ZnxCd1-xS Solid Solution Research Articles

Influence mechanism of ZnCdS solid solution composition regulation on its energy band and photocatalytic hydrogen performance

The regulation of the band structure is crucial for the improvement of the photocatalytic performance, but the relationship between the composition of solid solution catalyst and their band structure is still unclear. Herein, the solid solution catalysts ZnxCd1-xS (1 > x > 0) were designed and synthesized using a handy solid-phase thermal decomposition strategy. It is interesting that the band structure and photocatalytic hydrogen production (PHP) performance of the obtained solid solution catalyst can be cleverly regulated by controlling the atomic ratio of the solid solution. Among the obtained series of ZnxCd1-xS solid solution catalysts, the optimal solid solution catalysts Zn0.5Cd0.5S exhibits the best PHP activity and favorable cycle stability: the corresponding PHP rate is 41211.2 μmol·h−1·g−1 and the QE value is 7.7 % at 400 nm. The outstanding photocatalytic hydrogen production performance is the result of significantly narrowing the band gap of sulfide solid solution. Additionally, the effective separation and transfer rate of photogenerated carrier has also been improved effectively. The construction of bimetallic sulfide solid solution photocatalyst via an ingenious solid-state thermal decomposition strategy in this work provided a new idea for improving the photocatalytic performance of bimetallic catalysts.

Anchored MoS2 co-catalysts on ZnxCd1-xS solid solution for photocatalytic reduction of U(VI)

In recent years, a great deal of attention has focused on achieving higher photocatalytic performance by modifications. However, external modification methods, such as heterojunction, defect engineering and doping, bring the disadvantage of mismatch of energy band positions or uncontrollable defects and doping positions, resulting in different photocatalytic efficiencies for different batches of materials. As a result, the search for new modification methods is currently the focus of photocatalytic reduction of U(VI). In this work, the modification method of forming a solid solution between Zn, Cd and S by adjusting the ratio of Zn /Cd precursors, i.e., the internal modification method, is proposed to solve the problem of matching the energy band structure, keeping the conduction band in the right position and facilitating efficient charge separation, and complexing with MoS2 co-catalysts to improve the catalytic performance of the catalyst. A novel complex, MoS2/Zn0.2Cd0.8S, has been designed and synthesized. And the photocatalytic reduction of U(VI) by Zn0.2Cd0.8S was 27 and 373 times higher than that of pure CdS and ZnS, respectively, and MoS2/Zn0.2Cd0.8S was 24.45 % higher than that of Zn0.2Cd0.8S (74.75 %), with a reduction rate of 99.20 % under 60 min of illumination. Gladly, its photocatalytic activity remained above 95.67 % after five cycles, and there was no difference in the performance of catalysts synthesised in different batches, showing excellent stability and reproducibility. Moreover, the mechanism of U(VI) reduction was investigated by MoS2/Zn0.2Cd0.8S. This study provides a new strategy to guarantee the preparation of photocatalysis with stable performance and improve photocatalytic performance.

Photocatalytic C-C coupling and H2 production with tunable selectivity based on ZnxCd1-xS solid solutions for benzyl alcohol conversions under visible light

Photocatalytic C-C coupling is a green and sustainable route to produce value-added chemicals. However, the product selectivity is generally non-tunable and there is a lack of an in-depth understanding of the dependence of product selectivity on the band structure of the semiconductor photocatalyst. Here, ZnxCd1-xS solid solutions have been explored for photocatalytic C-C coupling using benzyl alcohol as a typical reactant. The conversion rate of benzyl alcohol and selectivity of C-C coupling products is inherently linked to the solid solution level of ZnxCd1-xS which can be readily tuned. An optimal solid solution level has been found at Zn0.6Cd0.4S (x = 0.6) which delivers a conversion rate of 91.61% and a selectivity of 98.83% for C-C coupling products. These findings not only deepen the understanding on factors that affect product selectivity but also justify the usefulness of solid solutions in tuning the C-C coupling reactions.

Highly efficient visible-light-driven photocatalytic hydrogen production on Cu7S4/Zn0.2Cd0·8S p-n binary heterojunctions

In this work, a series of ZnxCd1-xS solid solutions are firstly prepared by a solvothermal process. The optimized composition of ZnxCd1-xS solid solution is determined to be Zn0·2Cd0.8S. On this basis, the Cu7S4/Zn0·2Cd0·8S composite photocatalyst with a binary p-n heterojunction has been synthesized by a co-precipitation process followed by a solvothermal method. Owning to the synergistic effect of the heterojunction structure in the interface of Cu7S4 (p-type) and Zn0·2Cd0·8S (n-type) and the built-in electric field in binary p-n heterojunction, the as-prepared Cu7S4/Zn0·2Cd0·8S composite photocatalyst exhibits a significantly improved photocatalytic activity toward hydrogen production from water with visible light response, which is approximately 5.0 times and 16.5 times higher than of pristine Zn0·2Cd0·8S and CdS, respectively. The possible photocatalytic mechanism has been proposed basing on a series of experimental results. The current work might be valuable inspirations for designing highly efficient heterojunction composite photocatalyst for solar hydrogen evolution.

One-step chemical bath co-precipitation method to prepare high hydrogen-producing active ZnxCd1-xS solid solution with adjustable band structure

A series of ZnxCd1−xS solid solutions were synthesized through a simple one-step chemical bath co-precipitation route. The microstructure, morphology, composition and optical properties had been thoroughly investigated. The results showed that the as-obtained ZnxCd1−xS samples exhibited monodisperse spherical feature. These monodisperse ZnxCd1−xS spheres were composed of a large number of 5–10 nm crystal grains. The chemical composition of the ZnxCd1−xS solid solutions can be controlled by adjusting the ratio of Zn source to Cd source and the dosage of ammonia solution. Meanwhile, the energy band structure and photocatalytic properties can be optimized. The photocatalysis experiment results revealed that the as-synthesized Zn0.30Cd0.70S sample exhibited optimum water splitting performance. The satisfactory hydrogen evolution rate (HER) of Zn0.30Cd0.70S reached 27.004 mmol g−1 h−1 even without any cocatalysts, which was more than 48 times that of pure CdS (0.561 mmol g−1 h−1). This enhancing effect can owe to the balance between light absorption capacity and redox potential caused by the incorporation of Zn in the ZnxCd1−xS solid solutions.

An amorphous nickel boride-modified ZnxCd1-xS solid solution for enhanced photocatalytic hydrogen evolution.

In this work, the rational design of amorphous NixB as a co-catalyst for the modification of ZnxCd1-xS was achieved. First, NixB was prepared by the redox method and ZnxCd1-xS was synthesized by the hydrothermal method. Then, the electrostatic self-assembly method was used to complete the coupling of NixB and ZnxCd1-xS. The experimental results of H2 production showed that when the mass ratio (wt%) of NixB in NixB/ZnxCd1-xS was 7 wt%, it had the highest activity, and the hydrogen production could reach 1521 μmol under irradiation with light for 5 h. The hydrogen production activity of the composite catalyst was 4.75 times higher than that of pure ZnxCd1-xS. The improvement in the photocatalytic activity can be attributed to the following aspects: (i) UV-vis DRS showed that the addition of NixB increased the absorption of visible light; (ii) the PL, TRPL, IT, EIS and LSV experiments further proved that the composite catalyst had excellent photoelectrochemical properties; (iii) the zeta potential results indicated that the electrostatic attraction between NixB and ZnxCd1-xS provided favorable conditions for the rapid transfer of electrons. This work shows that amorphous NixB has a prominent effect on the modification of ZnxCd1-xS, which provides more ways for the study of photocatalytic H2 evolution.

Simultaneous visible-light-induced hydrogen production enhancement and antibiotic wastewater degradation using MoS2@ZnxCd1-xS: Solid-solution-assisted photocatalysis

In this study, a ZnxCd1-xS solid solution was successfully synthesized using a hydrothermal method. MoS2 serving as a co-catalyst for hydrogen evolution was also prepared through a one-pot hydrothermal method. The structures, morphology, chemical states, and optical properties were characterized using powder X-ray diffraction, scanning electron microscopy, high-angle annular dark field-scanning transmission electron microscopy, elemental mapping, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflection spectroscopy. Visible-light-driven photocatalytic experiments were conducted to simultaneously achieve hydrogen production and amoxicillin antibiotic wastewater degradation. The results indicated 8%MoS2/ZnxCd1-xS achieves the best photocatalytic performance. The ZnxCd1-xS samples illustrated a superior performance to that of CdS, which can be attributed to a thermodynamic improvement. Based on the results of PL and TRPL analyses, the enhancement of the hydrogen production mechanisms can be ascribed to the prolonged separation process of the photocarriers. Furthermore, the degradation results were analyzed using the HPLC method and the possible degradation pathways were determined through the HPLC-MS techniques.

Highly efficient and irreversible removal of cadmium through the formation of a solid solution

Sulfur-containing materials are very attractive for the efficient decontamination of some heavy metals. However, the effective and irreversible removal of Cd2+, coupled with a high uptake efficiency, remains a great challenge due to the relatively low bond dissociation energy of CdS. Herein, we propose a new strategy to overcome this challenge, by the incorporation of Cd2+ into a stable ZnxCd1-xS solid solution, rather than into CdS. This can be realised through the adsorption of Cd2+ by ZnS nanoparticles, which have exhibited a Cd2+ uptake capacity of approximate 400 mg g−1. Through this adsorption mechanism, the Cd2+ concentration in a contaminated solution could effectively be reduced from 50 ppb to <3 ppb, a WHO limit acceptable for drinking water. In addition, ZnS continued to exhibit this noteworthy uptake capacity even in the presence of Cu2+, Pb2+, and Hg2+. ZnS displayed high chemical stability. Particles aged in air for 3 months still retained a> 80% uptake capacity for Cd2+, compared with only 9% uptake capacity for similarly-aged FeS particles. This work reveals a new mechanism for Cd2+ removal with ZnS and establishes a valuable starting point for further studies into the formation of solid solutions for hazardous heavy metal removal applications.

Hollow microspheres consisting of uniform ZnxCd1-xS nanoparticles with noble-metal-free co-catalysts for hydrogen evolution with high quantum efficiency under visible light

Utilizing solar energy in order to produce hydrogen from water is one of the key technologies to deal with energy and environment issues. A photocatalyst with a small band gap, good charge separation, and high stability plays an important role in this process. Recently, zinc cadmium sulfide (ZnxCd1-xS) has caught researchers’ attention due to its unique photocatalytic properties such as the wide range of visible light energy absorption and strong stability during water splitting. Moreover, a unique feature of this semiconductor is the capability of modifying its band gap structure by changing the Zn/Cd ratio. Herein, a series of ZnxCd1-xS solid solutions was synthesized by utilizing metal-glycerate followed by calcination in air and sulfuration under flowing H2S. As a result, a homogeneous hexagonal wurtzite ZnxCd1-xS solid solution could produce hydrogen in a wide range of visible light region. Moreover, using MoS2 as a cocatalyst resulted in the same amount of hydrogen as Pt. The best result was obtained for the Zn30Cd70S solid solution that showed a hydrogen evolution of 12 mmol h−1 g−1 under solar simulator. The calculated quantum efficiencies (QE) in visible light region are: 46.6% at 400 nm to 23.4% at 500 nm as well as 11.3% at 550 nm. There are among the highest QE that have been ever reported for this kind of material under visible light region.

Facile Synthesis of ZnxCd1-xS Solid Solution Microspheres through Ultrasonic Spray Pyrolysis for Improved Photocatalytic Activity

Nanocrystal ZnxCd1-xS solid solutions were successfully prepared using a facile and reproducible method of ultrasonic spray pyrolysis with Cd(Ac)2·2H2O, ZnCl2, and thiourea as precursors. Scanning electron microscopy and transmission electron microscopy images show that the prepared particles possess microspherical morphology. The band gaps of the solid solutions can be tuned by changing the constituent stoichiometries of Cd and Zn. The X-ray diffraction peaks gradually shift to small angle, and the absorption edge shifts to long wavelength with increasing Cd molar fraction in the solid solution. The sample prepared at the Cd/Zn ratio of 1 : 1 displays the optimal activity by using the photocatalytic degradation of methyl orange in the aqueous solution as model reactions under visible light irradiation. This study provides an effective route to prepare spherical ternary photocatalysts with mesoporous structure for further investigations and practical applications.

Morphology-Controlled Synthesis of Zn&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;Cd&amp;lt;sub&amp;gt;1-x&amp;lt;/sub&amp;gt;S Solid Solutions: An Efficient Solar Light Active Photocatalyst for the Degradation of 2,4,6-Trichlorophenol

ZnxCd1-xS solid solutions with controlled morphology have been successfully synthe-sized by a facile solution-phase method. The prepared samples were characterized by X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectra, X-ray photoelec-tron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission elec-tron microscopy (TEM). The photocatalytic activity of ZnxCd1-xS was evaluated in the 2,4,6-trichlorophenol (TCP) degradation and mineralization in aqueous solution under direct solar light illumination. The experiment demonstrated that TCP was effectively degraded by more than 95% with 120 min. The results show that ZnS with Cd doping (ZnxCd1-xS) exhibits the much stronger visible light adsorption than that of pure ZnS, the light adsorption increasing as the Cd2+ doping amount. These results indicate that Cd doping into a ZnS crystal lattice can result in the shift of the valence band of ZnS to a positive direction. It may lead to its higher oxidative ability than pure ZnS, which is important for organic pollutant degradation under solar light irradiation. Further-more, the photocatalytic activity studies reveal that the prepared ZnxCd1-xS nanostructures exhibit an excellent photocatalytic performance, degrading rapidly the aqueous 2,4,6-trichlorophenol solution under solar light irradiation. These results sug-gest that ZnxCd1-xS nanostructure will be a promising candidate of photocatalyst working in solar light range.

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.

ＺｎｘＣｄ１−ｘＳ固溶体薄膜の作成とその光学的性質

ZnxCd1-xS solid-solution films were prepared by annealing the ZnS/CdS double films on a Pyrex glass at 600°C for 3hrs in argon gas atmosphere. These films had hexagonal, wurtzite-type structure. The compositions and lattice parameters of the films can be controlled by the thicknesses of starting CdS and ZnS films. The solid solution films doped with small amounts of Ag and Cl in their preparation processes showed various emission colors from blue to red corresponding to composition of ZnxCd1-xS films.