Electrochemically active biofilm-assisted biogenic synthesis of an Ag-decorated ZnO@C core–shell ternary plasmonic photocatalyst with enhanced visible-photocatalytic activity

Abstract

Colonies of electrochemically active microorganisms called electroactive biofilms (EABs) have potential applications in bioenergy and chemical production. In the present study, an EAB was used as a reducing tool to synthesize Ag-decorated ZnO@C core–shell (Ag–ZnO@C) ternary plasmonic photocatalysts. A simple thermal decomposition route was followed to synthesize ZnO@C nanoparticles using a zinc aniline nitrate complex. The simultaneous adsorption of Ag⁺ in the carbon shell of the ZnO@C particles during reduction using an EAB allowed the direct contact among Ag nanoparticles, the ZnO core, and the carbon shell. Therefore, the synthesized Ag–ZnO@C ternary photocatalysts showed a stronger interconnection among all the components, which allowed the easy transfer of photogenerated charges and provided enhanced charge carrier separation. Optical characterization showed that the enhanced absorption of visible light along with a decrease in the band gap and a red shift in the valence band maximum occurred due to the decoration of Ag-nanoparticles on ZnO@C. Ag–ZnO@C exhibited higher photocatalytic activity for the degradation of rhodamine blue and 4-nitrophenol under visible light irradiation than ZnO@C and bare ZnO without any significant loss after five successive cycles. Finally, a possible photocatalytic mechanism for charge transfer was proposed to explain the enhanced photocatalytic performance of the Ag–ZnO@C ternary photocatalyst. This study provides insights into the ternary photocatalytic system with a core–shell material and offers a biogenic route for the facile fabrication of Ag–ZnO@C photocatalysts.