Recent Advances in Cadmium Sulfide-Based Photocatalysts for Photocatalytic Hydrogen Evolution

High-efficiency photocatalytic hydrogen evolution(PHE)relies on the development of inexpensive,stable,and efficient photocatalysts.Cadmium sulfide(CdS),as a typical binary metal sulfide,has attracted considerable research attention due to its negative conduction band position,narrow band gap for visible-light response,and strong driving force for PHE.However,the construction of CdSbased photocatalysts and the PHE rate still require improvement for practical applications.In this review,recent advances in CdS-based photocatalysts for PHE via water splitting are systematically summarized.First,the semiconductor properties of CdS,including the crystal and band structures,are briefly introduced.Afterward,the fundamental mechanisms of PHE using semiconductor photocatalysts via water splitting are discussed.Subsequently,the photoactivity of bare CdS with different morphologies and structures,CdS with cocatalyst loading,and CdS-based heterojunction photocatalysts are reviewed and discussed in detail.Finally,the challenges and prospects for exploring advanced CdS-based photocatalysts are provided.

Cadmium sulfide thin films growth by chemical bath deposition

Cadmium sulfide（Cd S） thin films have been prepared by a simple technique such as chemical bath deposition（CBD）. A set of samples Cd S were deposited on glass substrates by varying the bath temperature from 55 to 75 °C at fixed deposition time（25 min） in order to investigate the effect of deposition temperature on Cd S films physical properties. The determination of growth activation energy suggests that at low temperature Cd S film growth is governed by the release of Cd^（2＋） ions in the solution. The structural characterization indicated that the Cd S films structure is cubic or hexagonal with preferential orientation along the direction（111） or（002）, respectively. The optical characterization indicated that the films have a fairly high transparency, which varies between55% and 80% in the visible range of the optical spectrum, the refractive index varies from 1.85 to 2.5 and the optical gap value of which can reach 2.2 e V. It can be suggested that these properties make these films perfectly suitable for their use as window film in thin films based solar cells.

Self-aligned on-chip coupled photonic devices using individual cadmium sulfide nanobelts

Nanowires(NWs)and nanobelts(NBs)have been widely studied and fabricated into a variety of nanoscale devices such as light emitting diodes(LEDs),lasers and biosensors.These unique materials have attracted sustained attention due to their novel properties,ease of growth,and the ability to fabricate highly engineered devices.However,their widespread application remains hindered due to the difficulty in integrating multiple NWs or NBs together for more complex devices.Integration of multiple NWs and NBs together on the same chip can enable the coupling of different devices to help realize complex on-chip architectures such as photonic integrated circuits or nanoscale diagnostic tools,which currently require outcoupling using larger components.In this letter we report the coupling of on-chip NB LEDs and photodetectors using a single,precisely self-aligned,cadmium sulfide(CdS)NB fabricated on a silicon-on-insulator(SOI)substrate.Electroluminescence generated by the CdS NB is waveguided and measured across the self-aligned device and demonstrates an on/off ratio of 10^2-10^3.This work describes a new method for fabricating and integrating more complex nanoscale devices that can enable advances in areas such as on-chip optical computational components and nanoscale optical biodiagnostics.

Cadmium sulfide as bifunctional mimics of NADH oxidase and cytochrome c reductase takes effect at physiological pH

Recently,a study of mimic enzyme has received more attentions.However,the investigation on the oxidoreductase activity of electron mediators in the biological respiratory chain is still rare.Herein,we found that cadmium sulfide(CdS)nanorods can catalyze the formation of superoxide anions.Due to the role of the photo-generated holes and the nicotinamide adenine dinucleotide(NADH)oxidation promoted by superoxide anion(O_(2)^(•−)),the CdS exhibits NADH oxidase-like activity and can be coupled with dehydrogenase to realize the recycling of NADH.It is worth mentioning that the bio-electron acceptor,cytochrome c(Cyt c),as a chromogenic substrate,can accept electrons transferred from O_(2)^(•−),which demonstrates the Cyt c reductase-like activity of CdS under physiological pH conditions.For different substrates,O_(2)^(•−)induced from CdS show oxidizing capacity for NADH and reducing capacity for Cyt c,which provides a new perspective for the in-depth study of new nanozyme.

Resonant and nonresonant second-harmonic generation in a single cadmium sulfide nanowire

We experimentally investigate the resonant and nonresonant second-harmonic generation in a single cadmium sulfide（Cd S） nanowire. The second-order susceptibility tensor is determined by analyzing the forward secondharmonic signals of the Cd S nanowire. Our results show that（1） d33∕d31=-2.5 at a nonresonant input wavelength of 1050 nm;（2） d33∕d31=-1.9 at a resonant wavelength of 740 nm. The difference can be attributed to the polarization-dependent resonance.

Photocatalytic degradation of methyl orange over ITO/CdS/ZnO interface composite films

ITO/CdS/ZnO interface composite films were successfully prepared by subsequent electrodeposition of CdS and ZnO onto indium tin oxide （ITO） glass substrates. The obtained ITO/CdS/ZnO composite films were characterized with X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and UV-Vis spectroscopy. The photocatalytic activity of ITO/CdS/ZnO composite films were investigated using methyl orange （MO） as a model organic compound under UV light irradiation. The influence of operating parameters on MO degradation including initial concentration of MO, pH value of solution, and inorganic anion species over the composite films were examined. A blue shift of absorption threshold was observed for the ITO/CdS/ZnO film in comparison with ITO/ZnO film. ITO/CdS/ZnO composite films prepared under specific conditions showed a higher photocatalytic activity than that of ITO/ZnO films. It was also found that the photocatalytic degradation of MO on the composite films followed pseudo-first order kinetics.

Enhanced photocatalytic degradation of methyl orange by CdS quantum dots sensitized platelike WO_3 photoelectrodes

CdS quantum dots sensitized platelike WO_3 photoelectrodes were successfully synthesized by a facile hydrothermal method and a modified chemical bath deposition(CBD) technique.To further improve the stability of the photoelectrodes in alkaline environment,the platelike WO_3 films were treated with TiCl_4 to form a nano-TiO_2 buffer layer on the WO_3 plate surface before loading CdSQDs.The resulting electrodes were characterized by using XRD,SEM,HR-TEM and UV-vis spectrum.The photocatalytic activity of the resulting electrodes was investigated by degradation of methyl orange(MO) in aqueous solution.The photoelectrochemical(PEC) property of the resulting electrodes was also characterized by the linear sweep voltammetry.The results of both the degradation of MO and photocurrent tests indicated that the as-prepared CdSQDs sensitized WO_3 platelike photoelectrodes exhibit a significant improvement in photocatalytic degradation and PEC activity under visible light irradiation,compared with unsupported CdSQDs electrodes.Significantly,coating the WO_3 plates with nano-TiO_2 obviously facilitate the charge separation and retards the charge-pair recombination,and results in a highest activity for QDsCdS/TiO_2/WO_3 photoelectrodes.

A Simple Approach to Fabricate CdS-SiO_2 Hybrid Microspheres by Producing CdS Nanoparticles on the Surface of Thiolated SiO_2 Microspheres

We have developed a simple synthetic method to prepare the hybrid microspheres of CdS nanoparticles on the surface of silica microspheres modified by（3-mercaptopropyl） trimethoxysilane（MPS）. The--SH groups of MPS can bind with the Cd^2＋ ions on the surface of SiO2. When thioacetamide releases H2S, the nanosized CdS particles（ 1-6 nm） will successfully be generated on the silica surface under the experimental conditions. The size of the CdS nanoparticles was found to be related to the concentration of Cd^2 ＋ feed and the size of silica spheres, the higher the concentration of Cd^2＋ and the larger of silica microspheres, the bigger the size of CdS nanoparticles. Techniques including UV, PL, TEM and XPS were used to characterize the CdS-SiO2 hybrid microspheres.

RESEARCH ON FACTORS AFFECTING THE COLOURATION OF RED GLASS-CERAMICS

In this pater, effect of alkali, zinc oxide and colorants such as cadmiun sulfide and selenium powder on the colouration of the red glass-ceramic materials in the CaO-Al2O3-SiO2 system has been studied. The relevant laws have been presented and analyzed.

Enhancement of Raman Scattering of 1,4-Benzenedithiol by CdS Nanoparticles Assembled on a Silver Surface

CdS nanoparticles were assembled on the smooth surface of a piece of silver by using 1,4-benzenedithiol as coupling molecules. The SEM and resonance Raman spectroscopic characterizations demonstrate that the nanosized structure of CdS was still preserved upon assembly, and a two-dimensional structure of CdS nanoparticles was formed on the substrate surface. The FT-Raman spectra indicate that 1,4-benzenedithiol was coupled between CdS nanoparticles and the silver surface with a tilted orientation. The Raman scattering of 1,4-benzenedithiol was substantially enhanced by the assembled CdS nanoparticles, probably due to the alteration of the polarizability of 1,4-benzenedithiol and the electromagnetic interaction between the dipoles of the CdS particle with its image in the metal substrate.

Formation and Characterization of CdS Hollow Structures

CdS hollow structures were built up by using the one pot method and using carbon disulfide （CS2） and ethylenediamine as starting materials. CS2 is insoluble in water and could form metastable oil droplets in the water at a moderate temperature. The oil droplets formed chains in the circumvolving water. CdS crystals grew and mineralized on the surfaces of the CS2 droplet chains, forming CdS shells around the unreacted CS2 cores. After the surrounding temperature was raised above the boiling point of CS2, the unreacted CS2 cores vaporized, leaving the CdS shelled hollow structures. The CdS hollow structures were characterized by using a transmission electron microscope, an X-ray diffractometer, a UV-Visible spectrophotometer and a fluorescence spectrophotometer. The CdS hollow structures were mainly tubes with closed ends. The exterior diameter and the interior diameter of tubes were about 50 nm and about 15 nm, respectively. Compared with the absorption onset wavelength of the bulk CdS, the CdS hollow structures exhibited a blue shift of about 57 nm. While excited at 213 nm, the CdS hollow structures emitted greenish blue light centered at 470 nm.

Effects of Growth Conditions on the Microstructure Characteristics of CdS Thin Films by AP-MOCVD

Growth of cadmium sulfide （CdS） thin films on glass substrates was carried out by atmospheric pressure metal-organic chemical vapor deposition （AP-MOCVD） using Cd（S2CNEt2）2 as the single precursor. Changes in the surface morphology of the deposited CdS thin films were investigated by atomic force microscope （AFM） as the function of substrate temperature （Ts）, vaporizing temperature （Tv）, and Ar flow rate. With the increase of Tv, CdS thin films evolved from pyramidal structure with fine grains to columnar structure with large grains. X-ray diffraction （XRD） patterns indicated that the CdS films had random orientation at the lower Tv and preferred orientation at the higher Tv. In addition, Ts had a great effect on the surface roughness of the CdS films, and a quantum dot-like structural CdS films were obtained in a narrow range of Ts with high Ar flow rate. Furthermore, the optical properties of the CdS films were measured using ultraviolet-visible （UV/VIS） spectrometer.

Electronic Structure of CdS Nanoparticles and CdSe/CdS Nanosystems

The electronic states of“wurtzite”CdS nanoparticles and CdSe/CdS nanosystems with up to 80 pairs of Cd-Se or CdS atoms were calculated.The results for CdS particles were compared with the results obtained earlier for CdSe particles of the same size and with published calculations of other authors.The calculated gap values in the range of 2.84 eV~3.78 eV are typical for CdS particles of studied sizes in accordance with results of published data.The CdSe/CdS nanosystems were considered as layered ones and as quantum dots.The layered CdSe/CdS systems with two-layer CdS coverings can be interpreted in terms of combinations of two semiconductors with different energy band gaps(2.6 eV and 3.3 eV),while analogous systems with single-layer CdS coverings do not demonstrate a two-gap electron structure.Simulation of a CdSe/CdS quantum dot shows that the single-layer CdS shell demonstrates a tendency for the formation of the electronic structure with two energy gaps:approximately of 2.5 eV and 3.0 eV.

Biosynthetic CdS-Thiobacillus thioparus hybrid for solar-driven carbon dioxide fixation

Synergistically combining biological whole-cell bacteria with man-made semiconductor materials innovates the way for sustainable solar-driven CO_(2)fixation,showing great promise to break through the bottleneck in traditional chemical photocatalyst systems.However,most of the biohybrids require uneconomical organic nutrients and anaerobic conditions for the successful cultivation of the bacteria to sustain the CO_(2)fixation,which severely limits their economic viability and applicability for practical application.Herein,we present an inorganic-biological hybrid system composed of obligate autotrophic bacteria Thiobacillus thioparus(T.thioparus)and CdS nanoparticles(NPs)biologically precipitated on the bacterial surface,which can achieve efficient CO_(2)fixation based entirely on cost-effective inorganic salts and without the restriction of anaerobic conditions.The optimized interface between CdS NPs and T.thioparus formed by biological precipitation plays an essential role for T.thioparus efficiently receiving photogenerated electrons from CdS NPs and thus changing the autotrophic way from chemoautotroph to photoautotroph.As a result,the CdS-T.thioparus biohybrid realizes the solar-driven CO_(2)fixation to produce multi-carbon glutamate synthase and biomass under visible-light irradiation with CO_(2)as the only carbon source.This work provides significant inspiration for the further exploration of the solar-driven self-replicating biocatalytic system to achieve CO_(2)fixation and conversion.

Engineering interfacial band hole extraction on chemical-vapor-deposited MoS 2/CdS core-shell heterojunction photoanode:The junction thickness effects on photoelectrochemical performance

Heterojunction fabrication is a promising strategy that can greatly boost the charge carrier separation and improve the solar-to-hydrogen conversion efficiency of photoelectrochemical(PEC)cells.However,such technology still suffers from limited contact interfaces.In this study,the chemical vapor deposition(CVD)technique was for the first time used to construct the CdS/MoS_(2)heterojunction photoanode with a unique core-shell nanoarchitecture,in which a continuous crystalline MoS_(2)nanosheet layer was grown directly on one-dimensional(1D)oriented CdS nanorods(NRs)in a plane-to-plane stacking fashion.The optimization of junction thickness with adjustable MoS_(2)loading from mono to a few layers was achieved by experimental parameters variation.Systematic characterizations show that the MoS_(2)shell plays a dual role as an optical absorption booster for more photo-exciton generation and a surface passivator of trap states.Meanwhile,the formed heterojunction helps regulate the unidirectional charge migration for a significantly suppressed electron-hole recombination process,which synergistically contributes to higher quantum yield and efficiency.As a result,the optimized CdS/MoS_(2)heterojunction photoanode with 3-layered MoS_(2)wrapping exhibits the highest photocurrent density and photoconversion efficiency,over a two-fold increase,compared to those of pristine CdS and the previously reported CdS/MoS_(2)hetero-junctions.Moreover,due to the rapid hole extraction from CdS and transferred surface oxidation sites,the present CdS/MoS_(2)heterostructure demonstrates better corrosion resistance and higher photostability.The present work is expected to provide a versatile platform for exploiting the CVD technique to develop other MoS_(2)-based heterojunction photoelectrodes with extensive PEC applications.

Hierarchically 1D CdS decorated on 2D perovskite-type La_(2)Ti_(2)O_(7) nanosheet hybrids with enhanced photocatalytic performance

In this paper,a heterojunction of hierarchically one-dimensional(1D)cadmium sulfide(CdS)nanowires decorated on the two-dimensional(2D) La_(2)Ti_(2)O_(7) (LTO)has been fabricated by a simple two-step hydrothermal process.The structure,morphology and surface chemical composition of CdS/LTO were studied by a variety of characterizations,in which the X-ray photoelectron spectroscopy(XPS)results showed a strong interaction between CdS and LTO through S-O bonds.The typeⅡband alignment of CdS/LTO for favorable electron transfer from CdS to LTO and hole transfer from LTO to CdS was clarified by ultraviolet-visible(UV-Vis)diffuse reflectance spectroscopy and Mott-Schottky(M-S)plot measurements.In the absence of any co-catalyst,H2 production from water splitting and Rhodamine B(RhB)decomposition in aqueous solution were carried out to evaluate the photocatalytic activities,showing that the photocatalytic performance of CdS/LTO was superior to that of pure LTO and CdS under visible light and simulated sunlight.The optimal CdS content in the CdS/LTO system was determined to be 7.5 wt%.The present results show an effective pathway to design a 1D/2D heterojunction photocatalyst in the face of overwhelming problems of energy crisis and environmental pollution.

Hydrogen production from water splitting on CdS-based photocatalysts using solar light

Hydrogen energy has been regarded as the most promising energy resource in the near future due to that it is a clean and sustainable energy. And the heterogeneous photocatatytic hydrogen production is increasingly becoming a research hotspot around the world today. As visible light response photocatalysts for hydrogen production, cadmium sulfide （CdS） is the most representative material, the research of which is of continuing popularity. In the past several years, there has been significant progress in water splitting on CdS-based photocatalysts using solar light, especially in the develop- ment of co-catalysts. In this paper, recent researches into photocatalytic water splitting on CdS-based photocatalysts are reviewed, including controllable synthesis of CdS, modifications with different kinds of cocatalysts, solid solution, intercalated with layered nanocomposites and metal oxides, and hybrids with graphenes etc. Finally, the problems and future challenges in photocatalytic water splitting on CdS-based photocatalysts are described.

Synthesis of CdS/m-Ti02 Mesoporous Spheres and Their Application in Photocatalytic Degradation of Rhodamine B Under Visible Light

CdS/m-TiO2 heteroarchitecture with CdS nanocrystals loaded on mesoporous TiO2（m-TiO2） spheres was successfully synthesized via sol-gel method followed by solvothermal treatment. The material with uniform diameter of ca. 750 nm possesses regular mesoporous structure and large specific surface area of 100.5 m2/g. When used to photodegradate Rhodamine B（RB） under visible light, the CdS/m-TiO2 heteroarchitecture exhibits improved photo-catalytic performance in comparison with pure m-TiO2 or CdS. The excellent photocatalytic activity is closely related to the facilitated separation of electron-hole pairs derived from the CdS/m-TiO2 heterojunction and mesoporous structure with high specific surface area and adequately exposed active sites.

Spatially Isolated Noble-Metal-Free Redox Cocatalysts on CdS Nanorods for Increased Photocatalytic Hydrogen Generation

Spatially isolated oxidation and reduction cocatalysts on a semiconductor can realize efficient charge separation and thereby lead to increased photocatalytic hydrogen generation. However, the effective preparation of such photocatalysts has proven challenging.Herein, we report the facile synthesis of a novel noblemetal-free CdS/MoS/CoPi ternary photocatalyst via a visible light-induced synthesis route, in which MoSreduction cocatalysts were precisely grown on the two terminals of CdS nanorods, while CoPi oxidation cocatalysts were preferentially anchored onto the sidewalls of CdS nanorods. Such spatially isolated MoSand CoPi redox cocatalysts endow CdS nanorods with a rapid charge separation, which enhances their hydrogen generation activity. The CdS/MoS/CoPi photocatalyst with optimized CoPi amount achieves the highest Hgeneration rate of 206 μmol/h, which is 21 and 2 times higher than that achieved by using CdS alone(9.7 μmol/h) and CdS/MoS(105 μmol/h), respectively. The present work highlights the effectiveness of the spatial isolation of reduction and oxidation sites for efficient charge separation and thereby provides a promising strategy for the preparation of highly active photocatalysts.

A Rational Design of Heterojunction Photocatalyst Cd S Interfacing with One Cycle of ALD Oxide

Photo-corrosion is one of the major obstacles for CdS application in wet chemical fields, and atomic layer deposition （ALD） has been proposed as an effective way to suppress the corrosion. Here, prior to ALD coating, CdS, one facilely corrosive photocatalyst, was synthesized via hydrothermal synthesis to access the fundamental corrosion mechanism and the according corrosive sites. X-ray photoelectron spectros- copy （XPS） and X-ray diffraction （XRD） demonstrated that the failure of catalytic decomposition of methylene blue originated from the formation of soluble CdSO4 by oxidizing S2 of as-prepared CdS. High resolu- tion transmission electron microscopy （HRTEM） further identified the active sites in the V-shaped regions ofCdS nanoparticles, confirmed by the simulated electric field distribution. To rationally coat oxides on CdS, the right candidates and their thicknesses have been considered by our tunneling model with trans- fer matrix method based on quantum mechanism, upon which the thickness of protective layer should be less than 0.5 nm to maintain a high tunneling probability, and thus one cycle of ALD TiO2 or AbO3 was proposed to passivate the CdS powder to balance the carrier transportation and corrosion suppres- sion. Based on HRTEM results, we found that the active V-shaped region was covered by ALD oxides （TiO2 or AbO3）. For each case, no soluble CdSO4 has been found before and after photocatalytic reactions based XPS measurements. Importantly, we noticed that with the passivation of one cycle of ALD, the catalyst＇s lifetime was elongated up to 〉14 times higher than that of the as-prepared CdS.