In this study, In₂S₃/CuSe (ICS) carboxymethyl cellulose (CMC) 3D photocatalytic hydrogels were developed for the efficient degradation of sulfamethoxazole under LED light irradiation through peroxymonosulfate (PMS) activation. The ICS composites were synthesized via a hydrothermal reaction and incorporated into hydrogels using a blend-crosslinking technique with FeCl₃. The structural, morphological, and optical characterizations confirmed strong interfacial contact between the semiconductors, bandgap modulation, accelerated electron-hole pair transfer, and improved charge separation, all of which contributed to enhanced catalytic performance. The ICS carboxymethyl cellulose hydrogels achieved 100 % sulfamethoxazole degradation within 5 min and demonstrated high reusability, maintaining activity for up to 20 cycles. A type-II heterojunction assisted electron migration mechanism, supported by scavenger tests and optical analysis, was proposed. The presence of selenium, copper and iron in the ICS hydrogel also facilitated the cyclic conversion of transition metals which ubiquitously produced ROS species to aid SMX degradation. The integration of CMC as a catalytic support enhanced reusability, and facilitated catalyst recovery. A special emphasis was given to the sustainability metrics analysis of the ICS hydrogels, evaluating their environmental impact and long-term viability. Overall, the ICS heterojunction system exhibits significant potential for environmental remediation, providing enhanced versatility and durability.