Research progress on the application of hydrogel adsorbent materials in wastewater treatment: A review

Owing to their high specific surface area, low density, three-dimensional network structure, and rich functional groups, hydrogel materials can be used as adsorbents to capture a wide range of pollutants, such as heavy metal ions and organic dyes, from wastewater. Currently, the optimized hydrogel materials can remove over 98 % of heavy metal ions and dyes, making them a promising adsorbent for wastewater treatment. In recent years, an increasing number of researchers have recognized the value of hydrogels as adsorbents in wastewater treatment, but few reviews have comprehensively and systematically summarized this area. Based on this, this paper establishes a classification system based on the crosslinking mechanism, and focuses on the process characteristics of three synthetic routes, including physical cross-linking, chemical cross-linking and mixed cross-linking. The unique performance and adsorption mechanism of the three synthetic routes are discussed in detail, and the characteristics of various adsorption models are summarized. This paper also compares the advantages and disadvantages of hydrogel sorbents with those of other adsorbents, highlights the challenges in the large-scale application of hydrogel adsorbents in wastewater treatment, and outlines the future development trends of hydrogel adsorbents towards economy, efficiency, environmental protection and multi-functionality. It is hoped that this review will provide valuable insights into the efficient preparation and application of hydrogels.