Sunlight-Driven Combustion Synthesis of Defective Metal Oxide Nanostructures with Enhanced Photocatalytic Activity

Synthesis of metal oxide nanostructures through combustion routes is a promising technique owing to its simplicity, rapidity, scalability, and cost-effectiveness. Herein, a sunlight-driven combustion approach is developed to synthesize pristine metal oxides and their heterostructures. Sunlight, a sustainable energy source, is used not only to initiate the combustion reaction but also to create oxygen vacancies on the metal oxide surface. ZnO nanostructures are successfully synthesized using this novel approach, and the products exhibit higher photocatalytic activity in the decomposition of methyl orange (MO) than ZnO nanostructures synthesized by the conventional methods. The higher photocatalytic activity is due to the narrower band gap, higher porosity, smaller and more uniform particle size, surface oxygen vacancies, as well as the enhanced exciton dissociation efficiency induced by the sunlight. Porous Fe3O4 nanostructures are also prepared using this environmentally benign method. Surprisingly, few-layer Bi2O3 nanosheets are successfully obtained using the sunlight-driven combustion approach. Moreover, the approach developed here is used to synthesize Bi2O3/ZnO heterostructure exhibiting a structure of few-layer Bi2O3 nanosheets decorated with ZnO nanoparticles. Bi2O3 nanosheets and Bi2O3/ZnO heterostructures synthesized by sunlight-driven combustion route exhibit higher photocatalytic activity than their counterparts synthesized by the conventional solution combustion method. This work illuminates a potential cost-effective method to synthesize defective metal oxide nanostructures at scale. Copyright - 2019 American Chemical Society.This study was supported by University Grants Commission, India, under University with Potential for Excellence (UPE) program at University of Mysore, UGC JRF (Award No. F.19-1/2013(SA-I)), and Deanship of Scientific Research (DSR) at King Fahd University of Petroleum & Minerals (KFUPM) through project no. DF181021.Scopu

Microstructure Evaluation and Impurities in La Containing Silicon Oxynitrides

Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, we investigated the microstructure and instinctive defects in nitrogen rich La-Si-O-N glasses. Glasses were prepared by heating a powder mixture of pure La metal, Si3N4, and SiO2 in a nitrogen atmosphere at 1650-1800 °C. The microstructure and impurities in the glasses were examined by optical microscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy in conjunction with electron energy-loss spectroscopy. Analyses showed that the glasses contain a small amount of spherical metal silicide particles, mostly amorphous or poorly crystalline, and having sizes typically ranging from 1 µm and less. The amount of silicide was estimated to be less than 2 vol. %. There was no systematic relation between silicide formation and glass composition or preparation temperature. The microstructure examination revealed that the opacity of these nitrogen rich glasses is due to the elemental Si arise from the decomposition reaction of silicon nitride and silicon oxide, at a high temperature above ~1600 °C and from the metallic silicide particles formed by the reduction of silicon oxide and silicon nitride at an early stage of reaction to form a silicide intermetallic with the La metal

Role of Post-Hydrothermal Treatment on the Microstructures and Photocatalytic Activity of TiO2-Based Nanotubes

The present study demonstrates the thermal stability and photocatalytic activity of TiO2-based nanotubes with respect to post-hydrothermal treatment. Titanate nanotubes were synthesized by adapting an alkali hydrothermal method from TiO2sol using NaOH as a catalyst. The effect of post-hydrothermal heating on the properties—such as structure, morphology, textural properties, and activity—of as-synthesized one-dimensional titania nanostructure is investigated in detail. The characterizations are carried out using SEM, EDX, TEM, XRD, and a BET surface area analyzer. When heated in the presence of water in an autoclave, the protonated titanate phase of the nanotubes converts to anatase phase. Meanwhile, the tubular morphology is gradually lost as the post-hydrothermal heating duration increases. The photocatalytic activity was assessed utilizing the photo-oxidation of an amaranth dye. It is discerned that the as-prepared nanotubes are photocatalytically inactive but become active after post-hydrothermal processing. The activity trend follows the formation of the active phase—the titanate phase crystallizes into a photocatalytically-active anatase phase during post-hydrothermal heating. The effect of experimental parameters, such as reaction pH, dye concentration, and amount of catalyst, on the dye removal is studied. The findings also highlight that the role of holes/OH•− is more prominent as compared to conduction band electron/O2•− for the removal of the dye. In addition, the photocatalyst exhibited excellent stability and reusability.Theauthorswouldliketoexpresstheir appreciation to Ministry of Higher Education Malaysia for Fundamental Research Grant SchemewithProject Code: FRGS/1/2019/STG07/USM/02/12

Underwater Leidenfrost nanochemistry for creation of size-tailored zinc peroxide cancer nanotherapeutics

The dynamic underwater chemistry seen in nature is inspiring for the next generation of eco-friendly nanochemistry. In this context, green synthesis of size-tailored nanoparticles in a facile and scalable manner via a dynamic process is an interesting challenge. Simulating the volcano-induced dynamic chemistry of the deep ocean, here we demonstrate the Leidenfrost dynamic chemistry occurring in an underwater overheated confined zone as a new tool for customized creation of nanoclusters of zinc peroxide. The hydrodynamic nature of the phenomenon ensures eruption of the nanoclusters towards a much colder region, giving rise to growth of monodisperse, size-tailored nanoclusters. Such nanoparticles are investigated in terms of their cytotoxicity on suspension and adherent cells to prove their applicability as cancer nanotherapeutics. Our research can pave the way for employment of the dynamic green nanochemistry in facile, scalable fabrication of size-tailored nanoparticles for biomedical applications.Peer reviewe

Polymer-Templated Durable and Hydrophobic Nanostructures for Hydrogen Gas Sensing Applications

A simple and hands-on one-step process has been implemented to fabricate polymer-templated hydrophobic nanostructures as hydrogen gas sensing platforms. Topographic measurements have confirmed irregular hills and dips of various dimensions that are responsible for creating air bubble pockets that satisfy the Cassie–Baxter state of hydrophobicity. High-resolution field-emission scanning electron microscopy (FESEM) has revealed double-layer structures consisting of fine microscopic flower-like structures of nanoscale petals on the top of base nanostructures. Wetting contact angle (WCA) measurements further revealed the contact angle to be ~142.0° ± 10.0°. Such hydrophobic nanostructures were expected to provide a platform for gas-sensing materials of a higher surface area. From this direction, a very thin layer of palladium, ca. 100 nm of thickness, was sputtered. Thereafter, further topographic and WCA measurements were carried out. FESEM micrographs revealed that microscopic flower-like structures of nanoscale petals remained intact. A sessile drop test reconfirmed a WCA of as high as ~130.0° ± 10.0°. Due to the inherent features of hydrophobic nanostructures, a wider surface area was expected that can be useful for higher target gas adsorption sites. In this context, a customized sensing facility was set up, and H2 gas sensing performance was carried out. The surface nanostructures were found to be very stable and durable over the course of a year and beyond. A polymer-based hydrophobic gas-sensing platform as investigated in this study will play a dual role in hydrophobicity as well as superior gas-sensing characteristics

Ternary Bi2S3/MoS2/TiO2 with double Z-scheme configuration as high performance photocatalyst

Due to unique electron transport properties, nanostructured catalysts with certain morphology, such as nanotube, nanosheet and nanorods, have shown outstanding photocatalytic performance. Herein, preparation of ternary photocatalytic architecture is demonstrated using a facile microwave-assisted hydrothermal method. The as-prepared ternary photocatalyst (denoted as Bi2S3/MoS2/TiO2) comprises bismuth sulfide (Bi2S3) nanorods, molybdenum sulfide (MoS2) nanosheets, and titanium dioxide (TiO2) nanotubes. The photocatalytic performance of the as-prepared nanocomposite is evaluated by monitoring water splitting and dye degradation. The results show that the Bi2S3/MoS2/TiO2 exhibits stable and highly efficient photocatalytic hydrogen production under visible light, and photocatalytic degradation of methylene blue (MB) under sunlight. The photocatalytic performance of Bi2S3/MoS2/TiO2 is much better than that of TiO2, MoS2, or Bi2S3. The improved performance is correlated to the high surface area and the formation of the double Z-scheme heterostructure, which together render abundant catalytic sites and efficient charge separation with strong redox capability. Additionally, X-ray photoelectron spectroscopy and electron spin resonance spectroscopies, combined with reactive species trapping experiments, confirm that the surface charge transport in Bi2S3/MoS2/TiO2 occurs through the double Z-scheme approach. This work paves the way for designing more photocatalytic systems with double Z-scheme for high efficiency and wide practical applications

X-Ray Photoelectron Spectroscopy Depth Profiling of As-Grown and Annealed Titanium Nitride Thin Films

Titanium nitride thin films were grown on Si(001) and fused silica substrates by radio frequency reactive magnetron sputtering. Post-growth annealing of the films was performed at different temperatures from 300 °C to 700 °C in nitrogen ambient. Films annealed at temperatures above 300 °C exhibit higher surface roughness, smaller grain size and better crystallinity compared to the as-grown film. Bandgap of the films decreased with the increase in the annealing temperature. Hall effect measurements revealed that all the films exhibit n-type conductivity and had high carrier concentration, which also increased slightly with the increase in the annealing temperature. A detailed depth profile study of the chemical composition of the film was performed by x-ray photoelectron spectroscopy confirming the formation of Ti-N bond and revealing the presence of chemisorbed oxygen in the films. Annealing in nitrogen ambient results in increased nitrogen vacancies and non-stoichiometric TiN films