Photocatalytic Activity of S-Scheme Heterostructure for Hydrogen Production and Organic Pollutant Removal: A Mini-Review

Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties

Achieving high photoelectrochemical conversion efficiency requires the logical layout of a composite photocatalyst with optimal charge separation and transfer with ideal light harvesting capabilities to enhance the photocatalytic performance and the degradation rate towards organic pollutants. Herein, a novel In2O3/WO3@Ti4N3Tx S-scheme heterojunction was successfully synthesized and confirmed through valence band VB-XPS and Mott Schottky combined analysis. The formed MXene-doped In2O3/WO3@Ti4N3Tx S-scheme significantly enhances the charge flow and spatial separation with an improved oxidation and reduction ability. An in-built interfacial electric field at the WO3-In2O3 boundary enhanced the light-harvesting capacity, whereas Ti4N3Tx MXene offers a unique electron trapping effect which effectively lowers high charge carrier recombination rate-related photocatalytic deficit. It preserves the exceptional redox potency of the photocatalyst by providing a directed acceleration and effective separation of the photogenerated charges. A high carrier density (ND = 7.83 × 1021 cm-3) with a lower negative flat band (VFB = -0.064 V vs. Ag/AgCl) was obtained by Mott-Schottky analysis for 3 wt% In2O3/WO3@Ti4N3Tx, an indicator that a low overpotential is needed to activate photocatalytic reactions. This study, therefore, provides a novel thought for the design and fabrication of an S-scheme heterojunction for photocatalytic reactions for mineralization of organic pollutants in water and clean energy production.

Construction of 2D S-Scheme Heterojunction Photocatalyst

Semiconductor photocatalytic technology holds immense promise for converting sustainable solar energy into chemically storable energy, with significant applications in the realms of energy and the environment. However, the inherent issue of rapid recombination of photogenerated electrons and holes hinders the performance of single photocatalysts. To overcome this challenge, the construction of 2D S-scheme heterojunction photocatalysts emerges as an effective strategy. The deliberate design of dimensionality ensures a substantial interfacial area; while, the S-scheme charge transfer mechanism facilitates efficient charge separation and maximizes redox capabilities. This review commences with a fresh perspective on the charge transfer mechanism in S-scheme heterojunctions, followed by a comprehensive exploration of preparation methods and characterization techniques. Subsequently, the recent advancements in 2D S-scheme heterojunction photocatalysts are summarized. Notably, the mechanism behind activity enhancement is elucidated. Finally, the prospects for the development of 2D S-scheme photocatalysts are presented.

Photocatalytic Antimicrobials: Principles, Design Strategies, and Applications

Nowadays, the increasing emergence of antibiotic-resistant pathogenic microorganisms requires the search for alternative methods that do not cause drug resistance. Phototherapy strategies (PTs) based on the photoresponsive materials have become a new trend in the inactivation of pathogenic microorganisms due to their spatiotemporal controllability and negligible side effects. Among those phototherapy strategies, photocatalytic antimicrobial therapy (PCAT) has emerged as an effective and promising antimicrobial strategy in recent years. In the process of photocatalytic treatment, photocatalytic materials are excited by different wavelengths of lights to produce reactive oxygen species (ROS) or other toxic species for the killing of various pathogenic microbes, such as bacteria, viruses, fungi, parasites, and algae. Therefore, this review timely summarizes the latest progress in the PCAT field, with emphasis on the development of various photocatalytic antimicrobials (PCAMs), the underlying antimicrobial mechanisms, the design strategies, and the multiple practical antimicrobial applications in local infections therapy, personal protective equipment, water purification, antimicrobial coatings, wound dressings, food safety, antibacterial textiles, and air purification. Meanwhile, we also present the challenges and perspectives of widespread practical implementation of PCAT as antimicrobial therapeutics. We hope that as a result of this review, PCAT will flourish and become an effective weapon against pathogenic microorganisms and antibiotic resistance.

Novel PWO/ ZnO heterostructured nanocomposites: Synthesis, characterization, and photocatalytic performance

Photocatalytic degradation is becoming an increasingly attractive method for addressing environmental remediation challenges. In this work, the novel pure PWO/ZnO and doped PWO: Er/ZnO: Ag heterostructure nanocomposites with premier photocatalytic efficiency were synthesized via a simple co-precipitation method followed by a solvothermal procedure. X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX), and ultraviolet-visible (UV-Vis) absorbance measurements techniques were employed to characterize the structural and optical properties. HRTEM images prove the possibility of intimate contact formation at the pure and doped PWO/ZnO heterostructure nanocomposite interfaces. The photocatalytic performance of the PWO/ZnO heterostructure nanocomposites in the degradation of the methylene blue (MB) and methyl orange (MO) dyes under UVA light was evaluated. The photocatalysts' ability in the mineralization of organic pollutants was confirmed by the TOC test. BET and zeta potential analyses were used to study the dye adsorption mechanisms. Additionally, adsorption isotherms and kinetics have been investigated to describe the adsorption of MB and MO into the samples. The degradation rates of MB with PWO/ZnO and PWO: Er/ZnO: Ag heterostructure nanocomposites were 4.7 and 6.6 times higher than those of PWO and PWO: Er nanoparticles. This rate for MO degradation is 5.2 and 3.5 times higher than that of pure PWO and PWO: Er nanoparticles, respectively. This study outlines an easy method to develop innovative, highly effective heterostructure nanocomposites capable of converting UVA light into photocatalytic performance.

Hydrogen Production as a Clean Energy Carrier through Heterojunction Semiconductors for Environmental Remediation

Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is stimulated by exposure to light and generates an electron–hole pair that subsequently takes part in redox reactions leading to hydrogen production. This review paper tries to thoroughly introduce and discuss various semiconductor-based photocatalysis processes for environmental remediation with a specific focus on heterojunction semiconductors with the hope that it will pave the way for new designs with higher performance to protect the environment.

Synergistic effect of sorption and photocatalysis on the degree of dye removal in single and multicomponent systems on ZnO-SnO2

The paper presents the photodegradation process of one-, two- and three-component dye mixtures by ZnO-SnO₂ nanoparticles. After 60 min of running the processes, the dye removal efficiencies of 76.44, 72.69, 62.43, 77.00 and 92.46% for MB, RB, TB, MO and YQ degradation, respectively, were obtained. For binary and ternary systems, dye removal efficiencies for all cases exceeded 70%. When the binary and ternary dye mixtures were tested, the photodegradation efficiencies of ZnO-SnO₂ were similar to those of the single mixtures, indicating that this material could be used in industrial applications in the future. The focus of the study was to investigate the effect of sorption on photodegradation efficiency and the presence of both cationic and anionic dyes on their degradation efficiency under UV light. The significance of the effect of sorption on the degradation efficiency allowing the interaction of the catalyst with the dyes removed was confirmed. The main factor influencing sorption and consequently photocatalysis was the nature of the dye. It was confirmed that the positively charged ZnO-SnO₂ surface effectively sorbs the dyes and causes their degradation.

Progress on photocatalytic semiconductor hybrids for bacterial inactivation

Due to its use of green and renewable energy and negligible bacterial resistance, photocatalytic bacterial inactivation is to be considered a promising sterilization process. Herein, we explore the relevant mechanisms of the photoinduced process on the active sites of semiconductors with an emphasis on the active sites of semiconductors, the photoexcited electron transfer, ROS-induced toxicity and interactions between semiconductors and bacteria. Pristine semiconductors such as metal oxides (TiO₂ and ZnO) have been widely reported; however, they suffer some drawbacks such as narrow optical response and high photogenerated carrier recombination. Herein, some typical modification strategies will be discussed including noble metal doping, ion doping, hybrid heterojunctions and dye sensitization. Besides, the biosafety and biocompatibility issues of semiconductor materials are also considered for the evaluation of their potential for further biomedical applications. Furthermore, 2D materials have become promising candidates in recent years due to their wide optical response to NIR light, superior antibacterial activity and favorable biocompatibility. Besides, the current research limitations and challenges are illustrated to introduce the appealing directions and design considerations for the future development of photocatalytic semiconductors for antibacterial applications.

Main Hydrogen Production Processes: An Overview

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use.