Improved photoinduced charge carrier separation through the built-in electric field in a rationally designed Ag-ZnMnO/exfoliated g-CN, a plasmonic p-n junction for solar-driven reduction of dissolved Cr(VI).

Sensitization of wide bandgap semiconductors by coupling with a low-band-gap semiconductor to improve photoinduced charge carrier separation by the built-in electric field is one of the attractive approaches to develop an efficient photocatalyst. Here we present the development of Ag-ZnMnO/exfoliated g-CN (Ag-ZMO/ECN), a novel photocatalyst designed to remove an inorganic pollutant Cr(VI) under direct solar light irradiation. The enhanced performance of Ag-ZMO/ECN is attributed to efficient charge separation, facilitated by the formation of a p-n junction at the interface of narrow-bandgap p-type ZMO and n-type ECN, and the localized surface plasmon resonance (LSPR) effect of the deposited Ag nanoparticles. The Mott-Schottky plot of the composite revealed an inverted "V" shape, which is characteristic of a p-n junction, while UV-visible diffuse reflectance spectroscopy (UV-DRS) confirmed the LSPR effect, showing broad visible range absorption with Ag plasmon-related peaks between 400-500 nm. Photoluminescence (PL) studies and electrochemical impedance spectroscopy (EIS) results further validated that Ag-ZMO/ECN achieved the most effective charge separation and transport compared to pure ZMO, ECN, and ZMO/ECN. The pseudo-first-order rate constant for photocatalytic Cr(VI) reduction increased significantly from 0.01445 min⁻ when treated individually to 0.03779 min⁻ in the presence of methylene blue (MB) dye. This indicates a pronounced synergistic effect between the reduction of Cr(VI) and the oxidation of MB in the combined system. The enhanced photocatalytic performance of Ag-ZMO/ECN in this dual system compared to the individual system highlights its potential as an efficient photocatalyst for the simultaneous remediation of both inorganic and organic pollutants.