ZnxCd1 xS Research Articles

Metalloporphyrin based MOF-545 coupled with solid solution ZnxCd1-xS for efficient photocatalytic hydrogen production

The growing concern over the rapid consumption of fossil fuels has spurred scientists to seek environment-friendly and sustainable energy alternatives. The utilization of photocatalytic water splitting shows great potential in generating environmentally friendly hydrogen energy. Zirconium-based porphyrin MOF-545 has drawn extensive attention in photocatalysis since it has strong light absorption and fast electron transfer capability. A series of Zr-based metalloporphyrins containing different metals, MOF-545M (M = Co, Ni, Cu, Zn), were synthesized and assembled with solid solution ZnxCd1-xS (ZCS) nanoparticle to develop the corresponding of hybrid photocatalysts, ZCS/MOF-545M. Various characterizations show that introducing the porphyrin MOF-545Co not only improve the visible light response range of Zn0.5Cd0.5S (ZCS-0.5) but also enhance the carrier separation efficiency of ZCS-0.5. The carrier transfer direction during the reaction was confirmed by surface photovoltage spectroscopy and shows the formation of S-scheme. Under visible light irradiation, the hybrid photocatalyst ZCS-0.5/MOF-545Co exhibits a high H2 evolution rate of 148 μmol h−1, with increases of 52.8, 22.9 and 6.5 times than those of bare ZnS, CdS and ZCS-0.5, respectively. The present work gives a strategy for erecting S-scheme heterojunction to inhibit the photocorrosion of metal sulfides and enhancement the carrier separation efficiency.

Heterojunction architecture of Ce2S3 nanocubes with ZnxCd1-xS photocatalyst enables efficient hydrogen evolution

Heterojunction coupling with narrow bandgap semiconductor can effectively promote light absorption, inhibits photoinduced carrier recombination and enhances redox performance. Herein, a novel Ce2S3 nanocube was synthesized via a high-temperature sulfating method, then ZnxCd1-xS (ZCS) was grown on Ce2S3 cube to form a tight junction for the photocatalytic hydrogen evolution (PHE) activity. The experimental results confirm that this novel composite vastly boosts the redox performance due to superior visible light absorbance, narrow bandgap and fast charge carrier separation via a Z-scheme mechanism. Consequently, the optimized Ce2S3/ZCS composite presents the best PHE rate of 35.35 mmol h−1 g−1 without an obvious reduction in efficiency for cycling experiments, which has a 4.8-fold increase over Pt/ZCS. This strategy proposes a novel method for optimizing ZCS-based photocatalysis by introducing Ce2S3 component to improve the property of PHE.

Revealing Photocatalytic Performance of ZnxCd1-xS Nanoparticles Depending on the Irradiation Wavelength.

Photocatalysts are useful for various applications, including the conservation and storage of energy, wastewater treatment, air purification, semiconductors, and production of high-value-added products. Herein, ZnxCd1-xS nanoparticle (NP) photocatalysts with different concentrations of Zn2+ ions (x = 0.0, 0.3, 0.5, or 0.7) were successfully synthesized. The photocatalytic activities of ZnxCd1-xS NPs varied with the irradiation wavelength. X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet-visible spectroscopy were used to characterize the surface morphology and electronic properties of the ZnxCd1-xS NPs. In addition, in situ X-ray photoelectron spectroscopy was performed to investigate the effect of the concentration of Zn2+ ions on the irradiation wavelength for photocatalytic activity. Furthermore, wavelength-dependent photocatalytic degradation (PCD) activity of the ZnxCd1-xS NPs was investigated using biomass-derived 2,5-hydroxymethylfurfural (HMF). We observed that the selective oxidation of HMF using ZnxCd1-xS NPs resulted in the formation of 2,5-furandicarboxylic acid via 5-hydroxymethyl-2-furancarboxylic acid or 2,5-diformylfuran. The selective oxidation of HMF was dependent on the irradiation wavelength for PCD. Moreover, the irradiation wavelength for the PCD depended on the concentration of Zn2+ ions in the ZnxCd1-xS NPs.

Gradient Conduction Band Energy Engineering Driven High‐Efficiency Solution‐Processed Cu2ZnSn(S,Se)4/ZnxCd1–x S Solar Cells

AbstractThe photovoltaic performance of the environmentally friendly Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is lower than its predecessor Cu(In,Ga)Se2 solar cells. Severe carrier recombination at the CZTSSe/CdS interface is one major reason that results in a large open‐circuit voltage loss. Doping zinc into CdS is a feasible strategy to modifying the CdS buffer layer film, but the present methods are not satisfactory. In this study, novel zinc incorporation strategy is developed to deposit a gradient composition ternary ZnxCd1–xS buffer layer for optimizing the heterojunction interface. The application of gradient composition ZnxCd1–xS buffer layer constructs a gradient conduction band energy configuration in the CZTSSe/buffer layer interface, which highly reduces the interface recombination. The suppressed interface recombination contributes to the enhanced open circuit voltage and device performance. Consequently, the CZTSSe solar cell based on gradient composition ZnxCd1–xS buffer layers achieves champion efficiency of 12.35% with VOC of 504.81 mV, JSC of 36.90 mA cm−2, and FF of 66.28%. It is worth noting that flammable and the toxic hydrazine solvent are replaced by the safe and low‐toxic 2‐methoxyethanol, making it more promising for the future commercialization of CZTSSe solar cells.

Concentrating photoelectrons on sulfur sites of ZnxCd1–xS to active H–OH bond of absorbed water boosts photocatalytic hydrogen generation

Highly hydrophobic polypyrrole (PPy), as a promising conjugated polymer with good electron conductivity and excellent environmental stability, has received active attention in various fields. As is well known, the adsorption and dissociation of water molecules are the rate–limiting step of photocatalytic hydrogen evolution (PHE) reaction in the alkaline media. Herein, highly–hydrophilic polypyrrole–poly(sodium–p–styrenesulfonate) (PPy–PSS) were sectionally wrapped on the surface of ZnxCd1–xS (ZCS) nanorods via redox initiate polymerization to improve the hydrophily of ZCS, which favors water absorption. The density functional theory (DFT) calculation shows the sulfur electronic structure of ZCS is modulated in PPy–PSS–ZCS (PP–ZCS) composite. Specifically, the constituent PPy and PSS polymers through strong electronic interactions with ZCS could improve the water dissociation and the adsorption/desorption of hydrogen intermediates on ZCS component. After activating H–OH bond, the optimized PP–ZCS composite reveals an improved PHE efficiency of 46.1 mmol h−1 g−1 without an obvious decrease for continuous 24 h in visible light, which is 8.67 and 1.68 times higher than those of ZCS and PPy–ZCS. This strategy paves a new way for activating ZnxCd1–xS–based composite by highly hydrophilic and conductive conjugated polymer.

ZnxCd1–xS quantum dot with enhanced photocatalytic H2-production performance

H2 is an important energy carrier for replacing fossil fuel in the future due to its high energy density and environmental friendliness. As a sustainable H2-generation method, photocatalytic H2 production by water splitting has attracted much interest. Here, oil-soluble ZnxCd1–xS quantum dot (ZCS QD) with a uniform particle size distribution were prepared by a hot-injection method. However, no photocatalytic H2-production activity was observed for the oil-soluble ZCS QD due to its hydrophobicity. Thus, the oil-soluble ZCS QD was converted into a water-soluble ZCS QD by a ligand-exchange method. The water-soluble ZCS QD exhibited excellent photocatalytic H2-production performance in the presence of glycerin and Ni2+, with an apparent quantum efficiency of 15.9% under irradiation of 420 nm light. Further, the photocatalytic H2-generation activity of the ZCS QD was ∼10.7 times higher than that of the ZnxCd1–xS relative samples prepared by the conventional co-precipitation method. This work will inspire the design and fabrication of other semiconductor QD photocatalysts because QD exhibits excellent separation efficiency for photogenerated electron–hole pairs due to its small crystallite size.

ZnxCd1-xS nanoparticles dispersed on CoAl-layered double hydroxide in 2D heterostructure for enhanced photocatalytic hydrogen evolution

CoAl-LDH and ZnxCd1-xS (ZCS) were successfully assembled. By studying the microstructure of the catalysts, it was found that the agglomerated ZCS nanoparticles were equably dispersed on the hexagonal plate-like CoAl-LDH surface. The increase of the specific surface area of the composite catalyst further proves that the agglomeration state of ZCS nanoparticles has been improved. When the mass of the introduced CoAl-LDH is 20% of the ZCS, the maximum hydrogen production after the optimization is 1516 μmol/5h, which is about 6.9 times that of pure ZCS. UV–vis DRS in the range of 250–800 nm proved that the visible light absorption intensity of the composite is enhanced compared to pure materials. Electrochemical and photoluminescence experiments proved that the heterostructure formed between ZCS and CoAl-LDH accelerates photoelectron transfer and inhibits the recombination of electrons and holes. In addition, possible mechanisms of the sample were explored by UV–vis DRS and Mott-Schottcky.

Morphology and Current Transport in a Thin-Film Polycrystalline Au–ZnxCd1–xS–Mo Structure with Wide Photosensitivity Range in the Ultraviolet and Visible Radiation Spectral Region

Studies are carried out on the morphology of the surface and photovoltaic characteristics of a thinfilm Au–ZnxCd1–xS–Mo structural injection photodetector with a wide photosensitivity range in the ultraviolet and visible radiation spectral regions. The composition of ZnxCd1–xS film in the Au–ZnxCd1–xS–Mo structure with a wide photosensitivity spectrum in the ultraviolet and visible spectrum, where x on the surface varies from 0.22 to 0.24, is studied. The mechanism of current transport is investigated, and the main electrophysical parameters of the semiconducting materials are determined. The use of ZnxCd1–xS film with a variable band gap in the thin-film heterojunction solar cells, where they are used as the buffer layer, will provide an opportunity to increase the photosensitivity of the structure in the short-wave region of the radiation spectrum, increase the value of the built-in potential, short-circuit current and value of the open-circuit voltage of the structure.

Investigation of composition and current transport mechanism in polycrystalline thin film ultra violet Au–Zn x Cd1–x S–Mo-structure with narrow spectrum of photosensitivity

The composition and photovoltaic characteristics of Au–Zn x Cd1–x S–Mo–thin film structural injection photo detectors sensitive to narrow the ultraviolet region of the electromagnetic spectrum created and investigated. Studies of the morphology and composition of Zn x Cd1–x S films showed that in the Au–Zn x –Cd1–x S–Mo–UV structure, with a narrow photosensitivity spectrum, x = 0.6 ± 0.02. The features of current transport mechanism in the structure and the basic parameters of semiconductor material are defined. Polycrystalline Zn x Cd1–x S is a wide-band-semiconductor material may be used instead of the CdS buffer layer in various types of heterostructural solar cells. This will give an opportunity to increase the photo sensitivity of the structure in the short-wave part of the radiation spectrum, increase the built-in potential and solve the problem of open circuit voltage deficiency in the thin-film solar cells.

Band-tunable photodetectors based on graphene/alloyed ZnxCd1−xS film hybrids

We have achieved band-tunable photodetectors based on graphene/alloyed ZnxCd1–xS film hybrids with cut-off edge in spectra response gradually changed from 410 nm to 580 nm.

Industrially scalable and cost-effective Mn2+ doped ZnxCd1−xS/ZnS nanocrystals with 70% photoluminescence quantum yield, as efficient down-shifting materials in photovoltaics

We present colloidally stable and highly luminescent ZnxCd1–xS:Mn/ZnS core–shell nanocrystals (NCs) as cost-effective light converters for silicon photovoltaic (PV).

Surface complexation reaction for phase transfer of hydrophobic quantum dot from nonpolar to polar medium.

Chemical reaction between oleate-capped Zn(x)Cd(1-x)S quantum dots (Qdots) and 8-hydroxyquinoline (HQ) led to formation of a surface complex, which was accompanied by transfer of hydrophobic Qdots from nonpolar (hexane) to polar (water) medium with high efficiency. The stability of the complex on the surface was achieved via involvement of dangling sulfide bonds. Moreover, the transferred hydrophilic Qdots--herein called as quantum dot complex (QDC)--exhibited new and superior optical properties in comparison to bare inorganic complexes with retention of the dimension and core structure of the Qdots. Finally, the new and superior optical properties of water-soluble QDC make them potentially useful for biological--in addition to light emitting device (LED)--applications.

Versatile and Low-Toxic Solution Approach to Binary, Ternary, and Quaternary Metal Sulfide Thin Films and Its Application in Cu2ZnSn(S,Se)4 Solar Cells

We developed a versatile and environmentally friendly solution approach for the fabrication of a variety of metal sulfide nanocrystal thin films. Metal oxides, metal hydroxides, metal chlorides, metal acetates, and metal acetylacetonates can be used as the starting materials and dissolved in thioglycolic acid and ethanolamine, forming many types of metal–organic precursor solutions. High quality CdS, SnS, CuInS2, CuSbS2, Cu2ZnSnS4, Cu(In0.7Ga0.3)S2, and luminescent Ag-doped ZnxCd1–xS nanocrystal thin films have been successfully prepared by spin-coating their corresponding metal precursor solutions. Cu2ZnSn(S,Se)4 thin film solar cell with a power conversion efficiency of 6.83% has been realized by this versatile method.

Efficient and stable photocatalytic hydrogen production from water splitting over ZnxCd1–xS solid solutions under visible light irradiation

A simple co-precipitation method was employed to synthesize a series of cubic zinc-blende phase of ZnxCd1−xS photocatalysts using Na2S as the S source. Structural, morphological and optical properties of the samples have been investigated by XRD, SEM, EDS, XRF, ICP, N2 physisorption and UV–vis diffuse reflectance techniques. The ZnxCd1−xS solid solution is not a simple compound mixture of ZnS and CdS, its XRD patterns show new structural peaks instead of mixture of original peaks. The lattice parameter a measured from the XRD patterns of the ZnxCd1−xS samples exhibits a slightly nonlinear relationship with the Zn mole fraction, which is slightly inconsistent with Vegard's law, thus suggesting that a nonhomogeneous alloy structure exists in ZnxCd1−xS solid solution. The photocatalytic H2 evolution from water splitting in the sacrificial reagents of 0.25 M Na2S/0.35 M K2SO3 under visible light at 30 °C and 55 °C were also examined in the study. It is found that ZnxCd1−xS solid solution with composition x = 0.4–0.5 shows the highest photocatalytic H2 production performance. The studied ZnxCd1−xS exhibits at least 50 h stable photocatalytic activity under outdoor sunlight irradiation.

Facile one-pot synthesis and band gap calculations of ZnxCd1−xS nanorods

Abstractz We reported that Zn x Cd 1− x S (ZnCdS) nanorods could be synthesized via a facile, nontoxic one-pot method. Structural and optical properties of ZnCdS nanorods were characterized by relevant equipments. The x value (Zn/(Zn+Cd)) could be altered across the entire range from 0.21 to 0.89 by changing the ratio of cation precursor contents. The band gap energy ( E g ) could be tuned linearly from 2.68 eV to 3.59 eV with respect to x . We also performed first-principles calculations to prove the experimental variation trend of band gap energy. Results showed that the replacement between Zn and Cd influenced the distribution of the electronic structure, and therefore determined the band gap energy.

Structure and Composition of ZnxCd1–xS Films Synthesized through Chemical Bath Deposition

Zinc cadmium sulfide (ZnxCd1-xS) thin films grown through chemical bath deposition are used in chalcopyrite solar cells as the buffer layer between the n-type zinc oxide and the p-type light absorbing chalcopyrite film. To optimize energetic band alignment and optical absorption, advanced solar cell architectures require the ability to manipulate x as a function of distance from the absorber-ZnCdS interface. Herein, we investigate the fundamental factors that govern the evolution of the composition as a function of depth in the film. By changing the initial concentrations of Zn and Cd salts in the bath, the entire range of overall compositions ranging from primarily cubic ZnS to primarily hexagonal CdS could be deposited. However, films are inhomogeneous and x varies significantly as function of distance from the film-substrate interface. Films with high overall Zn concentration (x > 0.5) exhibit a Cd-rich layer near the film-substrate interface because Cd is more reactive than Zn. This layer is typically beneath a nearly pure ZnS film that forms after the Cd-rich layers are deposited and Cd is depleted in the bath. In films with high overall Cd concentration (x < 0.5) the Zn concentration rises towards the film's surface. Fortunately, these gradients are favorable for solar cells based on low band gap chalcopyrite films.

Vapor-phase synthesis of one-dimensional ZnS, CdS, and ZnxCd1–xS nanostructures

One-dimensional (1D) nanostructures have received prime attention due to their high potential in understanding fundamental physical concepts and constructing nanoscale electronic devices. ZnS and CdS, the well-known direct and wide bandgap semiconductors, have recently attracted significant research interest due to their special properties and applications in sensing, optoelectronics, piezoelectronics, and lasing. This article reviews the most recent activities in ZnS and CdS nanostructures, with an emphasis on the authors’ own results, and on 1D ZnS and CdS nanostructures, especially those synthesized using vapor deposition techniques. The review begins with a survey of ZnS and CdS nanostructures, and then is primarily focused on their 1D nanostructures, syntheses, characterizations, formation mechanisms, and optical and field-emission (FE) properties. Additionally, developments of ZnxCd1–xS composite nanostructures, including nanocombs and zigzag nanowires, are also discussed. Finally, we conclude this review with the perspectives and outlook on the future developments in this field.

Dependence of optical, structural and electrical properties of Zn x Cd1–x S thin films prepared by co-evaporation on the composition for x = 0 – 1

Abstract Thin films of zinc cadmium sulphide – a ternary compound intended to be used in solar cells – are prepared by co-evaporation. The films are prepared at room temperature, in a vacuum better than 10–5 Torr. The composition of these films is varied from x = 0 to x = 1 in the compound Zn x Cd1–x S. The structural, optical and electrical properties have been investigated as a function of x. The direct band gap varies from 2.415 eV to 3.41 eV for x = 0 to x = 1 respectively. The crystal structure is found to be hexagonal (Wurtzite) for 0 ≤ x ≤ 0.8 and cubic zinc-blende for x &gt; 0.8. The lattice constants decrease and the optical bandgap increases with the increase in the value of x. The resistivity of the Zn x Cd1–x S films is found to decrease from 3.6 × 104 Ω cm for x = 0 to 69.5 Ω cm for x = 0.3 and again increases beyond this range to a value of 6.3 × 103 Ω cm for x = 1.0.

Tunable and Predetermined Bandgap Emissions in Alloyed ZnSxSe1–x Nanowires

1D nanostructures such as nanowires, nanorods, nanobelts, and nanotubes have become the focus of intensive research owing to their novel physical properties and applications in the fabrication of nanoscale devices. They are expected to be as interconnects and functional units in electronic, optoelectronic, and other devices with nanoscale dimensions. Wide-gap II-VI semiconductors can be efficient emitters in the blue to ultraviolet spectral region, and excitons in these compounds are much more stable than those in the conventional III-V semiconductors that are widely used in optoelectronic field. In the past decade, considerable efforts were made to prepare 1D II-VI semiconductors and to investigate their optoelectronic properties. Among these researches, only the fixed bandgap emissions of binary II-VI semiconductors were studied; however, obtaining tunable and predetermined optoelectronic properties is significant for the practical applications of these 1D II-VI semiconductors. Therefore, it is important and desired to achieve tunable and predetermined bandgap emissions in 1D II-VI semiconductors. Alloying of binary II-VI semiconductors is an important method to obtain tunable bandgap emissions through composition modulation. Scheme 1 illustrates that Eg(ABxC1–x) (the energy gap of the alloyed ABxC1–x) can be continuously tuned from Eg(AB) (the energy gap of the binary compound AB) to Eg(AC) (the energy gap of the binary compound AC) as the composition x decreases. This method has been widely used in thin films or nanocrystals in order to obtain tunable optical properties; however, there are few reports on the fabrication of alloyed 1D nanostructures. Recently, alloyed ZnxCd1–xS nanoribbons and CdSxSe1–x nanobelts were obtained by means of a laser ablation-assisted CVD method and a simple one-step physical evaporation process, respectively. Furthermore, the previous studies show that the variation of Eg(ABxC1–x) can be represented as a quadratic function of composition x, Eg(ABxC1–x) = xEg(AB) + (1 – x)Eg(AC) – x(1 – x)b, where b is the bowing parameter. [12]

Wavelength-Controlled Lasing in Znx Cd1- x S Single-Crystal Nanoribbons.

Znx Cd1 - x S single-crystal nanoribbons of controlled composition (where 0 ≤ x ≤ 1) can be synthesized by combining laser ablation with thermal evaporation. The nanoribbons exhibit lasing emission that can be continuously tuned within the ranges of 340-390 nm and 485-515 nm. These results suggest that Znx Cd1- x S nanoribbon lasers of pre-selected "tunable" wavelengths between 340 and 515 nm may be achievable by tailoring the value of x.