J. Archana

Morphological evolution of monodispersed ZnO nanorods to 3 dimensional hierarchical flowers by hydrothermal growth

The morphological transformation of one dimensional ZnO nanorods to three dimensional hierarchical nanoflowers was observed by hydrothermal growth. The growth period was found to influence the morphology change from rod to flower-like morphology. Hierarchical flower-like nanostructures with an average diameter of 8 μm were obtained for a growth period of 48 h.

Enhanced visible light induced photocatalytic activity on the degradation of organic pollutants by SnO nanoparticle decorated hierarchical ZnO nanostructures

One (1D) and two-dimensional (2D) nanostructures of zinc oxide and tin oxide (ZnO/SnO) nanocomposites were synthesized by a hydrothermal method using ethylenediamine (EDA) as a capping ligand. The effect of Sn concentration on the morphology of the nanocomposites has been investigated. X-ray diffraction analysis indicated good crystallinity of samples with the presence of both ZnO and SnO phases. The morphological analysis revealed the morphological transformation from ZnO nanorods to ZnO/SnO nanosheets by adding Sn. X-ray photoelectron spectra analyses showed significant peak shift in the electronic state of Zn at the higher concentration of Sn. Elemental mapping results clearly evidenced that both ZnO and SnO moieties were uniformly distributed in the nanosheets. Photocatalytic degradation of methylene blue using as-prepared ZnO/SnO nanocomposites was nine times faster than that of pure ZnO under visible light irradiation. It could be attributed to the formation of a hetero-junction between ZnO and SnO. Our experimental results revealed that photogenerated superoxide (O2−˙) radicals were the main reactive species for the degradation of MB. The maximum degradation efficiency was observed for the sample with 1 wt% of tin chloride, the MB related absorption peak completely disappeared after 6 min of irradiation. ZnO/SnO composites extended the light absorption spectra of ZnO to a visible light region and enhanced the visible light photocatalytic activity.

Highly efficient visible-light photocatalytic activity of MoS2–TiO2 mixtures hybrid photocatalyst and functional properties

2-D-layered molybdenum disulfide (MoS2) and MoS2/TiO2 nanocomposite were synthesized by a hydrothermal method. The effects of the concentration of TiO2 on the formation of MoS2/TiO2 composites and functional properties were investigated. X-ray diffraction patterns revealed the formation of hexagonal and anatase structure of MoS2 and TiO2, respectively. Core-level X-ray photoelectron spectroscopy confirmed the presence of Mo and Ti interaction by a significant peak shift. Morphological analysis revealed the formation of TiO2 on the surface of the MoS2 nanosheets. The photocatalytic degradation of methylene blue (MB) in an aqueous suspension was employed to evaluate the visible-light activity of the as-prepared composite photocatalyst. The MB absorption peaks completely disappeared after 12 min with 99.33% of degradation under visible-light irradiation at the TiO2 concentration of 0.005 M. It was found that hydroxyl radical (˙OH) played an important role in the degradation of MB under visible-light irradiation. The possible charge-transfer mechanism has been proposed in this study.

Highly efficient dye-sensitized solar cell performance from template derived high surface area mesoporous TiO2 nanospheres

High surface area mesoporous anatase TiO2 spheres are synthesized using ethylene glycol as a template by a solvothermal method. Electron microscopy studies revealed the formation of smooth surfaced mesoporous spheres with uniform size. A high surface area of 221.52 m2 g−1 is obtained for the titanium tetraisopropoxide concentration of 0.5 mL. X-Ray diffraction and Raman analyses revealed the formation of anatase phase TiO2. Uniform deposition of a mesoporous film for a photoanode was achieved by an optimized spray deposition method. The effects of the ruthenium dye-sensitizer N719 and indoline dye-sensitizer D205 on the dye sensitized solar cell performance are investigated. Maximum efficiencies of 8.96 and 9.02% are achieved using the sensitizers N719 and D205, respectively; from the mesoporous anatase TiO2 sphere coated DSSC. IPCE analyses revealed that the mesoporous spheres efficiently collected the incident photons and achieved a conversion efficiency over 80% by internal reflections and a scattering process.

ZnS quantum dots impregnated-mesoporous TiO2 nanospheres for enhanced visible light induced photocatalytic application

ZnS quantum dots were impregnated on the surface of TiO2 mesospheres by a soft template-assisted solvothermal approach. XRD and elemental analysis confirmed the presence of ZnS in the TiO2 nanostructures. Morphological analysis showed that the ZnS quantum dots were firmly immobilized on the TiO2 mesospheres, which improved electron and hole pair separation at the TiO2/ZnS interface. The photocatalytic activity of the mesoporous nanostructures was assessed by photodegradation of methylene blue (MB) as a model pollutant under visible light irradiation. Impregnation with ZnS quantum dots enhanced reaction activity remarkably compared with mesoporous TiO2. The maximum degradation efficiency was observed for 0.025 M of ZnS impregnated on TiO2. The MB-related absorption peak completely disappeared after 32 min of irradiation. Photo-charge scavenger analysis indicated that hydroxyl radicals played a pivotal role in the photodegradation mechanism. The mesoporous photocatalyst was stable and can be used repeatedly under visible irradiation.

Synergetic effect of CuS@ZnS nanostructures on photocatalytic degradation of organic pollutant under visible light irradiation

Ultrafast visible light active CuS/ZnS nanostructured photocatalysts were synthesized by a hydrothermal method. The effect of the CuS concentration on the morphological, structural and optical properties of ZnS nanostructures were investigated. X-ray diffraction analysis indicated the formation of CuS/ZnS phases with good crystallinity. The presence of ZnS on CuS was confirmed by X-ray photoelectron spectroscopy, elemental mapping, scanning electron microscopy and high resolution transmission electron microscopy analyses. CuS/ZnS nanocomposites efficiently decomposed methylene blue (MB) upon irradiation with visible light. The degradation time was 3 times faster than that of bare ZnS and CuS. The scavenger analysis results revealed that photogenerated superoxide (O2−˙) radicals were the main reactive species for the degradation of MB. The maximum degradation efficiency of 95.51% was observed within 5 min for samples of 0.050 M CuS/ZnS composites. The obtained results suggested that the enhanced photocatalytic activity was due to the formation of CuS/ZnS heterojunctions which led to the efficient separation of the photoinduced carriers.

Controlled exfoliation of monodispersed MoS2 layered nanostructures by a ligand-assisted hydrothermal approach for the realization of ultrafast degradation of an organic pollutant

Molybdenum disulfide (MoS2) layered nanosheets were synthesized by the hydrothermal method. Citric acid was used as an organic ligand to obtain the monodispersed layered MoS2 nanostructures. The effect of citric acid on the formation and functional properties of the layered MoS2 nanostructures was investigated. The X-ray diffraction patterns revealed the formation of a hexagonal crystal structure of MoS2. Significant peak shift was observed for the interaction of citric acid and Mo in the core level spectra of X-ray photoelectron spectroscopy. Citric acid-free hydrothermal growth resulted in the formation of micron-sized MoS2 nanospheres, whereas citric acid-assisted hydrothermal growth resulted in the formation of well dispersed layers of MoS2, confirmed by morphological analysis. However, the highest concentration of citric acid resulted in the formation of aggregated layers. The obtained MoS2 nanostructures were used as photocatalysts to decompose methylene blue (MB) as a model pollutant. The obtained results showed that the MoS2 layered nanosheets could effectively decompose the organic pollutant. The MB absorption peaks completely disappeared after 24 min of irradiation when using the nanosheets synthesized with a citric acid concentration of 0.04 M. The effect of pH on the MoS2 nanosheets was studied, and 96% MB degradation was observed at pH 12 after 2 min of visible-light irradiation.

Ultrathin layered MoS2 nanosheets with rich active sites for enhanced visible light photocatalytic activity

Edge-rich active sites of ultrathin layered molybdenum disulphide (MoS2) nanosheets were synthesized by a hydrothermal method. The effect of pH on the formation of MoS2 nanosheets and their photocatalytic response have been investigated. Structural and elemental analysis confirm the presence of S–Mo–S in the composition. Morphological analysis confirms the presence of ultrathin layered nanosheets with a sheet thickness of 10–28 nm at pH 1. The interplanar spacing of MoS2 layers is in good agreement with the X-ray diffraction and high-resolution transmission electron microscopy results. A comparative study of the photocatalytic performance for the degradation of methylene blue (MB) and rhodamine B (RhB) by ultrathin layered MoS2 under visible light irradiation was performed. The photocatalytic activity of the edge-rich ultrathin layered nanosheets showed a fast response time of 36 min with the degradation rate of 95.3% of MB and 41.1% of RhB. The photocatalytic degradation of MB was superior to that of RhB because of the excellent adsorption of MB than that of RhB. Photogenerated superoxide radicals were the key active species for the decomposition of organic compounds present in water, as evidenced by scavenger studies.

ZnO:SnO nanorods and nanosheets and their enhanced photocatalytic activity under visible light irradiation

ZnO-SnO nanocomposites were synthesized by a simple hydrothermal method. It was found that Sn concentration acted as a crucial factor in determining the morphology of ZnO-SnO nanostructures, in the presence of ethylenediamine (EDA) as a stabilizing agent. XRD analysis confirmed the formation of ZnO and SnO with good crystallinity. The morphological analysis revealed tin oxide (SnO) nanoparticles coated on the surface of ZnO nanorods and nanosheets. The photocatalytic activity of synthesized samples were evaluated by methylene blue (MB) as a model pollutant under visible light irradiation. Photocatalysis studies revealed that, ZnO-SnO nanocomposites show the enhanced photocatalytic activity compared to ZnO, which could be attributed to the formation of hetero-junction between ZnO and SnO of MB degradation. Sn concentration can extend the light absorption spectra of ZnO to visible light region and enhance the visible light photocatalytic activity. This research could provide new insights to the development of excellent photocatalyst with efficient performance for pollution control.