Enhanced photocatalytic degradation of Reactive Red 120 dye under solar light using BiPO4@g-C3N4 nanocomposite photocatalyst

Azo dyes such as Reactive Red 120 raise great concerns about their increased harmfulness. Photocatalytic degradation is considered to be one of the most efficient techniques for Reactive Red 120 degradation. Herein, a highly solar active graphitic carbon nitride-assisted bismuth phosphate nanocomposite (BiPO4@g-C3N4) was synthesized by the thermal decomposition of melamine followed by the co-precipitation method. Various analytical techniques were utilized to characterize the prepared BiPO4, g-C3N4, and BiPO4@g-C3N4 nanocomposites. Scanning electron microscopy (SEM) shows the nanorods and particle morphology of the bare BiPO4 and g-C3N4 respectively. Furthermore, the optical band gap energies of the BiPO4, g-C3N4, and BiPO4@g-C3N4 nanocomposite have been calculated to be 4.20, 2.66, and 2.68 eV respectively. Under sunlight, the BiPO4@g-C3N4 nanocomposite showed higher photocatalytic activity towards the degradation of RR120. The BiPO4@g-C3N4 nanocomposite efficiently degrades the RR120 under sunlight with a higher first-order reaction rate constant of 0.0145 min(-1). This is seven times higher than that of bare BiPO4 (0.0019 min(-1)) nanorods and four times greater than g-C3N4 (0.0036 min(-1)). The photocatalytic efficiency was found to be maximum at pH 4 and decreased as the pH of the solution increased. Even after five recycle runs, the catalyst performance of the RR120 dye has decreased by less than 5%, indicating the high stability of the BiPO4@g-C3N4 nanocomposite. Furthermore, the radical trapping experiment demonstrates that the active species in the dye degradation process are holes and hydroxide radicals. The photocatalytic mechanism was proposed for the BiPO4@g-C3N4 nanocomposite and further validated by the electrochemical impedance spectroscopy analysis.