Studies on optical absorption and photoluminescence of thioglycerol-stabilized ZnS nanoparticles

ZnS quantum dots of size 3 nm are prepared at 303 K using ZnSO₄ and Na₂S₂O₃ precursors with thioglycerol as stabilizing agent. Cd²⁺ doped ZnS were prepared by varying doping concentration from 1 to 8 wt.%. ZnS quantum dots were mixed with CdS quantum dots of size 4 nm in the 3:1, 2:1, 1:1, 1:2, 1:3 and 1:4 M ratio. The nanoparticles were characterized by UV–vis, photoluminescence (PL), XRD and high-resolution TEM measurements. The XRD pattern, high-resolution TEM image and SAED pattern reveal that the nanoparticles are in well-crystallized cubic phase. The band gap of ZnS has increased from the bulk value 3.7 to 4.11 eV showing quantum size effect. Excitonic transition is observed at 274 nm in UV absorption and PL emission at 411 nm. Doping with Cd²⁺ red-shifts both UV and PL spectral bands and enhances the PL band of ZnS nanoparticles. Mixing CdS and ZnS quantum dots in different molar ratios shows red-shift of the band edge in the CdS/ZnS hybrid system. In the 1:1 hybrid system of CdS/ZnS nanoparticles, PL band is red-shifted and the intensity is almost doubled with respect to that of CdS nanoparticles.     

A facile synthesis of ZnS nanocrystallites by pyrolysis of single molecule precursors,Zn (cinnamtscz)<Subscript>2</Subscript> and ZnCl<Subscript>2</Subscript> (cinnamtsczH)<Subscript>2</Subscript>

ZnS nanocrystallites were synthesised by pyrolysis method using Zn (cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ (cinnamtsczH = cinnamaldehyde thiosemicarbazone) as single source precursors. The prepared ZnS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, UV-Vis and fluorescence spectroscopy. The peak broadening in XRD and emission at shorter wavelength in fluorescence spectra showed the presence of nanocrystallites. The blue shift in UV-Vis absorption spectroscopy also proved the formation of nanocrystallites. TEM images show presence of plate-like and spherical ZnS nanoparticles obtained from Zn(cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ respectively.     

Formation of transition-metal sulfide microspheres or microtubes

Cu_xS (x = 1, 2) microtubes, and a series of transition-metal sulfide (CdS, ZnS, NiS, CoS, CuS and Cu₂S) compounds microspheres were successfully synthesized through a facile hydrothermal reaction. These compounds have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The optical properties of ZnS and CdS have also been investigated by UV–vis absorption and fluorescence spectroscopy. The possible formation mechanism of these microspheres or microtubes was discussed based on the experimental results.     

A hydrothermal method to prepare the spherical ZnS and flower-like CdS microcrystallites

The spherical ZnS and flower-like CdS microcrystallites are prepared by a convenient hydrothermal process through the reactions of Zn(CH₃COO)₂·2H₂O or Cd(CH₃COO)₂·2H₂O with S and NaH₂PO₂·H₂O in aqueous solution at 180 °C for 12 h. Powder X-ray diffraction (XRD) is used to confirm the cubic phases of the ZnS and CdS microcrystallites. Their chemical compositions are characterized by X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images show the morphologies of the as-synthesized ZnS and CdS. The photoluminescence spectra (PL) exhibit their optical properties.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.     

Effect of swift heavy ion irradiation on bare and coated ZnS quantum dots

The present study compares structural and optical modifications of bare and silica (SiO₂) coated ZnS quantum dots under swift heavy ion (SHI) irradiation. Bare and silica coated ZnS quantum dots were prepared following an inexpensive chemical route using polyvinyl alcohol (PVA) as the dielectric host matrix. X-ray diffraction (XRD) and transmission electron microscopy (TEM) study of the samples show the formation of almost spherical ZnS quantum dots. The UV-Vis absorption spectra reveal blue shift relative to bulk material in absorption energy while photoluminescence (PL) spectra suggests that surface state and near band edge emissions are dominating in case of bare and coated samples, respectively. Swift heavy ion irradiation of the samples was carried out with 160 MeV Ni¹²⁺ ion beam with fluences 10¹² to 10¹³ ions/cm². Size enhancement of bare quantum dots after irradiation has been indicated in XRD and TEM analysis of the samples which has also been supported by optical absorption spectra. However similar investigations on irradiated coated quantum dots revealed little change in quantum dot size and emission. The present study thus shows that the coated ZnS quantum dots are stable upon SHI irradiation compared to the bare one.     

Novel approach to control CdS morphology by simple microwave-solvothermal method

Nanosize CdS powders with different microstructures are prepared in different solvents by using rapid microwave irradiation. Effect of solvents and Cd²⁺ precursors are to be able to control the particle size, and microstructures of CdS have been investigated by X-ray diffraction and TEM. The different particle size and morphologies are observed using different Cd²⁺ precursors in different solvents. TEM micrographs clearly show multiarmed nanorods and spherical shape morphologies of CdS powders are obtained in polar solvent like water (H₂O), whereas non-polar polyol solvent like ethylene glycol (EG), prickle and cluster like morphologies of CdS are achieved with different Cd²⁺ precursors such as CdSO₄ and Cd (CH₃COO)₂. The spectroscopy studies of nanosize CdS are examined by photo-luminescence spectra. Band gap and the absorption co-efficient for nano CdS is also evaluated from optical absorption studies.     

Preparation and photo-induced charge transfer of the composites based on branched CdS nanocrystals and PCPDTBT

Rich branched CdS nanocrystals were synthesized by a facile hydrothermal treatment from Cd(NO₃)₂, thiourea and hexamethylenetetramine [(CH₂)₆N₄, HMT], where HMT acted as a capping agent. The morphology, structure and phase composition of CdS nanostructures were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and high-resolution TEM. The composites based on CdS nanocrystals and Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b’]dithiophene-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) have been prepared by mixing of the two components in chloroform. The optical properties of the composites are investigated using ultraviolet–visible (UV–Vis) absorption and photoluminescence (PL) spectroscopies. A significant fluorescence quenching of PCPDTBT in the composites is observed at high CdS nanocrystals/PCPDTBT ratios, indicating that the photo-induced charge transfer occurred due to the energy level offset between the donor PCPDTBT and the acceptor CdS nanocrystals.     

Synthesis of TiO2 nanotubes coupled with CdS nanoparticles and production of hydrogen by photocatalytic water decomposition

The CdS/TiO₂NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO₂NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV-Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO₂NTs and the absorption spectrum of TiO₂NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO₂NTs composite was examined under visible light irradiation (λ > 400 nm) and the quantity of H₂ evolution was ca. 1708 μL/g for 6 h.     

Electrodepositions of CdS,ZnS and Cd1-xZnxS films

Thin films of CdS, ZnS and Cd_1-xZn_xS, (0< x<1) have been electrodeposited from acidic bath using CdSO₄, ZnSO₄ and Na₂S₂O₃ at pH between 2 to 2.5 onto different substrates. The structural and optical properties of these films have been studied. It was found that CdS, ZnS and Cd_1-x Zn_x S film could be electrodeposited from acidic bath. The XRD patterns showed that the films consist of mixed phases of CdS and ZnS with presence of free Cd, Zn and S. The optical properties showed that bandgaps of CdS and ZnS are 2.4 and 3.55 eV respectively. The bandgaps of Cd_1-x Zn_x S films varied between 2.4 to 3.55 eV, depending upon Zn content in the film.     

Synthesis and kinetics research of ZnS nanoparticles prepared by sonochemical process

Abstract

ZnS nanocrystallites have been successfully prepared by a sonochemical process. The reaction kinetics of the process was also investigated. The as prepared ZnS nanocrystallites were characterised by XRD and TEM. Results show that ZnS nanoparticles can be obtained by sonochemical process using ZnCl₂ and thiacetamide as raw materials. It is found that the as prepared ZnS nanoparticles are hexagonal phase with spherical or spherical-like morphologies. The grain size decreases with increasing ultrasonic irradiation power. Reaction kinetics shows that the weight content of ZnS nanoparticles increases linearly with reaction time at different temperatures. The synthesis activation energy of ZnS nanoparticles is calculated to be 27·80 kJ mol^–1.     

One-step and rapid synthesis of composition-tunable and water-soluble ZnCdS quantum dots

ZnCdS quantum dots have been successfully prepared at room temperature in aqueous solution with sodium hexametaphosphate as stabilizer and thioacetamide as the source of S. The photoluminescence (PL) spectra and UV-Vis absorption spectra of the ZnCdS quantum dots were determined on the basis of the initial Cd/Zn mole ratio (Cd/Zn = 8/0, 7/1, 6/2, 5/3, 4/4, 3/5, 2/6, 1/7 and 0/8) and the concentration of thioacetamide. The emission peaks first showed a red shift and then a blue shift with the increasing initial Zn concentration, which provided the evidence of formation of CdS/ZnCdS core/shell and ZnCdS alloyed quantum dots. The ZnCdS quantum dots were compared with CdS (ZnS) quantum dots doped with Zn2+ (Cd2+). The samples have also been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS).     

Controlled synthesis of NiS nanoparticle/CdS nanowire heterostructures via solution route and their optical properties

In the present study, we have successfully synthesized the novel heterostructure of NiS nanoparticle (NP)/CdS nanowire (NW) through solution approach. The first step, CdS nanowires were synthesized by a convenient solvothermal route. Then, NiS nanoparticles were grown on the surface of CdS nanowires in a chemical solution of NiCl₂·6H₂O and anhydrous ethanol at 200 °C. The new catalyst-assisted growth mechanism of the NiS NP/CdS NW heterostructure has been tentatively discussed on the basis of experimental results. A detailed study of the effect of experimental parameters, such as reaction time, reaction temperature, and reaction solvent are also studied. The as-prepared products are characterized by field-emission scan electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their optical properties are measured by Raman spectra and PL spectra. Furthermore, using CdS nanowires and NiS NP/CdS NW heterostructure as examples, our study suggests that this general method can be employed for construction of other semiconductor heterostructures with novel properties.     

TiO2 nanowires sensitized with CdS quantum dots and the surface photovoltage properties

TiO₂ nanowires prepared by thermal annealing of anodized Ti foil were sensitized with CdS quantum dots (QDs) via chemical bath deposition (CBD). Microstructural characterizations by SEM, TEM and XRD show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO₂ nanowires. The amount of CdS QDs can be controlled by varying the CBD cycles. The experiment results demonstrate that the surface photovoltage (SPV) response intensity was significantly enhanced and the surface photovoltage response region was also expanded obviously for the TiO₂ NWs sensitized by CdS QDs.     

Synthesis of wurtzite ZnS nanocrystals at low temperature

Nanocrystallites of wurtzite hexagonal ZnS have been successfully synthesized without using any capping agent by simple chemical precipitation method at a low calcination temperature of 150 °C. It has been found that the size of the synthesized ZnS nanocrystallites decreases as Zn²⁺:S^2? ratio is decreased. The synthesized nanoparticles have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis absorption spectroscopy and M–H characteristics. The XRD patterns have confirmed that the prepared ZnS nanoparticles are of wurtzite hexagonal phase. XRD, SEM and TEM studies have shown the decrease in the particle size with the increase in S^2? source. TEM images have clearly shown that size distribution of the particles lie in the range of 5–30 nm. The optical absorption bandgap of the synthesized nanocrystals has been found to be in the range of 3.69–3.74 eV. Magnetization study has shown the ‘diamagnetic’ behavior of synthesized ZnS nanocrystallites with a weak ferromagnetic behavior in the low field regime. The observed weak ferromagnetism has been understood due to the presence of defects in the synthesized ZnS nanoparticles.     

Photocatalytic hydrogen production over Na2Ti2O4(OH)2 nanotube sensitized by CdS nanoparticles

Na₂Ti₂O₄(OH)₂ nanotubes were obtained by hydrothermal reaction of TiO₂ with concentrated NaOH solution. CdS nanoparticles were then decorated on Na₂Ti₂O₄(OH)₂ nanotubes through partial ion-exchange method. The composite photocatalysts were characterized by X-ray diffraction (XRD), ultraviolet-visible spectra (UV-vis), transmission electron microscope (TEM), etc. The results showed that CdS nanoparticles of 5-6 nm were anchored on the surface of the Na₂Ti₂O₄(OH)₂ nanotubes. Under irradiation of visible light (λ ≥ 430 nm), the prepared CdS/Na₂Ti₂O₄(OH)₂ showed high photoactivity for hydrogen production.     

Rapid fabrication and optical properties of zinc sulfide nanocrystallines in a heterogeneous system

ZnS nanoparticles about 3 nm in size were prepared by a simple, rapid and reliable route under microwave irradiation in a heterogeneous system, using ZnAc₂·2H₂O (AcCH₃COO) and Na₂S·9H₂O as the starting materials, ethylene glycol (EG) as the medium. The product was characterized with X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and ED, respectively. The optical properties of ZnS nanoparticles were studied.     

Controllable synthesis of ZnS holely microspheres in solution containing ethylenediamine and CS<Subscript>2</Subscript>

ZnS holey microspheres (HMSs) were prepared by reacting ZnSO₄ with sulfide source from CS₂ and ethylenediamine at 50 °C, then aging at room temperature. The synthesized HMSs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–visible absorption measurement. The results showed that the holes were formed by gas of H₂S, and the small ZnS HMSs were formed by particles reaggregating with the aid of ethylenediamine. In addition, the size- and shape-controlled synthesis of ZnS HMSs was achieved by varying the process parameters, such as the aging time of the final solution, the molar ratio of CS₂ and ethylenediamine, and so on. A gas obtruding mechanism was proposed.     

Solvothermal synthesis of uniform hexagonal-phase ZnS nanorods using a single-source molecular precursor

Pure and uniform hexagonal-phase ZnS nanorods with quantum confinement effect were synthesized by solvothermal decomposition of an air-stable, easily obtained single-source molecular precursor (zinc diethyldithiocarbamate, Zn-(DDTC)₂) in hydrazine hydrate aqueous solutions at 150–200 °C, and characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and UV–vis absorption spectra. The possible formation mechanism of one-dimensional ZnS nanostructure in the present system was also briefly discussed.     

Synthesis and characterization of CdS doped TiO2 nanocrystalline powder: A spectroscopic study

This report aimed to study the effect of CdS doping in TiO₂ on the phase transformation of TiO₂ from anatase to rutile using X-ray diffraction (XRD) and Raman spectroscopy. CdS-doped TiO₂ nanocomposites have been prepared and characterized using Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). We have observed that contrary to bare TiO₂, phase transformation of TiO₂ from anatase to rutile is hindered when doped with CdS at high temperature. Raman spectroscopy is found to be more sensitive for detection of the surface of TiO₂ as compared to XRD.