LAUSR

Abstract In this work, colloidal solutions of gold nanoparticles (AuNPs) with an average diameter of 16 nm and gold nanorods (AuNRs) with an average aspect ratio of 6.8 were synthesized. These gold nanostructures were decorated on nanosheets assembled 3D ZnO microflower (ZnO-MF) synthesized via facile and cost-effective co-precipitation method. Plasmonic gold nanostructures act as optical concentrators and a reservoir of electrons under LSPR excitation. They extend the light harvesting capability of ZnO from UV-VIS-NIR region, promotes interfacial charge transfer process and helps in electron-hole pair separation. We report the occurrence of FRET (Fluorescence Resonance Energy Transfer) between defect rich ZnO-MF and gold nanostructures under UV light excitation as evident from micro-PL spectra. This triggers surface plasmon resonance in gold nanostructures which causes direct transfer of hot electrons to ZnO-MF. Time-resolved Photoluminescence of the hybrid samples monitored at near band edge of ZnO shows elongated decay kinetics as compared to bare samples which could be attributed to direct transfer of hot electrons from gold to conduction band of ZnO-MF after LSPR excitation. Thereafter, the photocatalytic activity of the hybrids is evaluated by degradation of four different dyes under sunlight. ZnO-MF/AuNPs exhibited superior photocatalytic activity compared to ZnO-MF/AuNRs. This could be attributed to numerous reasons like better energy transfer efficiency, effective near-field enhancement, small size of AuNPs and enhanced electron-hole pair separation which makes ZnO-MF/AuNPs a promising photocatalyst.