Hydrogen spillover effect induced by ascorbic acid in CdS/NiO core-shell p-n heterojunction for significantly enhanced photocatalytic H2 evolution

A bioetching-induced visualized-organic photoelectrochemical transistor dual-signal mode sensor for alkaline phosphatase detection

A study of an integrated OPECT biosensor gate and the EC color-changing region on the same chip was carried out, achieving sensitive detection through bioetching-induced signal changes. Enzymatic bioetching enables specific alkaline phosphatase (ALP) detection by catalyzing the production of CdS, which modulates the channel current and generates a visual signal.

NiCS3: A cocatalyst surpassing Pt for photocatalytic hydrogen production

Cocatalysts play a key role in improving photocatalytic performance by enhancing conductivity and providing an enormous number of active sites simultaneously. However, cocatalysts are usually made of noble metals such as Pt, which are expensive and rare. Therefore, cocatalysts derived from cheap and abundant elements are highly desirable. Here, for the first time, we demonstrate that NiCS3, which is made from nickel that is abundant and costs less than 0.04 % of Pt, is an effective substitute for Pt cocatalysts for the photocatalytic activity of CdS nanorods in hydrogen evolution reaction (HER). Under visible light, the NiCS3/CdS composite with NiCS3 as the cocatalyst achieved an astonishing H2 production of 61.9 mmol·g-1·h-1 while maintaining high stability, which is 14 times higher than that observed when using CdS alone and nearly 2 times higher than that of Pt/CdS. We also established that the metallicity of NiCS3 results in good carrier conductivity, which promotes the electron transfer and the separation of photo-induced carriers. Due to the appropriate adsorption energy ΔGH*, NiCS3 more readily adsorbs hydrogen protons and desorbs molecular hydrogen during the photocatalytic process compared with Pt. Additionally, NiCS3 can effectively inhibit the photo-corrosion effect of CdS itself, ensuring a good stability of HER. These results suggest that NiCS3 is a promising substitute for Pt cocatalysts.

A high-performance photoelectrochemical sensor based on CdS-Au composite nanomaterials and localized surface plasmon resonance for ultrasensitive detection of ascorbic acid

Ascorbic acid (AA), which plays a vital role in the metabolism of the human body, is closely correlated with various diseases, including rheumatoid arthritis, scurvy, Parkinson's disease, urinary stones, and diarrhea. The detection of AA is of great significance for early prevention and diagnosis of related diseases. In this paper, a high-performance photoelectrochemical (PEC) sensor was constructed based on cadmium sulfide-gold (CdS-Au) composite nanomaterials for ultrasensitive ascorbic acid (AA) detection. Due to the localized surface plasmon resonance (LSPR) effect of gold nanoparticles (AuNPs), the PEC performance of CdS-Au composite nanomaterials was significantly improved compared to CdS semiconductor nanomaterials. Under the optimal conditions, the AA concentration was linearly related to the photocurrent signal in the range of 0.01 μM-200 μM, with the detection limit being 0.2 nM (S/N = 3) and the sensitivity being 642.9 μA mM-1 cm-2. In addition, the mechanism of the PEC sensor based on CdS-Au composite nanomaterials for ultrasensitive AA detection was discussed. Lastly, the self-constructed PEC sensors have been successfully applied in detecting AA in vitamin C tablets and actual blood samples, meeting the detection criteria required by the Chinese Pharmacopoeia (CP, 2020 edition). The self-fabricated PEC sensors in this paper are expected to be used for quality assessment of AA-related drugs and diagnosis of relevant diseases.

Enhanced photocatalytic hydrogen evolution of Ru/TiO2-x via oxygen vacancy-assisted hydrogen spillover process

Hydrogen spillover effects will significantly improve the activity of photocatalytic hydrogen evolution reactions (HER), while their introduction and optimization require the construction of an excellent metal/support structure. In this study, we have synthesized Ru/TiO2-x catalysts with controlled oxygen vacancy (OVs) concentrations using a simple one-pot solvothermal method. The results show that Ru/TiO2-x3 with the optimal OVs concentration exhibits an unprecedentedly high H2 evolution rate of 13604 μmol·g-1·h-1, which was 45.7 and 2.2 times higher than that of TiO2-x (298 μmol·g-1·h-1) and Ru/TiO2 (6081 μmol·g-1·h-1). Controlled experiments, detailed characterizations, and theoretical calculations have revealed that the introduction of OVs on the carrier contributes to the hydrogen spillover effect in the metal/support system photocatalyst and that the process of hydrogen spillover in this system can be optimized by modulating the OVs concentration. This study proposes a strategy to decrease the energy barrier of hydrogen spillover and enhance photocatalytic HER activity. Moreover, it investigates the effect of OVs concentration on the hydrogen spillover effect in the photocatalytic metal/supports system.

Construction of ZnIn2 S4 /CdS/PdS S-Scheme Heterostructure for Efficient Photocatalytic H2 Production

It is facing a tremendous challenge to develop the desirable hybrids for photocatalytic H₂ generation by integrating the advantages of a single semiconductor. Herein, an all-sulfide ZnIn₂ S₄ /CdS/PdS heterojunction is constructed for the first time, where CdS and PdS nanoparticles anchor in the spaces of ZnIn₂ S₄ micro-flowers due to the confinement effects. The morphology engineering can guarantee rapid charge transfer owing to the short carrier migration distances and the luxuriant reactive sites provided by ZnIn₂ S₄ . The S-scheme mechanism between ZnIn₂ S₄ and CdS assisted by PdS cocatalyst is testified by in situ irradiated X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR), where the electrons and holes move in reverse driven by work function difference and built-in electric field at the interfaces. The optimal ZnIn₂ S₄ /CdS/PdS performs a glaring photocatalytic activity of 191.9 µmol h^-1 (10 mg of catalyst), and the largest AQE (apparent quantum efficiency) can reach a high value of 26.26%. This work may afford progressive tactics to design multifunctional photocatalysts.

Strong synergy between gold nanoparticles and cobalt porphyrin induces highly efficient photocatalytic hydrogen evolution

The reaction efficiency of reactants near plasmonic nanostructures can be enhanced significantly because of plasmonic effects. Herein, we propose that the catalytic activity of molecular catalysts near plasmonic nanostructures may also be enhanced dramatically. Based on this proposal, we develop a highly efficient and stable photocatalytic system for the hydrogen evolution reaction (HER) by compositing a molecular catalyst of cobalt porphyrin together with plasmonic gold nanoparticles, around which plasmonic effects of localized electromagnetic field, local heating, and enhanced hot carrier excitation exist. After optimization, the HER rate and turn-over frequency (TOF) reach 3.21 mol g^-1 h^-1 and 4650 h^-1, respectively. In addition, the catalytic system remains stable after 45-hour catalytic cycles, and the system is catalytically stable after being illuminated for two weeks. The enhanced reaction efficiency is attributed to the excitation of localized surface plasmon resonance, particularly plasmon-generated hot carriers. These findings may pave a new and convenient way for developing plasmon-based photocatalysts with high efficiency and stability.

Hydroxyl-modified Nb4C3Tx MXene@ZnIn2S4 sandwich structure for photocatalytic overall water splitting

Herein, a hydroxyl-modified MXene@ZnIn₂S₄ (Nb₄C₃T_x MXene@ZIS-OH) overall water splitting photocatalyst with a sandwich structure was prepared through an in-situ growth strategy and peroxyl plasma post-treatment. The Nb₄C₃T_x MXene@ZIS-OH exhibits outstanding catalytic performance, which generates the release rates of hydrogen (53.8 μmol g^-1h^-1) and oxygen (26.7 μmol g^-1h^-1) from the water under visible light irradiation. After four photocatalytic cycling, the photocatalytic overall water splitting activity of Nb₄C₃T_x MXene@ZIS-OH is still 95.9% of the initial activity, which indicates that Nb₄C₃T_x MXene@ZIS-OH exhibits excellent cycling stability. Notably, the Nb₄C₃T_x MXene@ZIS-OH achieves an AQY of 1.2% for the overall photocatalytic water splitting at 380 nm. The sandwich structure and matched heterointerface between high work function Nb₄C₃T_x MXene and ZnIn₂S₄ nanosheets promote the electron transport, inhibit the charge recombination, and separate the generated H₂ and O₂ with effectiveness. Importantly, the Finite-Difference Time-Domain (FDTD) simulation suggests the hydroxyl groups on the surface of ZnIn₂S₄ could increase the hydrophilicity of photocatalyst and capture the holes generated by photoexcitation, thereby promoting the separation of electron-hole pairs rapidly. This work presents a successful example of constructing overall water splitting photocatalysts by energy level regulation, structure design and functional group modification.

Fabrication of TaON/CdS Heterostructures for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

Developing high-performance photocatalysts for H2 production via fabricating heterojunctions has attracted much attention. Herein, we design a simple strategy to prepare composites that consist of TaON/CdS hybrids via a hydrothermal process. The results show that the pristine CdS nanoparticles loaded with 20 wt% TaON (TC4) could maximize the photocatalytic hydrogen evolution rate to 19.29 mmol g−1 h−1 under visible light irradiation, which was 2.13 times higher than that of the pristine CdS (9.03 mmol g−1 h−1) under the same conditions. The apparent quantum yield (AQY) of the TC4 nanocomposites at 420 nm was calculated to be 18.23%. The outstanding photocatalytic performance of the composites can be ascribed to the formation of heterojunctions. The electrochemical measurements indicate that the decoration facilitates the generation of extra photo-electrons, prolonging the recombination rate of photogenerated charge carriers, offering adequate active sites and improving catalytic stability. This study sheds light on the construction strategy and the deep understanding of the novel CdS-based composites for high-performance photocatalytic H2 production.

In situ growth of hierarchical phase junction CdS on a H-mordenite zeolite for enhanced photocatalytic properties

A kind of cadmium sulfide (CdS) nanocomposite with different crystalline phases was grown on the surface of H-mordenite zeolite (HMOR) by a chemical liquid-phase co-precipitation method. In this work, 2 wt% CdS@HMOR photocatalytic material with the coexistence phase (hexagonal phase and cubic phase) of cadmium sulfide was grown on the surface of HMOR by controlling the reaction temperature and ammonia concentration. Photocatalytic degradation of methylene blue (MB) was used as an index to detect the photocatalytic performance of materials. The results indicated that the photocatalytic degradation efficiency of the system with HMOR was significantly improved in comparison to that without HMOR (CdS, 40.34%, 0.2578 h^-1). It was found that 2 wt% CdS@HMOR had the best photocatalytic activity. The degradation rate of MB was 84.15% in 2 h, and the degradation rate constant was 0.8884 h^-1. When 1.5 ml H₂O₂ was introduced into the system, the degradation rate of MB was increased to 98.98%, and the degradation rate constant was 1.9976 h^-1. SEM, HRTEM, PL, EIS and photocurrent showed that the cubic and hexagonal phases of CdS were in contact with each other on the HMOR surface, forming a good electron transport. By XRD, XPS and SEM tests, the results of materials after four cycles of reactions showed that the structure of the 2 wt% CdS@HMOR was still stable. Therefore, HMOR may provide a good support for CdS, and the synergistic effect between them is beneficial for the occurrence of photocatalytic reactions. HMOR can act as an electron receptor to inhibit the recombination of carriers. The homo-junction between different phases of CdS on the surface of HMOR is beneficial to the separation of photo-induced carriers. These results indicate that the construction of phase heterojunctions on zeolites and the synergism among them are a method for improving the photocatalytic activity.

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.

An electron-hole separation mechanism caused by the pseudo-gap formed at the interfacial Co-N bond between cobalt porphyrin metal organic framework and boron-doped g-C3N4 for boosting photocatalytic H2 production

Photocatalytic hydrogen evolution from water splitting presents an attractive prospect in dealing with the energy crisis, but the low efficiency of charge separation and migration still seriously hinders its further practical application. Here, an acidified boron-doped g-C₃N₄ (HBCNN) and cobalt porphyrin metal organic frameworks (CoPMOF) self-assembled two-dimensional and two-dimensional (2D/2D) hybrid photocatalyst is fabricated successfully. The resultant HBCNN/CoPMOF with optimum ratio exhibits a superior H₂ evolution rate of 33.17 mmol g^-1 h^-1, which is 3.04 and 100.50 times higher than the single HBCNN and CoPMOF, respectively. It is found that a coordination connection has formed between CoPMOF and HBCNN through Co-N bond, and the interfacial Co-N bond then forms a pseudo-gap in the up-spin channel of electronic states, establishing an electron-hole separation mechanism. It is this electron-hole separation mechanism that contributes to a Z-scheme transport mode of photogenerated carriers, which greatly promotes the photocatalytic H2 production performance of HBCNN/CoPMOF heterostructure. This work may provide an idea for the design of heterojunction to improve the photocatalytic performance by constructing electron-hole separation through interfacial bond.

Nanoscale Assembly of CdS/BiVO4 Hybrids for Coupling Selective Fine Chemical Synthesis and Hydrogen Production under Visible Light

Simultaneously utilizing photogenerated electrons and holes in one photocatalytic system to synthesize value-added chemicals and clean hydrogen (H₂) energy meets the development requirements of green chemistry. Herein, we report a binary material of CdS/BiVO₄ combining one-dimensional (1D) CdS nanorods (NRs) with two-dimensional (2D) BiVO₄ nanosheets (NSs) constructed through a facile electrostatic self-assembly procedure for the selectively photocatalytic oxidation of aromatic alcohols integrated with H₂ production, which exhibits significantly enhanced photocatalytic performance. Within 2 h, the conversion of aromatic alcohols over CdS/BiVO₄-25 was approximately 9-fold and 40-fold higher than that over pure CdS and BiVO₄, respectively. The remarkably improved photoactivity of CdS/BiVO₄ hybrids is mainly ascribed to the Z-scheme charge separation mechanism in the 1D/2D heterostructure derived from the interface contact between CdS and BiVO₄, which not only facilitates the separation and transfer of charge carriers, but also maintains the strong reducibility of photogenerated electrons and strong oxidizability of photogenerated holes. It is anticipated that this work will further stimulate interest in the rational design of 1D/2D Z-scheme heterostructure photocatalysts for the selective fine chemical synthesis integrated with H₂ evolution.

Insights into the Operation of Noble-Metal-Free Cocatalyst 1T-WS2 -Decorated Zn0.5 Cd0.5 S for Enhanced Photocatalytic Hydrogen Evolution

Due to inefficient charge separation and low surface catalytic conversion efficiencies, cocatalysts are required for achieving photocatalytic hydrogen evolution. Being a noble-metal-free cocatalyst, metallic 1T-WS₂ with excellent conductivity can function for this reaction. Herein, 1T-WS₂ /Zn_0.5 Cd_0.5 S is constructed via a simple and feasible grinding approach. The composite containing 7.5 % 1T-WS₂ in 1T-WS₂ /Zn_0.5 Cd_0.5 S achieves a hydrogen evolution rate of 61.65 mmol g^-1  h^-1 and an external quantum efficiency of 8.04 % at 420 nm, which is 37 times that of bare Zn_0.5 Cd_0.5 S (1.67 mmol g^-1  h^-1 ). The electrical conductivity of metallic 1T-WS₂ reduces the transfer impedance at the interface and thus accelerates the non-radiative energy transfer and electron transport rate. The different Fermi levels of 1T-WS₂ and Zn_0.5 Cd_0.5 S form a Schottky junction, which promotes the transfer of photogenerated electrons from Zn_0.5 Cd_0.5 S to 1T-WS₂ . More importantly, the close interface contact between 1T-WS₂ and Zn_0.5 Cd_0.5 S results in strong electron interactions, which is conducive to the spatial separation of photogenerated electrons and holes. This work will further expand the application of 1T-WS₂ in the photocatalytic hydrogen evolution process.