Visible light emission and enhanced electrocatalytic activity of pure ZnS nanoparticles synthesized via thermal decomposition route

ZnS nanoparticles have been synthesized using facile thermal decomposition route by varying the concentration of sulphur source. Increase in sulphur concentration increases the crystallinity of the synthesized samples, confirmed by calculation of various structural parameters or lattice defects using XRD data and FESEM images. The crystal structure and crystallinity have a great influence on charge separation and the migration of generated charge carriers. Higher the crystallinity, smaller the number of defects. The defects work as traps and recombination centres between generated electrons and holes, which result in deterioration of device performance. A material with better crystalline structure provides longer diffusion length and lifetime of charge carriers. With increase in the sulphur concentration, various other characteristics like optical and electro catalytic properties have also been improved. It is seen that an increase in sulphur concentration increases the conductivity of the synthesized samples as energy band gap has been reduced. The band gap for least crystalline T1 is higher than T2 and T3. This variation in the band gap is in complete agreement with the quantum confinement effect comparing with their crystallite size. Photoluminescence study reveals that prepared samples show emission in visible range i.e., violet, blue, green and orange without adding any dopant. Electrocatalytic performance has been conducted using EIS and CV studies which suggest that increase in sulphur concentration increases the capacitive behaviour. Charge transfer resistance value of highly crystalline sample T3 is found to be 16.26Ω which is smaller than T1 and T2. The charge transfer resistance of sample T3 could be credited to the enhanced conductivity and crystallinity due to the presence of highest concentration of sulphur in T3 when compared to T1 and T2. (author)