Abstract

Water pollution caused by persistent azo dyes, pharmaceutical residues, and microbial contaminants remains a major environmental challenge due to the limited efficiency of conventional treatment methods. In this study, a BiOI-decorated graphitic carbon nitride (g-C3N4) heterostructure was synthesized through an eco-friendly solid-state dispersion-precipitation approach for broad-spectrum wastewater purification. Structural and surface analyses (XRD, FT-IR, UV-DRS, PL, FE-SEM, HR-TEM, XPS) confirmed the formation of a well-integrated BiOI/g-C3N4 heterojunction. The optimized composite exhibited excellent photocatalytic activity, achieving nearly 100 % degradation of Reactive Red 120 (50 mg/L) and similar to 98 % degradation of Acid Black 1 (20 mg/L) under UV-A (120 min) and sunlight (180 min) irradiation. Photocatalytic experiments were conducted using 50 mg catalyst in 100 mL solution at pH 7 under a UV-A irradiance of 280 mW cm(-2) (photon flux: 1.381 x 10(-3) einstein L-1 s(-1)), while sunlight-driven tests were performed under direct solar illumination of 125,000 +/- 10,000 lx (irradiance: 95 +/- 4 mW cm(-2)). The material also degraded pharmaceutical pollutants, removing 62.3 % ciprofloxacin and 65.5 % ofloxacin (20 mg/L each) under UV-A within 60 min. A custom-designed column-type photoreactor further enhanced sunlight-driven degradation, and real water studies using tap, Cauvery River, and Puliyancholai Falls water achieved 69-86 % pollutant removal under UV-A light. Reactive species trapping identified O center dot- (2) and h(+) as key oxidative agents. Although some GC-MS-detected intermediates exhibited higher predicted toxicity than the parent dye, they were subsequently degraded and progressively mineralized during the reaction. The photocatalyst showed good stability over repeated cycles and demonstrated antibacterial activity against both Gram-positive and Gram-negative bacteria. Overall, the BiOI-g-C3N4 heterostructure represents a robust, solar-responsive, and scalable candidate for the simultaneous removal of dyes, antibiotics, and microbial contaminants from wastewater.