Visible Light Driven Photocatalytic Degradation of Antibiotics Using Hydrothermally Engineered AgInS ₂ /Er‐g‐C ₃ N ₄ Heterocomposite

Abstract To develop an efficient visible light responsive photocatalyst remains a major challenge for sustainable wastewater purification. In this work, a novel erbium‐doped graphitic carbon nitride (Er‐g‐C 3 N 4 ) supported with silver indium sulfide (AgInS 2 ) heterocomposite was rationally designed via a solid‐state hydrothermal approach to overcome the limitations of poor charge separation and narrow light absorption in conventional photocatalysts. The introduction of Er 3+ ions and the formation of an intimate heterocomposite synergistically enhanced visible light harvesting and charge carrier migration, leading to superior photocatalytic efficiency. Comprehensive structural and optical analyses (XRD, XPS, FTIR, BET, and UV–Vis DRS) confirmed successful integration and improved surface properties. Cyclic voltammetry revealed enhanced redox capability, while radical trapping experiments identified superoxide radicals and photogenerated holes as the main reactive species responsible for pollutant degradation. The optimized 6 wt.% of heterocomposite (6 wt.% AgInS 2 /Er‐g‐C 3 N 4 ) exhibited exceptional photodegradation and mineralization performance against methylene blue (MB) dye, tetracycline (TC), and oxytetracycline (OTC) antibiotics under visible light irradiation. Mechanistic investigations, supported by photoluminescence quenching, impedance spectroscopy, and radical scavenging tests, revealed that enhanced redox activity and efficient electron–hole separation primarily drive the photocatalytic process. The remarkable activity of the 6 wt.% AgInS 2 /Er‐g‐C 3 N 4 heterocomposite in real wastewater highlights its potential as a promising and scalable material for practical environmental remediation applications.