Controlled synthesis of heterostructured Ag@AgI/ZnS microspheres with enhanced photocatalytic activity and selective separation of methylene blue from mixture dyes

Abstract

Novel heterostructured Ag@AgIgnS microspheres were fabricated through a soft chemical route using polyvinylpyrrolidone (PVP). Their formation was confirmed by SEM, TEM, XRD, XPS, and FTIR analyses, which revealed that the Ag@AgI/ZnS nanocomposites comprised Ag, AgI, and ZnS nanoparticles. Luminescence quenching in the Ag@AgI/ZnS nanocomposites indicated that the hetero-junction between Ag@Agl and ZnS effectively accelerated charge separation and transferred electrons from the Agl to Ag and ZnS nanostructures. The photocatalytic activity was evaluated via the decomposition of organic dyes and phenol oxidation under simulated sunlight irradiation. All the Ag@Agl/ZnS heterostructures exhibited better photocatalytic performance than the pure AgI and ZnS nanostructures. Ag@Agl-ZnS (5 wt%) possesses the optimal photocatalytic degradation efficiency, and colorless phenol oxidation performance. More specifically, in the presence of the nanocomposite, 95% degradation rate was achieved within 80 min of sunlight irradiation, while AgI, only reached 64.12%. The enhanced photocatalytic activity is associated with effective transfer and separation of photogenerated electron-hole pairs at the interface of the Ag@AgI/ZnS nanocomposite because of their matching band positions. The nanocomposites exhibit good photocatalytic stability with almost no loss of photocatalytic activity after five recycles. These nanostructures show the best catalytic activity for selective separation of methylene blue (MB) dye from mixed organic dyes. Photocatalytic experiments with MB-RhB as the target pollutants, within 70 min of irradiation time 96.44% of MB and 64.68% of RhB were degraded, and the rate constants were 0.044 and 0.013 min-1 for RhB and MB, respectively. MB-MO as the target pollutant within 80 min of irradiation time, 95.29% of the MB and 41.37% of the RhB were degraded. The rate constants were 0.031 and 0.005 min-1 for MB and MO, respectively. This work will promote further interest in the fabrication of various heterostructured nanocomposites and their applications as sunlight-driven photocatalysts for purifying polluted water resources. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.