Bio-surfactant mediated synthesis of Au/g-C3N4 plasmonic hybrid nanocomposite for enhanced photocatalytic reduction of mono-nitrophenols

Abstract

A bio-surfactant assisted synthesis route has demonstrated in room temperature for decoration of gold nanoparticles (AuNPs) on g-C3N4 using Averrhoa carambola leaf extract towards mono-nitrophenol reduction under visible light irradiation. Biomolecules of the leaf extract and optimised reaction condition played a vital role on tuning the morphology and optoelectronic properties of AuNPs. The size of AuNPs were found to be 15 ± 3 nm on 2D g-C3N4 sheets by TEM and STEM-HAADF analysis. Among the designed plasmonic hybrid photocatalysts 3-wt% loaded AuNPs on g-C3N4 showed 99.01% of 4-nitrophenol, 97.70% of 3-nitrophenol and 98.50% of 2-nitrophenol photoreduction. The photocatalytic efficiency of Au/g-C3N4 was investigated under several parameters such as pH, initial nitrophenol concentration, and in presence of external inorganic anions. The mechanism of photoreduction of nitrophenol to aminophenol by Au/g-C3N4 was proposed based on the intermediate obtained from GCMS analysis. The observed higher catalytic activity of plasmonic hybrid photcatalysts is due to the synergic chemistry between the conduction band of g‐C3N4 and AuNP plasmonic band, which is well supported by PL, EIS, and transient photocurrent analysis. Kinetic rate constant for 3Au/g-C3N4 was found to be 0.43 min−1 at pH 3. Moreover, the rate of reaction significantly increased in presence of Cl−. ICP-OES analysis of as synthesised 3Au/g-C3N4 plasmonic photocatalyst shows there was no gold leaching even after ten cycles confirming the stability and reusability of the catalyst.