Surfaces

14 pages, 3426 KiB

Open AccessArticle

Preparation, Characterization and CO Oxidation Performance of Ag₂O/γ-Al₂O₃ and (Ag₂O+RuO₂)/γ-Al₂O₃ Catalysts

by Antony Ananth, Rak Hyun Jeong and Jin-Hyo Boo

Surfaces 2020, 3(2), 251-264; https://doi.org/10.3390/surfaces3020019 - 23 Jun 2020

Cited by 4 | Viewed by 3012

This research dealt with the preparation and characterization of silver oxide (SLO) nanomaterials (NMs) and their composite catalysts (i.e., silver and ruthenium oxide (SLORUO)). The prepared materials were tested for their catalytic performance in carbon monoxide (CO) oxidation. Generally, silver in its pure [...] Read more.

This research dealt with the preparation and characterization of silver oxide (SLO) nanomaterials (NMs) and their composite catalysts (i.e., silver and ruthenium oxide (SLORUO)). The prepared materials were tested for their catalytic performance in carbon monoxide (CO) oxidation. Generally, silver in its pure state is not widely used for CO oxidation due to stability and structural issues. However, the usage of subsurface oxygen and oxygen-induced reconstruction could be effective as an oxidation catalyst at a slightly high temperature. The low-temperature reaction of highly active RuO₂ (RUO) is a well-known phenomenon. Thus, the possibility of using it with SLO to observe the combined catalytic behavior was investigated. The wet chemically prepared SLO and SLORUO NMs exhibited spherical and rods in spherical aggregate-type surface morphology belonging to cubic and rutile crystalline structures, respectively. The NMs and catalysts (i.e., the NMs on γ-Al₂O₃ catalyst support at 0.5 and 1.0 wt.% ranges) showed good thermal stability. The dry and wet CO oxidation using RUO and SLO showed concentration-dependent catalytic activity. The RUO, SLO, and SLORUO composites using 0.5 wt.% showed full CO oxidation at 200, 300, and 225 °C, respectively. The reasons for the observed activity of the catalysts are explained based on the pore characteristics, chemical composition, and dispersion using H₂ temperature-programmed reduction (TPR) behaviors. Full article

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14 pages, 2472 KiB

Open AccessArticle

Fabrication and Characterization of Zein/Hydroxyapatite Composite Coatings for Biomedical Applications

by Yusra Ahmed, Muhammad Yasir and Muhammad Atiq Ur Rehman

Surfaces 2020, 3(2), 237-250; https://doi.org/10.3390/surfaces3020018 - 19 Jun 2020

Cited by 16 | Viewed by 3305

Abstract

Stainless steel is renowned for its wide use as a biomaterial, but its relatively high corrosion rate in physiological environments restricts many of its clinical applications. To overcome the corrosion resistance of stainless steel bio-implants in physiological environments and to improve its osseointegration [...] Read more.

Stainless steel is renowned for its wide use as a biomaterial, but its relatively high corrosion rate in physiological environments restricts many of its clinical applications. To overcome the corrosion resistance of stainless steel bio-implants in physiological environments and to improve its osseointegration behavior, we have developed a unique zein/hydroxyapatite (HA) composite coating on a stainless steel substrate by Electrophoretic Deposition (EPD). The EPD parameters were optimized using the Taguchi Design of experiments (DoE) approach. The EPD parameters, such as the concentration of bio-ceramic particles in the polymer solution, applied voltage and deposition time were optimized on stainless steel substrates by applying a mixed design orthogonal Taguchi array. The coatings were characterized by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and wettability studies. SEM images and EDX results indicated that the zein/HA coating was successfully deposited onto the stainless steel substrates. The wettability and roughness studies elucidated the mildly hydrophilic nature of the zein/HA coatings, which confirmed the suitability of the developed coatings for biomedical applications. Zein/HA coatings improved the corrosion resistance of bare 316L stainless steel. Moreover, zein/HA coatings showed strong adhesion with the 316L SS substrate for biomedical applications. Zein/HA developed dense HA crystals upon immersion in simulated body fluid, which confirmed the bone binding ability of the coatings. Thus the zein/HA coatings presented in this study have a strong potential to be considered for orthopedic applications. Full article

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12 pages, 2130 KiB

Open AccessArticle

In Situ Study of Graphene Oxide Quantum Dot-MoS_x Nanohybrids as Hydrogen Evolution Catalysts

by Marco Favaro, Mattia Cattelan, Stephen W. T. Price, Andrea E. Russell, Laura Calvillo, Stefano Agnoli and Gaetano Granozzi

Surfaces 2020, 3(2), 225-236; https://doi.org/10.3390/surfaces3020017 - 16 Jun 2020

Cited by 3 | Viewed by 3511

Abstract

Graphene quantum dots (GOQDs)-MoS_x nanohybrids with different MoS_x stoichiometries (x = 2 and 3) were prepared in order to investigate their chemical stability under hydrogen evolution reaction (HER) conditions. Combined photoemission/electrochemical (XPS/EC) measurements and operando X-ray absorption spectroscopy (XAS) were employed [...] Read more.

Graphene quantum dots (GOQDs)-MoS_x nanohybrids with different MoS_x stoichiometries (x = 2 and 3) were prepared in order to investigate their chemical stability under hydrogen evolution reaction (HER) conditions. Combined photoemission/electrochemical (XPS/EC) measurements and operando X-ray absorption spectroscopy (XAS) were employed to determine the chemical changes induced on the MoS_x-based materials as a function of the applied potential. This in situ characterization indicates that both MoS₂ and MoS₃ materials are stable under operating conditions, although sulfur terminal sites in the MoS₃ nanoparticles are converted from S-dimer (S₂²⁻) to S-monomer (S²⁻), which constitute the first sites where the hydrogen atoms are adsorbed for their subsequent evolution. In order to complete the characterization of the GOQDs-MoS_x nanohybrids, the composition and particle size were determined by X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy; whereas the HER activity was studied by conventional electrochemical techniques. Full article

(This article belongs to the Special Issue Surface Science and Catalysis of Graphene-Related 2D Materials)

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14 pages, 5391 KiB

Open AccessArticle

Glass Fracture during Micro-Scratching

by Islam Zakiev, George A. Gogotsi, Michael Storchak and Vadim Zakiev

Surfaces 2020, 3(2), 211-224; https://doi.org/10.3390/surfaces3020016 - 10 Jun 2020

Cited by 8 | Viewed by 4537

Abstract

The regularity of glass surface fracture and resistance to destruction were investigated by the methods of progressive and static microscratching with the Berkovich indenter. The research hardware was the original nanoindentation/microscratching devices and a non-contact interference profilometer for studying the morphology of the [...] Read more.

The regularity of glass surface fracture and resistance to destruction were investigated by the methods of progressive and static microscratching with the Berkovich indenter. The research hardware was the original nanoindentation/microscratching devices and a non-contact interference profilometer for studying the morphology of the formed microscratches. The regularities of the fracture stages and the cracks growth along the microscratch were established depending on the indenter applied load. Based on analysis of the microcracks profile formed at various loads on the indenter immediately after the process of applying these scratches and after several hours of rest, it was found that the process of crack propagation along the scratch continues for a long time. Taking into account this established fact, a discrete-statistical method of the cracks formation for a long time is proposed. In accordance with this method, scratching is carried out with a constant load on short and separated tracks. The load on the indenter in each track increases discretely with a certain step. The influence of the medium on the scratching process is analyzed. The breaking mechanism in the glasses scratching process is formulated as the load on the indenter increases, and a model of the glass fracture stages is proposed. Full article

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14 pages, 2486 KiB

Open AccessReview

Farnesol-Containing Macromolecular Systems for Antibiofilm Strategies

by Maria Nowacka, Anna Kowalewska and Dorota Kręgiel

Surfaces 2020, 3(2), 197-210; https://doi.org/10.3390/surfaces3020015 - 21 May 2020

Cited by 6 | Viewed by 3506

Abstract

Farnesol is a natural sesquiterpenoid and an interesting quorum-sensing molecule. Its insolubility in water is the biggest obstacle to its application for bacterial biofilm treatments since it compromises the bioavailability. Recently, an increasing interest in farnesol encapsulation or loading in polymeric materials may [...] Read more.

Farnesol is a natural sesquiterpenoid and an interesting quorum-sensing molecule. Its insolubility in water is the biggest obstacle to its application for bacterial biofilm treatments since it compromises the bioavailability. Recently, an increasing interest in farnesol encapsulation or loading in polymeric materials may be noted due to the prolonged action of the active macromolecular systems. In this short review, we present an overview of methods leading to improved interactions between farnesol and microbial biofilms. Full article

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15 pages, 9662 KiB

Open AccessReview

Diazonium Gold Salts as Novel Surface Modifiers: What Have We Learned So Far?

by Ahmad A. L. Ahmad, Bizuneh Workie and Ahmed A. Mohamed

Surfaces 2020, 3(2), 182-196; https://doi.org/10.3390/surfaces3020014 - 29 Apr 2020

Cited by 6 | Viewed by 3476

Abstract

The challenges of diazonium salts stabilization have been overcome by their isolation as metal salts such as tetrachloroaurate(III). The cleavage of molecular nitrogen from diazonium salts even at very low potential or on reducing surfaces by fine tuning the substituents on the phenyl [...] Read more.

The challenges of diazonium salts stabilization have been overcome by their isolation as metal salts such as tetrachloroaurate(III). The cleavage of molecular nitrogen from diazonium salts even at very low potential or on reducing surfaces by fine tuning the substituents on the phenyl ring expanded their applications as surface modifiers in forensic science, nanomedicine engineering, catalysis and energy. The robustness of the metal–carbon bonding produced from diazonium salts reduction has already opened an era for further applications. The integration of experimental and calculations in this field catalyzed its speedy progress. This review provides a narrative of the progress in this chemistry with stress on our recent contribution, identifies potential applications, and highlights the needs in this emerging field. For these reasons, we hope that this review paper serves as motivation for others to enter this developing field of surface modification originating from diazonium salts. Full article

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14 pages, 3154 KiB

Open AccessArticle

Ni-Doped Titanium Dioxide Films Obtained by Plasma Electrolytic Oxidation in Refrigerated Electrolytes

by Hamed Arab, Gian Luca Chiarello, Elena Selli, Giacomo Bomboi, Alberto Calloni, Gianlorenzo Bussetti, Guglielmo Albani, Massimiliano Bestetti and Silvia Franz

Surfaces 2020, 3(2), 168-181; https://doi.org/10.3390/surfaces3020013 - 17 Apr 2020

Cited by 7 | Viewed by 2918

Abstract

Porous crystalline Ni-doped TiO₂ films were produced using DC plasma electrolytic oxidation in refrigerated H₂SO₄ aqueous solutions containing NiSO₄. The crystalline phase structure consisted of a mixture of anatase and rutile, ranging from ~30 to ~80 wt [...] Read more.

Porous crystalline Ni-doped TiO₂ films were produced using DC plasma electrolytic oxidation in refrigerated H₂SO₄ aqueous solutions containing NiSO₄. The crystalline phase structure consisted of a mixture of anatase and rutile, ranging from ~30 to ~80 wt % rutile. The oxide films obtained at low NiSO₄ concentration showed the highest photocurrent values under monochromatic irradiation in the UV-vis range, outperforming pure TiO₂. By increasing NiSO₄ concentration above a threshold value, the photoelectrochemical activity of the films decreased below that of undoped TiO₂. Similar results were obtained using cyclic voltammetry upon polychromatic UV-vis irradiation. Glow discharge optical emission spectrometry (GD-OES) analysis evidenced a sulfur signal peaking at the TiO₂/Ti interface. XPS spectra revealed that oxidized Ni²⁺, S⁴⁺ and S⁶⁺ ions were included in the oxide films. In agreement with photocurrent measurements, photoluminescence (PL) spectra confirmed that less intense PL emission, i.e., a lower electron-hole recombination rate, was observed for Ni-doped samples, though overdoping was detrimental. Full article

(This article belongs to the Special Issue Surface Aspects of Semiconductor Photochemistry)

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36 pages, 17347 KiB

Open AccessReview

Catalysis Mediated by 2D Black Phosphorus Either Pristine or Decorated with Transition Metals Species

by Matteo Vanni, Maria Caporali, Manuel Serrano-Ruiz and Maurizio Peruzzini

Surfaces 2020, 3(2), 132-167; https://doi.org/10.3390/surfaces3020012 - 01 Apr 2020

Cited by 12 | Viewed by 4088

Abstract

Among the novel class of mono-elemental two-dimensional (2D) materials, termed Xenes, phosphorene is emerging as a great promise for its peculiar chemical and physical properties. This review collects a selection of the recent breakthroughs that are related to the application of phosphorene in [...] Read more.

Among the novel class of mono-elemental two-dimensional (2D) materials, termed Xenes, phosphorene is emerging as a great promise for its peculiar chemical and physical properties. This review collects a selection of the recent breakthroughs that are related to the application of phosphorene in catalysis and electrocatalysis. Noteworthy, thanks to its intrinsic Lewis basic character, pristine phosphorene turned out to be more efficient and more selective than other non-metal catalysts, in chemical processes as the electroreduction of nitrogen to ammonia or the alkylation of nucleophiles with esters. Once functionalized with transition metals nanoparticles (Co, Ni, Pd, Pt, Ag, Au), its catalytic activity has been evaluated in several processes, mainly hydrogen and oxygen evolution reactions. Under visible light irradiation, it has shown a great improvement of the activity, demonstrating high potential as a photocatalyst. Full article

(This article belongs to the Special Issue Surface Science and Catalysis of Graphene-Related 2D Materials)

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Surfaces, Volume 3, Issue 2 (June 2020) – 8 articles

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