Sustainable metal–carbon composite derived from pharmaceutical waste: Using expired acetaminophen and aluminum ion precursors for photoreduction of Cr(VI) under visible light

Improper management and inadequate disposal of pharmaceutical waste release hazardous compounds into the environment, raising significant ecological concerns. In this study, expired acetaminophen was utilized to fabricate a functional aluminum-based metal–carbon photocatalyst, presenting an innovative strategy for handling pharmaceutical waste. The resulting composite, obtained through pyrolysis of precursors including aluminum ions and expired acetaminophen at elevated temperatures, was used for the photoreduction of hexavalent chromium (Cr(VI)), a highly soluble and carcinogenic pollutant, under visible light irradiation in aqueous solution. By investigating the AlCl 3 /acetaminophen mole ratio and pyrolysis temperature, the optimized composite (0.25 molar ratio, 450 ° C) exhibited a narrow band gap (2 eV), strong visible-light absorption, and high photocatalytic efficiency. Under optimal conditions (pH = 2, formic acid = 2 mL/100 mL, and photocatalyst dosage = 2 g L -1 ), 99.66% Cr(VI) removal was achieved at a concentration of 100 mg L -1 within 45 min. The photocatalyst demonstrated sustained efficiency over five consecutive reuse cycles and performed well under natural sunlight. Additionally, its activity remained unaffected by interfering ions. These results highlight the potential of pharmaceutical waste to be transformed into valuable materials applicable to wastewater remediation and to offer an alternative to existing pharmaceutical waste disposal methods.