-ChNF film with an 1.84 DA value on surface showed values of 44.1 MPa and 24.9% for tensile strength and elongation at break, respectively. Full article

Flexible and binderless electrodes have become a promising candidate for the next generation of flexible power storage devices. However, developing high-performance electrode materials with high energy density and a long cycle life remains a serious challenge for sodium-ion batteries (SIBs). The main issue is the large volume change in electrode materials during the cycling processes, leading to rapid capacity decay for SIBs. In this study, flexible electrodes for a SnSb alloy–carbon nanofiber (SnSb@NC) membrane were successfully synthesized with the aid of hydrothermal, electrospinning and annealing processes. The as-prepared binderless SnSb@NC flexible anodes were investigated for the storage properties of SIBs at 500 °C, 600 °C and 700 °C (SnSb@NC-500, SnSb@NC-600 and SnSb@NC-700), respectively. And the flexible SnSb@NC-700 electrode displayed the preferable SIB performances, achieving 240 mAh/g after 100 cycles at 0.1 A g⁻¹. In degree-dependent I-V curve measurements, the SnSb@NC-700 membrane exhibited almost the same current at different bending degrees of 0°, 45°, 90°, 120° and 175°, indicating the outstanding mechanical properties of the flexible binderless electrodes. Full article

The search of active, stable and low costs catalysts for the oxygen reduction reaction (ORR) is crucial for the extensive use of fuel cells and metal–air batteries. The development of metal-free catalysts, instead of platinum-based materials, can dramatically reduce the cost and increase the efficiency of these devices. In this work, carbon nanohorns (CNHs) have been covalently functionalized with N-containing heterocycles by the Tour reaction protocol and tested as metal-free ORR catalysts. The insertion of N-functionalities favored the complete reduction of oxygen to hydroxyl ions, while their absence favored the production of hydrogen peroxide. With the aim of determining the N-species responsible for the ORR activity of CNHs, photoemission and electrochemical measurements were combined. Results suggest that protonated N is the main species involved in the ORR process, facilitating the adsorption of oxygen, with their consequent reduction to neutral hydrogenated N species. Full article