CdS Clusters Research Articles

High‐Performance Bi2Te3‐Based Thermoelectrics Enabled by ≈1 nm Metal Chalcogenide Clusters with Size‐Dependent Electron and Phonon Structures

AbstractThe untapped potential of sub‐nanometric materials (SNMs) in constructing high‐performance thermoelectrics (TE) presents a promising yet unexplored avenue. This study investigates the utilization of supertetrahedral CdS clusters, representing SNMs, in conjunction with state‐of‐the‐art Bi2Te3‐based systems. The CdS cluster with size‐dependent electronic structure enables selective interface scattering of carriers, while its 1 nm size and size‐dependent phonon density of states (DOS) contribute to significant interfacial thermal resistance. Furthermore, interfacial dislocations and significant grain refinement induced by the incorporation of the CdS cluster boost the mechanical properties. Consequently, a remarkable peak figure of merit (ZT) value of 1.47 at 350 K and a record‐high Vickers hardness of 1.08 GPa is achieved in the Bi0.5Sb1.5Te3/0.1 wt% CdS cluster composite. The robust TE module achieves an excellent conversion efficiency of about 6.1% under a ΔT of 241 K. This work opens up exciting possibilities for utilizing 1 nm clusters in thermoelectrics and even inspires other fields involving size‐dependent electrical and thermal transport behaviors.

Formation and Transformation of CdS Clusters during the Prenucleation Stage and in a Dilute Dispersion at Room Temperature.

The formation and transformation of colloidal semiconductor clusters remain poorly understood. With CdS as a model system, we show that, in the reaction of cadmium myristate (Cd(MA)2) and S powder in 1-octadecene (ODE), clusters form in the prenucleation stage of quantum dots (QDs). Called precursor compounds (PCs), the clusters can transform to magic-size clusters (MSCs) in reaction at a relatively high temperature (MSC-322 displaying optical absorption peaking at 322 nm) or in a dispersion at room temperature (MSC-360). When the reaction temperature is increased, PC-360 forms at 140 °C, while PC-322 and MSC-322 form at 180 °C. In a dispersion of cyclohexane and octylamine, MSC-322 transforms to MSC-360 via MSC-345. The MSC-345 to MSC-360 transformation displays continuous and discontinuous shifts in the optical absorption. The PCs and MSCs are a group of isomers. The present findings bring insight into the cluster formation and isomerization in the prenucleation stage of QDs and in a dispersion.

Temperature Dependence of the CdS Bandgap in the Extreme Confinement Regime.

A non-empirical equation describing the effect of size on the temperature dependence of the optical bandgap of CdS (dEg/dT) is obtained on the basis of the Brus equation. Intriguingly, we find that dEg/dT diverges strongly from bulk values only within the "extreme confinement" (EC) regime. We conducted both experimental and theoretical investigations of the absorption spectra of CdS clusters and quantum dots as a function of temperature above room temperature. Our results show that the value of dEg/dT obtained from absorption spectra in the EC regime is 2.5 times higher than in the strong confinement regime. Notable ligand sensitivities are also observed for dEg/dT in the case of CdS clusters. Ab initio molecular dynamics simulations and density functional theory calculations reveal that thermal fluctuations are the crucial factor influencing the bandgap temperature coefficient. Our results help resolve some long-standing debates regarding the dEg/dT behavior of semiconductor quantum dots.

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.

Integrating CdS and Titanium Oxide Clusters with Molecular Redox Catalysts into Metal‐Organic Frameworks Promoting Photocatalytic Efficient H2 Evolution

AbstractA new quaternary crystalline catalyst was obtained by a mixed hydrothermal method of integrating inorganic semiconductors, titanium oxide cluster (TOC) and molecular redox centers orderly into metal organic framework (MOF) materials. It shows a hydrogen production rate 3711.53 μmol g−1 h−1 under visible light irradiation, exceeds most of the same type of catalyst reported in recent years, and a favorable stability with. The excellent performance of the CdS/TOC/UiO‐67‐bpy/Co composites due to efficient promotion of photo‐induced carrier separation and migration, and offering abundant active sites for generating hydrogen. This work will help to guide the preparation of new efficient and stable photocatalysts and promote the effective conversion of solar energy to chemical energy.

Construction of immobilized films photocatalysts with CdS clusters decorated by metal Cd and BiOCl for photocatalytic degradation of tetracycline antibiotics

A kind of CdS/Cd-BiOCl immobilized films photocatalyst was prepared. The optical and physicochemical properties of the CdS/Cd-BiOCl photocatalysts were analysed, and the detailed characterization revealed CdS/Cd-BiOCl films photocatalyst with good charge carrier separation effect. The reusabilities and photocatalytic properties of the samples were studied. The 15%CdS/Cd-BiOCl photocatalyst exhibited superior performance in photocatalytic degradation of tetracycline (TC) and favorable stability under visible light irradiation. As for the photodegradation rate of TC, 15%CdS/Cd-BiOCl exhibited an excellent photodegradation activity, which is 4.06 and 9.53 times higher than that of CdS/Cd and BiOCl, respectively. The results showed that dominant active species are •O2− and •OH radicals during photodegradation. The charge transfer in Z-scheme CdS/Cd-BiOCl films photocatalyst could synchronously generate conduct band (CB) electrons in BiOCl and valence band (VB) holes in CdS, and metal Cd served as electron mediator. This work can be a reference for the design of film photocatalysts and new insight for photodegradating towards contaminants.

Systematic Study of the Properties of CdS Clusters with Carboxylate Ligands Using a Deep Neural Network Potential Developed with Data from Density Functional Theory Calculations.

Although structures of the inorganic core of CdS atomically precise quantum dots were reported, characterizing the nature of the metal-carboxylate coordination in these materials remains a challenge due to the large number of possible isomers. The computational cost imposed by first-principles methods is prohibitive for such a configurational search, and empirical potentials are not available. In this work, we applied deep neural network algorithms to train a potential for CdS clusters with carboxylate ligands using a database of energies and gradients obtained from density functional theory calculations. The derived potential provided energies and gradients based on a set of reference structures. Our trained potential was then used to accelerate genetic algorithm and molecular dynamics simulations searches of low-energy structures, which in turn, were used to compute the X-ray diffraction and electronic absorption spectra. Our results for CdS clusters with carboxylate ligands, analyzed and compared with experimental findings, demonstrated that the structure of a cluster whose properties agree better with experiment may deviate from the one previously assumed.

Quantum confinement effects of formation energies and vibrational properties of CdS clusters: A DFT study

Formation energies of cadmium sulfide clusters are calculated with the help of density functional theory. The investigated structures include clusters that represent the CdS three main phases, wurtzite, zincblende and rock-salt. The investigation includes electronic, vibrational and thermal properties. CdS clusters are represented by wurtzoids, diamondoids and cuboids for the three phases, wurtzite, zincblende and rock-salt, respectively. The energy gap of the largest investigated molecules approaches that of bulk experimental 2.42 eV. The calculated longitudinal optical (LO) vibrational mode is 304.2 cm[Formula: see text] which is in good agreement with the experimental bulk value of 305 cm[Formula: see text]. To calculate Gibbs free energy, enthalpy and entropy of formation for the clusters, we redefined these quantities so that they represent the difference between the CdS formation energy and their constitutes Cd and S clusters energy. The calculated Gibbs free energy of formation, enthalpy and entropy of the investigated clusters approach that of bulk. Wurtzoids are more stable than diamondoids and cuboids with the release of more heat as deduced from their cluster Gibbs energy and enthalpy of formation. The entropy of clusters is dependent on the size of the cluster. The present method draws a relation between known solid state phases and small cluster calculations.

Расчет электронных переходов в кластерах CdS, связанных с кумариновым красителем

Расчет электронных переходов в кластерах CdS, связанных с кумариновым красителем

X-ray total scattering study of magic-size clusters and quantum dots of cadmium sulphide.

Four types of magic-size CdS clusters and three different CdS quantum dots have been studied using the technique of X-ray total scattering and pair distribution function analysis. We found that the CdS quantum dots could be modelled as a mixed phase of atomic structures based on the two bulk crystalline phases, which is interpreted as representing the effects of random stacking of layers. However, the results for the magic-size clusters are significantly different. On one hand, the short-range features in the pair distribution function reflect the bulk, indicating that these structures are based on the same tetrahedral coordination found in the bulk phases (and therefore excluding new types of structures such as cage-like arrangements of atoms). But on the other hand, the longer-range atomic structure clearly does not reflect the layer structures found in the bulk and the quantum dots. We compare the effect of two ligands, phenylacetic acid and oleic acid, showing that in one case the ligand has little effect on the atomic structure of the magic-size nanocluster, and in another it has a significant effect.

Synthesis of 3D mesoporous alumina from natural clays for confining CdS nanoparticles and enhanced photocatalytic performances

Abstract A spatial confinement effect of CdS nanoparticles in mesoporous alumina, which is synthesized through evaporation-induced self-assembly (EISA) method, post-impregnation approach and microwave irradiation process, was investigated to verify the enhanced catalytic activity and stability with less aggregation of CdS crystallites during decoloration of organic dyes under visible-light irradiation. In this work, we utilize inexpensive natural clays for preparing mesoporous alumina via evaporation-induced self-assembly method, and used as the host for confining CdS nanoparticles to suppress the crystallite growth and aggregation. The loading amount and grain size of CdS nanoparticles significantly altered catalytic activity and stability. CdS clusters confined inside the mesoporous channels provided abundant reactive sites for photocatalytic reaction through spatial confinement effect, quantum size effect and sulfide-support interaction, thus greatly enhancing the reaction activity. CdS/MAl composites have large special surface area, strong visible light absorption and high quantum yields. CdS/MAl-25 photocatalyst has exhibited remarkably enhanced visible light photoactivities as compared to other catalysts, and the overall decoloration rate was up to 97.5% after visible light irradiation for 60 min. The CdS/MAl composites exhibit potential applications in the wastewater treatment under visible light irradiation.

Определение природы электронных переходов в комплексах родаминового красителя и кластерах CdS

Определение природы электронных переходов в комплексах родаминового красителя и кластерах CdS

Crystalline Superlattices of Nanoscopic CdS Molecular Clusters: An X-ray Crystallography and 111Cd SSNMR Spectroscopy Study.

Systematic 111Cd solid-state (SS) NMR experiments were performed to correlate X-ray crystallographic data with SSNMR parameters for a set of CdS-based materials, varying from molecular crystals of small complexes [Cd(SPh)4]2- and [Cd4(SPh)10]2- to superlattices of large monodisperse clusters [Cd54S32(SPh)48(dmf)4]4- and 1.9 nm CdS. Methodical data analysis allowed for assigning individual resonances or resonance groups to particular types of cadmium sites residing in different chemical and/or crystallographic environments. For large CdS frameworks, 111Cd resonances were found to form three groups. This result is noteworthy, since for related systems with size polydispersity and variations in composition, such as CdS or CdSe nanoparticles protected with an organic ligand shell, typically only two groups of resonances were observed. The generalized information obtained in this work can be used for the interpretation of 111/113Cd SSNMR data for large CdS clusters and nanoparticles, for which crystal structure analysis remains inaccessible. Comparison of the powder X-ray diffraction patterns for freshly prepared and dried superlattices of large CdS clusters revealed an interesting superstructure rearrangement that was not observed for the smaller frameworks.

Surface-decorated CdS nanoparticles for the recognition of K+ in aqueous medium: DFT and antibacterial studies

New CdS NPs decorated with 2-thiobenzimidazole (TB) were synthesized as chemo-sensors for selective recognition of potassium ions. The results show that CdS–TB NPs are sensitive and selectively detect K+ ions, finding that there is no interference from other metal ions (Mn2+, Mg2+, Cu2+, Co2+, Cr3+, Fe3+, Ni2+, Zn2+, Sr2+, Ag+, Sm3+, Al3+, Cd2+, Ba2+, Na+), and the detection limit was as low as 0.008 mM. In antibacterial studies, CdS–TB NPs exhibit non-toxicity towards bacterial systems, suggesting that the decoration of TB molecules reduces the toxicity of CdS NPs. In order to understand the binding nature of TB molecules with CdS, the structural and electronic properties of different CdS clusters [(CdS) n , n = 1–16] were analyzed by Density Functional Theory (DFT) before and after their interaction with TB, and the molecular orbitals and density of states were used to describe the nature of the bonding between metal oxide clusters and TB molecules.

Influence of organic ligands on the formation and functional properties of CdS nanostructures

The effect of capping agents (Piperazine, Polyvinylpyrrolidone and triton X) on the functional properties of CdS nanostructures have investigated. SEM analysis revealed the formation of different morphologies of CdS nanostructures in the presence of different capping agents. Surface passivation of CdS with polyvinylpyrrolidone and piperazine lead to the formation of CdS nanorods, whereas capping with triton X resulted in the formation of CdS clusters. XRD studies revealed the formation of cubic phase and hexagonal phase with polyvinylpyrrolidone, triton X and piperazine, respectively. Absorption and emission studies revealed that the capping agents play an important role in passivation of the dangling bonds on the nanoparticle surface and greatly influence the optical properties.

Structures of the Subnanometer Clusters of Cadmium Sulfide Encapsulated in Zeolite Y: Cd4S6+ and Cd(SHCd)46+

The structures of the subnanometer clusters of CdS that form in zeolite Y (FAU), prepared as follows, have been determined. A single crystal of Cd2+-exchanged zeolite Y was prepared by the exchange of Na75–Y (|Na75|[Si117Al75O384]–Y with aqueous Cd(NO3)2 at 294 K, followed by vacuum dehydration at 723 K (crystal 1). A second crystal, similarly prepared, was exposed to 6.7 × 104 Pa of dry H2S(g) for 6 h at 294 K and evacuated (crystal 2). Their structures were determined crystallographically using synchrotron X-rays and were refined using all data to the final error indices (calculated using only Fo > 4σ(Fo)) of R1/wR2 = 0.040/0.156 and 0.049/0.186, respectively. In crystal 1, Cd2+ ions primarily occupy sites I and II. In crystal 2, |Cd27(Cd4S6+)0.6(Cd(SHCd)46+)0.9H12|[Si117Al75O384]–FAU, tetrahedral Cd4S6+ ions center about 7.5% of the sodalite cavities and tetrahedral Cd(SHCd)46+ ions center about 11% of the supercages. In Cd(SHCd)46+, a Cd2+ ion at the center of a supercage bonds tetrahedrally to four S...

Colloidal Synthesis of Monodisperse Semiconductor Nanocrystals through Saturated Ionic Layer Adsorption

We demonstrate a general strategy for the synthesis of colloidal semiconductor nanocrystals (NCs) exhibiting size dispersion below 5%. The present approach relies on the sequential deposition of fully saturated cationic and anionic monolayers onto small-diameter clusters, which leads to focusing of nanocrystal sizes with the increasing particle diameter. Each ionic layer is grown through a room-temperature colloidal atomic layer deposition process that employs a two-solvent mixture to separate the precursor and nanocrystal phases. As a result, unreacted precursors can be removed after each deposition cycle, preventing the secondary nucleation. By using CdS NCs as a model system, we demonstrate that a narrow size dispersion can be achieved through a sequential growth of Cd2+ and S2– layers onto starting CdS cluster “seeds”. Besides shape uniformity, the demonstrated methodology offers an excellent batch-to-batch reproducibility and an improved control over the nanocrystal surface composition. The present s...

Influence of Bath Temperature on CBD-CdS Thin Films

CdS thin films were grown on conducting glass substrates at different bath temperatures in order to investigate their influence on opto-electrical properties of the chemical bath deposited (CBD) CdS thin films. The CBD-CdS process was carried out with 0.001M CdSO4, 0.002M CS(NH2)2 and NH3 solution at different bath temperatures from 40 to 80 0C for one hour. Fabricated films were characterized using UV-Vis spectrometry, SEM, PEC cell and Profilometer.The optical transmittances of the films decreased with increasing bath temperature due to the increase of the film thickness. CdS cluster size of the thin films grown in the bath at a temperature of 60 0C was considerably larger compared to the films fabricated at other bath temperatures. The variation of optical band gap (Eg) was found to be in good agreement with cluster size variation while electrical characterizations reveal considerably high Voc and Isc values for the films fabricated at a bath temperature of 80 0C.

A DFT study of the effects of Sc doping on electronic and optical properties of CdS nanoparticles

AbstractIn the present work a systematic study was carried out to understand the influence of Sc doping on electronic and optical properties of CdS nanoparticles. The geometry optimization and symmetry computation for CdS and Sc doped CdS nanoparticles using Density Functional Theory (DFT) on B3LYP level with the QZ4P for Cd and DZ2P for sulphur and Sc were performed by Amsterdam Density Functional (ADF). The results show that HOMO-LUMO gap as well as electronic and optical properties of CdS clusters vary with Sc doping. The HOMO-LUMO gap is affected by the dopant and its value decreases to 0.6 eV. Through considering the numerical integration scheme in the ADF package, we investigated different vibrational modes and our calculated Raman and IR spectra are consistent with the reported result. The calculated IR and Raman peaks of CdS and Sc doped CdS clusters were in the range of 100 to 289 cm−1, 60 cm−1 to 350 cm−1 and 99 cm−1 to 282 cm−1, 60 cm−1 to 350 cm−1, respectively, which was also confirmed by experiment as well as a blue shift occurrence. Subsequently, for deeper research of pure and doped CdS clusters, their absorption spectra were calculated using time-dependent DFT method.

Properties of transition metal doped cadmium sulfide hexamers and dodecamers

The electronic and geometrical properties of endohedrally and substitutionally doped Cd6S6 and Cd12S12 clusters were analyzed by means of Density Functional Theory. The results are compared to those of ZnS clusters of the same size. There is a clear correlation between CdS and ZnS when doped with the same element due to the chemical interaction between the dopant and its host. This is particularly evident from endohedrally doped Cd6S6. The change in properties across the 3d series in doped CdS clusters is not as great as in ZnS clusters.