Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production.

We have demonstrated the controlled synthesis of hierarchical nanostructured ZnIn2S4 using a facile template free hydrothermal/solvothermal method. The effect of solvents on the morphology and microstructure of ZnIn2S4 has been studied by using water, methanol and ethylene glycol as a solvents. The hierarchical nanostructure, i.e., rose-like morphology composed of very thin (5­6 nm) nanoplates of length ˜1 µm which was obtained in aqueous mediated ZnIn2S4. The porous structure (distorted flowers) and agglomerated nanoparticles were obtained using methanol-and ethylene glycol-mediated ZnIn2S4. Considering the band gap in the visible region, ZnIn2S4 is used as a solar light driven photocatalyst. An ecofriendly photocatalytic process for the conversion of poisonous H2S into H2 which is a green unconventional energy source has been demonstrated. The nanostructured ZnIn2S4 is employed as a photocatalyst for hydrogen production from H2S via a solar light-driven eco-friendly approach. The stable photocatalytic activity of hydrogen evolution, i.e., 3964 µmol ⁻¹ was obtained using 0.5 gm of such hierarchical nanostructured ZnIn2S4 under visible light irradiation. The unique hierarchical nanostructured ZnIn2S4 ternary semiconductor having hexagonal layer is expected to have potential applications in solar cells, LEDs, charge storage, electrochemical recording, thermoelectricity, other prospective electronic and optical devices.

Hierarchical 3D ZnIn2S4/graphene nano-heterostructures: their in situ fabrication with dual functionality in solar hydrogen production and as anodes for lithium ion batteries.

Hierarchical 3D ZnIn2S4/graphene (ZnIn2S4/Gr) nano-heterostructures were successfully synthesized using an in-situ hydrothermal method. The dual functionality of these nano-heterostructures i.e. for solar hydrogen production and lithium ion batteries has been demonstrated for the first time. The ZnIn2S4/Gr nano-heterostructures were optimized by varying the concentrations of graphene for utmost hydrogen production. An inspection of the structure shows the existence of layered hexagonal ZnIn2S4 wrapped in graphene. The reduction of graphene oxide (GO) to graphene was confirmed by Raman and XPS analyses. The morphological analysis demonstrated that ultrathin ZnIn2S4 nanopetals are dispersed on graphene sheets. The optical study reveals the extended absorption edge to the visible region due to the presence of graphene and hence is used as a photocatalyst to transform H2S into eco-friendly hydrogen using solar light. The ZnIn2S4/Gr nano-heterostructure that is comprised of graphene and ZnIn2S4 in a weight ratio of 1 : 99 exhibits enhanced photocatalytically stable hydrogen production i.e. ∼6365 µmole h(-1) under visible light irradiation using just 0.2 g of nano-heterostructure, which is much higher as compared to bare hierarchical 3D ZnIn2S4. The heightened photocatalytic activity is attributed to the enhanced charge carrier separation due to graphene which acts as an excellent electron collector and transporter. Furthermore, the usage of nano-heterostructures and pristine ZnIn2S4 as anodes in lithium ion batteries confers the charge capacities of 590 and 320 mA h g(-1) after 220 cycles as compared to their initial reversible capacities of 645 and 523 mA h g(-1), respectively. These nano-heterostructures show high reversible capacity, excellent cycling stability, and high-rate capability indicating their potential as promising anode materials for LIBs. The excellent performance is due to the nanostructuring of ZnIn2S4 and the presence of a graphene layer, which works as a channel for the supply of electrons during the charge-discharge process. More significantly, their dual functionality in energy generation and storage is quite unique and commendable.

In-situ preparation of N-TiO2/graphene nanocomposite and its enhanced photocatalytic hydrogen production by H2S splitting under solar light.

Highly monodispersed nitrogen doped TiO2 nanoparticles were successfully deposited on graphene (N-TiO2/Gr) by a facile in-situ wet chemical method for the first time. N-TiO2/Gr has been further used for photocatalytic hydrogen production using a naturally occurring abundant source of energy i.e. solar light. The N-TiO2/Gr nanocomposite composition was optimized by varying the concentrations of dopant nitrogen and graphene (using various concentrations of graphene) for utmost hydrogen production. The structural, optical and morphological aspects of nanocomposites were studied using XRD, UV-DRS, Raman, XPS, FESEM, and TEM. The structural study of the nanocomposite shows existence of anatase N-TiO2. Further, the details of the components present in the composition were confirmed with Raman and XPS. The morphological study shows that very tiny, 7-10 nm sized, N-TiO2 nanoparticles are deposited on the graphene sheet. The optical study reveals a drastic change in absorption edge and consequent total absorption due to nitrogen doping and presence of graphene. Considering the extended absorption edge to the visible region, these nanocomposites were further used as a photocatalyst to transform hazardous H2S waste into eco-friendly hydrogen using solar light. The N-TiO2/Gr nanocomposite with 2% graphene exhibits enhanced photocatalytic stable hydrogen production i.e. ∼5941 µmol h(-1) under solar light irradiation using just 0.2 gm nanocomposite, which is much higher as compared to P25, undoped TiO2 and TiO2/Gr nanocomposite. The enhancement in the photocatalytic activity is attributed to 'N' doping as well as high specific surface area and charge carrier ability of graphene. The recycling of the photocatalyst shows a good stability of the nanocomposites. This work may provide new insights to design other semiconductor deposited graphene novel nanocomposites as a visible light active photocatalyst.