Construction of dual sites on FeS2 surface for enhanced electrocatalytic reduction of nitrite to ammonia

Cost-effective iron sulfides (FeS2) hold great potential as high-performance catalysts for NO2- electroreduction to NH3 (NO2ER), which is hindered by the weak NO2 activation. Herein, the design of nonmetal-doped FeS2 electrocatalysts was initially conducted by density functional theory (DFT) computations. We found that doping with different nonmetal atoms effectively not only regulates the electronic structures of the d-electrons of Fe atoms but also creates the unique p-d hybridized dual active sites, thereby boosting the efficient NO2 activation. Owing to the optimal NO2 adsorption strength, N-doped FeS2 demonstrates a low limiting potential for the NO2--to-NH3 conversion, thus significantly improving NO2ER activity. Direct experimental evidence was provided afterward: an NH3 yield rate of 424.5 μmol/hcm-2 with a 92.4 % Faradaic efficiency was achieved. Our findings not only suggest a promising NO2ER catalyst through theoretical computations to guide experiments but also provide a comprehensive understanding of the structure-properties relationship.

Leaf-like MSX/TiN heterojunction photocathodes mimicking plant cell - An effective strategy to enhance photoelectrocatalytic carbon dioxide reduction and systematic mechanism investigation

Semiconductors, such as metal oxides and metal sulfides (MSX), are widely investigated as effectively catalytic materials to convert carbon dioxide (CO2) and water into chemicals under simulated solar light. These valuable investigations might address both the energy crisis and climate change in our modern society. Herein, a novel strategy to construct leaf-like heterojunctions of VS-ZnIn2S4/TiN-x is reported. The new semiconductor heterojunctions were then applied to photoelectrocatalytic CO2 reduction, achieving excellent performance (formate formation rate of 1173.2 μM h-1 cm-2) attributed to the plant cell-like morphology and enhanced electron mobility from the heterojunction interfaces to the active sites on the surface. Our findings suggest that titanium nitride (TiN) with good conductivity can improve the photoelectrocatalytic ability of MSX through heterojunction construction. The photocathode VS-ZnIn2S4/TiN-3 exhibits 81.0 % selectivity toward C2 products by optimizing the material structure and reaction conditions. According to the systematic investigation of operando Fourier transform infrared (FTIR) spectra, common intermediates such as *COO-, *COOH, *CO, *CHO, *COCHO, and *COCH3 reported in the literature were carefully verified. Among these, the carbene specie serve as the key intermediate responsible for generating other intermediates and resulting in all products.

Developing a vanillin-derived imidazo-pyridin-containing fluorescent probe for imaging cysteine in living pulmonary cells under oxygen supply variation

In this work, derived from vanillin and imidazo-pyridin backbone, a fluorescent probe IPV-Cys was developed for imaging the cysteine (Cys) level in living pulmonary cells under oxygen supply variation. By mimicking the oxygen supply variation in both the solution test and cellular imaging, the optical performance and imaging effect of IPV-Cys was investigated. In the solution system, the oxygen supply variation caused no impact on the reporting signals. The fluorescence reporting signal intensity at 490 nm suggested the enhancement along with the increase of the Cys concentration. The advantages of IPV-Cys included relatively high sensitivity, high stability, and high selectivity. On the basis of the low cyto-toxicity, IPV-Cys achieved the monitoring the endogenous Cys level in in living pulmonary cells and the impact of the oxygen supply variation by reporting fluorescence signals. The information here was meaningful for both the pre-clinical diagnosis and surgical techniques.

A novel structurally modified isophorone fluorescent probe for H2S detection

Hydrogen sulfide (H2S) has a comprehensive contribution to the normal operation and stability of organisms and is also present in environmental water samples and food deterioration. Thus, it is exceedingly promising and significant to develop a highly sensitive detection technique for tracing H2S. Inspired by this, we designed and synthesized a new fluorescent probe 2-[3-[2-[3-bromo-4-(2,4- dinitrobenzenesulfonate)] ethenyl]-5,5-dimethyl-2-cyclohexen-1-ylidene]propanedinitrile (SP-Br) for hydrosulfide ion detection by introducing bromine atom. Compared with reported H2S probes based on the same fluorescent parent, SP-Br has longer fluorescence emission (λem = 670 nm), shorter response time (3 min), lower detection limit (149 nM), and wider detection range (0-30 nM). SP-Br can emit weak yellow fluorescence, and the emission intensity at 670 nm is considerably enhanced in the presence of hydrosulfide ions. The identification mechanism of hydrosulfide ion by SP-Br was verified by high-resolution mass spectrometry, fluorescence, and UV-vis absorption spectroscopy. In addition, SP-Br has been successfully applied to the monitoring of actual water samples and beer samples and has certain development prospects and value in the fields of environmental pollution and food quality analysis.

Site engineering of linear conjugated polymers to regulate oxygen adsorption affinity for boosting photocatalytic production of hydrogen peroxide without sacrificial agent

Artificial photosynthesis of hydrogen peroxide (H2O2) is a hopeful alternative to the industrial anthraquinone process. However, rational fabrication of the photocatalysts for the production of H2O2 without any sacrificial agents is still a formidable challenge. Herein, two kinds of linear conjugated polymers (LCPs) including pyridinic N functionalized polymer (DEB-N2) and pyridinic N non-contained polymer (DEB-N0) were successfully synthesized. DEB-N2 displays enhanced light capturing ability and good dispersion in water, leading to a substantial initial H2O2 generation rate of 3492μmol g-1h-1 as well as remarkable photocatalytic stability in pure water. Furthermore, the temperature programmed desorption (TPD) and density functional theory (DFT) analysis reveal that highly electronegative pyridine-N atoms in DEB-N2 boost the adsorption affinity of oxygen molecules, which facilitates the occurrence of the oxygen reduction reaction, therefore enhancing the performance of photocatalytic H2O2 production. This study unveils that the presence of pyridinic N in DEB-N2 has a significant impact on photocatalytic H2O2 production, suggesting the precise manipulation of the chemical structure of polymer photocatalysts is essential to achieve efficient solar-to-chemical energy conversion.

Cu-doped CdZnS nanocrystals: a leap forward in selective photocatalytic CO2 reduction to methane

Our research has demonstrated a significant correlation between the Cu doping concentration in CdZnS and its photocatalytic performance, with CZS-2 exhibiting a 15-fold increase in methane (CH4) production rate compared to pristine CZS, reaching a peak value of 519.2 μL g-1 h-1. Moreover, CZS-2 demonstrates an unprecedented CH4 selectivity of 85.3%, surpassing previously reported values for analogous systems. In-depth electrochemical analysis reveals that Cu doping strategically modifies the electronic structure of CZS-x, facilitating efficient charge separation and transfer. This optimization minimizes charge recombination, leading to the selective promotion of CO2 reduction to CH4.

Atomic Manipulation to Create High-Valent Fe4+ for Efficient and Ultrastable Oxygen Evolution at Industrial-Level Current Density

Manipulating the electronic structure of a catalyst at the atomic level is an effective but challenging way to improve the catalytic performance. Here, by stretching the Fe-O bond in FeOOH with an inserted Mo atom, a Fe-O-Mo unit can be created, which will induce the formation of high-valent Fe4+ during the alkaline oxygen evolution reaction (OER). The highly active Fe4+ state has been clearly revealed by in situ X-ray absorption spectroscopy, which can both enhance the oxidation capability and lead to an efficient and stable adsorbate evolution mechanism (AEM) pathway for the OER. As a result, the obtained Fe-Mo-Ni3S2 catalyst exhibits both superior OER activity and outstanding stability, which can achieve an industrial-level current density of 1 A cm-2 at a low overpotential of 259 mV (at 60 °C) and can stably work at the large current for more than 2000 h. Moreover, by coupling with commercial Pt/C, the Fe-Mo-Ni3S2∥Pt/C system can be used in the anion exchange membrane cell to acquire 1 A cm-2 for overall water splitting at 1.68 V (2.03 V for 4 A cm-2), outperforming the benchmark RuO2∥Pt/C system. The efficient, low-cost, and ultrastable OER catalyst enabled by manipulating the atomic structure may provide potential opportunities for future practical water splitting.

Unlocking the Electrocatalytic Behavior of Cu2MnS2 Nanoflake-Anchored rGO for the Oxygen Evolution Reaction in an Alkaline Medium

A catalyst of the oxygen evolution reaction (OER) that is viable, affordable, and active for effective water-splitting applications is critical. A variety of electrocatalysts have been discovered to replace noble metal-based catalysts. Of these, transition metal-based sulfides are essential for incorporating carbonaceous materials to improve electrical conductivity, resulting in better electrocatalytic performance. Our study illustrates the synthesis of Cu2MnS2 (CMS) nanoflakes and their different rGO composites (10 to 40 wt %) via a hydrothermal technique for an effective water oxidation reaction. The X-ray diffraction pattern reveals that the prepared Cu2MnS2 nanoflakes exhibit a cubic crystal structure. The high-resolution scanning electron microscopy and the high resolution transmission electron microscopy images corroborate the formation of the nanoflake-like morphology of Cu2MnS2 with the strong interaction of rGO. The selected area electron diffraction analysis pattern reveals a polycrystalline nature. The Fourier transform infrared spectrum shows the existence of a metal sulfur vibrational band at 590 cm-1, and Raman analysis infers the presence of rGO. The X-ray photoelectron spectroscopy spectra reveal the oxidation states of the elements present in the samples. Using Brunauer-Emmett-Teller analysis, the surface area of CMS-20 is found to be 117.04 m2/g. The measured OER overpotentials using linear sweep volammetry and the values are 380, 370, 340, 376, and 400 mV at 10 mA/cm2 for CMS, CMS-10, CMS-20, CMS-30, and CMS-40, respectively, and the corresponding Tafel slope values are 179, 158, 149, 206, and 240 mV/decade, respectively. The electrochemical active surface area is estimated using cyclic voltammetry for all of the catalysts, where CMS-20 showed a larger surface area. Also, the same catalyst exhibits good stability for ∼24 h at a constant potential, which is confirmed via chronoamperometry. Thus, combining transition metal-based sulfides with carbonaceous materials indicates improved catalytic behavior for the preparation of high-performance OER electrocatalysts. Overall, the prepared CMS-20 performed as an efficient OER electrocatalyst and can be utilized for practical applications in energy conversion.

The Influence of Exogenous CdS Nanoparticles on the Growth and Carbon Assimilation Efficiency of Escherichia coli

This study investigated the impact of CdS nanoparticles (NPs) on Escherichia coli growth and metabolism under varying conditions. Under illumination, CdS NPs significantly enhanced bacterial growth, glucose assimilation, and biomass accumulation. Key metabolic and stress response genes showed increased expression, indicating improved ATP synthesis and oxidative stress resistance. Additionally, CdS NPs enhanced the electrochemical properties of E. coli, promoting efficient electron transfer. No significant changes were observed in the dark. These findings suggest that light-activated CdS NPs promote E. coli growth and metabolic efficiency by upregulating crucial genes involved in growth and oxidative stress management.

Visible light mediated photocatalysis by lanthanide metal-organic frameworks: enhanced specificity and mechanistic insights

The utilization of earth-abundant photosensitizers with visible light absorption to enable sustainable photocatalysis is a long-standing challenge. Overcoming such a challenge, in this work, two lanthanide (Ln3+ = Tb, Eu) based metal-organic frameworks (Ln-MOFs) have been synthesized utilizing a Co3+-based metalloligand. Both Ln-MOFs function as remarkable photocatalysts for the selective oxidation of assorted alcohols and sulfides to their corresponding aldehydes/ketones and sulfoxides using visible light. The photophysical behavior of both Ln-MOFs and mechanism of photocatalysis is comprehensively investigated using time-resolved transient absorption spectroscopy, electrochemical impedance spectroscopy, electron paramagnetic resonance spectroscopy, photoluminescence and phosphorescence studies. In both Ln-MOFs, a metalloligand acts as a light-harvester, being excited by visible light, while Ln3+ ions endow the resulting MOFs with long-lived triplet excited states. Ultrafast transient absorption spectroscopy, further supported by electron paramagnetic resonance spectra, revealed excited-state electron transfer from metalloligands to the Ln3+ ions and transient generation of Ln2+ sites alongside the facilitation of intersystem crossing. The excited Ln2+ ions transfer energy to the ground-state triplet oxygen (3O2) to generate singlet oxygen (1O2). The HOMO-LUMO positions of both Ln-MOFs support the generation of ˙O2 - and 1O2 but inhibit strongly-oxidizing yet non-selective ˙OH radicals. Scavenger experiments, 1O2 traps and electron paramagnetic resonance spectra confirmed the generation of singlet oxygen. The heavy-metal effect of a lanthanide ion in Ln-MOFs for the generation of triplet excitons is confirmed by the synthesis of a non-heavy-metal analogue involving a zinc ion via a single-crystal-to-single-crystal transformation strategy. The present results are noteworthy and may aid in the development of other earth-abundant metalloligand-based photocatalysts for challenging yet sustainable catalysis.

Sparkling Synergy: Enhancing Hydrogen Evolution with a Mesoporous CoP/FeP Interface

The reaction kinetics is predominantly determined by the surface and interface engineering of electrocatalysts. Herein, we demonstrate the growth of cobalt monophosphide and iron monophosphide (CoP/FeP) with an effective solid interface. The surface of CoP/FeP is mesoporous, which is obtained by phosphidizing mesoporous CoFe2O4. The CoP/FeP electrode exhibits substantially superior hydrogen evolution reaction (HER) performance compared to CoP and FeP. The overpotentials (η) required to generate 10 mA cm-2 are determined to be around 98 mVRHE (CoP/FeP), 220 mVRHE (FeP), and 265 mVRHE (CoP) in an acidic electrolyte. The exchange current density and Tafel slopes suggest that CoP/FeP has better redox properties and kinetic abilities compared to FeP and CoP. Furthermore, the CoP/FeP electrode exhibits reduced electrochemical impedance and superior surface charge transport characteristics in comparison to both the CoP and FeP electrodes. In addition to having a greater number of catalytically active sites, the turnover frequency of CoP/FeP is approximately 2 and 5 times higher than that of FeP and CoP, respectively. The CoP/FeP electrode maintains a consistent current density of around 25 mA cm-2 for a continuous period of 24 h during the HER, attesting to the excellent durability of the CoP/FeP electrode. In addition, a relationship between differential hydrogen adsorption energy (ΔEH), the corresponding Gibbs free energy change (ΔGH), and the hydrogen coverage on distinct surfaces, namely, CoP, FeP, and CoP/FeP, is established. The calculation findings show that the CoP/FeP surface, which is predominantly exposed with CoP, exhibits the highest catalytic potential for the HER. The estimation of the specific HER activity of the electrodes, normalized to the electrochemically active surface area, corroborates the calculation findings.

Polytypic metal chalcogenide nanocrystals

By engineering chemically identical but structurally distinct materials into intricate and sophisticated polytypic nanostructures, which often surpass their pure phase objects and even produce novel physical and chemical properties, exciting applications in the fields of photovoltaics, electronics and photocatalysis can be achieved. In recent decades, various methods have been developed for synthesizing a library of polytypic nanocrystals encompassing IV, III-V and II-VI polytypic semiconductors. The exceptional performances of polytypic metal chalcogenide nanocrystals have been observed, making them highly promising candidates for applications in photonics and electronics. However, achieving high-precision control over the morphology, composition, crystal structure, size, homojunctions, and periodicity of polytypic metal chalcogenide nanostructures remains a significant synthetic challenge. This review article offers a comprehensive overview of recent progress in the synthesis and control of polytypic metal chalcogenide nanocrystals using colloidal synthetic strategies. Starting from a concise introduction on the crystal structures of metal chalcogenides, the subsequent discussion delves into the colloidal synthesis of polytypic metal chalcogenide nanocrystals, followed by an in-depth exploration of the key factors governing polytypic structure construction. Subsequently, we provide comprehensive insights into the physical properties of polytypic metal chalcogenide nanocrystals, which exhibit strong correlations with their applications. Thereafter, we emphasize the significance of polytypic nanostructures in various applications, such as photovoltaics, photocatalysis, transistors, thermoelectrics, stress sensors, and the electrocatalytic hydrogen evolution. Finally, we present a summary of the recent advancements in this research field and provide insightful perspectives on the forthcoming challenges, opportunities, and future research directions.

Size Dependent Photocatalytic Activity of Mesoporous ZnIn2S4 Nanocrystal Networks

Understanding of the band-edge electronic structure and charge-transfer dynamics in size-confined nanostructures is vital in designing new materials for energy conversion applications, including green hydrogen production, decomposition of organic pollutants and solar cells. In this study, a series of mesoporous materials comprising continuous networks of linked zinc indium sulfide (ZnIn2S4) nanocrystals with a tunable diameter (ranging from 4 to 12 nm) is reported. These nanomaterials demonstrate intriguing size-dependent electronic properties, charge-transfer kinetics and photocatalytic behaviors. Our extensive characterizations uncover strong size effects on the catalytic activity of constituent ZnIn2S4 nanocrystals in the photochemical hydrogen evolution reaction. As an outcome, the optimized single-component ZnIn2S4 mesostructure produces hydrogen at a 7.8 mmol gcat -1 h-1 release rate under ultraviolet (UV)-visible light irradiation associated with an apparent quantum yield (AQY) of 17.2% at 420 ± 10 nm, far surpassing its microstructured counterpart by a factor of 10.7×. These findings provide a valuable perspective for the rational design of semiconductor nanostructures through synthetic engineering, aiming at the development of high-performance catalysts for zero-carbon energy-related applications.

Dissolution Manufacturing Strategy for the Facile Synthesis of Nanoporous Metallic Glass Multifunctional Catalyst

The quest for heightened energy efficiency is inextricably linked to advancements in energy storage and conversion technologies, wherein multifunctional catalysts play a pivotal role by mitigating the slow kinetics endemic to many catalytic reactions. The intricate synthesis and bespoke design of such catalysts, however, present notable challenges. Addressing this, the present study capitalizes on a novel dissolution manufacturing strategy to engineer self-supporting, nanoporous multifunctional electrocatalysts, circumventing the prevalent issue of customizing catalytic functionalities upon demand. This innovative approach grants the flexibility to finely tune the incorporation of active species and metalloid binders, culminating in the creation of a self-supporting nanoporous metal glass electrocatalyst doped with RuO2 (NPMG@RuO2) with outstanding performance in alkaline media. The catalyst showcases superior electrocatalytic activity, achieving low overpotentials of 41.50 mV for the Hydrogen Evolution Reaction and 226.0 mV for Oxygen Evolution Reaction alongside sustained stability over 620 hours.These achievements are attributed to the distinct nanoporous architecture that ensures a high density of catalytic sites and mechanical strength, bolstered by the synergistic interplay between RuO2 and Pt-based metallic glass. The findings provide a versatile template for the development of nanoporous multifunctional catalysts, signifying a leap forward in the realm of energy conversion technologies.

Reasonable Design and Deep Insight of Efficient Integrated Photorechargeable Li-Ion Batteries by Using a Cu/CuO/Cu2S Electrode

Herein, Cu-foam-supported CuO nanowire arrays covered with Cu2S nanosheet substrates (Cu/CuO/Cu2S) are adopted as efficient photoelectrodes for photorechargeable lithium-ion batteries (PR-LIBs). The assembled PR-LIB exhibits remarkable solar energy conversion efficiency alongside superior lithium storage capabilities. Without an electrical power supply, the photocharged PR-LIB sustained a discharge process for 63.0 h under a constant current density of 0.05 mA cm-2. The corresponding solar-to-electrical energy conversion efficiency is 4.50%, which is an impressive achievement among recently reported contemporary technologies. Mechanism investigation shows that the Cu/CuO/Cu2S photogenerated carriers augment the extraction and insertion of Li+ according to different oxidation and reduction reactions in the charging and discharging reactions. This research delineates a refined model system and proposes innovative directions for developing efficient heterojunction photoelectrodes, significantly propelling the development of PR-LIB technology.

Assessment of transport phenomena in catalyst effectiveness for chemical polyolefin recycling

Since the dawn of agitated brewing in the Paleolithic era, effective mixing has enabled efficient reactions. Emerging catalytic chemical polyolefin recycling processes present unique challenges, considering that the polymer melt has a viscosity three orders of magnitude higher than that of honey. The lack of protocols to achieve effective mixing may have resulted in suboptimal catalyst effectiveness. In this study, we have tackled the hydrogenolysis of commercial-grade high-density polyethylene and polypropylene to show how different stirring strategies can create differences of up to 85% and 40% in catalyst effectiveness and selectivity, respectively. The reaction develops near the H2-melt interface, with the extension of the interface and access to catalyst particles the main performance drivers. Leveraging computational fluid dynamics simulations, we have identified a power number of 15,000-40,000 to maximize the catalyst effectiveness factor and optimize stirring parameters. This temperature- and pressure-independent model holds across a viscosity range of 1-1,000 Pa s. Temperature gradients may quickly become relevant for reactor scale-up.

Promoting Electrocatalytic Oxygen Reactions Using Advanced Heterostructures for Rechargeable Zinc-Air Battery Applications

In order to facilitate electrochemical oxygen reactions in electrically rechargeable zinc-air batteries (ZABs), there is a need to develop innovative approaches for efficient oxygen electrocatalysts. Due to their reliability, high energy density, material abundance, and ecofriendliness, rechargeable ZABs hold promise as next-generation energy storage and conversion devices. However, the large-scale application of ZABs is currently hindered by the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of heterostructure-based electrocatalysts has the potential to surpass the limitations imposed by the intrinsic properties of a single material. This Account begins with an explanation of the configurations of ZABs and the fundamentals of the oxygen electrochemistry of the air electrode. Then, we summarize recent progress with respect to the variety of heterostructures that exploit bifunctional electrocatalytic reactions and overview their impact on ZAB performance. The range of heterointerfacial engineering strategies for improving the ORR/OER and ZAB performance includes tailoring the surface chemistry, dimensionality of catalysts, interfacial charge transfer, mass and charge transport, and morphology. We highlight the multicomponent design approaches that take these features into account to create advanced highly active bifunctional catalysts. Finally, we discuss the challenges and future perspectives on this important topic that aim to enhance the bifunctional activity and performance of zinc-air batteries.

Electrocatalytic activity of tungsten carbide hybrids with two different MOFs for water splitting: a comparative analysis

Conventional energy resources are diminishing, and environmental pollution is constantly increasing because of the excessive use of fossil fuels to sustain the ever-increasing population and industrialization. This has raised concerns regarding a sustainable future. In the pursuit of addressing sustainability in industrial processes and energy systems, the production of green hydrogen is considered a promising and crucial solution to meet the growing energy demands. Water-splitting is one of the most effective technologies for producing clean and carbon-neutral hydrogen. Water-splitting is a scientifically emerging application, but it is commercially limited due to its economic non-viability. The sluggish kinetics and the high overpotential needed for the water-splitting reactions (HER and OER) have encouraged the scientific community to design electrocatalysts that address the concerns of low activity, efficiency and stability. Designing a hybrid catalyst using metal-organic frameworks (MOFs) with transition metal carbides can be a suitable approach to address the deficiencies of conventional water-splitting catalysts. In this study, we have designed and fabricated an electrocatalyst of tungsten carbide (WC) with two different MOFs (Zr-based and Fe-based) and explored their electrocatalytic activity for hydrogen generation in an alkaline medium. It should be noted that hybrids of tungsten carbide with a zirconia MOF (UiO-66) showed better electrocatalytic activity with low overpotentials of 104 mV (HER) and 152 mV (OER) at a current density of 10 mA cm-2. This superior activity of WC with the Zr-MOF in comparison to the Fe-MOF is due to the synergistic effect of Zr present in UiO-66 grown on the WC matrix. Moreover, UiO-66 provides a larger electrocatalytic active surface area, so available active sites are more in UiO-66 as compared to the Fe-MOF. These findings set the stage for the systematic development and production of bi-functional hybrid catalysts with the potential to be utilized in water-splitting processes.

Transparent TiO2 nanotubes supporting silver sulfide for photoelectrochemical water splitting

Differences between photoelectrochemical and electrochemical activity were thoroughly investigated for the oxygen evolution reaction mediated by Ag2S deposited on two types of ordered titania substrates. Titanium dioxide nanotubes were fabricated by anodization of magnetron sputtered Ti films on ITO-coated glass substrates or directly from Ti foil. Further, Ag2S deposition on the nanotubes was carried out using successive ionic layer adsorption and reaction, known as SILAR, with 5, 25, and 45 cycles performed. Two types of nanotubes, one on transparent the other on non-transparent substrates were compared regarding their geometry, structure, optical, and electrochemical properties. It was demonstrated that the composite of Ag2S grown on transparent nanotubes exhibits higher catalytic activity compared to Ag2S grown on the nanotubes formed on Ti foil. The results showed that transparent nanotubes after modification with Ag2S by 25 SILAR cycles exhibit ca. 3 times higher photocurrent under visible light illumination than non-transparent ones treated with the same number of cycles. Furthermore, transparent nanotubes after 45 SILAR cycles of Ag2S exhibit enhanced activity towards oxygen evolution reaction with 9.3 mA cm-2 at 1.1 V vs. Ag/AgCl/0.1 M KCl which is six times higher than titania alone on Ti foil.

Photoelectrocatalytic Hydrogen Generation: Current Advances in Materials and Operando Characterization

Photoelectrochemical (PEC) hydrogen generation is a promising technology for green hydrogen production yet faces difficulties in achieving stability and efficiency. The scientific community is pushing toward the development of new electrode materials and a better understanding of the underlying reactions and degradation mechanisms. Advances in photocatalytic materials are being pursued through the development of heterojunctions, tailored crystal nanostructures, doping, and modification of solid-solid and solid-electrolyte interfaces. Operando and in situ techniques are utilized to deconvolute the charge transfer mechanisms and degradation pathways. In this review, both materials development and Operando characterization are covered for advancing PEC technologies. The recent advances made in the PEC materials are first reviewed including the applied improvement strategies for transition metal oxides, nitrites, chalcogenides, Si, and group III-V semiconductor materials. The efficiency, stability, scalability, and electrical conductivity of the aforementioned materials along with the improvement strategies are compared. Next, the Operando characterization methods and cite selected studies applied for PEC electrodes are described. Operando studies are very successful in elucidating the reaction mechanisms, degradation pathways, and charge transfer phenomena in PEC electrodes. Finally, the standing challenges and the potential opportunities are discussed by providing recommendations for designing more efficient and electrochemically stable PEC electrodes.

Construction of Heterojunction-Rich Metal Nitrides Porous Nanosheets Electrocatalyst for Alkaline Water/Seawater Splitting at Large Current Density

The exploiting electrocatalysts for water/seawater electrolysis with remarkable activity and outstanding durability at industrial grade current density remains a huge challenge. Herein, CoMoNx and Fe-doped CoMoNx nanosheet arrays are in-situ grown on Ni foam, which possess plentiful holes, multilevel heterostructure, and lavish Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF interfaces. They require low overpotentials of 213 and 296 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline media to achieve current density of 800 mA cm-2, respectively, and both possess low Tafel slopes (51.1 and 49.1 mV dec-1) and undiminished stability over 80 h. Moreover, the coupled Co5.47N/MoN@NF and Fe-Co5.47N/MoN@NF electrolyzer requires low voltages of 1.735 V to yield 500 mA cm-2 in alkaline water. Notably, they also exhibit exceptional electrocatalytic properties in alkaline seawater (1.833 V@500 mA cm-2). The experimental studies and theoretical calculations verify that Fe doping does reduce the energy barrier from OH* to O* intermediates during OER process after catalyst reconstruction, and the non-metallic N site from MoN exhibits the lowest theoretical overpotential. The splendid catalytic performance is attributed to the optimized local electron configuration and porous structure. This discovery provides a new design method toward low-cost and excellent catalysts for water/seawater splitting to produce hydrogen.

Sustainable chitosan-based materials as heterogeneous catalyst for application in wastewater treatment and water purification: An up-to-date review

Water pollution is one of serious environmental issues due to the rapid development of industrial and agricultural sectors, and clean water resources have been receiving increasing attention. Recently, more and more studies have witnessed significant development of catalysts (metal oxides, metal sulfides, metal-organic frameworks, zero-valent metal, etc.) for wastewater treatment and water purification. Sustainable and clean catalysts immobilized into chitosan-based materials (Cat@CSbMs) are considered one of the most appealing subclasses of functional materials due to their high catalytic activity, high adsorption capacities, non-toxicity and relative stability. This review provides a summary of various upgrading renewable Cat@CSbMs (such as cocatalyst, photocatalyst, and Fenton-like reagent, etc.). As for engineering applications, further researches of Cat@CSbMs should focus on treating complex wastewater containing both heavy metals and organic pollutants, as well as developing continuous flow treatment methods for industrial wastewater using Cat@CSbMs. In conclusion, this review abridges the gap between different approaches for upgrading renewable and clean Cat@CSbMs and their future applications. This will contribute to the development of cleaner and sustainable Cat@CSbMs for wastewater treatment and water purification.

A triazine-based covalent organic framework decorated with cadmium sulfide for efficient photocatalytic hydrogen evolution from water

Construction of inorganic/organic heterostructures has been proven to be a very promising strategy to design highly efficient photocatalysts for solar driven hydrogen evolution from water. Herein, we report the preparation of a direct Z-scheme heterojunction photocatalyst by in situ growth of cadmium sulfide on a triazine-based covalent organic framework (COF). The triazine based-COF was synthesized by condensation reaction of precursors 1,3,5-tris-(4-formyl-phenyl) triazine (TFPT) and 2,5-bis-(3-hydroxypropoxy) terephthalohydrazide (DHTH), termed as TFPT-DHTH-COF. Widely distributed nitrogen atoms throughout TFPT-DHTH-COF skeletons serve as anchoring sites for strong interfacial interactions with CdS. The CdS/TFPT-DHTH-COF composite showed a hydrogen evolution rate of 15.75 mmol h-1 g-1, which is about 75 times higher than that of TFPT-DHTH-COF (0.21 mmol h-1 g-1) and 3.4 times higher than that of CdS (4.57 mmol h-1 g-1). With the properly staggered band alignment and strong interfacial interaction between TFPT-DHTH-COF and CdS, a Z-scheme charge transfer pathway is achieved. The mechanism has been systematically analyzed by steady state and time-resolved photoluminescence measurements as well as in situ irradiated X-ray photoelectron spectroscopy.

Enhancing the electronic structure of Ni-based electrocatalysts through N element substitution for the hydrogen evolution reaction

The weak orbital coupling between Ni3N and H2O, caused by its interstitial structure and attenuated Ni-N interaction, is attributed to the high unoccupied d orbital energy of Ni3N. Consequently, the kinetics for water dissociation in the HER are slow. In this study, we effectively lowered the energy state of vacant d orbitals in Ni3N, which resulted in an exceptionally efficient HER. The as-synthesized Ni3N catalyst demonstrates an overpotential of 135 mV when subjected to a current density of 10 mA cm-2. The refined structural characterization suggests that the introduction of oxygen results in a reduction in electron densities surrounding the Ni sites. Furthermore, DFT calculations provide additional evidence that the electrocatalyst of Ni3N generates a greater number of lowest unoccupied orbitals (LUMOs) and improved alignment, thereby enhancing the adsorption and splitting of water. The notion of orbital-regulated electronic levels on Ni sites introduces a distinctive methodology for the systematic development of catalysts used in hydrogen evolution and other applications.

Fabrication of Flower-Shaped Sb2S3/Fe2O3 Heterostructures for Enhanced Photoelectrochemical Performance

Antimony sulfide (Sb2S3) has been recognized as a catalytic material for splitting water by solar energy because of its suitable narrow band gap, high absorption coefficient, and abundance of elements. However, many deep-level defects in Sb2S3 result in a significant recombination of photoexcited electron-hole pairs, weakening its photoelectrochemical performance. Here, by using a simple hydrothermal and spin-coating method, we fabricated a step-scheme heterojunction of Sb2S3/α-Fe2O3 to improve the photoelectrochemical performance of pure Sb2S3. Our Sb2S3/α-Fe2O3 photoanode has a photocurrent density of 1.18 mA/cm2 at 1.23 V vs reversible hydrogen electrode, 1.39 times higher than that of Sb2S3 (0.84 mA/cm2). In addition, our heterojunction has a lower onset potential, a higher absorbance intensity, a higher incident photon-to-current conversion efficiency, a higher applied bias photon-to-current efficiency, and a lower charge transfer resistance compared to pure Sb2S3. Based on ultraviolet photoelectron spectroscopy, we constructed a step-scheme band structure of Sb2S3/α-Fe2O3 to explain its photoelectrochemical enhancement. This work offers a promising strategy to optimize the performance of Sb2S3 photoelectrodes for solar-driven photoelectrochemical water splitting.

Enhanced performance of a Na3.5Co4[Bi2Co2W19.75O70(H2O)6]/porous graphitic carbon nitride heterojunction based photocatalyst realized by the addition of copper sulfide nanoparticles

Photocatalytic hydrogen (H2) evolution can effectively solve the global energy problem, in which the key factor is the synthesis of efficient photocatalytic materials. In this study, we successfully synthesized a novel photocatalyst, BiWCo/CuS/PGCN, by functionalizing porous graphitic carbon nitride (PGCN) with sandwich-type polyoxometalate Na3.5Co4[Bi2Co2W19.75O70(H2O)6]·39.5H2O (BiWCo) and introducing copper sulfide (CuS) nanoparticles as a cocatalyst. This approach was aimed at enhancing the built inner electric field between interfaces, resulting in a significant improvement in photocatalytic H2 evolution performance. This research adopts a step-by-step method to synthesize BiWCo/CuS/PGCN composites with p-n heterojunctions, which has high visible light absorption and a synergistic effect of multiple elements. PGCN with a high specific surface area contributes to the uniform distribution of active sites. In addition, the nano-CuS cocatalyst provides abundant active sites and more electron transfer pathways for photocatalysis. Therefore, the H2 production efficiency of BiWCo/CuS/PGCN is 6.3 times that of PGCN, 4.5 times that of BiWCo and 2.5 times that of BiWCo/PGCN under visible light. The H2 production rate of BiWCo/CuS/PGCN reaches 3477.58 μmol g-1 h-1. At the same time, the ternary photocatalyst shows high stability after 30 hours and 5 cycles. This work demonstrates that BiWCo/CuS/PGCN has good application prospects in H2 evolution, and provides a new strategy for the design of efficient ternary photocatalytic materials.

The Zn Vacancy-Mediated De-Accumulation Based Process for Hydrogen Production Performance Promotion of 1D Zn─Cd─S Nanorods

Due to their anisotropy, 1D semiconductor nanorod-based materials have attracted much attention in the process of hydrogen production by solar energy. Nevertheless, the rational design of 1D heterojunction materials and the modulation of photo-generated electron-hole transfer paths remain a challenge. Herein, a ZnxCd1-xS@ZnS/MoS2 core-shell nanorod heterojunction is precisely constructed via in situ growth of discontinuous ZnS shell and MoS2 NCs on the Zn─Cd─S nanorods. Among them, the Zn vacancy in the ZnS shell builds the defect level, and the nanoroelded MoS2 builds the electron transport site. The optimized photocatalyst shows significant photocatalytic activity without Platinum as an auxiliary catalyst, mainly due to the new interfacial charge transfer channel constructed by the shell vacancy level, the vertical separation and the de-accumulation process of photo-generated electrons and photo-generated holes. At the same time, spectral analysis, and density functional theory (DFT) calculations fully prove that shortening difference of speed between the photogenerated electron and hole movement process is another key factor to enhance the photocatalytic performance. This study provides a new path for the kinetic design of enhanced carrier density by shortening the carrier retention time of 1D heterojunction photocatalysts with improved photocatalytic performance.

MXene/ZnS/chitosan-cellulose composite with Schottky heterostructure for efficient removal of anionic dyes by synergistic effect of adsorption and photocatalytic degradation

Nowadays, dye water pollution is becoming increasingly severe. Composite of MXene, ZnS, and chitosan-cellulose material (MX/ZnS/CC) was developed to remove anionic dyes through the synergistic effect of adsorption and photocatalytic degradation. MXene was introduced as the cocatalyst to form Schottky heterostructure with ZnS for improving the separation efficiency of photocarriers and photocatalytic performance. Chitosan-cellulose material mainly served as the dye adsorbent, while also could improve material stability and assist in generation of free radicals for dye degradation. The physics and chemistry properties of MX/ZnS/CC composite were systematically inspected through various characterizations. MX/ZnS/CC composite exhibited good adsorption ability to anionic dyes with adsorption capacity up to 1.29 g/g, and excellent synergistic effects of adsorption and photodegradation with synergistic removal capacity up to 5.63 g/g. MX/ZnS/CC composite performed higher synergistic removal ability and better optical and electrical properties than pure MXene, ZnS, chitosan-cellulose material, and MXene/ZnS. After compounding, the synergistic removal percentage of dyes increased by a maximum of 309 %. MX/ZnS/CC composite mainly adsorbs anionic dyes through electrostatic interactions and catalyzes the generation of •O2-, h+, and •OH to degrade dyes, which has been successfully used to remove anionic dyes from environmental water, achieving a 100 % removal of 50 mg/L dye.

Nanocosmos of catalysis: a voyage through synthesis, properties, and enhanced photocatalytic degradation in nickel sulfide nanocomposites

Nanomaterials play a decisive role in environmental applications such as water purification, pollutant monitoring, and advanced oxidation-based remediation processes, particularly in semiconductor and metal sulfide-based photocatalysis. Metal sulfides are ideal for photocatalysis because of their unique optical, structural, and electronic characteristics. These properties enable the effective use of solar energy to drive various catalytic reactions with potential uses in environmental remediation with sustainable energy production. Among them, nickel sulfides (NiS) stand out for their narrow band gaps, high stability, and cost-effectiveness. This review thoroughly analyzes recent advancements in employing nickel-sulfide-based nanostructures for water decontamination. It begins by addressing environmental material needs and emphasizing the properties of nickel sulfide. To improve photocatalytic performance, controlled processes that affect the active structure, shape, composition, and size of nickel sulfide photocatalysts are examined, along with their synthesis methods. The heart of the review article is a detailed analysis of the modification of NiS through metal and non-metal doping, heterojunction, and nanocomposite formation for enhanced photocatalytic performance. The discussion also includes metal-modified nanostructures, metal oxides, and carbon-hybridized nanocomposites. This study underscores notable advancements in the degradation efficiency of NiS photocatalysts, rivaling their costly noble-metal counterparts. The analysis concludes with potential future directions for nickel sulfide-based photocatalysts in sustainable environmental remediation.

Vertical Dipole Dominates Charge Carrier Lifetime in Monolayer Janus MoSSe

Two-dimensional semiconductor materials with vertical dipoles are promising photocatalysts as vertical dipoles not only promote the electron-hole separation but also enhance the carrier redox ability. However, the influence of vertical dipoles on carrier recombination in such materials, especially the competing relationship between vertical dipoles and band gaps, is not yet clear. Herein, first-principles calculations and nonadiabatic molecular dynamics simulations were combined to clarify the influence of band gap and vertical dipole on the carrier lifetime in Janus MoSSe monolayer. By comparing with the results of MoS2 and MoSe2 as well as exploring the carrier lifetime of MoSSe under strain regulation, it has been demonstrated that the vertical dipole, rather than the band gap, is the dominant factor affecting the carrier lifetime. Strikingly, a linear relationship between the carrier lifetime and vertical dipole is revealed. These findings have important implications for the design of high-performance photocatalysts and optoelectronic devices.

Synergistic effect of dual phase cocatalysts: MoC-Mo2C quantum dots anchored on g-C3N4 for high-stability photocatalytic hydrogen evolution

The extensive examination of hexagonal molybdenum carbide (β-Mo2C) as a non-noble cocatalyst in the realm of photocatalytic H2 evolution is predominantly motivated by its exceptional capacity to adsorb H+ ions akin to Pt and its advantageous conductivity characteristics. However, the H2 evolution rate of photocatalysts modified with β-Mo2C is limited as a result of their comparatively low ability to release H through desorption. Therefore, a facile method was employed to synthesize carbon intercalated dual phase molybdenum carbide (MC@C) quantum dots (ca. 3.13 nm) containing both α-MoC and β-Mo2C decorated on g-C3N4 (gCN). The synthesis process involved a simple and efficient combination of sonication-assisted self-assembly and calcination techniques. 3-MC@C/gCN exhibited the highest efficiency in generating H2, with a rate of 4078 µmol g-1h-1 under 4 h simulated sunlight irradiation, which is 13 times higher than pristine gCN. Furthermore, from the cycle test, 3-MC@C/gCN showcased exceptional photochemical stability of 65 h, as it maintained a H2 evolution rate of 40 mmol g-1h-1. The heightened level of activity observed in the 3-MC@C/gCN system can be ascribed to the synergistic effects of MoC-Mo2C that arise due to the existence of a carbon layer. The presence of a carbon layer enhanced the transmission of photoinduced electrons, while the MoC-Mo2C@C composite served as active sites, thereby facilitating the H2 production reaction of gCN. The present study introduces a potentially paradigm-shifting concept pertaining to the exploration of novel Mo-based cocatalysts with the aim of augmenting the efficacy of photocatalytic H2 production.

Precious Metal Free Hydrogen Evolution Catalyst Design and Application

The quest to identify precious metal free hydrogen evolution reaction catalysts has received unprecedented attention in the past decade. In this Review, we focus our attention to recent developments in precious metal free hydrogen evolution reactions in acidic and alkaline electrolyte owing to their relevance to commercial and near-commercial low-temperature electrolyzers. We provide a detailed review and critical analysis of catalyst activity and stability performance measurements and metrics commonly deployed in the literature, as well as review best practices for experimental measurements (both in half-cell three-electrode configurations and in two-electrode device testing). In particular, we discuss the transition from laboratory-scale hydrogen evolution reaction (HER) catalyst measurements to those in single cells, which is a critical aspect crucial for scaling up from laboratory to industrial settings but often overlooked. Furthermore, we review the numerous catalyst design strategies deployed across the precious metal free HER literature. Subsequently, we showcase some of the most commonly investigated families of precious metal free HER catalysts; molybdenum disulfide-based, transition metal phosphides, and transition metal carbides for acidic electrolyte; nickel molybdenum and transition metal phosphides for alkaline. This includes a comprehensive analysis comparing the HER activity between several families of materials highlighting the recent stagnation with regards to enhancing the intrinsic activity of precious metal free hydrogen evolution reaction catalysts. Finally, we summarize future directions and provide recommendations for the field in this area of electrocatalysis.

Dual-vacancies modulation of 1T/2H heterostructured MoS2-CdS nanoflowers via radiolytic radical chemistry for efficient photocatalytic H2 evolution

Precise defect engineering of photocatalysts is highly demanding but remains a challenge. Here, we developed a facile and controllable γ-ray radiation strategy to assemble dual-vacancies confined MoS2-CdS-γ nanocomposite photocatalyst. We showed the solvated electron induced homogeneous growth of defects-rich CdS nanoparticles, while the symbiotic •OH radicals etched flower-like 1T/2H MoS2 substrate surfaces. The optimal MoS2-CdS-γ exhibited a H2 evolution rate of up to 37.80 mmol/h/g under visible light irradiation, which was 36.7 times higher than that of bare CdS-γ, and far superior to those synthesized by hydrothermal method. The microscopic characterizations and theoretical calculations revealed the formation of such unprecedented dual-sulfur-vacancies ensured the tight interfacial contact for fast charge separation. Besides, the existence of 1T-MoS2 phase further improved the conductivity and strengthened the adsorption interaction with H+ intermediate. Therefore, the radiolytic radical chemistry offered a facile, ambient and effective synthetic strategy to improve the catalytic performances of photocatalytic materials.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

ZnIn2S4 Heterojunctions Constructed with In-MOF Precursor for Photocatalytic Hydrogen Evolution without Cocatalysts

Znln2S4 has great prospects for photocatalytic water splitting to hydrogen by visible light. Herein, a novel Znln2S4-In-MOF (ZnInMS4) photocatalyst is elaborately synthesized by in situ method with In-MOF as the template and In3+ as the source. ZnInMS4 overcomes the fast interface charge recombination and a sluggish charge lifetime via the formed heterojunctions. Photoelectrochemical measurements reveal that the charge-transfer kinetics is enhanced since In-MOF is introduced to act as a reliable charge-transport channel. ZnInMS4 exhibits outstanding cocatalyst-free H2 evolution rate of 70 μmol h-1 under irradiation (λ > 420 nm), which is 3.2-fold higher than that of Znln2S4. In addition, the ZnInMS4 photocatalyst shows good stability in the 16 h continuous reaction. This work illustrates the feasibility of the MOF precursor instead of inorganic salts to directly synthesize photocatalysts with high performance.

Facilitated Unidirectional Electron Transmission by Ru Nano Particulars Distribution on MXene Mo2C@g-C3N4 Heterostructures for Enhanced Photocatalytic H2 Evolution

Precious metals exhibit promising potential for the hydrogen evolution reaction (HER), but their limited abundance restricts widespread utilization. Loading precious metal nanoparticles (NPs) on 2D/2D heterojunctions has garnered considerable interest since it saves precious metal consumption and facilitates unidirectional electron transmission from semiconductors to active sites. In this study, Ru NPs loaded on MXenes Mo2C by an in-site simple strategy and then formed 2D/2D heterojunctions with 2D g-C3N4 (CN) via electrostatic self-assembly were used to enhance photocatalytic H2 evolution. Evident from energy band structure analyses such as UV-vis and TRPL, trace amounts of Ru NPs as active sites significantly improve the efficiency of the hydrogen evolution reaction. More interestingly, MXene Mo2C, as substrates for supporting Ru NPs, enriches photoexcited electrons from CN, thereby enhancing the unidirectional electron transmission. As a result, the combination of Ru-Mo2C and CN constructs a composite heterojunction (Ru-Mo2C@CN) that shows an improved H2 production rate at 1776.4 μmol∙g-1∙h-1 (AQE 3.58% at 400 nm), which is facilitated by the unidirectional photogenerated electron transmission from the valence band on CN to the active sites on Ru (CN→Mo2C→Ru). The study offers fresh perspectives on accelerated unidirectional photogenerated electron transmission and saved precious metal usage in photocatalytic systems.

Ordered Mesoporous Crystalline Frameworks Toward Promising Energy Applications

Ordered mesoporous crystalline frameworks (MCFs), which possess both functional frameworks and well-defined porosity, receive considerable attention because of their unique properties including high surface areas, large pore sizes, tailored porous structures, and compositions. Construction of novel crystalline mesoporous architectures that allows for rich accessible active sites and efficient mass transfer is envisaged to offer ample opportunities for potential energy-related applications. In this review, the rational synthesis, unique structures, and energy applications of MCFs are the main focus. After summarizing the synthetic approaches, an emphasis is placed on the delicate control of crystallites, mesophases, and nano-architectures by concluding basic principles and showing representative examples. Afterward, the currently fabricated components of MCFs such as metals, metal oxides, metal sulfides, and metal-organic frameworks are described in sequence. Further, typical applications of MCFs in rechargeable batteries, supercapacitors, electrocatalysis, and photocatalysis are highlighted. This review ends with the possible development and synthetic challenges of MCFs as well as a future prospect for high-efficiency energy applications, which underscores a pathway for developing advanced materials.

Sulfur vacancy-enhanced In2S3-x hollow microtubes for photocatalytic Cr (VI) and tetracycline removal

Morphological regulation and defect engineering are efficient methods for photocatalytic technology by improving photon absorption and electron dissociation. Herein, In2S3-x hollow microtubes with S-vacancies (MIS) were fabricated via a simple solvothermal reaction using In-based metal-organic frameworks (In-MOFs) as a precursor. Experimental results demonstrate that the hollow structure and optimal S-vacancies can jointly accelerate the photocatalytic reaction, attributed to a larger specific surface area, more active sites, and faster electron transfer efficiency. The champion MIS(2) displayed significantly better photocatalytic activity for Cr(VI) reduction and tetracycline (TC) degradation. The Cr(VI) reduction rate by MIS(2) is 3.67 and 2.82 times higher than those of optimal In2S3 template-free (HIS(2)) and MIS(1) with poor S-vacancies, respectively. The removal efficiency of TC by MIS(2) is 1.37 and 1.15 times higher than those of HIS(2) and MIS(1). Further integration of MIS(2) with aerogel simplifies the recovery process significantly.

Fabrication of carbon-based materials derived from a cobalt-based organic framework for enhancing photocatalytic degradation of dyes

The pyrolysis of metal-organic frameworks (MOFs) has emerged as a promising route to synthesize carbon/metal oxide-based materials with diverse phase compositions, morphologies, sizes and surface areas. In this paper, 1,3,5-benzoic acid (BTC) and 2,4,6-tri(4-pyridinyl)-1-pyridine (TPP) were used as ligands to prepare a novel cobalt-based MOF (Co-MOF) which was used as a precursor to obtain five carbon-based materials at different temperatures (Co-C200/400/600/800/1000). Furthermore, five dyes were used as degradation targets to investigate the photocatalytic degradation performance of the title materials under UV light irradiation. Co-C1000 exhibited the best photocatalytic degradation performance for methyl orange (MO), and the degradation rate could reach 99.21%. The enhanced photocatalytic activity was attributed to narrower band-gaps and a synergistic effect originating from the well-aligned straddling band structures between Co/CoO/Co3O4 and C, also resulting in a faster interfacial charge transfer during the photocatalytic reaction. This study will aid in the development of photocatalysts generated from carbon-based materials via the pyrolysis transformation of MOFs, therefore greatly enhancing the photocatalytic performance.

Surface Structure to Tailor the Electrochemical Behavior of Mixed-Valence Copper Sulfides during Water Electrolysis

The semiconducting behavior of mixed-valence copper sulfides arises from the pronounced covalency of Cu-S bonds and the exchange coupling between CuI and CuII centers. Although electrocatalytic study with digenite Cu9S5 and covellite CuS has been performed earlier, detailed redox chemistry and its interpretation through lattice structure analysis have never been realized. Herein, nanostructured Cu9S5 and CuS are prepared and used as electrode materials to study their electrochemistry. Powder X-ray diffraction (PXRD) and microscopic studies have found the exposed surface of Cu9S5 to be d(0015) and d(002) for CuS. Tetrahedral (Td) CuII, distorted octahedral (Oh) CuII, and trigonal planar (Tp) CuI sites form the d(0015) surface of Cu9S5, while the (002) surface of CuS consists of only Td CuII. The distribution of CuI and CuII sites in the lattice, predicted by PXRD, can further be validated through core-level Cu 2p X-ray photoelectron spectroscopy (XPS). The difference in the electrochemical response of Cu9S5 and CuS arises predominantly from the different copper sites present in the exposed surfaces and their redox states. In situ Raman spectra recorded during cyclic voltammetric study indicates that Cu9S5 is more electrochemically labile compared to CuS and transforms rapidly to CuO/Cu2O. Contact-angle and BET analyses imply that a high-surface-energy and macroporous Cu9S5 surface favors the electrolyte diffusion, which leads to a pronounced redox response. Post-chronoamperometric (CA) characterizations identify the potential-dependent structural transformation of Cu9S5 and CuS to CuO/Cu2O/Cu(OH)2 electroactive species. The performance of the in situ formed copper-oxides towards electrocatalytic water-splitting is superior compared to the pristine copper sulfides. In this study, the redox chemistry of the Cu9S5/CuS has been correlated to the atomic arrangements and coordination geometry of the surface exposed sites. The structure-activity correlation provides in-depth knowledge of how to interpret the electrochemistry of metal sulfides and their in situ potential-driven surface/bulk transformation pathway to evolve the active phase.

Recent advances in the role of MXene based hybrid architectures as electrocatalysts for water splitting

The development of non-noble metal based and cost-effective electrocatalysts for water splitting has attracted significant attention due to their potential in production of clean and green hydrogen fuel. Discovered in 2011, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides, have demonstrated promising performance as electro catalysts in the water splitting process due to their high electrical conductivity, very large surface area and abundant catalytic active sites. However, their-long term stability and recyclability are limited due to restacking and agglomeration of MXene flakes. This problem can be solved by combining MXene with other materials to create their hybrid architectures which have demonstrated higher electrocatalytic performance than pristine MXenes. Electrolysis of water encompasses two half-cell reactions, hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Firstly, this concise review explains the mechanism of water splitting. Then it provides an overview of the recent advances about applications of MXenes and their hybrid architectures as HER, OER and bifunctional electrocatalysts for overall water splitting. Finally, the recent challenges and potential outlook in the field have been presented. This concise review may provide further understanding about the role of MXene-based hybrid architectures to develop efficient electrocatalysts for water splitting.

A hair-ball heterostructure of MnS-MnS2/CdS with compact linking interface for ultrasensitive photoelectrochemical bioanalysis of carcinoembryonic antigen

The heterostructured photoelectric material is supposed to markedly promote the photoelectrochemical (PEC) property. Herein, the species heterostructured MnS/CdS and MnS-MnS2/CdS(1∼2) composites derived from Mn-ZIF MOFs via a sulfofication reaction using Cd(NO3)2, CdC12 cadmium source, respectively. Under irradiation, the PEC tests showed that the photocurrent response of MnS-MnS2/CdS(1∼2) signally enhanced compared to globose MnS/CdS heterostructure and pure MnS or CdS. It was ascribed to the matching band-gap to form type II heterojunction in MnS-MnS2/CdS(1∼2) which dramatically facilitated photo-induced electron/hole (e-/h+) separation and transfer. The hair-ball morphologies structure of MnS-MnS2/CdS(1∼2) with large number of pores was beneficial to improve penetrating efficiency of the electrolyte liquid. Meanwhile, the well-synergistic effect on the MnS, MnS2, CdS components and with tight connecting heterojunction interface among MnS-MnS2/CdS(1∼2) which also led to violently photocurrent output. Besides, the chitosan (CS) was covalently coupled with glutaraldehyde (GLD) to obtain steady composite film, and the cross-linker of GLD can achieve the high efficiency to graft the Apt-CEA (aptamer) biomolecules, which resulting in the promotion of hybridization reaction efficiency of the CEA target. Hence, this created biosensor of Apt-CEA/GLD-CS/MnS-MnS2/CdS(1)/ITO for the CEA detection displayed a wide linear range from 0.001 to 18 ng mL-1 and with ultralow detection limit of 0.313 pg mL-1. This research innovatively prepared a contact heterojunction interface with special porosities structure, which had superior PEC nature for the fabrication of high-performance biosensor.

Recent insights on the use of modified Zn-based catalysts in eCO2RR

Converting CO2 into valuable chemicals can provide a new path to mitigate the greenhouse effect, achieving the aim of "carbon neutrality" and "carbon peaking". Among numerous electrocatalysts, Zn-based materials are widely distributed and cheap, making them one of the most promising electrocatalyst materials to replace noble metal catalysts. Moreover, the Zn metal itself has a certain selectivity for CO. After appropriate modification, such as oxide derivatization, structural reorganization, reconstruction of the surfaces, heteroatom doping, and so on, the Zn-based electrocatalysts can expose more active sites and adjust the d-band center or electronic structure, and the FE and stability of them can be effectively improved, and they can even convert CO2 to multi-carbon products. This review aims to systematically describe the latest progresses of modified Zn-based electrocatalyst materials (including organic and inorganic materials) in the electrocatalytic carbon dioxide reduction reaction (eCO2RR). The applications of modified Zn-based catalysts in improving product selectivity, increasing current density and reducing the overpotential of the eCO2RR are reviewed. Moreover, this review describes the reasonable selection and good structural design of Zn-based catalysts, presents the characteristics of various modified zinc-based catalysts, and reveals the related catalytic mechanisms for the first time. Finally, the current status and development prospects of modified Zn-based catalysts in eCO2RR are summarized and discussed.

Integration of a Cu2O/ZnO heterojunction and Ag@SiO2 into a photoanode for enhanced solar water oxidation

Photoelectrochemical water splitting (PEC-WS) has attracted considerable attention owing to its low energy consumption and sustainable nature. Constructing semiconductor heterojunctions with controllable band structure can effectively facilitate photogenerated carrier separation. In this study, a FTO/ZnO/Cu2O/Ag@SiO2 photoanode with a Cu2O/ZnO p-n heterojunction and Ag@SiO2 nanoparticles is constructed to investigate its PEC-WS performance. Compared with a bare ZnO photoanode, the photocurrent density of the FTO/ZnO/Cu2O/Ag@SiO2 photoanode (0.77 mA cm-2) at 1.23 VRHE exhibits an increment of 88%, and a cathodic shift of 0.1 V for the on-set potential (0.4 VRHE). Detailed photoelectrochemical analyses reveal that the Cu2O/ZnO p-n heterojunction formed between Cu2O and ZnO can effectively promote photogenerated carrier separation. The surface plasmonic effect of the Ag@SiO2 nanoparticles can further promote the photogenerated carrier transfer efficiency, which synergistically improves the PEC-WS performance.

Amorphous Nickel Hydroxide Shell on Ni8P3 Nanorods for Boosted Highly Stable Overall Water Splitting at High Current

Developing highly active, highly stable, and cheap electrocatalysts for water splitting is of great significance for hydrogen production. Herein, we report an amorphous Ni(OH)2-clothed transition Ni8P3 catalyst, in which the amorphous Ni(OH)2 shell provides catalytic active sites and serves as a proton conductive encapsulation layer to ensure efficient proton supply to the active Ni8P3 sites. As expected, the Ni8P3@Ni(OH)2 catalyst exhibits significant water decomposition performance at low and high current densities of 10, 100, and 1000 mA cm-2 at 1.45, 1.71, and 2.21 V, respectively, which is comparable to those of commercial electrocatalysts. In particular, the prepared Ni8P3@Ni(OH)2 electrodes possess exceptional long-term durability (200 h) at high current (over 1 A). The significantly improved water-splitting activity and durability in alkaline medium are expected to make them attractive catalyst materials to produce renewable chemical fuels.

Large electronegativity differences between adjacent atomic sites activate and stabilize ZnIn2S4 for efficient photocatalytic overall water splitting

Photocatalytic overall water splitting into hydrogen and oxygen is desirable for long-term renewable, sustainable and clean fuel production on earth. Metal sulfides are considered as ideal hydrogen-evolved photocatalysts, but their component homogeneity and typical sulfur instability cause an inert oxygen production, which remains a huge obstacle to overall water-splitting. Here, a distortion-evoked cation-site oxygen doping of ZnIn2S4 (D-O-ZIS) creates significant electronegativity differences between adjacent atomic sites, with S1 sites being electron-rich and S2 sites being electron-deficient in the local structure of S1-S2-O sites. The strong charge redistribution character activates stable oxygen reactions at S2 sites and avoids the common issue of sulfur instability in metal sulfide photocatalysis, while S1 sites favor the adsorption/desorption of hydrogen. Consequently, an overall water-splitting reaction has been realized in D-O-ZIS with a remarkable solar-to-hydrogen conversion efficiency of 0.57%, accompanying a ~ 91% retention rate after 120 h photocatalytic test. In this work, we inspire an universal design from electronegativity differences perspective to activate and stabilize metal sulfide photocatalysts for efficient overall water-splitting.

Solution-processed Sb2Se3 photocathodes under Se-rich conditions and their photoelectrochemical properties

In this study, selenium (Se)-rich antimony selenide (Sb2Se3) films were fabricated by applying a solution process with the solvents ethylenediamine and 2-mercaptoethanol to optimize the photoelectrochemical (PEC) performance of the Sb2Se3 photocathode. Various antimony (Sb)-Se precursor solutions with different molar ratios of Sb and Se (Sb : Se = 1 : 1.5, 1 : 3, 1 : 4.5, 1 : 7.5, and 1 : 9) were prepared to attain Se-rich fabrication conditions. As a result, the Se-rich Sb2Se3 films fabricated using the Sb-Se precursor solution with a molar ratio of Sb : Se = 1 : 7.5 exhibited an improved PEC performance, compared to the stoichiometric Sb2Se3 film. The charge transport was improved by the abundant Se element and thin selenium oxide (Se2O3) layer in the Se-rich Sb2Se3 film, resulting in a decrease in Se vacancies and substitutional defects. Moreover, the light utilization in the long wavelength region above 800 nm was enhanced by the light-trapping effect because of the nanowire structure in the Se-rich Sb2Se3 film. Hence, the optimal Se-rich Sb2Se3 photocathodes showed an improved photocurrent density of -0.24 mA cm-2 at the hydrogen evolution reaction potential that was three times higher than that of the stoichiometric Sb2Se3 photocathodes (-0.08 mA cm-2).

Twin Zn1- x Cdx S Solid Solution: Highly Efficient Photocatalyst for Water Splitting

Twins in crystal defect, one of the significant factors affecting the physicochemical properties of semiconductor materials, are applied in catalytic conversion. Among the catalysts serving for photocatalytic water splitting, Zn1- x Cdx S has become a hot-point due to its adjustable energy band structure. Via limiting mass transport to control the release rate of anions/cations, twin Zn1- x Cdx S solid solution is prepared successfully, which lays a foundation for the construction of other twin crystals in the future. On twin Zn1- x Cdx S, water tends to be dissociated after being adsorbed by Zn2+ /Cd2+ at twin boundary, then the fast-moving electrons at twin boundary quickly combine with the protons already attached to S2- to form hydrogen. According to the theoretical calculation, not only the intracrystalline electron mobility, but also the extracrystalline capacity of water-adsorption/dissociation and proton-adsorption on the twin boundary are superior to those of the counterpart plane in defect-free phase. The synthetic twin Zn1- x Cdx S apparent quantum efficiency of photocatalysis water splitting for hydrogen reached 82.5% (λ = 420 nm). This research opens up an avenue to introduce twins in crystals and it hopes to shed some light on photocatalysis.

One-Step Fabricated Sn0 Particle on S-Vacancies SnS2 to Accelerate Photoelectron Transfer for Sterling Photocatalytic CO2 Reduction in Pure Water Vapor Environment

Promoting the proton-coupled electron transfer process in order to solve the sluggish carrier migration dynamics is an efficient way to accelerate the photocatalytic CO2 reduction (PCR) process. Herein, through the reduction of Sn4+ by amino and sulfhydryl groups, Sn0 particles are lodged in S-vacancies SnS2 nanosheets. The high conductance of Sn0 particles expedites the collection and transport of photogenerated electrons, activating the surrounding surface of unsaturated sulfur (Sx 2- ) and thus lowering the energy barrier for generation of *COOH. Meanwhile, S-vacancies boost H2 O adsorption while Sx 2- increases CO2 adsorption, as demonstrated by density functional theory (DFT), obtaining a selectivity of 97.88% CO and yield of 295.06 µmol g-1 h-1 without the addition of co-catalysts and sacrificial agents. This work provides a new approach to building a fast electron transfer interface between metal particles and semiconductors, which works in tandem with S-vacancies and Sx 2- to boost the efficiency of photocatalytic CO2 reduction to CO in pure water vapor environment.

Interface engineering of NiS/NiCo2S4 heterostructure with charge redistribution for boosting overall water splitting

Developing highly efficient bifunctional non-noble metal-based electrocatalysts is pivotal to fulfilling practical water electrolysis. In this work, NiS/NiCo2S4 heterostructured electrocatalysts are prepared through a simply controlling sulfurization process by employing a one-pot solvothermal strategy. The alteration of cobalt addition amount can affect the crystalline phase, morphology, and catalytic activity of the resulting heterostructured materials. The successful integration of NiS with NiCo2S4 is realized by deliberately tuning the cobalt addition amount. The resulting Co-Ni-S5:1 delivers high activity with low overpotentials of 198 and 259 mV to attain 10 mA cm-2 when used as electrocatalysts toward hydrogen evolution reaction and oxygen evolution reaction, respectively. Experimental and theoretical calculations evidence the strong interface coupling between NiS and NiCo2S4 leads to increased electronic conductivity, electron migration near lattice-matched interface and interfacial charge redistribution, thereof enhancing the reaction kinetics rate and activity. Moreover, the potential application is demonstrated by employing Co-Ni-S5:1 in a two-electrode electrolyzer which can efficiently catalyze water electrolysis and work stably for 100 h. This work not only provides highly efficient bifunctional heterostructured electrocatalysts by simply regulating the metal components in sulfides but also further broadens the application of interface engineering.