Efficient Degradation of 2,4-D by TIO2-rGO-PANI-PPy Nanocomposite Photocatalyst under Visible Light Irradiation: Mechanisms and Degradation Pathways

Herein, an effective photocatalyst involving titanium dioxide (TiO2) on reduced graphene oxide (rGO), coated with conducting polymers, polyaniline (PANI), and polypyrrole (PPy) has been synthesized to investigate the adsorption kinetics and photodegradation reaction employing 2,4-dichlorophenoxyacetic acid (2,4-D) a chlorophenoxy herbicide. The efficiency of photodegradation of the as-prepared catalyst, TiO2-rGO-PANI-PPy has been studied against pristine TiO2, rGO, and the nanocomposites TiO2-rGO, TiO2-PANI-PPy, TiO2-rGO-PANI and TiO2-rGO-PPy under simulated sunlight. The structural and optical properties of the composite have been validated through characterization by XRD, FTIR, Raman, FESEM, EDS, UV-DRS and BET surface area analysis. TiO2-rGO-PANI-PPy showed maximum adsorption in a short time of 30 minutes with an adsorption capacity (Q(max)) of 35.3 mg/g. Pseudo-second-order and Freundlich isotherm models were effectively employed to describe the adsorption behavior of 2,4-D. TiO2-rGO-PANI-PPy exhibited significantly enhanced photocatalytic performance on the degradation of 2,4-D under visible light irradiation compared to pure TiO2 or the composites, TiO2-rGO, TiO2-PANI-PPy, TiO2-rGO-PANI and TiO2-rGO-PPy. Complete mineralization of 2,4-D has been observed after 40 minutes of reaction in pH 7. 2,4-D was degraded fastest at the strong acidic conditions. The transformed intermediates were identified by HPLC-MS/MS, and a possible degradation reaction pathway has been proposed.