Hexagonal CdS Nanocrystals Research Articles

Enhanced photocatalytic properties of CdS -decorated BiPO4 heterogeneous semiconductor catalyst under UV-light irradiation

CdS@BiPO4 nanocomposite photocatalysts, composed of monoclinic BiPO4 nanorods with an average diameter of 150 nm and length of 1.0 μm and hexagonal CdS nanocrystals with an average diameter of 8.0 nm, were synthesized by an in-situ heterogeneous nucleation and growth in the solutions at room temperature. Their phase components, microstructures and surface morphologies were characterized by XRD, FESEM, HRTEM and XPS and, in particular, the catalytic performance of CdS@BiPO4 composites with different CdS/BiPO4 weight ratios were studied through the degradation of methyl orange (MO) solution under UV-light irradiation. It has been found that the CdS nanocrystals are uniformly attached on the surface of BiPO4 nanorods and no impurity phases are detected by XRD in the CdS@BiPO4 composite catalysts, while their photocatalytic performances are notably enhanced compared with their individual constituent phases. Moreover, the composite catalyst with 6 wt% of CdS has been shown to possess the highest photocatalytic activity, which promotes MO to degrade to 95.4% in 45 min under UV light irradiation, about 1.40 and 7.50 times higher than that of single phases BiPO4 and CdS, respectively. The formation of BiPO4/CdS heterojunctions apt to reduce recombination of the photogenerated carriers in CdS@BiPO4 due to the favorable built-in electric fields at their interfacial area is believed responsible for the improved photocatalytic performances. On the basis of the experimental results and discussions, a possible charge transfer mechanism for the enhanced photocatalytic activity under UV light irradiation was also proposed.

Preparation of CdS Nanoparticles from Thiosemicarbazone Complexes: Morphological Influence of Chlorido and Iodido Ligands

AbstractCadmium(II) thiosemicarbazone complexes were prepared and characterized by elemental analysis and IR and NMR spectroscopy. The complexes were then investigated as potential single‐source precursors for the synthesis of oleylamine‐capped cadmium sulfide nanoparticles by solvothermal decomposition. The resulting nanomaterials were characterized by powder XRD, TEM, HRTEM, energy‐dispersive X‐ray analysis, and UV/Vis spectroscopy. Peak broadening in the XRD patterns confirmed the presence of relatively small hexagonal CdS nanocrystals. The TEM studies evidenced that the chlorido precursors produced CdS nanostructures whose morphologies differed from those obtained from the iodido precursors. CdS nanoparticles in the form of cubes/spheres/rods and nanodendrite structures were obtained from CdCl2 and CdI2 thiosemicarbazone complexes, respectively. The UV/Vis spectra revealed that the as‐synthesized CdS nanoparticles exhibited a quantum effect due to their sharp band edges, which are blueshifted relative to those of bulk CdS. The size, morphology and shape of the nanoparticles were also shown to depend on the temperature of formation.

In-situ synthesis of C3N4/CdS composites with enhanced photocatalytic properties

A hybrid semiconductor composed of a carbon nitride/cadmium sulfide nanocomposite (C3N4/CdS) was synthesized by a template-free one-step calcination route at high temperature using ammonium thiocyanate and cadmium chloride as starting materials. The crystal structure, composition and morphology of the hybrid samples were studied by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The photocatalytic degradation of Rhodamine B as a model compound was carried out to evaluate the photocatalytic activity of the nanocomposites under visible light irradiation. Hexagonal CdS nanocrystals were uniformly distributed in the bulk C3N4. After coupling with CdS the basic C3N4 structure was mostly unchanged. The visible light absorption properties of the hybrid materials were enhanced. The as-prepared C3N4/CdS hybrid photocatalyst exhibited superior degradation performance under visible light irradiation compared with pure C3N4. The well-matched band energy improved the transfer efficiency of the photoinduced carriers and this was responsible for the enhanced photocatalytic activity and stability of the hybrid photocatalysts.

Effect of key operational factors on decolorization of methyl orange during H 2O 2 assisted CdS/TiO 2/ploymer nanocomposite thin films under simulated solar light irradiation

CdS/TiO 2/polymer nanocomposite thin films (CdS/TiO 2/polymer NTFs) as photocatalyst were prepared and characterized by wide angle X-ray diffraction (WXRD). The effect of key operational factors, i.e. catalyst amount, H 2O 2 dosage, solution pH, initial dye concentration, coexisting anions and reuse of catalyst on decolorization of methyl orange (MO) was investigated systematically. WXRD results indicated that CdS/TiO 2/polymer NTFs presented a mixture of anatase TiO 2 and hexagonal CdS nanocrystals. 99.5% of MO was successfully decolorized after 130 min simulated solar light irradiation at 3.9 mmol L −1 H 2O 2, 1.0 g L −1 CdS/TiO 2/polymer NTFs and pH 6.0 for 15 mg L −1 MO aqueous solution. All examined anions (Cl −, NO 3 −, SO 4 2−, CO 3 2− and PO 4 3−) had an inhibitory effect on the decolorization of MO. When the photocatalyst was used for the fifth time, decolorization efficiency was still about 99% after 130 min irradiation. These results demonstrated that H 2O 2 assisted CdS/TiO 2/polymer NTFs under simulated solar light irradiation was an effective and promising process for decolorization of dye-containing wastewater.

Green synthesis of metal sulfide nanocrystals through a general composite-surfactants-aided-solvothermal process

In this paper, we developed a generalized and greener composite-surfactants-assisted-solvothermal process (CSSP) to produce colloidal nanoparticles of metal sulfides. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS) revealed that single-molecular-layer type of MoS 2 nanoparticles with diameter 6–10 nm were successfully synthesized. The molecular structure model of the capped MoS 2 nanoparticles was suggested through further examination by infrared spectra. Hexagonal CdS nanocrystals with spherical, triangle, and hollow sphere shapes were controllably synthesized by varying the experimental conditions. A possible in-situ reduction–sulfidation mechanism was proposed for the formation of Ag 2S nanocrystals, where the metal ions were reduced to metallic nanoparticles before the generation of sulfides. The obtained nanocrystals through this CSSP approach could provide the building blocks for the bottom-up approach to nanoscale fabrication in nanoscience and nanotechnology.

Facile Cd−Thiourea Complex Thermolysis Synthesis of Phase-Controlled CdS Nanocrystals for Photocatalytic Hydrogen Production under Visible Light

We describe a simple cadmium−thiourea complex thermolysis route for the formation of CdS nanocrystals with controlled dispersity, crystalline phase, composition, average grain size, and band gap. Visible-light-driven photocatalytic activities for hydrogen production over the different CdS products have been compared. Phase structure and composition of the obtained CdS nanocrystals has been optimized either by changing the ratio of thiourea to Cd or by changing the annealing temperature. Over a broad annealing temperature range of 150−500 °C, either cubic, a mixture of cubic and hexagonal, or hexagonal CdS nanocrystals are obtained at thiourea/Cd molar ratios of <1.0, 1.5−2.5, and 3.0−4.5, respectively. Nanocrystalline cubic CdS is stable at temperatures as high as 500 °C for 0.5 h, and is converted to hexagonal CdS for annealing time longer than 1 h. The phase transition from cubic to hexagonal CdS occurs at temperatures of 200−300 °C, and pure hexagonal CdS is formed at annealing temperatures higher than...

Synthesis and Self‐Assembly of Triangular and Hexagonal CdS Nanocrystals

Synthesis and Self‐Assembly of Triangular and Hexagonal CdS Nanocrystals

Microemulsion-mediated synthesis of cadmium zinc sulfide nanocrystals with composition-modulated optical properties

Cadmium zinc sulfide nanocrystals were synthesized by a microemulsion-mediated process, which involving two steps: the preparation of CdS (or ZnS) seeds and the succedent hydrothermal growth of ZnS (or CdS) component. The XRD results show that the cadmium zinc sulfide nanocrystals with CdS seeds present a hexagonally homogeneous alloyed structure, while the ones with ZnS seeds mainly take on the characteristic of hexagonal CdS nanocrystals. The intrinsic factors influencing the crystal structures were discussed. The UV–vis and photoluminescence (PL) spectra indicate that the optical properties of the obtained nanocrystals with CdS seeds can be continuously modulated by tuning their compositions, although their sizes and size distributions are not under a strict control. The composition-modulated strategy, along with the hydrothermal microemulsion process, will be an effective route to achieve semiconductor nanocrystals with tunable optical properties under more manageable conditions.

Photoluminescence Spectra and Dynamics of Single CdS Nanocrystals Studied by Scanning Near-Field Optical Microscopy

Photoluminescence (PL) spectra and dynamics of hexagonal CdS nanocrystals embedded in Al 2 O 3 matrices have been studied by means of a scanning near-field optical microscope at 8 K. The PL spectra of individual CdS nanocrystals show narrow lines with single-exponential decay profiles, although the macroscopic PL spectra measured by conventional optics show a broad band with non-exponential decay profiles. The PL peaks are observed at energies below the lowest free-exciton energy of CdS nanocrystals. The luminescence mechanism of CdS nanocrystals is discussed.

Photoluminescence from surface-capped CdS nanocrystals by selective excitation

We have studied photoluminescence (PL) properties of hexagonal CdS nanocrystals whose surface is capped by pentafluorothiophenol and N, N-dimethylformamide, by means of florescence-line-narrowing spectroscopy. Both the sharp band-edge and the broad trap-state emission are strongly modified by exciton-phonon interactions enhanced by quantum confinement. The LO-phonon modified structures in the band-edge emission spectra show the existence of two excitonic states at the band edge. The broad trap-state luminescence is modified by the strong coupling between localized excitons and polar vibrations at the surface. The selectively excited luminescence properties and the coupling between electronic and vibrational excitations in CdS nanocrystals are discussed.