Application of modified pumice particles with a metal-organic composite prepared by m-phenylenediamine an Iron (II) for photoreduction of Cr(VI) under visible light

Discharging heavy metals into water bodies results in global environmental risks. Hexavalent chromium (Cr(VI)) is known as a harmful substance that poses substantial health hazards to humans. This study aimed to modify the pumice beads using a metal-organic composite synthesized by m-Phenylenediamine (mPD) and Iron (II) (FeCl₂·4H₂O) via a solvent-free method for photoreduction of the Cr(VI) to Cr(III) in wastewater. In the proposed method, iron (II) ions serve both as an electron generator and as a linker for the polymerization of mPD on the pumice surface in the high-temperature pyrolysis process. The optimum molar ratio of FeCl₂·4H₂O/mPD and the pyrolysis temperature were determined to be 1 and 700 °C. Moreover, the operative parameters such as pH, hole scavenger (formic acid) dosage, photocatalyst mass, Cr(VI) initial concentration, and reaction time were studied and the optimum condition was obtained as pH of 2.0, hole scavenger dosage of 20 mL L⁻¹, photocatalyst mass of 2 g, chromium concentration of 100 mg L⁻¹ and 13 min for irradiation time. The ability of the photocatalyst to reduce Cr(VI) at a concentration of 50 and 100 mg L⁻¹ under natural sunlight irradiation was also examined and a reduction efficacy of 100 % was achieved under optimum conditions within 40 and 60 min; respectively. Finally, the reusability test was conducted up to 10 cycles, and the results proved the durability and practicality of the prepared photocatalyst. The easy separation, short reaction time, and functioning under natural sunlight exhibited a promising application of the proposed photocatalyst for Cr(VI) reduction.