Graphene-Draped Semiconductors for Enhanced Photocorrosion Resistance and Photocatalytic Properties

Rationally designed hierarchical hollow CuS/CdIn2S4 heterostructure nanoboxes for boosted photoreduction of CO2

A novel double-shelled CuS/CdIn2S4 photocatalyst was rationally designed using CdIn2S4 sheets in situ grown upon the exterior of hollow CuS nanocubes. The unique hierarchical hollow structure of CuS/CdIn2S4 provides numerous active sites and reduces carrier diffusion length. Surface sulfur vacancies mitigate the detachment of the intermediate, which is favorable for a multi-electron reaction path such as that in the production of CH4. Meanwhile, a suitable band-structure alignment between p-type CuS and n-type CdIn2S4 leads to the formation of a type-II heterostructure, thus resulting in effective light-harvesting and spatial separation of electron-hole pairs for CO2 photoreduction. The CuS/CdIn2S4 heterostructure exhibits significantly enhanced performance with a boosted CO yield of 40.73 μmol g-1 h-1 as well as a noticeably improved CH4 selectivity (36.5%, 23.41 μmol g-1 h-1). This work introduces innovative concepts in designing photocatalytic systems with unique morphologies and rational band structures, promising advancements in CO2 photoreduction at reduced costs.

A review on transition metal oxides based photocatalysts for degradation of synthetic organic pollutants

This review provides insight into the current research trend in transition metal oxides (TMOs)-based photocatalysis in removing the organic colouring matters from water. For easy understanding, the research progress has been presented in four generations according to the catalyst composition and mode of application, viz: single component TMOs (the first-generation), doped TMOs/binary TMOs/doped binary TMOs (the second-generation), inactive/active support-immobilized TMOs (the third-generation), and ternary/quaternary compositions (the fourth-generation). The first two generations represent suspended catalysts, the third generation is supported catalysts, and the fourth generation can be suspended or supported. The review provides an elaborated comparison between suspended and supported catalysts, their general/specific requirements, key factors controlling degradation, and the methodologies for performance evaluation. All the plausible fundamental and advanced dye degradation mechanisms involved in each generation of catalysts were demonstrated. The existing challenges in TMOs-based photocatalysis and how the researchers approach the hitch to resolve it effectively are discussed. Future research trends are also presented.

Progress in layered double hydroxides (LDHs): Synthesis and application in adsorption, catalysis and photoreduction

Layered double hydroxides (LDHs), also known as anionic clays, have attracted significant attention in energy and environmental applications due to their exceptional physicochemical properties. These materials possess a unique structure with surface hydroxyl groups, tunable properties, and high stability, making them highly desirable. In this review, the synthesis and functionalization of LDHs have been explored including co-precipitation and hydrothermal methods. Furthermore, extensive research on LDH application in toxic pollutant removal has shown that modifying or functionalizing LDHs using materials such as activated carbon, polymers, and inorganics is crucial for achieving efficient pollutant adsorption, improved cyclic performance, as well as effective catalytic oxidation of organics and photoreduction. This study offers a comprehensive overview of the progress made in the field of LDHs and LDH-based composites for water and wastewater treatment. It critically discusses and explains both direct and indirect synthesis and modification techniques, highlighting their advantages and disadvantages. Additionally, this review critically discusses and explains the potential of LDH-based composites as absorbents. Importantly, it focuses on the capability of LDH and LDH-based composites in heterogeneous catalysis, including the Fenton reaction, Fenton-like reactions, photocatalysis, and photoreduction, for the removal of organic dyes, organic micropollutants, and heavy metals. The mechanisms involved in pollutant removal, such as adsorption, electrostatic interaction, complexation, and degradation, are thoroughly explained. Finally, this study outlines future research directions in the field.

Development of stable S-scheme 2D-2D g-C3N4/CdS nanoheterojunction arrays for enhanced visible light photomineralisation of nitrophenol priority water pollutants

The investigation focused on creating and studying a new 2D-2D S-scheme CdS/g-C3N4 heterojunction photocatalyst. Various techniques examined its structure, composition, and optical properties. This included XRD, XPS, EDS, SEM, TEM, HRTEM, DRS, and PL. The heterojunction showed a reduced charge recombination rate and more excellent stability, helping to lessen photocorrosion. This was due to photogenerated holes moving more quickly out of the CdS valence band. The interface between g-C3N4 and CdS favored a synergistic charge transfer. A suitable flat band potential measurement supported enhanced reactive oxygen species (ROS) generation in degrading 4-nitrophenol and 2-nitrophenol. This resulted in remarkable degradation efficiency of up to 99% and mineralization of up to 79%. The findings highlighted the practical design of the new 2D-2D S-scheme CdS/g-C3N4 heterojunction photocatalyst and its potential application in various energy and environmental settings, such as pollutant removal, hydrogen production, and CO2 conversion.

Dual Z-scheme TCN/ZnS/ ZnIn2S4 with efficient separation for photocatalytic nitrogen fixation

The development of an efficient catalyst that can use solar energy for NH3 production is of great significance in solving the environmental and energy crisis caused by the traditional ammonia synthesis process. In this work, a dual Z-scheme tubular carbon nitride/zinc sulfide/zinc indium sulfide ternary composited photocatalyst (TCN/ZnS/ZnIn2S4) with excellent nitrogen photofixation performance under visible light was prepared by self-assembly and hydrothermal methods. The crystal structure studies confirmed that tubular carbon nitride (TCN) had more active sites that could promote N2 adsorption. The photochemical studies proved that the double charge transfer channel provided by the dual Z-scheme heterojunction could improve the efficiency of electron-hole separation and achieve excellent photocatalytic nitrogen fixation. The ammonia production rate of the TCN/ZnS/ZnIn2S4 catalyst was up to 136.56 μmol/L, and it also has good stability and reusability. This work provides new insight into the development of Z-scheme heterojunction photocatalysts with green and efficient nitrogen fixation.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO₂ reduction, N₂ reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.

Synthesis of Fe3O4@CdS@CQDs ternary core-shell heterostructures as a magnetically recoverable photocatalyst for selective alcohol oxidation coupled with H2O2 production

Photocatalytic aerobic oxidation of aromatic alcohols to corresponding aldehydes coupled with producing hydrogen peroxide (H₂O₂) represents one of the most efficient strategies for converting solar energy into chemical energy. In this work, a magnetically recoverable photocatalyst of Fe₃O₄@CdS@CQDs ternary core-shell heterostructures is elaborately fabricated through the hydrothermal growth of CdS on Fe₃O₄ nanospheres with in-situ incorporation of carbon quantum dots (CQDs) and used for selective alcohol oxidation coupled with H₂O₂ production. The Fe₃O₄@CdS@CQDs photocatalyst possess distinct advantages of full solar spectral absorption, efficient charge separation, and high stability. The Fe₃O₄-nanosphere cores not only endow photocatalyst with the characteristics of magnetic recovery but also form Fe₃O₄@CdS Z-scheme heterojunction to prevent CdS from photocorrosion. The in-situ modified CQDs act as charge mediators to accelerate the photogenerated electron-hole separation and afford active sites to facilitate H₂O₂ production. As a result, the Fe₃O₄@CdS@CQDs photocatalyst exhibits excellent performance in selectively converting benzyl alcohol to benzaldehyde accompanied with H₂O₂ production. The generation rates of benzaldehyde and H₂O₂ reach up to 57.22 and 27.06 mmol·g_CdS^-1·h^-1, respectively. This work highlights a rational construction of magnetic heterostructure photocatalyst and its application in the photo-redox coupling reactions.

Effects of Photodynamic Therapy on Streptococcus mutans and Enamel Remineralization of Multifunctional TiO2-HAP Composite Nanomaterials

BACKGROUND

As photosensitizer and photocatalyst, titanium dioxide (TiO₂) can produce a photodynamic reaction for antibacterial treatment. This study aims to explore a Titanium dioxide/nano-hydroxyapatite (TiO₂-HAP) composite combined with the dental curing lamp (385-515 nm) in clinical which could inhibit the dental plaque biofilm formed by Streptococcus mutans (S. mutans) and promote the enamel surface remineralization simultaneously.

METHODS

X-ray Diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to detect the characterization of TiO₂-HAP composite nanomaterials. Photodynamic properties of TiO₂-HAP were detected by Diffuse reflectance spectrum (DRS) and fluorescence spectroscopy. Bacterial growth was measured by reading the absorbance of bacterial cultures and confocal microscope was used to observe the biofilm removal ability of nanomaterials. The ability of TiO₂-HAP to promote enamel remineralization was measured by Scanning electron microscope (SEM).

RESULTS

The OD 600 of S. mutans was 0.76 in the control group and 0.13 in group of TiO₂-HAP with exposure to light-emitting diode (LED) (150 mW/cm²) for 5 min, suggesting its sustained antibacterial potency and inhibition of the metabolic activity of dental plaque microcosm biofilm. Also, the release of calcium and phosphorus ions in TiO₂-HAP can promote enamel mineralization simultaneously. After 15 days of remineralization, the Ca/P ratio of demineralized enamel surface increased from 1.28 to 1.67, which was similar to that of normal enamel.

CONCLUSIONS

The TiO₂-HAP exhibit a promising anti-bacterial activity and remineralization capacity which can prevent the occurrence of caries to the greatest extent and promote the biomimetic mineralization of dental tissues.

Highly Crystalline Graphene as the Atomic 2D Blanket of a Perovskite Absorber for Enhanced Photovoltaic Performance

Perovskite solar cells (PSCs) have demonstrated enormous potential for next-generation low-cost photovoltaics. However, due to the intrinsically low bond energy of the perovskite lattice, the long-term stability is normally undermined by ion migration initiated by the electric field and atmospheric conditions. Therefore, ideal ion migration inhibition is important to achieve an enhanced stability of PSCs. Herein, we first introduce a chemical vapor deposition (CVD) fabricated highly crystalline graphene as an atomic 2D blanket directly for the perovskite absorber of PSCs. Iodine and lithium ion migration is effectively inhibited for perovskite solar cells under a continuous static electric field. The water and oxygen corrosion of the unencapsulated device has been dramatically mitigated with atomic graphene blanketing on the perovskite film. With triphenylamine (TPA) molecule modification, the photoconversion efficiencies (PCEs) of the blanketed devices reach 21.54%. The sample with blanket graphene maintains 85% of the initial efficiency, in comparison to 52% of the control sample under voltage bias. After 600 h of aging at 25 °C and 55 RH%, 86% in comparison to <30% of the PCE for the control device is obtained for the sample with a graphene blanket. Thus, we propose that crystalline graphene has an excellent and effective ion-blocking blanket potential for highly stable perovskite devices.

TiO2 nanotube arrays sensitized by copper (II) porphyrins with efficient interfacial charge transfer for the photocatalytic degradation of 4-nitrophenol

In this paper, photocatalysts based on TiO₂ nanotubes (TNTs) and TiO₂ nanotube arrays (TNTAs) sensitized by Cu(II) meso-tetrakis(N-ethylpyridinium-4-yl) porphyrin (CuTEPyP) were synthesized and their structures were characterized by various analytical methods. The photocatalytic activities of both composites were then investigated through degradation of 4-nitrophenol (4-NP) in aqueous solutions under visible light irradiation. It was found that CuTEPyP/TNTAs could eliminate 95% 4-NP within 4 h, which was considerably higher than the yield obtained with CuTEPyP/TNTs (56%) under the same conditions. Compared to CuTEPyP/TNTs, the improved photocatalytic activity of CuTEPyP/TNTAs can be ascribed to increased light absorption, high separation rate of photo-generated charge pairs, and efficient charge transfer. A plausible photocatalytic degradation mechanism involving hydroxyl radicals, superoxide radical anions and singlet oxygen species was also proposed. This work presents an efficient paradigm for eliminating 4-NP under visible light irradiation.

Cr(VI)-imprinted polymer wrapped on urchin-like Bi2S3 for reduced photocorrosion and improved photoreduction of aqueous Cr(VI)

Just like other metal sulfides, the misfortune of photocorrosion and undesired photogenerated electron-hole recombination for Bi₂S₃ was inevitable. In this work, a viable route to reduce photocorrosion of Bi₂S₃ and improve photoreduction of aqueous Cr(VI) was developed via "dressed" a Cr(VI) imprinting polymer (Cr(VI)-IP) on urchin-like Bi₂S₃ (U-Bi₂S₃). Cr(VI)-IP wrapped on the three dimensional U-Bi₂S₃ was implemented by a bulk polymerization. The wrapped Cr(VI)-IP enabled to fast enrich and adsorb Cr(VI) on U-Bi₂S₃ leading to improve the photoreduced efficiency of photogenerated carriers and restrain the photogenerated electron-hole recombination. What's more, Cr(VI)-IP wrapped on U-Bi₂S₃ was just like an "armor" which could support the three dimensional construction of U-Bi₂S₃ from the structural collapse of photocorrosion and retard the direct contact of oxygen and H₂O from the surrounding media. As expected, the obtained U-Bi₂S₃@Cr(VI)-IP exhibited higher photostability, adsorption, photoreduction capacities towards the target Cr(VI) than the bare U-Bi₂S₃. The photocatalytic kinetic constant of U-Bi₂S₃@Cr(VI)-IP was 6 times higher than U-Bi₂S₃. After 3 times recycling uses, the morphology, crystal structure and chemical constitution of U-Bi₂S₃@Cr(VI)-IP were maintained. In addition, the removal efficiency of Cr(VI) by U-Bi₂S₃@Cr(VI)-IP was kept at 58% whereas U-Bi₂S₃ was almost lost to zero.

Surface Engineering of Nanoporous Silicon Photocathodes for Enhanced Photoelectrochemical Hydrogen Production

Silicon (Si) is a promising semiconductor material in photoelectrochemical (PEC) H2 evolution due to its advantages of Earth-abundant element, non-toxicity, broad absorption of the solar spectrum, high saturated-current and industrial...

Preventing colour fading in artworks with graphene veils

Modern and contemporary art materials are generally prone to irreversible colour changes upon exposure to light and oxidizing agents. Graphene can be produced in thin large sheets, blocks ultraviolet light, and is impermeable to oxygen, moisture and corrosive agents; therefore, it has the potential to be used as a transparent layer for the protection of art objects in museums, during storage and transportation. Here we show that a single-layer or multilayer graphene veil, produced by chemical vapour deposition, can be deposited over artworks to protect them efficiently against colour fading, with a protection factor of up to 70%. We also show that this process is reversible since the graphene protective layer can be removed using a soft rubber eraser without causing any damage to the artwork. We have also explored a complementary contactless graphene-based route for colour protection that is based on the deposition of graphene on picture framing glass for use when the direct application of graphene is not feasible due to surface roughness or artwork fragility. Overall, the present results are a proof of concept of the potential use of graphene as an effective and removable protective advanced material to prevent colour fading in artworks.

Differences and Similarities of Photocatalysis and Electrocatalysis in Two-Dimensional Nanomaterials: Strategies, Traps, Applications and Challenges

Photocatalysis and electrocatalysis have been essential parts of electrochemical processes for over half a century. Recent progress in the controllable synthesis of 2D nanomaterials has exhibited enhanced catalytic performance compared to bulk materials. This has led to significant interest in the exploitation of 2D nanomaterials for catalysis. There have been a variety of excellent reviews on 2D nanomaterials for catalysis, but related issues of differences and similarities between photocatalysis and electrocatalysis in 2D nanomaterials are still vacant. Here, we provide a comprehensive overview on the differences and similarities of photocatalysis and electrocatalysis in the latest 2D nanomaterials. Strategies and traps for performance enhancement of 2D nanocatalysts are highlighted, which point out the differences and similarities of series issues for photocatalysis and electrocatalysis. In addition, 2D nanocatalysts and their catalytic applications are discussed. Finally, opportunities, challenges and development directions for 2D nanocatalysts are described. The intention of this review is to inspire and direct interest in this research realm for the creation of future 2D nanomaterials for photocatalysis and electrocatalysis.

A critical review on bismuth oxyhalide based photocatalysis for pharmaceutical active compounds degradation: Modifications, reactive sites, and challenges

Pharmaceutical active compounds (PhACs), as a kind of widely used pharmaceutical drugs, has attracted much attention. The bismuth oxyhalides (BiOX)-based photocatalysis can remove PhACs efficiently due to its unique layered structure, optical and electronic properties. Nevertheless, the rapid recombination of photogenerated electron-hole pairs, and the inherent instability of structure have limited its practical application. In order to solve these problems, recent modification studies tend to focus on facet control, elemental doping, bismuth-rich strategies, defect engineering and heterojunction. Therefore, the objective of this review is to summarize the recent developments in multiply modified strategies for PhACs degradation. The synthesis methods, photocatalytic properties and the enhancement mechanism are elaborated. Besides, based on theoretical calculation, the reactive sites of typical PhACs attacked by different reactive oxygen species were also proposed. Subsequently, challenges and opportunities in applications are also featured which include factors, viz., dissolution of halogen ions, instability under visible light, applications of real water/wastewater, intermediates and byproducts toxicity analysis of BiOX-based photocatalysis. Finally, the perspectives of BiOX-based photocatalysis for PhACs photodegradation in actual water applications are highlighted.

Chemical reactions on surfaces for applications in catalysis, gas sensing, adsorption-assisted desalination and Li-ion batteries: opportunities and challenges for surface science

The study of chemical processes on solid surfaces is a powerful tool to discover novel physicochemical concepts with direct implications for processes based on chemical reactions at surfaces, largely exploited by industry. Recent upgrades of experimental tools and computational capabilities, as well as the advent of two-dimensional materials, have opened new opportunities and challenges for surface science. In this Perspective, we highlight recent advances in application fields strictly connected to novel concepts emerging in surface science. Specifically, we show for selected case-study examples that surface oxidation can be unexpectedly beneficial for improving the efficiency in electrocatalysis (the hydrogen evolution reaction and oxygen evolution reaction) and photocatalysis, as well as in gas sensing. Moreover, we discuss the adsorption-assisted mechanism in membrane distillation for seawater desalination, as well as the use of surface-science tools in the study of Li-ion batteries. In all these applications, surface-science methodologies (both experimental and theoretical) have unveiled new physicochemical processes, whose efficiency can be further tuned by controlling surface phenomena, thus paving the way for a new era for the investigation of surfaces and interfaces of nanomaterials. In addition, we discuss the role of surface scientists in contemporary condensed matter physics, taking as case-study examples specific controversial debates concerning unexpected phenomena emerging in nanosheets of layered materials, solved by adopting a surface-science approach.

Structural transformations of solid electrocatalysts and photocatalysts

Heterogeneous catalysts often undergo structural transformations when they operate under thermal reaction conditions. These transformations are reflected in their evolving catalytic activity, and a fundamental understanding of the changing nature of active sites is vital for the rational design of solid materials for applications. Beyond thermal catalysis, both photocatalysis and electrocatalysis are topical because they can harness renewable energy to drive uphill reactions that afford commodity chemicals and fuels. Although structural transformations of photocatalysts and electrocatalysts have been observed in operando, the resulting implications for catalytic behaviour are not fully understood. In this Review, we summarize and compare the structural evolution of solid thermal catalysts, electrocatalysts and photocatalysts. We suggest that well-established knowledge of thermal catalysis offers a good basis to understand emerging photocatalysis and electrocatalysis research.

Flexible photocatalytic membrane based on CdS/PMMA polymeric nanocomposite films: multifunctional materials

In this study, poly(methyl methacrylate) with different doping nano-cadmium sulfide (CdS/PMMA) is prepared and characterized. CdS/PMMA polymeric nanocomposite films were synthesized using solution casting methodology. SEM and XRD are used for structure analysis for the studied nanocomposite films. XRD revealed the amorphous domains of PMMA polymer, which increased with increasing CdS nanoparticle contents. SEM revealed the CdS dispersion within the PMMA matrix. CdS nanoparticles in the PMMA matrix are expected to be aggregated due to the casting technique. The optical energy gap is found to be decreased after the CdS addition. ε' and ε″ have the same behavior with the applied frequency. Maxwell-Wagner interfacial polarization is the responsible factor for higher values of ε'-ε″ at the higher frequencies. Electrical conductivity behavior σ_AC tends to obtain a constant value at lower frequencies that approach from its DC conductivity values. After doping PMMA with nano-CdS, an exponential increase after a critical frequency value and the values of σ_AC was also increased. Besides, a significant reduction in laser energy power is identified by the reduction of the output power. CdS/PMMA can attenuate the laser power due to its nonlinear effect. CdS/PMMA nanocomposite can act as a photocatalyst to improve the performance of the photodegradation of Rhodamine B (RhB). Among the different CdS/PMMA nanocomposite films, 3.33 wt% CdS/PMMA demonstrates the highest efficiency in visible photocatalysis of Rhodamine B. CdS/PMMA can be utilized as multifunctional materials use like laser optical limiting to reduce the power of laser sources and as a photocatalyst membranes.

Stabilization and Utilization of Pyrite under Light Irradiation: Discussion of Photocorrosion Resistance

The control of pyrite (FeS₂) oxidation from a source is a problem of great concern on treatment of acid mine drainage (AMD). Compared with air and water, the effect of light on pyrite oxidation has not attracted enough attention. However, we found that pyrite photocorrosion in the light promoted the oxidation of pyrite. Herein, we introduce a method of coating pyrite with graphene oxide (GO), which can inhibit the oxidation and photocorrosion of pyrite while it can also degrade organic pollutants. The characterization results show that a covalent bond forms between the GO and pyrite. The stable and uniform GO coating prevents the permeation of O₂ and H₂O and promotes the transfer of photogenerated electrons. Moreover, it changes the conduction band (CB) and valence band (VB) levels of GO-pyrite. All of these are vital for preventing the corrosion of pyrite and promoting its photocatalytic ability. More importantly, the effect of CB and VB levels on the oxidized species was discussed. The inhibition of photocorrosion is achieved by the reaction of GO with the photoinduced h⁺, ^•OH, and ^•O₂ ^-. The study provides insights for source treatment of AMD under light and the reuse of massive abandoned pyrite.

Pt Deposites on TiO2 for Photocatalytic H2 Evolution: Pt Is Not Only the Cocatalyst, but Also the Defect Repair Agent

Pt, as a common cocatalyst, has been widely used in photocatalytic H2 evolution. However, the specific role of Pt in photocatalytic H2 evolution has not been thoroughly studied. In this paper, by employing three Pt sources with different charges (positive, negative and neutral), we systematically studied the charge effect of Pt sources on photocatalytic H2 evolution via TiO2 catalyst. According to the results of Raman, X-ray photoelectron spectroscopy (XPS), recycle experiments and photocurrent characterizations, it was found that TiO2 would produce electropositive defects during photocatalytic H2 evolution, inevitably leading to the decline of H2 production activity. Thanks to the electrostatic interaction, the electronegative Pt source not only promoted charge separation, but preferential deposited on electropositive defects, which acted as the defect repair agent, and thus resulted in the increased photocatalytic stability. This work may provide a new perspective for enhancing photocatalytic stability of hydrogen production.

A Ternary Dumbbell Structure with Spatially Separated Catalytic Sites for Photocatalytic Overall Water Splitting

Solar-driven overall water splitting based on metal sulfide semiconductor photocatalysts remains as a challenge owing to the strong charge recombination and deficient catalytic active sites. Additionally, significant inhibition of back reactions, especially the oxidation of sulfide ions during the photocatalytic water oxidation catalysis, is an arduous task that requires an efficient photogenerated hole transfer dynamics. Here, a ternary dumbbell-shaped catalyst based on RuO2/CdS/MoS2 with spatially separated catalytic sites is developed to achieve simultaneous production of hydrogen and oxygen under simulated solar-light without any sacrificial agents. Particularly, MoS2 nanosheets anchored on the two ends of CdS nanowires are identified as a reduction cocatalyst to accelerate hydrogen evolution, while RuO2 nanoparticles as an oxidation cocatalyst are deposited onto the sidewalls of CdS nanowires to facilitate oxygen evolution kinetics. The density functional theory simulations and ultrafast spectroscopic results reveal that photogenerated electrons and holes directionally migrate to MoS2 and RuO2 catalytic sites, respectively, thus achieving efficient charge carrier separation. The design of ternary dumbbell structure guarantees metal sulfides against photocorrosion and thus extends their range in solar water splitting.

Laser-induced graphene hybrid photoelectrode for enhanced photoelectrochemical detection of glucose

The combination of an electrocatalyst with a semiconductor light absorber is of great importance to increase the efficiency of photoelectrochemical (PEC) glucose detection. Here, in situ and synchronous fabrication of a Ni-based electrocatalyst (NiEC) and CdS semiconductor in laser-induced graphene (LIG) on indium-tin oxide glass is demonstrated via a one-step laser-induced solid phase transition. A series of component and structural characterization experiments suggest that the laser-induced NiEC uniformly disperses in the hybrid nanocomposite and exists mainly in the Ni⁰ and NiO states. Moreover, both electrochemical and PEC investigations confirm that the as-prepared hybrid photoelectrode exhibits excellent photoelectrocatalytic ability towards glucose, which is not only attributed to the strong synergistic interaction between CdS and NiEC, but also benefited from the high conductivity as well as 3D macroporous configuration of the simultaneously formed LIG, providing the key factor to achieve sensitive non-enzymatic PEC glucose sensors. Therefore, the laser-induced hybrid photoelectrode is then applied to the PEC detection of glucose, and a low detection limit of 0.4 μM is obtained with good stability, reproducibility, and selectivity. This study provides a promising paradigm for the facile and binder-free fabrication of an electrocatalyst-semiconductor-graphene hybrid photoelectrode, which will find potential applications in sensitive PEC biosensing for a broad range of analytes.

All-solid-state Z-scheme WO3 nanorod/ZnIn2S4 composite photocatalysts for the effective degradation of nitenpyram under visible light irradiation

A Z-scheme WO₃/ZnIn₂S₄ photocatalyst was synthesized via a simple solvothermal method. Compared with pure WO₃ and ZnIn₂S₄, photocatalytic experiments showed that these Z-scheme photocatalysts exhibited enhanced activity for the degradation of nitenpyram (NTP). The apparent rate constant (k) of NTP degradation on 50WZ (WO₃/ 50 wt% Znln₂S₄) was 0.042 min^-1 (∼3.8 times higher than WO₃ and ∼2.5 times higher than ZnIn₂S₄). Photoluminescence (PL), photocurrent (PC), and electrochemical impedance spectroscopy (EIS) showed that the separation and transfer efficiency of photogenerated carriers in 50WZ was markedly enhanced, which was favorable for improving its photocatalytic activity. Active species capture experiments and electron spin resonance (ESR) measurements showed that superoxide radicals and holes were the main active species for NTP degradation, and they confirmed the formation of the Z-scheme structure. Furthermore, a possible NTP degradation pathway was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS).

Interlayer Photoelectron Transfer Boosted by Bridged RuIV Atoms in GaS Nanosheets for Efficient Water Splitting

Photocatalytic water splitting over layered nanosheet (NS) catalysts has caught a lot of attention for renewable hydrogen fuel production. However, the weak van der Waals interlayer interactions make it a great challenge to realize an effective dissociation of photogenerated excitons and efficient charge transfer across the interior of layered catalysts during the photocatalysis process. Here, we propose an intercalation strategy of high-valence Ru^IV atoms to render two-dimensional GaS NS photocatalysts with rapid electron-hole dissociation and long photocarrier lifetime in visible-light-driven water splitting. Experimental and theoretical results unravel that the intercalated single-site Ru, confined in interlayer of GaS NSs, with a hexagonal structural configuration of "Ru₁-S₆", can serve as an electron-trapped high-speed channel toward simultaneously accelerating electron-hole pairs dissociation and promoting photoelectron transportation through the van der Waals interlayer. Consequently, the as-developed Ru-intercalated GaS NSs can give a notable H₂ production rate of 340 μmol g^-1 h^-1 under visible-light irradiation and an apparent yield of 7% at 420 nm, 38 times that of pure GaS NSs. This study opens up a feasible way for a new design of highly active layered photocatalysts toward high-efficiency solar energy conversion.

Dual Metal-Organic Framework Heterointerface

Herein, a core-shell dual metal-organic framework (MOF) heterointerface is synthesized. The Prussian blue (PB) MOF acts as a core for the growth of a porphyrin-doped MOF which is named PB@MOF. Porphyrins can significantly enhance the transfer of photoinspired electrons from PB and suppress the recombination of electrons and holes, thus enhancing the photocatalytic properties and consequently promoting the yields of singlet oxygen rapidly under 660 nm illumination. PB@MOF can exhibit a better photothermal conversion efficiency up to 29.9% under 808 nm near-infrared irradiation (NIR). The PB@MOF heterointerface can possess excellent antibacterial efficacies of 99.31% and 98.68% opposed to Staphylococcus aureus and Escherichia coli, separately, under the dual light illumination of 808 nm NIR and 660 nm red light for 10 min. Furthermore, the trace amount of Fe and Zr ions can trigger the immune system to favor wound healing, promising that PB@MOF achieves the rapid therapy of bacterial infected wounds and environmental disinfection.

TiO2 Nanowire-Supported Sulfide Hybrid Photocatalysts for Durable Solar Hydrogen Production

As the feet of clay, photocorrosion induced by hole accumulation has placed serious limitations on the widespread deployment of sulfide nanostructures for photoelectrochemical (PEC) water splitting. Developing sufficiently stable electrodes to construct durable PEC systems is therefore the key to the realization of solar hydrogen production. Here, an innovative charge-transfer manipulation concept based on the aligned hole transport across the interface has been realized to enhance the photostability of In₂S₃ electrodes toward PEC solar hydrogen production. The concept was realized by conducting compact deposition of In₂S₃ nanocrystals on the TiO₂ nanowire array. Under PEC operation, the supporting TiO₂ nanowires functioned as an anisotropic charge-transfer backbone to arouse aligned charge transport across the TiO₂-In₂S₃ interface. Because of the aligned hole transport, the TiO₂ nanowire-supported In₂S₃ hybrid nanostructures (TiO₂-In₂S₃) exhibited improved hole-transfer dynamics at the TiO₂-In₂S₃ interface and enhanced hole injection kinetics at the electrode surface, substantially increasing the long-term photostability toward solar hydrogen production. The PEC durability tests showed that TiO₂-In₂S₃ electrodes can achieve nearly 90.9% retention of initial photocurrent upon continuous irradiation for 6 h, whereas the pure In₂S₃ merely retained 20.8% of initial photocurrent. This double-gain charge-transfer manipulation concept is expected to convey a viable approach to the intelligent design of highly efficient and sufficiently stable sulfide photocatalysts for sustainable solar fuel generation.

(111) Facets-Oriented Au-Decorated Carbon Nitride Nanoplatelets for Visible-Light-Driven Overall Water Splitting

Development of a simple and stable photocatalyst for overall water splitting is a promising avenue for solar energy conversion. Here, carbon nitride (CN) nanosheet panels decorated with in situ-formed (111) facets-oriented Au nanoparticles (AuNPs) have been prepared by vapor-deposition polymerization followed by an easy immersion technique. Benefiting from the enhanced visible light absorption, the surface plasmon resonance effect of AuNPs, rapid transportation and separation of charge carriers, as well as better-aligned valence band levels, the as-obtained photocatalyst shows effective overall water splitting with stoichiometric H₂ and O₂ evolution even without any sacrificial agent, distinct from the half-reaction of Pt-decorated CN. This work opens up a brand-new route for facet self-selective growth of metal on two-dimensional conjugated carbon nitride materials, which has been demonstrated to be effective for artificial photosynthesis applications.

Construction of Al-ZnO/CdS photoanodes modified with distinctive alumina passivation layer for improvement of photoelectrochemical efficiency and stability

ZnO/CdS-based nanorod arrays (NRs) are an excellent class of photoanode materials, which possess high photoelectric response for solar-driven water splitting. A highly efficient photoanode system consisting of Al-doped ZnO NRs as effective electron-transfer layers and CdS as a light harvesting layer was rationally designed. Al doping increased the conductivity of ZnO NRs and simultaneously coarsened the surface of ZnO due to expansion of ZnO lattice. The rough surface favoured the growth of a CdS coating layer on it through a successive ionic layer adsorption reaction. The integrated ZnO/CdS photoanode exhibited photocurrent of 10.4 mA cm^-2 at 1.23 V versus RHE (reversible hydrogen potential) and conversion efficiency of 5.75% at 0.38 V versus RHE for 60 SILAR CdS cycles. The coating of a protective Al₂O₃ passivation layer through the direct current magnetron sputtering technique significantly improved the stability of the electrode, and it was better than that of the conventional atomic layer deposition method.

Synthesis of Particulate Hierarchical Tandem Heterojunctions toward Optimized Photocatalytic Hydrogen Production

Photocatalytic hydrogen production using semiconductors is identified as one of the most promising routes for sustainable energy; however, it is challenging to harvest the full solar spectrum in a particulate photocatalyst for high activity. Herein, a hierarchical hollow black TiO₂ /MoS₂ /CdS tandem heterojunction photocatalyst, which allows broad-spectrum absorption, thus delivering enhanced hydrogen evolution performance is designed and synthesized. The MoS₂ nanosheets not only function as a cost-effective cocatalyst but also act as a bridge to connect two light-harvesting semiconductors into a tandem heterojunction where the CdS nanoparticles and black TiO₂ spheres absorb UV and visible light on both sides efficiently, coupling with the MoS₂ cocatalyst into a particulate photocatalyst system. Consequently, the photocatalytic hydrogen rate of the black TiO₂ /MoS₂ /CdS tandem heterojunction is as high as 179 µmol h^-1 per 20 mg photocatalyst under visible-light irradiation, which is almost 3 times higher than that of black TiO₂ /MoS₂ heterojunctions (57.2 µmol h^-1 ). Most importantly, the stability of CdS nanoparticles in the black TiO₂ /MoS₂ /CdS tandem heterojunction is greatly improved compared to MoS₂ /CdS because of the formation of tandem heterojunctions and the strong UV-absorbing effect of black TiO₂ . Such a tandem architectural design provides new ways for synthesizing particulate photocatalysts with high efficiencies.

New Insight into Procedure of Interface Electron Transfer through Cascade System with Enhanced Photocatalytic Activity

Recombination of photogenerated electron-hole pairs is extremely limited in the practical application of photocatalysis toward solving the energy crisis and environmental pollution. A rational design of the cascade system (i.e., rGO/Bi₂ WO₆ /Au, and ternary composites) with highly efficient charge carrier separation is successfully constructed. As expected, the integrated system (rGO/Bi₂ WO₆ /Au) shows enhanced photocatalytic activity compared to bare Bi₂ WO₆ and other binary composites, and it is proved in multiple electron transfer (MET) behavior, namely a cooperative electron transfer (ET) cascade effect. Simultaneously, UV-vis/scanning electrochemical microscopy is used to directly identify MET kinetic information through an in situ probe scanning technique, where the "fast" and "slow" heterogeneous ET rate constants (K_eff ) of corresponding photocatalysts on the different interfaces are found, which further reveals that the MET behavior is the prime source for enhanced photocatalytic activity. This work not only offers a new insight to study catalytic performance during photocatalysis and electrocatalysis systems, but also opens up a new avenue to design highly efficient catalysts in photocatalytic CO₂ conversion to useful chemicals and photovoltaic devices.

In situ fabrication of a direct Z-scheme photocatalyst by immobilizing CdS quantum dots in the channels of graphene-hybridized and supported mesoporous titanium nanocrystals for high photocatalytic performance under visible light

We report the considerable advantages of direct Z-scheme photocatalysts by immobilizing high-quality CdS quantum dots (QDs) in the channels of graphene-hybridized and supported mesoporous titania (GMT) nanocrystals (CdS@GMT/GR) under facile hydrothermal conditions. The photocatalysts have been characterized by XRD, PL, XPS, SEM, DRS, TEM, EIS, and N₂ adsorption. CdS QDs primarily serve as photosensitizers with a unique pore-embedded structure for the effective utilization of the light source. This direct Z-scheme CdS@GMT/GR exhibits higher photocatalytic activity than CdS/GR, GMT/GR, or CdS@MT. In addition, the rate constant of CdS@GMT/GR-2 is approximately twice the sum of those of CdS@MT and GMT/GR, because GR played the role of hole-transporting and collection layer as well as the hybridization level formation in terms of hybridizing MT and serving as a support. Therefore, the GR content tunes the energy band, affects the surface area, and controls the interfacial hole transfer and collection rate of the direct Z-scheme system. Furthermore, CdS@GMT/GR retains its high performance in repeated photocatalytic processes. This can be attributed to the fact that GR prevents QDs from photocorrosion by means of the hole-transporting and collection effect. A possible reaction mechanism is proposed. This work provides a promising strategy for the construction of highly efficient visible-light-driven photocatalysts to reduce the growing menace of environmental pollution.

CdS@GMT/GR exhibits high photocatalytic activity due to its direct Z-scheme structure obtained by immobilizing CdS quantum dots in the channels of GMT nanocrystals.

Recent advances in three-dimensional graphene based materials for catalysis applications

This review presents recent theoretical and experimental progress in the construction, properties, and catalytic applications of 3D graphene-based materials.