A novel fabrication methodology for sulfur-doped ZnO nanorods as an active photoanode for improved water oxidation in visible-light regime

Exploration of isoelectronic substitution in graphene dioxide for photocatalytic and photovoltaic applications - an ab-initio study

Herein, we propose graphene dioxide (GDO) derivatives as promising materials for green hydrogen production by photocatalytic water splitting. The optoelectronic and photocatalytic properties of GDO, an insulator with a wide band gap, are tuned by designing new compositions through isovalent substitution of S/Se at the O site, Si and (B,N) at the C site. The newly predicted GDO derivatives were studied using hybrid functional calculations and our results show that several of these materials exhibit semiconducting behavior with a direct band gap value higher than 1.23 eV, hence appropriate for visible light-driven photocatalytic water splitting. The structural stability of these materials was analyzed by total energy and lattice dynamical calculations. The photo generated charge carriers possess lower effective mass and hence higher carrier mobility resulting in suppressed recombination rate and hence improving the water splitting efficiency. Apart from low excitonic binding energy, the electronic structure analysis shows that in several of these compounds the electrons and holes reside in two different atomic sites ensuring further reduction in recombination rate. The relatively higher absorption coefficient of GDO derivatives in the visible part of the solar spectrum indicates enhanced photoconversion efficiency suitable for solar cell applications also and it was further determined by photovoltaic performance parameter analysis. The band edge potential of GDO derivatives is well straddled by the water redox potential at different pHs, suggesting their potential for water splitting along with the possibility of CO2 reduction. Our findings indicate that the newly predicted compositions hold significant promise for photocatalytic as well as photovoltaic applications.

Elucidating the significance of molecular interaction between sulphur doped zinc oxide nanoparticles and serum albumin using multispectroscopic approach

Ingenious nanomaterials with improved biocompatibility and multifunctional properties are gaining vital significance in biomedical applications, including advanced drug delivery and nanotheranostics. In a biological system, these nanoparticles interact with serum proteins forming a dynamic corona that affects their biological or toxicological properties producing undesirable effects. Thus, the current study focuses on the synthesis of sulphur-doped zinc oxide nanoparticles (ZnO/S NPs) and characterizing their mechanism of interaction with serum proteins using multispectroscopic approach. ZnO/S NPs were synthesized by employing a co-precipitation approach and characterized using various analytical techniques. The results of interaction studies demonstrated that ZnO/S NPs interact with serum albumins via the static quenching process. Analysis of thermodynamic parameters (ΔG, ΔH and ΔS) revealed that the binding process is spontaneous, exothermic and van der Waals force or hydrogen bonding plays a major role. The interaction of ZnO/S NPs with tyrosine residue in bovine serum albumin was established by synchronous fluorescence spectroscopy. In addition, the results of UV-visible, circular dichroism, Fourier transform infrared, Forster's resonance energy transfer theory and dynamic light scattering spectroscopic studies revealed that the ZnO/S NPs interact with albumin by inducing the conformational changes in secondary structure and reducing the α-helix content.

A Study on Doping and Compound of Zinc Oxide Photocatalysts

As an excellent semiconductor photocatalyst, zinc oxide is widely used in the field of photocatalysis and is regarded as one of the most reliable materials to solve environmental problems. However, because its band gap energy limits the absorption of visible light and reduces the efficiency of catalytic degradation, it needs to be doped with other substances or compounded with other substances and precious metal. This paper summarizes the research on this aspect at home and abroad in recent years, introduces the doping of transition metal ions by zinc oxide, the compounding of zinc oxide with precious metals or other semiconductors, and the prospect of further improving the catalytic efficiency of zno photocatalyst is also put forward.

ZnO-based antimicrobial coatings for biomedical applications

Rapid transmission of infectious microorganisms such as viruses and bacteria through person-to-person contact has contributed significantly to global health issues. The high survivability of these microorganisms on the material surface enumerates their transmissibility to the susceptible patient. The antimicrobial coating has emerged as one of the most interesting technologies to prevent growth and subsequently kill disease-causing microorganisms. It offers an effective solution a non-invasive, low-cost, easy-in-use, side-effect-free, and environmentally friendly method to prevent nosocomial infection. Among antimicrobial coating, zinc oxide (ZnO) stands as one of the excellent materials owing to zero toxicity, high biocompatibility to human organs, good stability, high abundancy, affordability, and high photocatalytic performance to kill various infectious pathogens. Therefore, this review provides the latest research progress on advanced applications of ZnO nanostructure-based antibacterial coatings for medical devices, biomedical applications, and health care facilities. Finally, future challenges and clinical practices of ZnO-based antibacterial coating are addressed.

Strategies to Enhance ZnO Photocatalyst's Performance for Water Treatment: A Comprehensive Review

Despite the photocatalytic organic pollutant degradation using ZnO started in 1910-1911, many challenges are still ahead, and several critical issues have to be addressed. Large band gap, and short life-time of photogenerated electrons and holes are critical issues negatively affect the photocatalytic activity of ZnO. Various approaches have been introduced to overcome these issues including intrinsic doping, extrinsic doping, and heterostructure. This review introduces unique and deep insights into tuning of the photocatalytic activity of ZnO. It starts by description of how to tune the photocatalytic activity of pristine ZnO through tuning its morphology, surface area, exposed face, and intrinsic defects. Afterward, the review explains how the Z-scheme approach succeed to address the redox weakened issue of heterojunction approach. In general, this review provides a clear image that helps the researcher to tune the photocatalytic activity of pristine ZnO and its heterostructure.

Fabrication of AgNi Nano-alloy-Decorated ZnO Nanocomposites as an Efficient and Novel Hybrid Catalyst to Degrade Noxious Organic Pollutants

Contamination through industrial effluents is a major threat to the environment. Degradation of organic pollutants remains a major challenge, and semiconductor-based catalysis is reported to be a viable solution. Recently, AgNi bimetallic alloy nanoparticles attracted great attention with superior properties. We report the synthesis of AgNi nano-alloy particles immobilized over the surface of ZnO hexagonal rods through an in situ chemical co-reduction process to develop a novel AgNi@ZnO nanocomposite for catalytic applications. The crystal structure, phase purity, morphology, particle size, and other properties of the as-synthesized AgNi@ZnO nanocomposite were scrutinized using powder X-ray diffraction, scanning electron microscopy, Raman spectroscopy, energy-dispersive X-ray analysis, multipoint Brunauer-Emmett-Teller, and transmission electron microscopy. The composite exhibits excellent catalytic activity toward the reduction of nitroarenes and environment polluting organic dyes. The synthesized nanocomposite shows enhanced catalytic activity with an incredible reaction rate constant, noticeable low degradation time, and greater stability. The catalyst is easily recyclable and exhibits consecutive catalytic cycle usage.

Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses

Innovative renewable routes are potentially able to sustain the transition to a decarbonized energy economy. Green synthetic fuels, including hydrogen and natural gas, are considered viable alternatives to fossil fuels. Indeed, they play a fundamental role in those sectors that are difficult to electrify (e.g., road mobility or high-heat industrial processes), are capable of mitigating problems related to flexibility and instantaneous balance of the electric grid, are suitable for large-size and long-term storage and can be transported through the gas network. This article is an overview of the overall supply chain, including production, transport, storage and end uses. Available fuel conversion technologies use renewable energy for the catalytic conversion of non-fossil feedstocks into hydrogen and syngas. We will show how relevant technologies involve thermochemical, electrochemical and photochemical processes. The syngas quality can be improved by catalytic CO and CO2 methanation reactions for the generation of synthetic natural gas. Finally, the produced gaseous fuels could follow several pathways for transport and lead to different final uses. Therefore, storage alternatives and gas interchangeability requirements for the safe injection of green fuels in the natural gas network and fuel cells are outlined. Nevertheless, the effects of gas quality on combustion emissions and safety are considered.

C, N dual-doped ZnO nanofoams: a potential antimicrobial agent, an efficient visible light photocatalyst and SXAS studies

It is crucial to develop an environmentally friendly and low-cost method to treat industrial effluent that contains soluble dyes and microbes. Most of the photocatalysts have been studied using an external light source that increases the cost of the purification process of effluent. This study focuses on developing efficient solar photocatalytic nanofoams. The controlled growth of ZnO nanofoams (CNZ nanofoams) in a simple method of thermal oxidation using a soft template is reported. Prepared nanofoams are characterized using X-ray diffraction, scanning electon microscopy and synchrotron soft X-ray absorption spectroscopy. By photocatalysis studies under direct sunlight it was found that within 120 min CNZ nanofoams degraded 99% of the dye. In addition, antimicrobial studies of multi-drug-resistant E. Fergusonii isolated from wastewater was carried out. These antimicrobial results showed a good inhibition zone, indicating that prepared nanofoams are both an effective solar photocatalyst and an antimicrobial agent.

Current progress in developing metal oxide nanoarrays-based photoanodes for photoelectrochemical water splitting

Solar energy driven photoelectrochemical (PEC) water splitting is a clean and powerful approach for renewable hydrogen production. The design and construction of metal oxide based nanoarray photoanodes is one of the promising strategies to make the continuous breakthroughs in solar to hydrogen conversion efficiency of PEC cells owing to their owned several advantages including enhanced reactive surface at the electrode/electrolyte interface, improved light absorption capability, increased charge separation efficiency and direct electron transport pathways. In this Review, we first introduce the structure, work principle and their relevant efficiency calculations of a PEC cell. We then give a summary of the state-of the-art research in the preparation strategies and growth mechanism for the metal oxide based nanoarrays, and some details about the performances of metal oxide based nanoarray photoanodes for PEC water splitting. Finally, we discuss key aspects which should be addressed in continued work on realizing high-efficiency metal oxide based nanoarray photoanodes for PEC solar water splitting systems.

Branched CdO/ZnO Core/Shell Heterogeneous Structure and Its Enhanced Photoelectrocatalytic Performance

Branched nanostructures of semiconductors based on one-dimensional heterostructures have many promising applications in optoelectronics, supercapacitors, photocatalysts, etc. Here, we report a novel branched core/shell CdO/ZnO hetero-nanostructure that resembles a Crimson bottlebrush (Callistemon Citrinus) but with intriguing hexagonal symmetry. The nanomaterials were fabricated via an improved one-step chemical vapor deposition method and consist of a CdO wire as the core and ZnO as the shell. With cadmium acting as a catalyst, ZnO nanowires grow as perpendicular branches from the CdO/ZnO one-dimensional core/shell structure. The nanostructures were characterized with X-ray diffraction scanning and transmission electron microscopy. A homogeneous epitaxial growth mechanism has been postulated for the formation of the nanostructure. The materials show a broad and strong absorption ranging from visible to ultraviolet and a better photoelectrocatalytic properties in comparison to pure ZnO or CdO. Our synthetic strategy may open up a new way for controlled preparation of one-dimensional nanomaterials with core/shell heterostructure, which could find potential applications in solar cells and opto-electrochemical water-splitting devices.

Characterization of visible-light photo-Fenton reactions using Fe-doped ZnS (Fex-ZnS) mesoporous microspheres

PNP was efficiently degraded by a Fe_6%-ZnS catalyst through photo-Fenton-like reactions under visible light irradiation.

The magnetic and adsorption properties of ZnO1-xSx nanoparticles

Sulfur is easy to be incorporated into ZnO nanoparticles by the solution-combustion method. Herein, the magnetic and adsorption properties of a series of ZnO_1-xS_x (x = 0, 0.05, 0.1, 0.15, and 0.2) nanoparticles were systematically investigated. The X-ray diffraction patterns show that the as-prepared ZnO_1-xS_x nanoparticles have the hexagonal wurtzite structure of ZnO with a low sulfur content that gradually transforms into the zinc blende structure of ZnS when the x value is greater than 0.1. PL spectra show several bands due to different transitions, which have been explained by the recombination of free excitons or defect-induced transitions. The introduction of sulfur not only modifies the bandgap of ZnO, but also impacts the concentration of Zn vacancies. The as-prepared ZnO shows weak room-temperature ferromagnetism, and the incorporation of sulfur improves the ferromagnetism owing to the increased concentration of Zn vacancies, which may be stabilized by the doped sulfur ions. The adsorption capability of ZnO_1-xS_x nanoparticles has been significantly improved, and the process can be well described by the pseudo-first-order kinetic model and the Freundlich isotherm model. The mechanism has been confirmed to be due to the active sulfate groups existing in zinc oxysulfide nanoparticles.