Sunlight-active hierarchical Ag@insulator@ZnO core-shell array based on natural diatoms for environmental remediation

A nature inspired plasmonic core-shell architecture was proposed by incorporating a natural siliceous insulator shell (Navicula salinicola frustules) in Ag/diatomite/ZnO hierarchical nanostructures to overcome the recombination of energetic charge carriers (e−/h+), corrosion of bare metal, and to facilitate the composite separation after reaction. The photocatalytic performance of the as-prepared composites, monitored by decomposition of methylene blue (MB), was investigated under both UV and simulated sunlight irradiation. Ag/diatomite/ZnO exhibited efficient photocatalytic performance (near 100% degradation and 95% mineralization) under simulated sunlight irradiation with apparent rate constant of 0.0246 min−1, which was found to follow pseudo-first order kinetics. The enhanced photocatalysis action of metal/insulator/semiconductor as compared to metal/semiconductor and the semiconductor alone could be ascribed to the synergistic effects of the photonic structure of regular frustules, improved sunlight harvesting efficiency, suppressed back electron transfer, and prohibited oxidization of Ag. While the as-synthesized composite was easy to separate from the reaction, however, it was in the throes of losing the photocatalytic activity after three rounds of reuse. A possible mechanism of photocatalytic degradation of MB induced by Ag/diatomite/ZnO under sunlight irradiation was proposed based on dye degradation measurements and reactive species trapping experiments. While the reusability of as-prepared composite will doubtless be much scrutinized, our study may provide a new insight into the design and fabrication of plasmonic-based nanomaterials for use in industry applications under solar light illumination.