Programmably Transient Graphene Quantum Dot–Based Hybrid Nanocomposites for Water Treatment: Design, Performance, and Environmental Fate

In the recent years, graphene quantum dot (GQD) hybrid nanocomposites have been widely used in water treatment for their photocatalytic and sorption properties but remain insufficiently evaluated for their environmental stability or post-use fate. This review offers a holistic approach to developing and designing transient and biodegradable GQD hybrids based on safe-by-design principles, examining how structures, surface chemistry, and hybrid composition govern not only the intended performance but also the degradation behavior and fate of the environment. The focus of this review is on structure–degradability–performance relationships, by examining how labile connections, biodegradable materials, or biomass-derived GQDs enable controlled disasembly after use. It examines chemical, photonic, and biological degradation pathways and environmental effects on these processes in real-world wastewater and provides a comparative view of the formation, transport, and ecotoxic degradation products in comparison with the standard persistent nanomaterials. With the combined knowledge from material science, environmental chemistry, and sustainability assessment, this review promotes the new approach to design of nanomaterials. Rather than analyzing how well materials function, it seeks to understand what remains after the product is no longer useful, enabling the next generation of green water treatment technologies.