Wurtzite CdS Research Articles

Theoretical Predictions for Elastic, Mechanical, Anisotropic, Electronic, and Optical Profiles of Wurtzite CdS, CdSe, and CdTe

Theoretical Predictions for Elastic, Mechanical, Anisotropic, Electronic, and Optical Profiles of Wurtzite CdS, CdSe, and CdTe

Investigating the effect of Pb doping on the structural, electronic, magnetic, and optical properties of wurtzite CdS

This study focuses on comprehensively investigating the crystal structure, electronic, magnetic and optical properties of pure and Pb-doped CdS at different concentrations using first-principles methods with the GGA-PBE+U approximation. Our calculations successfully reproduce the experimentally observed optimized lattice parameters and band gap values for both pure and Pb-doped CdS systems. Band structure results show a large and significant reduction in the band gap of Pb-doped CdS at low concentrations, followed by a steady increase at high Pb concentrations. The electron density distribution show the covalent nature between Cd-S and Pb-S. The optical properties of pur and Pb-doped CdS show: a significant increase in absorption and in reflectivity in the visible and ultraviolet domains with doping. Finally, a reduction in optical transmission in the visible energy domain. These optical analyzes provide essential information on the behavior of these materials, thus broadening its practical applications, notably in the design of optoelectronic devices.

Defect-mediated Fermi level modulation boosting photo-activity of spatially-ordered S-scheme heterojunction

Spatially-ordered S-scheme photocatalysts are intriguing due to their enhanced light harvesting, spatially isolated redox sites, and strong redox abilities. Nonetheless, heightening the performance of S-scheme photocatalysts via controllable defect engineering is still challenging to now. In this work, multi-armed MoSe2/CdS S-scheme heterojunction with intimate Mo-S bond coupling and adjustable Se vacancies (VSe) and Mo5+ concentrations was constructed, which consisted of few- or even single-layered MoSe2 growing on the {11–20} facets of wurtzite CdS arms. The S-scheme charge transmission mechanism of MoSe2/CdS heterojunction was validated by density functional theory calculation combined with in situ photo-irradiated X-ray photoelectron spectroscopy, surface photovoltage, and radical measurements. Moreover, the Fermi level gap between CdS and MoSe2 was enlarged by regulating the contents of donor (VSe) and acceptor (Mo5+) impurities with synthesis temperature, which strengthens the built-in electric field and carriers transfer driving force of MoSe2/CdS composites, contributing to an outstanding H2 evolution activity of 52.62 mmol·g−1·h−1 (corresponding to an apparent quantum efficiency of 34.8 % at 400 nm) under visible-light irradiation (λ > 400 nm), 25.8 times that of Pt-loaded CdS counterpart and a substantial amount of reported CdS-containing photocatalysts. Our study results are anticipated to facilitate the rational design of advanced semiconductor nanostructures for efficient solar conversion and utilization.

Crystal facet engineering of hollow cadmium sulfide for efficient photocatalytic hydrogen evolution

Metal sulfides have been considered as potential candidates for photocatalytic hydrogen production, but their practical applications are still limited by incident light utilization and charge separation despite the impressive advances in recent decades. To address these challenges, the construction of hollow nanostructure with exposing high active facets offers a desirable pathway for developing novel and high-efficiency photocatalysts. Here, by taking wurtzite CdS as an example, we first develop a general template-assisted cation exchange route for the preparation of hollow CdS nanostructures with diverse exposed facets. The obtained hollow CdS octahedrons with dominant {101} facets exhibit superior photocatalytic H2 evolution rate under visible-light irradiation compared with common CdS nanorods. According to the characterization results and density functional theory calculations, the excellent photocatalytic performance is attributed to the construction of hollow nano-octahedrons with exposed {101} active facets, which facilitates efficient light harvesting and photoinduced charge separation of CdS photocatalyst. The present approach gives a reference to design advanced semiconductors with remarkable photocatalytic activity for realizing efficient solar-to-chemical conversion.

Wurtzite CdS ratio tunability on α-Fe2O3/CdS synergistic heterostructure for enhanced UV-induced photocatalytic decomposition of rhodamine 6G dye pollutant

Hematite α-Fe2O3 exhibits a slow catalytic reaction rate and low performance in aqueous pollutant decomposition. In this work, α-Fe2O3/CdS binary heterostructure composites were created by introducing different ratios of wurtzite CdS into α-Fe2O3 within 0–100 wt% via precipitation and impregnation methods. The photocatalytic performance of α-Fe2O3/CdS was enhanced for the decomposition of aqueous rhodamine 6G (R6G) dye under ultraviolet (UV) irradiation. SEM images reveal that higher CdS loading results in increased interfacial contact between rod-like CdS and spherical-shaped α-Fe2O3. XRD and FTIR results confirm the coexistence of rhombohedral α-Fe2O3 and hexagonal CdS phases, with peak strength proportional to the ratio of component loading, as the respective elements were verified through EDX analysis. The UV-Vis spectroscopic analysis exhibits an enhancement in optical absorption and band gap broadening as the CdS loading rises. α-Fe2O3/CdS with increased CdS loading exhibits faster and more efficient R6G degradation under UV exposure, as evidenced by greater rate constants and degradation efficiency, with optimal CdS loading of 90 wt% achieving a maximum efficiency of 79.14%. The present heterostructure could be employed in future wastewater remediation for effective removal of organic dye pollutants, further promoting clean water preservation for global environmental sustainability.

Band Alignment Tunning via the Facets of CdS Nanocrystals with g‐C3N4 for Unveiling Their Enhanced Photocatalytical Property

AbstractThe heterojunction is a great approach to profit the photogenerated electrons and holes separation and then enhance the photoelectric current for the photochemical reactions, such as the hydrogen evolution reaction. The intrinsic of the enhanced electrons and hole separation is ascribed to the appropriate band alignment between the two contact materials and plenty of research has reported the different band alignments formed by the different contacted bulk nanomaterials. Few studies focus on the precious crystal structure‐related band alignment. Here, the polyheptazine structured g‐C3N4 together with the wurtzite CdS is investigated, and different band alignments are formed through the different exposed crystal planes of CdS. It is found that along with the annealing temperature, the CdS will dominantly expose with the (110) facets and then form the S‐scheme heterojunction with the g‐C3N4. The formed built‐in electric field between the valence band of CdS and the conductive band of g‐C3N4 accelerates the recombination between the photogenerated electrons from CdS and holes from g‐C3N4. Meanwhile, it promotes the separation of the photogenerated electrons with holes from g‐C3N4, resulting in the superior photocatalytic HER performance. The study supplies a new venue for preciously tunneling the band alignments between the heterogeneous catalysts for optimizing the photoelectric properties.

Relaxation effects on the structural and piezoelectric properties of wurtzite ZnS and CdS thin films under in-plane strain

Through first-principles investigations, we examine variations in the atomic crystal structure, thermal stability, electronic structure, and piezoelectric properties of wurtzite ZnS and CdS under in-plane strain. We specifically aim to elucidate the distinct effects arising from two relaxation modes: elastic and non-elastic. Our analyses reveal that the in-plane strain-induced deformation behaviors and performance changes in these sulfides are remarkably similar, attributable to the similar atomic arrangements, anionic sulfur elements, and analogous cation electronic configurations. However, following non-elastic relaxation, enhanced robustness emerges in the lattice volume and chemical bonding, alongside stronger thermal stability and attenuated modifications in the piezoelectric coefficient. We posit that these marked discrepancies from elastic relaxation may originate from subtle differences in the electronegativities and d-orbital electron configurations between the Zn2+ and Cd2+ cations. By offering fundamental new insights into the atomic-scale relaxation phenomena in wurtzite binaries, this work significantly furthers the fundamental understanding of structure-property relationships in these materials. Moreover, delineating the precise impacts of elastic versus non-elastic relaxation serves as an effective tuning methodology to engineer the piezoelectric and electronic traits of sulfide compounds for cutting-edge applications.

Ligand and solvent effects on the absorption spectra of CdS magic-sized clusters.

The absorption spectra of congenetic wurtzite (WZ) and zincblende (ZB) CdS magic-sized clusters are investigated. We demonstrate that the exciton peak positions can be tuned by up to 500meV by varying the strong coupling between X-type ligands and the semiconductor cores, while the addition of L-type ligands primarily affects cluster midgap states. When Z-type ligands are displaced by L-type ligands, red shifts in the absorption spectra are observed, despite the fact there is a small decrease in cluster size. Density functional theory calculations are used to explain these findings and they reveal the importance of Cd and S dangling bonds on the midgap states during the Z- to L-type ligand exchange process. Overall, ZB CdS clusters show higher chemical stability than WZ clusters but their optical properties exhibit greater sensitivity to the solvent. Conversely, WZ CdS clusters are not stable in a Lewis base-rich environment, resulting in various changes in their spectra. Our findings enable researchers to select capping ligands that modulate the optical properties of semiconductor clusters while maintaining precise control over their solvent interactions.

Hydrazine-induced synthesis of CdS nanorings for the application in photodegradation

In this paper, CdS nanorings synthesized by a facile hydrazine-induced microwave method for the photodegradation of pollutants were reported for the first time. Different reaction method, microwave power, the category and dosage of pH regulating reagent, reaction temperature and reaction time were investigated. The formation of CdS nanorings from the self-assembly of nanoparticles was attributed to the coordination of hydrazine producing the dipole–dipole interaction among the uniform nanoparticles prepared by microwave method. The crystal phase, composition, morphology and surface property of CdS nanorings were characterized. The results showed that 100 nm-sized wurtzite CdS nanorings generated with the self-assembly of 5–8 nm nanoparticles, which presented mesoporous structures. To study the influence of ring-like structures on the photocatalysis, the photodegradation of rhodamine B (RhB) with CdS nanorings and nanoparticles was compared. The results showed that, CdS nanorings displayed higher photodegradation efficiency, which were originated from more favorable band edge potential and effective electron–hole separation producing more superoxide radical and holes as active specifies. The photodegradation path of RhB contained the process of the demethylation, the decarboxylation process, the chromophore cleavage and ring-open reactions. Finally, the available photodegradation of multiple pollutants and reusability of CdS nanorings were carried out.

Cefotaxime degradation by the coupled binary CdS-PbS: characterization and the photocatalytic process kinetics.

Increased water pollution due to discharging industrial/urban/hospital wastewater has been adopted to introduce/develop novel removal techniques/catalyst/adsorbent. The hexagonal (wurtzite) CdS and the cubic PbS nanoparticles (NPs) were synthesized, coupled, and supported onto clinoptilolite NPs (CNP). Then, the sample was characterized by X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FTIR), and a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX) techniques. The average crystallite size for CdS NPs, PbS NPs, CNP, and CdS-PbS/CNP samples was obtained at about 24, 36, 27, and 14nm using the Scherrer formula value of nanometer, by the W-H formula, 31, 17, 39, and 51, respectively. Only a detectable slope can be observed from the DRS spectra for CdS NPs at 591nm corresponding to an Eg value of 2.1eV. PbS NPs have a broad abruption peak that begins from the visible region and extends to the IR region of the light. A boosted photocatalytic activity of the supported binary catalysts towards cefotaxime (CT) was reached. An apparent first kinetic model was reached with a k-value of 0.021min-1 corresponding to the t1/2 value of 33min. A decreased COD trend for the photodegraded CT solutions was reached, and the chemical oxygen demand (COD) results in the Hinshelwood model showed a k-value of 0.016min-1, corresponding to a t1/2 value of 43min.

Highly Crystalline Wurtzite CdS Prepared by a Flux Method and Application to Photocatalysis

Highly Crystalline Wurtzite CdS Prepared by a Flux Method and Application to Photocatalysis

A Z-scheme CdS/Ag3PO4 catalyst: Characterization, experimental design and mechanism consideration for methylene blue

Due to the explosive use of Azo dyes in various industries such as textiles, discharging these industrial effluents into the environment critically polluted water supplies. Accordingly, constructing/developing novel binary catalysts to diminish the pollution extent of such effluents before discharging into environment is an excellent issue in environmental chemistry. Here, a binary CdS/ Ag3PO4 was constructed, and its boosted photocatalytic activity was proven against methylene blue (MB), as a model dye pollutant. The Wurtzite CdS and Ag3PO4 cubic crystal nanoparticles were synthesized and coupled mechanically. The binary sample's lowest photoluminescence (PL) results confirm a higher e/h separation. DRS results confirmed a decreased energy gap for the coupled system. The semiconductors’ VB and CV potentials were calculated and used for constructing of Z-scheme mechanism. The photocatalytic activity was followed via an experimental design approach. The model F-value of 89.75 > F0.05,14,13 = 2.42 and LOF F-value of 6.57 < F0.05,10, 3 = 8.79 reveal that the model well processed data. The optimal run conditions were CMB: 5 ppm, Catalyst dose: 1 g/L, pH: 3.25, and irradiation time: 139 min, at which 85% of MB molecules were degraded. Based on the trend of ascorbic acid > isopropanol > formic acid ≈ nitrate obtained for the scavengers' importance in decreasing the photocatalyst activity, superoxide radicals had the highest effect in MB degradation and then •OH. The results showed the direct Z-scheme has the main effect on MB degradation by the binary sample.

The spontaneous polarization in CdS to enhance the piezo-PEC performance via phase transition stress engineering

The built-in electric field caused by piezoelectric polarization has emerged as one of the most effective strategies for photoelectrochemical (PEC) water splitting, but is challenged by low piezoelectric polarization efficiency. Herein, we firstly introduce residual stress into CdS through phase transition stress engineering for improving the spontaneous polarization of CdS with a view to revealing the mechanism of the piezoelectric PEC (piezo-PEC) performance of CdS is advanced by the spontaneous polarization. The spontaneous polarization of CdS caused via phase transition residual stress generated built-in electric field to advance carriers separation. Moreover, the spontaneous polarization of CdS is motived a greater potential under external force than hexagonal wurtzite CdS due to the existence of phase transition residual stress, which effectively improves the piezo-PEC performance of CdS. The photocurrent density of miscibility of cubic sphalerite and hexagonal wurtzite CdS (M−CdS) is 0.61 mA/cm2 at 1.23 V vs RHE, which is almost 1.79 times of hexagonal wurtzite (H-CdS). In addition, the value of M−CdS photocurrent density is reached 2.12 mA/cm2 at 1.23 V vs RHE after ultrasound, which is almost 6.2 times of H-CdS. Our detail work proves that this strategy not only stimulates the piezo-PEC performance of CdS, but also can be extended to other hexagonal wurtzite semiconductor phase transition piezoelectric fields.

The boosted photocatalytic effects of a zeolite supported CdS towards an antibiotic model pollutant: a brief kinetics study.

In recent decades, increased world population and industrial activities explosively polluted our environment, especially the aquatic resources. This requires introducing/developing novel methods to decrease the pollution extent of such resources. Here, the hexagonal (wurtzite) CdS nanoparticles (NPs) were synthesized and supported onto ball-mill prepared clinoptilolite NPs (CNP). Samples were briefly characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX), and diffuse reflectance spectroscopy (DRS) techniques. The average crystallite size for CdS NPs and CdS-CNP samples was estimated to be about 9.0nm and 12.3nm (from the Scherrer formula) and about 19.7 and 17.5nm (from the Williamson-Hall model), respectively. From the DRS spectra, the absorption wavelengths of 595 and 546nm correspond to band gap energies of 2.08, and 2.27eV was obtained for CdS NPs and CdS-CNP samples. The samples were then used in the photodegradation of cefotaxime (CT), and the results showed a boosted photocatalytic activity for CdS-CNP rather than CdS NPs. The photodegradation process obeyed the pseudo-first-order kinetic model, and the CdS and CdS-CNP catalysts obtained the k-values of 0.013min-1 and 0.023min-1. When the photodegraded CT solutions were used in COD experiments, the k-values changed to 0.011min-1 and 0.029min-1, respectively. The zeolite support is an eco-friendly natural zeolite with abundant deposits in Iran that yields a cost-effective method.

Manipulating Cation Exchange Reactions in Cu2-xS Nanoparticles via Crystal Structure Transformation.

Copper-deficient Cu2-xS nanoparticles (NPs) are extensively exploited as a superior cation exchange (CE) template to yield sophisticated nanostructures. Recently, it has been discovered that their CE reactions can be facilely manipulated by copper vacancy density, morphology, and NP size. However, the structural similarity of usually utilized Cu2-xS somewhat limits the manipulation of the CE reactions through the factor of crystal structure because it can strongly influence the process of the reaction. Herein, we report a methodology of crystal structure transformation to manipulate the CE reactions. Particularly, roxbyite Cu1.8S nanodisks (NDs) were converted into solid wurtzite CdS NDs and Janus-type Cu1.94S/CdS NDs by a "full"/partial CE reaction with Cd2+. Afterward, the roxbyite Cu1.8S were pseudomorphically transformed into covellite CuS NDs. Unlike Cu1.8S, the CuS was scarcely exchanged because of the unique disulfide (S-S) bonds and converted into hollow wurtzite CdS under a more reactive condition. The S-S bonds were gradually split and CuS@CdS core@shell-type NDs were generated. Therefore, our findings in the present study provide not only a versatile technique to manipulate CE reactions in Cu2-xS NPs but also a better comprehension of their reaction dynamics and pathways.

Electronic and Band Structure calculation of Wurtzite CdS Using GGA and GGA+U functionals

The wurtzite (wz) structure of CdS is analysed using density functional theory within the generalized gradient approximation (GGA) and Hubbard correction (GGA+U). The total energy convergence evaluation is carried out concerning energy cut-off (ecutwfc) and k-point sampling. The geometry optimization of wz-CdS is calculated using the total energy and force minimization process, which is based on the Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimization algorithm. Bulk modulus and lattice parameters are estimated to ensure accuracy of the calculations. The electronic band structure, density of states (DOS), and projected density of states (PDOS) of wz-CdS are analysed. The band structure calculation shows CdS as direct band gap semiconductor. The electronic correlation in CdS is altered by varying U-parameters of valence orbitals of Cd and S. The alteration of electronic correlation results in convergence of the band gap to the experimental value 2.4 eV. The alteration of U-parameter affects substantially the density of states near the band edges.

Structural and Optical Studies on Sol-Gel Driven Spin-Coated CdS Thin Films

Inorganic wide band gap semiconductors are considered as best for optoelectronic devices such as photovoltaic cells, photodetectors, thin film transistors etc. CdS is a more promising semiconductor due to its direct wide band-gap ∼ 2.42 eV and size dependent optical properties. In the present article, structural and optical properties of spin coated CdS thin films are investigated. CdS thin films are annealed at 400 °C for 60 minutes to improve crystalline quality. X-RAY diffraction pattern reveals (002) diffraction plane of wurtzite CdS. The optical properties are analyzed by UV-Visible-NIR spectroscopy. The optical band-gap of CdS thin films varies from 2.25 eV to 2.47 eV which depends on number of deposited layers and the annealing condition.

Calculation of lattice vibrational and thermal properties of cadmium sulfide nanocrystal and growth preference of cadmium sulfide powder during microwave‐hydrothermal process

AbstractCdS nanocrystal is investigated by first‐principles calculations and experiments. Based on phonon spectra, the wurtzite CdS structure is thermodynamically stable. Debye temperature, specific heat capacity and thermal expansion coefficient are calculated to be 221.51 K, 47.68 J·mol−1·K−1 and 1.95×10−4 K−1, respectively. Band gaps of CdS single crystal and monolayer CdS supercell calculated by GGA–mBJ function are 2.74 eV and 2.38 eV. CdS powder is synthesized by microwave‐hydrothermal process (140 °C + 15 min), with particle size ranging from 50 to 1000 nm. HRTEM shows the nanocrystal distance of 6.676 Å between the (0001) crystal faces and growth preference along the [002] direction. The band gap of CdS thin film evaluated by UV–Vis absorption spectra is 2.41 eV, close to 2.38 eV of monolayer supercell, which provides theoretical basis for CdS doping to improve photoanode performance of piezoelectric semiconductors.

CdS(ZB)/CdS(WZ)/Ni-BTC photocatalytic selective oxidation of benzyl alcohol to benzaldehyde coupled with hydrogen evolution

Development of difunctional photocatalyst for both hydrogen production and high value-added fine chemicals is of great industrial significance. Cubic crystal phase zinc blende CdS(ZB) and hexagonal crystal phase wurtzite CdS(WZ) in CdS(ZB)/CdS(WZ)/Ni-BTC (BTC = 1,3,5-benzene tricarboxylic acid) composites can form intergrowth homojunction to improve the photoelectron-hole separation efficiency, so that the composites show excellent catalytic activity in photocatalytic selective oxidation of benzyl alcohol to benzaldehyde coupled with hydrogen evolution reaction. The conversion of benzyl alcohol can up to 99.0%, the yield of benzaldehyde is 90.2%, and the yield of hydrogen is 2.891 mmoL·g−1·h−1. Meanwhile, styrene was reduced by hydrogen produced via photocatalytic oxidation benzyl alcohol using D2O as reaction solvent. The results demonstrate clearly that 41.6% of H2 come from benzyl alcohol, and 58.4% of D2 come from D2O by analysis of the benzene ethane product. The catalytic mechanism is speculated to be that the benzyl alcohol can simultaneous produce benzaldehyde and H2 by holes oxidation and dehydrogenation, and electron reduce the intrinsic hydrogen ion in water to H2. These results enrich the mechanism of photocatalytic benzyl alcohol oxidation coupled with hydrogen evolution, and provide a new experimental and technical strategy for the design and synthesis of dual-function photocatalysts.

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods