Influences of anionic and cationic dopants on the morphology and optical properties of PbS nanostructures

Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy （SEM） results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction （XRD） patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy （XPS）. Raman spectra of the synthesized samples con- firm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence （PL） and UV-Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared （IR） region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanos- tructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.

Influence of growth conditions on the electrochemical synthesis of SnS thin films and their optical properties

Tin sulfide （SnS） thin films were prepared by electrodeposition onto fluorine-doped tin oxide （FTO） glass substrates using an aqueous solution containing SnCl2 and Na2S2O3 at various deposition potentials （L） and bath concentrations. The pH value and temperature of the solution were kept constant. The deposited films were characterized using X-ray diffraction （XRD）, field-emission scanning electron microscopy （FESEM）, photoluminescence （PL）, and ultraviolet-visible （UV-Vis） spectroscopy. The FESEM images demonstrated that changes in the deposition potential （E） and solution concentration led to marked changes in the morphology of the deposited SnS films. Energy-dispersive X-ray analysis （EDXA） results showed that the SrdS atomic ratio strongly depended on both the solution concentration and the deposition potential. To obtain an SrdS atomic ratio approximately equal to l, the optimal Sn2＋/S2O2- 3 molar ratio and E parameter were 1/8 and -1.0 V, respectively. The XRD patterns showed that the synthesized SnS was obviously polycrystalline, with an orthorhombic structure. The effects of the variations of bath concentration and deposition potential on the band-gap energy （Eg） were studied using PL and UV-Vis experiments. The PL spectra of all the SnS films contained two peaks in the visible region and one peak in the infrared （IR） region. The UV-Vis spectra showed that the optical band-gap energy varies from 1.21 to 1.44 eV.

Excellent photocatalytic performance under visible-light irradiation of ZnS/rGO nanocomposites synthesized by a green method

ZnS/graphene nanocomposites with different graphene concentrations （5, 10 and 15 wt.%） were synthesized using L-cysteine as surfactant and graphene oxide （GO） powders as graphene source. Excellent performance for nanocomposites to remove methylene blue （MB） dye and hexavalent chromium （Cr（VI）） under visible-light illumina- tion was revealed. TEM images showed that ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in the ZnS diameter size. XRD patterns, XPS and FTIR spectroscopy results indicated that GO sheets changed into reduced graphene oxide （rGO） during the synthesis process. Photocurrent measurements under a visible- light source indicated a good chemical reaction between ZnS NPs and rGO sheets.