Efficient and reusable N-doped phenylenediamine/fly ash-based carbon composite derived from acid-washed municipal solid waste incinerator fly ash for Cr(VI) photoreduction under visible light

Annually, large amounts of fly ash are generated from the incineration of municipal solid waste, which is classified as hazardous due to its high content of heavy metals. In this study, acid-washed fly ash residue was utilized to fabricate an N-doped phenylenediamine-based photocatalyst through pyrolysis at high temperature for Cr(VI) reduction under visible light irradiation. Characterization was performed using FESEM, XRD, FTIR, BET, EDX, and EIS. The photocatalytic performance of the composite was evaluated by examining the influence of operational parameters, including solution pH, catalyst dosage, initial Cr(VI) concentration, and formic acid as a hole scavenger. Additionally, the phenylenediamine to fly ash mass ratio (0, 0.08, 0.12, and 0.15) was optimized, and 0.12 was identified as the optimal composition for the fabricated photocatalyst. The optimized conditions were determined at pH 2, a catalyst dosage of 2 g L −1 , and 2 mL of formic acid per 100 mL solution. Under these conditions, the photocatalyst achieved 99.8% removal at a Cr(VI) concentration of 100 mg L −1 within 40 min. Moreover, the photocatalyst demonstrated excellent reusability, maintaining high efficiency across five consecutive cycles. These results indicate that the produced photocatalyst is a waste-derived, sustainable material with significant promise for the removal of Cr(VI) from aquatic environments. • Incinerator fly ash is reused to prepare an efficient N-doped composite. • Visible light photoreduction achieved 99.8% Cr(VI) removal in 40 min. • Utilizing fly ash waste supports green and sustainable waste management. • The composite exhibited excellent recyclability over five cycles. • Reusing fly ash instead of disposing of it helps prevent environmental pollution.