Rapid population expansion, industrialization, accelerated urbanization, and ineffective governmental policies in certain areas have heightened the expenditure of resources and diverse environmental practices contributing to water contamination. Several materials, including quantum dots, metal oxides, carbonaceous substances, and metal sulfides, have effectively eliminated benign contaminants from polluted water. Among these, transition metal chalcogenides (TMCs) have garnered attention owing to their appropriate bandgap energy, earth abundance, optoelectronic characteristics, and catalyst stability. In this chapter, the causes of water pollution and techniques for water purification, including chemical (precipitation, adsorption, and disinfection), physical (flocculation, sedimentation, filtration, and flotation), and biological (aerobic, anaerobic, and anoxic) methods, are thoroughly discussed. This chapter covers the conventional and advanced photocatalysis mechanisms of transition metal chalcogenides for wastewater purification. Lastly, strategies to improve the photocatalytic activity of transition metal chalcogenides are examined. In particular, the advantages of TMC-based photocatalysis over conventional treatment methods are elucidated. Critical considerations regarding the environmental impact of TMCs—such as the potential toxicity of cadmium-containing chalcogenides and the energy footprint of their synthesis—are evaluated alongside proposed solutions like safer catalyst designs and green synthesis techniques. The influence of environmental factors (pH, temperature, and contaminant levels) on the photocatalytic efficacy and stability of TMCs in realistic wastewater conditions is also assessed. Additionally, recent progress in applying artificial intelligence (AI) and machine learning (ML) to TMC development is highlighted, demonstrating how data-driven approaches can improve catalyst design, scalability, and long-term performance in photocatalytic wastewater treatment.