Phytosynthesis of plasmonic Au@g-C3N4 nanophotocatalyst for potential degradation of methylene blue in wastewater

Abstract

Industrial dyes pose substantial environmental risks because of their hazardous chemical nature. We report a single-step phytosynthesis route for the fabrication of plasmonic Au@g-C3N4 nanocomposite utilizing Averrhoa Carambola L. bio-extract at room temperature. A. Carambola L acts as a reducing, capping, and stabilizing agent for the synthesis and well distribution of gold nanoparticles (Au NPs) on the 2D surface of g-C3N4 sheets. The average particle size of Au NPs was observed to be 27 ± 1 nm, confirmed from HR-TEM and HADDF-STEM analysis. Other characterization techniques such as XRD, FTIR, XPS, UV-DRS, PL, TGA, and BET surface area were performed to investigate the insight structural and physicochemical properties of Au@g-C3N4 nanocomposite. The 3Au@g-C3N4 nanocomposite exhibited an impressive Methylene Blue (MB) degradation efficiency of 97.5 % under visible light illumination for 1 h. The degradation follows a pseudo-first-order kinetics with a rate constant of 0.0375 min⁻¹. The enhanced photocatalytic activity is attributed to the surface plasmon resonance (SPR) properties of Au NPs and the electron-acceptor properties of g-C3N4.The as synthesised 3Au@g-C3N4 nanocomposite exhibited 1.6 fold higher photocurrent density than neat g-C3N4 which confirms high charge (e-/h+) separation. Additionally, the 3Au@g-C3N4 nanocomposite demonstrated excellent reusability, maintaining high activity over five cycles towards MB degradation under visible light illumination.