CdS Nanorods Coupled with WS2 Nanosheets for Enhanced Photocatalytic Hydrogen Evolution Activity

Advances in the heterostructures for enhanced hydrogen production efficiency: a comprehensive review

The growing global energy demand and heightened environmental consciousness have contributed to the increasing interest in green energy sources, including hydrogen production. However, the efficacy of this technology is contingent upon the efficient separation of charges, high absorption of sunlight, rapid charge transfer rate, abundant active sites and resistance to photodegradation. The utilization of photocatalytic heterostructures coupling two materials has proved to be effective in tackling the aforementioned challenges and delivering exceptional performance in the production of hydrogen. The present article provides a comprehensive overview of operational principles of photocatalysis and the combination of photocatalytic and piezo-catalytic applications with heterostructures, including the transfer behavior and mechanisms of photoexcited non-equilibrium carriers between the materials. Furthermore, the effects of recent advances and state-of-the-art designs of heterostructures on hydrogen production are discussed, offering practical approaches to form heterostructures for efficient hydrogen production.

Numerical characterization of thermal transport in hexagonal tungsten disulfide (WS2) nanoribbons

In this study, we have investigated the thermal transport characteristics of single-layer tungsten disulfide, WS2nanoribbons (SLTDSNRs) using equilibrium molecular dynamics simulations with the help of Green-Kubo formulation. Using Stillinger-Weber (SW) inter-atomic potential, the calculated room temperature thermal conductivities of 15 nm × 4 nm pristine zigzag and armchair SLTDSNRs are 126 ± 10 W m-1K-1and 110 ± 6 W m-1K-1, respectively. We have explored the dependency of thermal conductivity on temperature, width, and length of the nanoribbon. The study shows that the thermal conductivity of the nanoribbon decreases with the increase in temperature, whereas the thermal conductivity increases with an increase in either the width or length of the ribbon. The thermal conductivity does not increase uniformly as the size of the ribbon changes. We have also observed that the thermal conductivity of SLTDSNRs depends on edge orientations; the zigzag nanoribbon has greater thermal conductivity than the armchair nanoribbon, regardless of temperature or dimension variations. Our study additionally delves into the tunable thermal properties of SLTDSNRs by incorporating defects, namely vacancies such as point vacancy, edge vacancy, and bi-vacancy. The thermal conductivities of nanoribbons with defects have been found to be considerably lower than their pristine counterparts, which aid in enhanced values for the thermoelectric figure of merit (zT). We have varied the vacancy concentration within a range of 0.1% to 0.9% and found that a point vacancy concentration of 0.1% leads to a 64% reduction in the thermal conductivity of SLTDSNRs. To elucidate these phenomena, we have calculated the phonon density of states for WS2under different aspects. The findings of our work provide important understandings of the prospective applications of WS2in nanoelectronic and thermoelectric devices by tailoring the thermal transport properties of WS2nanoribbons.

Moisture-Resistant and Highly Selective NH3 Sensor Based on CdS/WS2 Composite Heterojunction

This study reports the synthesis of CdS/WS2 composites via a green and ultra-low-cost hydrothermal method. By controlling the relative mass ratio between WS2 and CdS, an n-n type CdS/WS2 heterostructure, with excellent NH3 gas-sensitive properties, was developed and investigated at room temperature. Compared with pristine WS2 and CdS, the CdS/WS2-40%wt composite exhibited excellent selectivity of more than 4 orders of magnitude for sensing NH3, a very short recovery time of 3 s, and ultrahigh selectivity at room temperature. The large specific surface area of the CdS/WS2 composite increased the active sites for the gas-sensitive reaction. Additionally, the 2D morphology of CdS/WS2 and the heterojunction formed between WS2 and CdS contributed to the improved performance. Anti-humidity interference tests showed that the CdS/WS2 sample remained stable under real-time monitoring of NH3 at different ambient humidity values. This study paves the way for designing high-performance gas sensors operating at room temperature.

Highly Efficient Photocatalysts: Polyoxometalate Synthons Enable Tailored CdS-MoS2 Morphologies and Enhanced H2 Evolution

The development of photocatalysts toward highly efficient H₂ evolution reactions is a feasible strategy to achieve the effective conversion of solar energy and meet the increasing demand for new energy. To this end, we prepared two different CdS-MoS₂ photocatalysts with unique morphologies ranging from hexagonal prisms to tetragonal nanotubes by carefully tuning polyoxometalate synthons. These two photocatalysts, namely, CdS-MoS₂-1 and CdS-MoS₂-2, both exhibited remarkable photocatalytic efficiency in H₂ generation, among which CdS-MoS₂-2 showed superior performance. In fact, the best catalytic hydrogen desorption rate of CdS-MoS₂-2 is as high as 1815.5 μmol g^-1 h^-1. Such performance is superior to twice that of single CdS and almost four times that of pure MoS₂. This obvious enhancement can be accredited to the highly open nanotube morphology and highly dispersed heterometallic composition of CdS-MoS₂-2, which represents an excellent example of the highest noble-metal-free H₂ evolution photocatalysts reported so far. Taken together, these findings suggest that the development of highly dispersed heterometallic catalysts is an auspicious route to realize highly efficient conversion of solar energy and that CdS-MoS₂-2 represents a major advance in this field.

Defected tungsten disulfide decorated CdS nanorods with covalent heterointerfaces for boosted photocatalytic H2 generation

Owing to their intrinsic and pronounced charge carrier transport when facing the formidable challenge of inhibiting severe surface charge recombination, one-dimensional (1D) CdS nanostructures are promising for advancing high-yield hydrogen production. We herein demonstrate an efficient strategy of boosting interfacial carrier separation by heterostructuring 1D CdS with defective WS₂. This process yields solid covalent interfaces for high flux carrier transfer that differ distinctively from those reported structures with physical contacts. As a nonnoble cocatalyst, WS₂ can accept photogenerated electrons from CdS, and the sulfur vacancies existing at its edges can effectively trap electrons as active sites for H₂ evolution. Moreover, due to its strong negative property, the H⁺ from the aqueous solution can gather around WS₂. WS₂ possesses a lower reaction barrier than CdS, which expedites the kinetic process for the reaction. The optimized sample exhibits a high photocatalytic H₂ evolution rate of 183.4 µmol/h (10 mg photocatalyst), which is as far as we know among the top in the records for CdS-based photocatalysts. We believe this present work will be inspiring in addressing the interfacial charge carrier transfer by constructing covalent heterointerfaces.

Covalent-anion-driven self-assembled cadmium/ molybdenum sulfide hybrids for efficient nitenpyram degradation

Photocatalytic technology is an attractive and promising approach for nitenpyram degradation; however, how to ensure the carrier separation efficiency and catalytic sites exposure is still great challenges. In this study, we construct CdS@MoS₂ (CM) nanohybrids with a 3D hierarchical configuration to enhance the separation and transfer efficiency of the photo-induced electron by a covalent-anion-driven self-assembly method. The vertical orientation of MoS₂ ultrathin nanosheets not only provides a large specific surface area for the oxidation and reduction reactions but also enables the active edge sites of MoS₂ to be maximally exposed. As a result, this structure drastically facilitates the exposure of the catalytic active region and the performance of the carrier transfer and injection into photocatalytic degradation for nitenpyram (NTP). The optimal CdS-MoS₂ has an impressive and stable NTP removal efficiency with a high reaction rate constant up to 0.078 min^-1, which is 3.25 times higher than that of pure cadmium sulfide. The photocatalytic degradation mechanism and degradation pathway of NTP were presented by synthesizing the results of experimental analysis and density flooding theory (DFT) calculations. In further, for the first time, the cytotoxicity and genotoxicity of NTP on moving bed biofilm reactors (MBBRs) was disclosed and a continuous photocatalytic wastewater pretreatment device based on the CM is proposed for the stable biological nitrogen removal activity of MBBRs, which can degrade more than 80% NTP per hour.

Impact of the number of surface-attached tungsten diselenide layers on cadmium sulfide nanorods on the charge transfer and photocatalytic hydrogen evolution rate

The selection of layered number and time-course destruction of layers may affect the charge transfer between 2D-to-1D heterostructure, making it possible to improve the efficiency of solar-to-hydrogen evolution. Herein, we demonstrate a simple, low-cost systematic protocol of 2D-WSe₂ nanolayer numbers ranging from 7 to 60 aiding the ultrasonication time-course. The resultant nanolayers were assembled on the surface of 1D-CdS nanorods, which demonstrated an improved surface shuttling property. Consequently, a drastic improvement in photocatalytic solar-driven hydrogen evolution was observed (103.5 mmol h^-1 g^-1) with seven-layered WSe₂ (few-layered WSe₂) attached on CdS nanorods surface. This enhanced photocatalytic performance is attributed to the selection of layers on CdS surface that expose abundant active sites; along with suitable energy levels, this can facilitate increased charge transfer leading to feasible photocatalytic reactions. Significantly, the present study proposes an efficient and sustainable process to produce hydrogen and demonstrates the potential of numbered WSe₂ nanosheets as a co-catalyst material.

Improved Mass-Transfer Enhances Photo-Driven Dye Degradation and H2 Evolution over a Few-Layer WS2/ZnO Heterostructure

In this study, we observed the enhanced photocatalytic activity of a few-layer WS₂/ZnO (WZ) heterostructure toward dye degradation and H₂ production. The few-layer WS₂ acted as a co-catalyst that separated photogenerated electron/hole pairs and provided active sites for reactions, leading to the rate of photocatalytic H₂ production of WZ being 35% greater than that over the bare ZnO nanoparticles. Moreover, vortex-stirring accelerated the mass-transfer of the reactants, leading to the efficiency of dye photodegradation being 3 times higher than that obtained without high-speed stirring. We observed a similar effect for H₂ production, with greater photocatalytic performance arising from the increased mass-transfer of H₂ from the catalyst surface to the atmosphere.

Near-infrared light responsive dendrimers facilitate the extraction of bicalutamide from human plasma and urine

BACKGROUND

Today, it is well accepted that the quantitative measurement of anti-cancer drugs in human biological samples requires the development and validation of efficient bioanalytical methods. This study attempts to provide a high-capacity and thermo-sensitive nano-adsorbent for bicalutamide extraction from human biological fluids.

MAIN METHODS AND MAJOR RESULTS

In this study, five generations of thermo-sensitive dendrimers were synthesized onto the surface of WS₂ nano-sheets. After drug-loading process from body fluids, the near-infrared (NIR) light (at 808 nm) was applied and light-to-heat conversion by the WS₂ nano-sheets led to shrinkage in polymer chains, resulting the release of the entrapped drug. Finally, the extracted drug was analyzed via HPLC-UV system (at 270 nm). The final nano-adsorbent was described via FE-SEM, XRD, FT-IR, and TGA techniques. The adsorption isotherm data were well fitted by Langmuier isotherm model (R²  = 0.9978). The mean recoveries for spiking bicalutamide at three different concentrations in plasma and urine samples were 92.12% and 94.54% under the NIR light irradiation.

CONCLUSIONS AND IMPLICATIONS

We have developed a smart strategy to analyze bicalutamide in biological samples using near-infrared light irradiation in a controlled manner. All the results indicate the promising application of the proposed method for the extraction and determination of bicalutamide.

Low-Dimensional Nanostructured Photocatalysts for Efficient CO2 Conversion into Solar Fuels

The ongoing energy crisis and global warming caused by the massive usage of fossil fuels and emission of CO2 into atmosphere continue to motivate researchers to investigate possible solutions. The conversion of CO2 into value-added solar fuels by photocatalysts has been suggested as an intriguing solution to simultaneously mitigate global warming and provide a source of energy in an environmentally friendly manner. There has been considerable effort for nearly four decades investigating the performance of CO2 conversion by photocatalysts, much of which has focused on structure or materials modification. In particular, the application of low-dimensional structures for photocatalysts is a promising pathway. Depending on the materials and fabrication methods, low-dimensional nanomaterials can be formed in zero dimensional structures such as quantum dots, one-dimensional structures such as nanowires, nanotubes, nanobelts, and nanorods, and two-dimensional structures such as nanosheets and thin films. These nanostructures increase the effective surface area and possess unique electrical and optical properties, including the quantum confinement effect in semiconductors or the localized surface plasmon resonance effect in noble metals at the nanoscale. These unique properties can play a vital role in enhancing the performance of photocatalytic CO2 conversion into solar fuels by engineering the nanostructures. In this review, we provide an overview of photocatalytic CO2 conversion and especially focus on nanostructured photocatalysts. The fundamental mechanism of photocatalytic CO2 conversion is discussed and recent progresses of low-dimensional photocatalysts for efficient conversion of CO2 into solar fuels are presented.

An effective photocatalytic hydrogen evolution strategy based on tunable band gap (CuIn)xZn2(1−x)S2 combined with amorphous molybdenum sulfide

The combination of crystalline band-tunable (CuIn)_xZn_2(1−x)S₂ and amorphous a-MoS_x provides a good strategy for photocatalysts.

Efficient and Stable Photocatalytic Hydrogen Evolution Activity of Multi-Heterojunction Composite Photocatalysts: CdS and NiS2 Co-modified NaNbO3 Nanocubes

In this study, a NaNbO₃/CdS/NiS₂ ternary composite photocatalyst containing no precious metals was successfully prepared by a simple hydrothermal method. The prepared ternary photocatalyst has a significant improvement in photocatalytic performance of hydrogen production from water splitting under visible light irradiation. The best sample NCN40% hydrogen production rate is 4.698 mmol g⁻¹ h⁻¹, which is about 24.7 times that of pure CdS sample. In addition, the stability of the composite catalyst in the long-term photocatalytic hydrogen production cycle is also improved. The reason for the enhanced hydrogen production performance may be the optimization of the microstructure of the catalyst and the reduction of photogenerated electron-hole recombination. The construction of multi-heterojunctions (NaNbO₃-CdS, CdS–NiS₂, and NaNbO₃-NiS₂) helps to reduce the recombination of carriers. Furthermore, the in-situ-formed NiS₂ nanoparticles can serve as active sites for hydrogen evolution. All of these factors induced the improved photocatalytic activity of the as-prepared ternary photocatalyst.

Conjugated Electron Donor⁻Acceptor Hybrid Polymeric Carbon Nitride as a Photocatalyst for CO2 Reduction

This work incorporates a variety of conjugated donor-acceptor (DA) co-monomers such as 2,6-diaminopurine (DP) into the structure of a polymeric carbon nitride (PCN) backbone using a unique nanostructure co-polymerization strategy and examines its photocatalytic activity performance in the field of photocatalytic CO2 reduction to CO and H2 under visible light irradiation. The as-synthesized samples were successfully analyzed using different characterization methods to explain their electronic and optical properties, crystal phase, microstructure, and their morphology that influenced the performance due to the interactions between the PCN and the DPco-monomer. Based on the density functional theory (DFT) calculation result, pure PCN and CNU-DP15.0 trimers (interpreted as incorporation of the co-monomer at two different positions) were extensively evaluated and exhibited remarkable structural optimization without the inclusion of any symmetry constraints (the non-modified sample derived from urea, named as CNU), and their optical and electronic properties were also manipulated to control occupation of their respective highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Also, co-polymerization of the donor-acceptor 2,6-diamino-purine co-monomer with PCN influenced the chemical affinities, polarities, and acid-base functions of the PCN, remarkably enhancing the photocatalytic activity for the production of CO and H2 from CO2 by 15.02-fold compared than that of the parental CNU, while also improving the selectivity.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

Electrochemically chopped WS2 quantum dots as an efficient and stable electrocatalyst for water reduction

A single-step electrochemical disintegration of bulk WS₂ led to a highly active WS₂ QDs electrocatalyst for HER.

Microwave synthesis of ZnIn2S4/WS2 composites for photocatalytic hydrogen production and hexavalent chromium reduction

A rapid microwave synthesis route for the fabrication of ZnIn₂S₄ powder and ZnIn₂S₄/WS₂ composites is presented.

Phase Transition of Two-Dimensional β-Ga2O3 Nanosheets from Ultrathin γ-Ga2O3 Nanosheets and Their Photocatalytic Hydrogen Evolution Activities

Monoclinic β-Ga₂O₃ nanosheets hold great potential applications in electronic, optical, and photocatalytic fields. In this study, two-dimensional β-Ga₂O₃ nanosheets were successfully fabricated through a simple crystalline phase transition from the as-prepared ultrathin γ-Ga₂O₃ nanosheets. The photocatalytic hydrogen evolution reaction under UV light irradiation was achieved on the two kinds of photocatalysts. However, β-Ga₂O₃ with a higher crystallinity shows a lower photocatalytic activity in comparison with γ-Ga₂O₃. The average apparent quantum yield is calculated to be 0.29% for β-Ga₂O₃ nanosheets and 1.82% for γ-Ga₂O₃. More efficient separation and transfer rates of photogenerated carriers and larger specific areas were found in γ-Ga₂O₃. On the basis of the analysis of the structures of γ-Ga₂O₃ and β-Ga₂O₃, it is proposed that the disordered or defective structure contributes to the improvement of photocatalytic activity to some extent. Therefore, it is significant to develop the photocatalyst with a stable structure and a certain number of defects at the same time.

Photocatalytic Activation of Saturated C-H Bond Over the CdS Mixed-Phase Under Visible Light Irradiation

Selective activation of saturated C–H bond in hydrocarbons to produce high-value-added chemicals is of great significance for chemical synthesis and transformation. Herein, we present a facile procedure to achieve Ni-doped CdS nanoparticles with mixed (cubic and hexagonal) phases, as well as its application to the photocatalytic activation of saturated primary C–H bond of toluene and its derivatives. The photocatalytic oxidation rate of toluene into benzaldehyde of formation reached up to 216.7 μmolh⁻¹g⁻¹ under visible light irradiation. The excellent photocatalytic performance of Ni(II)-doped CdS [Ni(II)/CdS] can be attributed to its unique structural assembly with cubic and hexagonal phases and also the addition of Ni ions, together taking effect in promoting the separation of photogenerated charge carriers. The possible reaction mechanism for the photocatalytic selective oxidation is illustrated in this work. The band width of the as-prepared mixed phase CdS is reduced, which can effectively expand the response range and improve photocatalytic performance.

2D/2D Heterostructured CdS/WS2 with Efficient Charge Separation Improving H2 Evolution under Visible Light Irradiation

Efficient water splitting for H₂ evolution under visible light irradiation has attracted more attention for solving the global environmental and energy issues, but it is still a major challenge to develop an earth-abundant and efficient photocatalyst. Herein, we report two-dimensional (2D)/2D heterostructured CdS/WS₂ (CdS/WS₂), composed of nanosheet CdS (CdS) and nanosheet WS₂ (WS₂), as an efficient photocatalyst for H₂ evolution. As a noble metal-free visible light-driven catalyst for H₂ evolution, CdS/WS₂ with 10 wt % WS₂ exhibited the largest H₂ evolution rate of 14.1 mmol g^-1 h^-1 under visible light irradiation to be 8 times larger than that of pure CdS. The lifetime and dynamics of photogenerated electrons were evaluated by femtosecond time-resolved diffuse reflectance spectroscopy, indicating that WS₂ works as an electron-trapping site and a cocatalyst to cause H₂ evolution under visible light irradiation. This work suggests that CdS/WS₂ has great potential as a low-cost and highly efficient photocatalyst for water splitting.

High Yield Exfoliation of WS2 Crystals into 1-2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS2/CdS Nanorod Composites

Monolayer WS₂ has interesting properties as a direct bandgap semiconductor, photocatalyst, and electrocatalyst, but it is still a significant challenge to prepare this material in colloidal form by liquid-phase exfoliation (LPE). Here, we report the preparation of 1-2 layer semiconducting WS₂ nanosheets in a yield of 18-22 wt % by a modified LPE method that involves preintercalation with substoichometric quantities of n-butyllithium. The exfoliated WS₂ nanosheeets are n-type, have a bandgap of ∼1.78 eV, and act as a cocatalyst with CdS nanorods in photocatalytic hydrogen evolution using lactate as a sacrificial electron donor. Up to a 26-fold increase in H₂ evolution rate was observed with WS₂/CdS hybrids compared with their pure CdS counterpart, and an absorbed photon quantum yield (AQE) of >60% was measured with the optimized photocatalyst.

One-pot hydrothermal synthesis of CdS decorated CuS microflower-like structures for enhanced photocatalytic properties

CdS decorated CuS structures have been controllably synthesized through a one-pot hydrothermal method. The morphologies and compositions of the as-prepared samples could be concurrently well controlled by simply tuning the amount of CdCl2 and thiourea. Using this strategy, the morphology of the products experienced from messy to flower-like morphologies with multiple porous densities, together with the phase evolution from pure CuS to the CdS/CuS composites. Serving as a photocatalyst, the samples synthesized with the addition of 1 mmol cadmium chloride and 3 mmol thiourea during synthetic process, showed the best photocatalytic activity, which could reach a maximum photocatalytic efficiency of 93% for methyl orange (MO) photodegradation after 150 min. The possible mechanism for the high photocatalytic efficiency of the sample was proposed by investigating the composition, surface area, structure, and morphology before and after photocatalytic reaction.