Solid state low temperature synthesis approach for ZnO-ZnS nanoheterostructure with functionality as a photocatalyst for H2 production and for DSSC

Abstract

Herein, we demonstrate a facile, template free, scalable, solid-solid, single step synthesis approach to produce ZnO/ZnS nanoheterostructure. Commercially available ZnO and thiourea have been used as precursors. Interestingly, it is observed that ZnO particle is covered with ZnS and the ZnS shell thickness can be varied depending on the sulfidation time. The crystal structures, morphology of samples are verified by XRD, FETEM and EDX. The XRD results show the mixed phases of hexagonal ZnO and ZnS. The broad peak of ZnS clearly reveals the nanocrystalline nature and also increase in intensity of peak with respect to sulfidation time. The optical spectra of the samples exhibits two band absorption edges and blue shift in the absorption edge depending on the ZnS thickness deposited. Particle size of the ZnS (5–3 nm) coated on the ZnO by varying the sulfidation time influences the performance of the DSSC and photocatalytic H2 evolution from water has been investigated, systematically. The DSSC performance of ZnO/ZnS nanoheterostructure shows maximum efficiency of 3.30% with increment in Jsc (9.04 mA/cm2). The performance is much better than pristine ZnO and earlier report of ZnO-ZnS nanostructure. This good performance is due to excellent light absorbing capability of the ZnO/ZnS nano heterostructure by providing ZnO core by providing easy electron transfer at the interface and the ZnS shell facilitate to reduce the recombination of diffuse electrons with either the dye or the electrolyte. The H2 evolution rate reported herewith is 3209 and 1685 μmol h−1g−1 under UV and Natural sunlight, respectively which is significantly higher than pristine ZnS and ZnO. The H2 evolution rate increases with decrease in particle size of ZnS which is quite ovibius because lowering particle size exhibits increase in surface area. The fabrication of ZnO/ZnS nanoheterostructure is the simple and cost effective, which can open new avenues strategy for large scale applications of the novel materials in the energy storage and photovoltaic devices.