With the rapid intensification of industrial and agricultural activities, water contamination by heavy metal ions has emerged as a critical global challenge, gravely imperiling ecosystem stability and public health. Among the various remediation technologies, adsorption has been widely adopted due to its high efficiency, low-cost water treatment, and simplicity of operation. However, conventional inorganic or synthetic adsorbents often exhibit poor degradability and pose a risk of secondary contamination, substantially limiting their sustainable application. Consequently, the development of environmentally benign and renewable adsorbent materials has become a central research focus in this field. Recently, cellulose-based composite hydrogels, derived from renewable resources and characterized by excellent eco-friendliness and highly tunable three-dimensional porous structures, have attracted considerable attention as promising green adsorption materials. These hydrogels demonstrate outstanding performance in the efficient sequestration of heavy metal contaminants from aqueous environments. This review systematically summarizes recent advances in cellulose-based composite hydrogels for heavy metal removal, to elucidate the structure–performance relationships linking material fabrication strategies, structural modulation, and adsorption efficiency. First, we outline the principal construction approaches, including physical crosslinking, chemical modification, and supramolecular self-assembly, and comprehensively analyze how different synthesis routes regulate pore architecture, mechanical properties, and the distribution of surface functional groups. Second, the underlying adsorption mechanisms, primarily coordination complexation, electrostatic interactions, and ion exchange, are discussed in detail. Finally, recent studies on the adsorption of cationic heavy metals (e.g., Pb(II), Cu(II), and Cd(II)) and anionic oxyanions (e.g., As(III) and Cr(VI)) are critically reviewed, with particular emphasis on the relationships between selective adsorption performance, material design principles, and specific recognition mechanisms. Overall, this review provides a theoretical foundation and practical guidance for the design and development of next-generation water treatment materials with high adsorption capacity, excellent selectivity, non-toxicity, and strong environmental compatibility, followed by future research recommendations.

Hydrogels (HGs), three-dimensional cross-linked hydrophilic polymer networks, have emerged as a promising class of functional materials for sustainable agriculture due to their exceptional water retention capacity, responsiveness to environmental stimuli, and favorable biocompatibility. This review systematically summarizes the key functional properties of hydrogels and critically examines their multidimensional roles within agricultural systems. The major synergistic benefits of hydrogels are highlighted, including (1) improvement of soil physical structure, chemical properties, and the biological microenvironment, thereby facilitating soil remediation; (2) direct enhancement of seed germination, root development, and crop productivity when employed as soil amendments or seed-coating materials; (3) controlled and sustained release of water, nutrients (N, P, K, and trace elements), and pesticides, leading to significant improvements in resource use efficiency; (4) functional delivery of beneficial microorganisms, enabling precise regulation of their activity and efficacy; and (5) advancement of soilless cultivation technologies through the development of sophisticated hydrogel-based substrates. Furthermore, this review discusses the key challenges that currently limit large-scale agricultural implementation, including insufficient biodegradability, potential ecotoxicological risks, and techno-economic constraints. Finally, future research directions are proposed from an interdisciplinary perspective, emphasizing rational material design, performance optimization, and practical field application. This comprehensive review aims to provide systematic theoretical guidance and practical insights for the development and deployment of hydrogel-based technologies in sustainable agriculture.