Surface Modifications of Layered Perovskite Oxysulfide Photocatalyst YTiOS to Enhance Visible-Light-Driven Water Splitting.

Increasing the efficiency of visible-light-driven water splitting systems will require improvements in the charge separation characteristics and redox reaction kinetics associated with narrow-bandgap photocatalysts. Although the traditional approach of loading a single cocatalyst on selective facets provides reaction sites and reduces the reaction overpotential, pronounced surface charge carrier recombination still results in limited efficiency increases. The present study demonstrates a significant improvement in the hydrogen evolution activity of the layered single-crystal photocatalyst YTiOS.

Phototriggered Hydrogen Persulfide Donors via Hydrosulfide Radical Formation Enhancing the Reactive Sulfur Metabolome in Cells.

Hydrogen persulfide (HS) is an important sulfur-containing signaling molecule that plays a crucial role in the homeostasis of various organ systems, such as the renal, cardiovascular, liver, and gastrointestinal systems. However, research on HS in biological settings is still challenging due to its instability and high reactivity. Compounds that can controllably release HS (also known as donors) are thus crucial research tools.

Best Practices for Assessing Performance of Photocatalytic Water Splitting Systems.

Photocatalytic water splitting has become a very popular research subject in recent years. Consequently, it is important to report appropriately standardized experimental data, so that each researcher can properly understand the results generated by others. However, experimental methods and measures of photocatalytic performance are not yet sufficiently systematic.

The SOD1 Inhibitor, LCS-1, Oxidizes H2S to Reactive Sulfur Species, Directly and Indirectly, through Conversion of SOD1 to an Oxidase.

LCS-1, a putative selective inhibitor of SOD1, is a substituted pyridazinone with rudimentary similarity to quinones and naphthoquinones. As quinones catalytically oxidize HS to biologically active reactive sulfur species (RSS), we hypothesized LCS-1 might have similar attributes. Here, we examine LCS-1 reactions with HS and SOD1 using thiol-specific fluorophores, liquid chromatography-mass spectrometry, electron paramagnetic resonance (EPR), UV-vis spectrometry, and oxygen consumption.

Reaction Mechanisms of HS Oxidation by Naphthoquinones.

1,4-naphthoquinones (NQs) catalytically oxidize HS to per- and polysufides and sulfoxides, reduce oxygen to superoxide and hydrogen peroxide, and can form NQ-SH adducts through Michael addition. Here, we measured oxygen consumption and used sulfur-specific fluorophores, liquid chromatography tandem mass spectrometry (LC-MS/MS), and UV-Vis spectrometry to examine HS oxidation by NQs with various substituent groups. In general, the order of HS oxidization was DCNQ ~ juglone > 1,4-NQ > plumbagin >DMNQ ~ 2-MNQ > menadione, although this order varied somewhat depending on the experimental conditions.

Carbon Nanotubes as a Solid-State Electron Mediator for Visible-Light-Driven Z-Scheme Overall Water Splitting.

So-called Z-scheme systems, which typically comprise an H evolution photocatalyst (HEP), an O evolution photocatalyst (OEP), and an electron mediator, represent a promising approach to solar hydrogen production via photocatalytic overall water splitting (OWS). The electron mediator transferring photogenerated charges between the HEP and OEP governs the performance of such systems. However, existing electron mediators suffer from low stability, corrosiveness to the photocatalysts, and parasitic light absorption.

Longevity control by supersulfide-mediated mitochondrial respiration and regulation of protein quality.

Supersulfides, which are defined as sulfur species with catenated sulfur atoms, are increasingly being investigated in biology. We recently identified pyridoxal phosphate (PLP)-dependent biosynthesis of cysteine persulfide (CysSSH) and related supersulfides by cysteinyl-tRNA synthetase (CARS). Here, we investigated the physiological role of CysSSH in budding yeast (Saccharomyces cerevisiae) by generating a PLP-binding site mutation K109A in CRS1 (the yeast ortholog of CARS), which decreased the synthesis of CysSSH and related supersulfides and also led to reduced chronological aging, effects that were associated with an increased endoplasmic reticulum stress response and impaired mitochondrial bioenergetics.

Efficient and stable visible-light-driven Z-scheme overall water splitting using an oxysulfide H evolution photocatalyst.

So-called Z-scheme systems permit overall water splitting using narrow-bandgap photocatalysts. To boost the performance of such systems, it is necessary to enhance the intrinsic activities of the hydrogen evolution photocatalyst and oxygen evolution photocatalyst, promote electron transfer from the oxygen evolution photocatalyst to the hydrogen evolution photocatalyst, and suppress back reactions. The present work develop a high-performance oxysulfide photocatalyst, SmTiOS, as an hydrogen evolution photocatalyst for use in a Z-scheme overall water splitting system in combination with BiVO as the oxygen evolution photocatalyst and reduced graphene oxide as the solid-state electron mediator.

Sub-50 nm perovskite-type tantalum-based oxynitride single crystals with enhanced photoactivity for water splitting.

A long-standing trade-off exists between improving crystallinity and minimizing particle size in the synthesis of perovskite-type transition-metal oxynitride photocatalysts via the thermal nitridation of commonly used metal oxide and carbonate precursors. Here, we overcome this limitation to fabricate ATaON (A = Sr, Ca, Ba) single nanocrystals with particle sizes of several tens of nanometers, excellent crystallinity and tunable long-wavelength response via thermal nitridation of mixtures of tantalum disulfide, metal hydroxides (A(OH)), and molten-salt fluxes (e.g.

Criteria for Efficient Photocatalytic Water Splitting Revealed by Studying Carrier Dynamics in a Model Al-doped SrTiO Photocatalyst.

Overall water splitting (OWS) using semiconductor photocatalysts is a promising method for solar fuel production. Achieving a high quantum efficiency is one of the most important prerequisites for photocatalysts to realize high solar-to-fuel efficiency. In a recent study (Nature 2020, 58, 411-414), a quantum efficiency of almost 100 % has been achieved in an aluminum-doped strontium titanate (SrTiO  : Al) photocatalyst.

An Oxysulfide Photocatalyst Evolving Hydrogen with an Apparent Quantum Efficiency of 30 % under Visible Light.

Photocatalytic water splitting is a simple means of converting solar energy into storable hydrogen energy. Narrow-band gap oxysulfide photocatalysts have attracted much attention in this regard owing to the significant visible-light absorption and relatively high stability of these compounds. However, existing materials suffer from low efficiencies due to difficulties in synthesizing these oxysulfides with suitable degrees of crystallinity and particle sizes, and in constructing effective reaction sites.

Flux-Assisted Synthesis of Y Ti O S for Photocatalytic Hydrogen and Oxygen Evolution Reactions.

Photocatalytic water splitting is an ideal means of producing hydrogen in a sustainable manner, and developing highly efficient photocatalysts is a vital aspect of realizing this process. The photocatalyst Y Ti O S (YTOS) is capable of absorbing at wavelengths up to 650 nm and exhibits outstanding thermal and chemical durability compared with other oxysulfides. However, the photocatalytic performance of YTOS synthesized using the conventional solid-state reaction (SSR) process is limited owing to the large particle sizes and structural defects associated with this synthetic method.

Cystathionine γ-Lyase Self-Inactivates by Polysulfidation during Cystine Metabolism.

Cystathionine γ-lyase (CSE) is an enzyme responsible for the biosynthesis of cysteine from cystathionine in the final step of the transsulfuration pathway. It also has β-lyase activity toward cystine, generating cysteine persulfide (Cys-SSH). The chemical reactivity of Cys-SSH is thought to be involved in the catalytic activity of particular proteins via protein polysulfidation, the formation of -S-(S)n-H on their reactive cysteine residues.

Co-doping of a LaTiCuAgOS photocatalyst ( < 700 nm) with Ga and Al to enhance photocatalytic H evolution.

LaTiCuAgOS (LTCA) ( < 700 nm) can function as a photocatalyst for H evolution. Co-doping LTCA with Ga and Al at Ti sites effectively enhanced the H evolution activity of LTCA, yielding an apparent quantum efficiency of 18% at 420 nm. The activity of this material was greater than that previously reported for Ga-doped LTCA by a factor of 1.

A perspective on two pathways of photocatalytic water splitting and their practical application systems.

Photocatalytic water splitting has been widely studied as a means of converting solar energy into hydrogen as an ideal energy carrier in the future. Systems for photocatalytic water splitting can be divided into one-step excitation and two-step excitation processes. The former uses a single photocatalyst while the latter uses a pair of photocatalysts to separately generate hydrogen and oxygen.

Overall Water Splitting by a SrTaON-Based Photocatalyst Decorated with an Ir-Promoted Ru-Based Cocatalyst.

The development of narrow-bandgap photocatalysts for one-step-excitation overall water splitting (OWS) remains a critical challenge in the field of solar hydrogen production. SrTaON is a photocatalytic material having a band structure suitable for OWS under visible light (λ ≤ 600 nm). However, the presence of defects in the oxynitride and the lack of cocatalysts to promote simultaneous hydrogen and oxygen evolution make it challenging to realize OWS using this material.

A hygroscopic nano-membrane coating achieves efficient vapor-fed photocatalytic water splitting.

Efficient water vapor splitting opens a new strategy to develop scalable and corrosion-free solar-energy-harvesting systems. This study demonstrates highly efficient overall water splitting under vapor feeding using Al-doped SrTiO (SrTiO:Al)-based photocatalyst decorated homogeneously with nano-membrane TiO or TaO thin layers (<3 nm). Here, we show the hygroscopic nature of the metal (hydr)oxide layer provides liquid water reaction environment under vapor, thus achieving an AQY of 54 ± 4%, which is comparable to a liquid reaction.

Methods in sulfide and persulfide research.

Sulfides and persulfides/polysulfides (R-S-R', n > 2; R-S-H, n > 1) are endogenously produced metabolites that are abundant in mammalian and human cells and tissues. The most typical persulfides that are widely distributed among different organisms include various reactive persulfides-low-molecular-weight thiol compounds such as cysteine hydropersulfide, glutathione hydropersulfide, and glutathione trisulfide as well as protein-bound thiols. These species are generally more redox-active than are other simple thiols and disulfides.

Photocatalytic solar hydrogen production from water on a 100-m scale.

The unprecedented impact of human activity on Earth's climate and the ongoing increase in global energy demand have made the development of carbon-neutral energy sources ever more important. Hydrogen is an attractive and versatile energy carrier (and important and widely used chemical) obtainable from water through photocatalysis using sunlight, and through electrolysis driven by solar or wind energy. The most efficient solar hydrogen production schemes, which couple solar cells to electrolysis systems, reach solar-to-hydrogen (STH) energy conversion efficiencies of 30% at a laboratory scale.

Chemical Biology of Reactive Sulfur Species: Hydrolysis-Driven Equilibrium of Polysulfides as a Determinant of Physiological Functions.

Polysulfide species ( R-S-R',  > 2; and R-S-H,  > 1) exist in many organisms. The highly nucleophilic nature of hydropersulfides and hydropolysulfides contributes to the potent antioxidant activities of polysulfide species that protect organisms against oxidative and electrophilic stresses. Accumulating evidence suggests that organic polysulfides (R-S-R') readily undergo alkaline hydrolysis, which results in formation of both nucleophilic hydrosulfide/polysulfide (R-SH) and electrophilic sulfenic acid (R'SOH) species.

Surface Modifications of (ZnSe)(CuGaSe) to Promote Photocatalytic Z-Scheme Overall Water Splitting.

Charge separation is crucial for an efficient artificial photosynthetic process, especially for narrow-bandgap metal sulfides/selenides. The present study demonstrates the application of a pn junction to particulate metal selenides to enhance photocatalytic Z-scheme overall water splitting (OWS). The constructed pn junction of CdS-(ZnSe)(CuGaSe) significantly boosted charge separation.

Simultaneously Tuning the Defects and Surface Properties of TaN Nanoparticles by Mg-Zr Codoping for Significantly Accelerated Photocatalytic H Evolution.

The simultaneous control of the defect species and surface properties of semiconducting materials is a crucial aspect of improving photocatalytic performance, yet it remains challenging. Here, we synthesized Mg-Zr-codoped single-crystalline TaN (TaN:Mg+Zr) nanoparticles by a brief NH nitridation process, exhibiting photocatalytic water reduction activity 45 times greater than that of pristine TaN under visible light. A coherent picture of the relations between the defect species (comprising reduced Ta, nitrogen vacancies and oxygen impurities), surface properties (associated with dispersion of the Pt cocatalyst), charge carrier dynamics, and photocatalytic activities was drawn.

Sequential cocatalyst decoration on BaTaON towards highly-active Z-scheme water splitting.

Oxynitride photocatalysts hold promise for renewable solar hydrogen production via water splitting owing to their intense visible light absorption. Cocatalyst loading is essential for activation of such oxynitride photocatalysts. However, cocatalyst nanoparticles form aggregates and exhibit weak interaction with photocatalysts, which prevents eliciting their intrinsic photocatalytic performance.