Hydrogel Nanocomposite Adsorbents and Photocatalysts for Sustainable Water Purification

Hydrogels have been employed for water purification applications, but their performance and strength are unsatisfactory for widespread adoption. Recently, hydrogel nanocomposites have been proposed to resolve the inherent challenges faced by hydrogels for water treatment. This review comprehensively analyzes hydrogel nanocomposites for water treatment using adsorbent and photocatalysis techniques. The structure, classification, and tunable synthesis methods of hydrogels are explained. Further, how hydrogels can be incorporated with functional nanoparticles (NPs) and can be used as templates/precursors for developing advanced 3D architectures, including the formation of hydrogel nanocomposite beads and 3D printing objects are discussed. Finally, the structure-property relationships of hydrogel nanocomposites are critically reviewed by considering introductory gelation chemistry, such as swelling characteristics, mechanical properties, stimuli-responsiveness, and ionic/electronic conduction. The extensive cross-linking of polymer chains with NPs offers high mass/charge transport, high surface areas, and enhanced polymer-water interactions to achieve high-performing adsorbents and photocatalysts. Several motivating examples of emerging NP-containing hydrogel nanocomposites for use in adsorbents and photocatalysis have been discussed. Such efforts validated the excellent technological potential held by hydrogel nanocomposites for water purification applications. Finally, future directions of hydrogel nanocomposites for sustainable water treatment are proposed.