Driven by sustainable-development strategies, photocatalysis has become a forefront approach for textile-dyeing wastewater remediation. ZnCdS possesses a well-matched conduction-band position, a narrow band gap and excellent chemical stability, making it a highly promising photocatalyst; however, it still suffers from severe photo-corrosion and ultrafast recombination of photogenerated carriers. Sodium alginate (SA) bears abundant -OH and -COOH groups that can build high-density adsorption sites for selective dye capture. After cross-linking modification, surface electrons are more readily excited, and an additional electron-buffer pool is created, which markedly suppresses ZnCdS electron-hole recombination and alleviates photo-corrosion, offering a new concept for constructing an efficient and stable "adsorption-photocatalysis" integrated system. Herein, ZnCdS/SA composite gel-beads were fabricated via a co-precipitation-cross-linking route. The removal of rhodamine B (RhB) was systematically evaluated under different light sources, and the effects of pH, irradiation time and cycle number on degradation efficiency were examined. Crystalline phase, morphology and functional-group evolution were analyzed by XRD, FTIR, etc. Under optimal conditions, RhB removal efficiency reached 98.77% while the gel-bead structure remained intact. The material exhibited the hexagonal ZnCdS phase with abundant surface protrusions and sufficient adsorption sites. Groups such as O-H, -COOH, COO-, and C-O-H captured RhB through electrostatic adsorption and redox synergy, while S, O, Fe and other elements participated in electron transfer. After five cycles, the degradation efficiency remained above 85%, confirming that ZnCdS/SA can efficiently and stably eliminate RhB from water via a dual "adsorption-photocatalysis" pathway, providing a feasible strategy for real textile wastewater treatment.