Advances and innovations in hydrogel particles for sustainable purification of contaminants in aqueous solutions

Hydrogel particles, encompassing spherical beads (microgels) and non-spherical particles (pears, cylindrical, or irregular shapes), show outstanding features including biocompatibility, good mechanical properties, tunable sizes ranging from micrometer to tens of nanometers, and large active surface areas. They also offer simplicity in design and operation, excellent regeneration capabilities, and non-generation of secondary contaminants. As a result, they are widely recognized as exceptional adsorbents and are extensively utilized in separating and purifying various contaminants in water and wastewater. Understanding the unique properties, preparation techniques, and innovations of hydrogel particles plays a vital role in the formulation of development strategies of novel hydrogel adsorbents towards sustainable purification of contaminants in aqueous solutions. Here, we provide a critical review of the interesting characteristics of hydrogel particles and several types of polymers for their design and fabrication. The state-of-the art applications, innovations, important adsorption mechanisms of hydrogel particles in the removal of various pollutants are also summarized and discussed. The advantages/disadvantages of different biopolymers and synthetic polymers, and advanced technologies for preparation of hydrogel particles are emphasized as well. This review aims to consolidate scientific evidence to facilitate the development of novel adsorbents based on hydrogel particles for water and wastewater treatment.