Gels for Water Remediation: Current Research and Perspectives

Abstract

The development of cost-effective and high-performance technologies for wastewater treatment is essential for achieving a sustainable economy. Among the various methods available for water remediation, adsorption is widely recognized as an effective and straightforward approach for removing a range of pollutants. Gel materials, particularly hydrogels and aerogels, have attracted significant research interest due to their unique properties. Hydrogels, for instance, are noted for their ability to be regenerated and reused, ease of separation and handling, and suitability for large-scale applications. Additionally, their low cost, high water absorption capacity, and contribution to environmental protection are important advantages. Aerogels, on the other hand, are distinguished by their low thermal conductivity, transparency, flexibility, high porosity, mechanical strength, light weight, large surface area, and ultralow dielectric constant. This review provides a comprehensive analysis of the current literature, highlighting gaps in knowledge regarding the classification, preparation, characterization, and key properties of these materials. The potential application of hydrogels and aerogels in water remediation, particularly in removing contaminants such as dyes, heavy metals, and various organic and inorganic pollutants, is also discussed.

Keywords: adsorption properties; aerogel materials; hydrogels; sustainable economy; wastewater treatment; water remediation.

Figure 1

Reusability studies of the hydrogels on the adsorption of methylene blue (left); effect of the initial methylene blue concentration on the adsorption of Ag/TPP/rGH (right). Source [35] with permission from the Elsevier and Copyright Clearance Center.

Figure 2

(a) Adsorption capacity of the CMCS-PA composite hydrogels for methyl orange and congo red dyes in different ratios; (b) Adsorption capacity for methyl orange and congo red dyes of the CMCS-PA (3:1 ratio) at different solution pH values. Source [39], with permission from Elsevier and the Copyright Clearance Center.

Figure 3

(a,b) SEM images of GO; (c,d) SEM images of freeze-dried agar-GO; (e,f) SEM images of powdered pure agar; (g) Photograph of the produced hydrogel. Source [41], with permission from Elsevier and the Copyright Clearance Center.

Figure 4

Changes in the absorption spectrum: (a) brilliant green (BG); (b) crystal violet (CV); (c) bismark brown (BB); (d) rose bengal (RB); (e) eosin blue (EB); (f) fuchsin acid (FA); (g) malachite green (MG); (h) the mixture of malachite green (MG) and fuchsin acid (FA). Source [43] with permission from the Elsevier and Copyright Clearance Center.

Figure 5

Schematic diagram of the study. Source [60], with permission from Elsevier and the Copyright Clearance Center.

Figure 6

Effect of co-existing cations on the adsorption of (a) Pb(II) and (b) Cu(II). Source [64], with permission from Elsevier and the Copyright Clearance Center.

Figure 7

Schematic diagram of the synthesis of hydrogel. Source [68], with permission from Elsevier and the Copyright Clearance Center.

Figure 8

(a) UV–vis absorption spectra of Rhodamine B, solution adsorbed by graphene oxide/locust bean gum (GO/LBG) aerogels with GO/LBG mass ratios of 1:4 (GO/LBG-1), 1:8 (GO/LBG-2), 1:16 (GO/LBG-3) for 24 h, (b) the maximum adsorption quantity on Rhodamine B of GO/LBG-1, GO/LBG-2, and GO/LBG-3 aerogels, (c) UV–vis absorption spectra of Indigo carmine solution adsorbed by GO/LBG-1, GO/LBG-2, and GO/LBG-3 aerogels for 24 h, and (d) the maximum adsorption quantity on Indigo carmine of GO/LBG-1, GO/LBG-2, and GO/LBG-3 aerogels. Source [88] with permission from the Elsevier and Copyright Clearance Center.

Figure 9

SEM images of CMC/O (a), CMC/CNF–C (b), CMC/CNFs (c), and CMC/CNWs (d). Source [81], with permission from Elsevier and the Copyright Clearance Center.

Figure 10

(a) Adsorption quantity of variable organic dyes, methylene blue (MB), malachite green (MG), rhodamine 6G (Rh6G), Rose bengal (RB), and methyl orange (MO) by CGA as a function of time. (b) Dye adsorption efficiency of CGA at equilibrium, along with the demonstration of the molecular structure of each dye. Source [89] with permission from the Elsevier and Copyright Clearance Center.

Figure 11

Schematic diagram of the synthesis of MOF-801 (a) and TMPA@MOF-801 aerogel (b). Source [91], with permission from Elsevier and the Copyright Clearance Center.