Polysaccharide-Based Composite Hydrogels as Sustainable Materials for Removal of Pollutants from Wastewater

Abstract

Nowadays, pollution has become the main bottleneck towards sustainable technological development due to its detrimental implications in human and ecosystem health. Removal of pollutants from the surrounding environment is a hot research area worldwide; diverse technologies and materials are being continuously developed. To this end, bio-based composite hydrogels as sorbents have received extensive attention in recent years because of advantages such as high adsorptive capacity, controllable mechanical properties, cost effectiveness, and potential for upscaling in continuous flow installations. In this review, we aim to provide an up-to-date analysis of the literature on recent accomplishments in the design of polysaccharide-based composite hydrogels for removal of heavy metal ions, dyes, and oxyanions from wastewater. The correlation between the constituent polysaccharides (chitosan, cellulose, alginate, starch, pectin, pullulan, xanthan, salecan, etc.), engineered composition (presence of other organic and/or inorganic components), and sorption conditions on the removal performance of addressed pollutants will be carefully scrutinized. Particular attention will be paid to the sustainability aspects in the selected studies, particularly to composite selectivity and reusability, as well as to their use in fixed-bed columns and real wastewater applications.

Keywords: adsorption; hydrogels; polysaccharides; sustainable development; wastewater treatment.

Figure 1

Illustrations of (A) batch and (B) column adsorption processes. (C) Parameters that affect the batch and column adsorption processes. (D) Cost per volume of treated water for various technologies applied in wastewater treatment (Reprinted with permission from Ref. [12]. Copyright 2019, Royal Society of Chemistry).

Figure 2

Chemical structures of a selection of polysaccharides, classified according to their natural sources.

Figure 3

Hydrogel network types and the rational design of different polysaccharide-based composites (containing CNT (Reprinted from Ref. [31]), GO (Reprinted from Ref. [32]), clays (Reprinted with permission from Ref. [33]. Copyright 2019, Royal Society of Chemistry.), MOFs (Reprinted with permission from Ref. [34]. Copyright 2018, John Wiley & Sons, Inc.), or metal nanoparticles (Reprinted with permission from ref. [35]. Copyright 2018, Royal Society of Chemistry.) with improved properties for wastewater treatment.

Figure 4

Timeline of the number of publications per year showing the development of the field of composite hydrogels used as sorbents.

Figure 5

(A) The preparation principle of PEC hydrogels by the SD-A-SGT method (the example of SL/CS hydrogels) (Reprinted with permission from Ref. [72]. Copyright 2020, Elsevier.) (B) The effect of SL/LCS PEC hydrogels composition (SC1: SL/LCS = 5/5; SC2: SL/LCS = 6/4; SC3: SL/LCS = 7/3; SC4: SL/LCS = 8/2) on Ni(II) sorption (Reprinted with permission from Ref. [73]. Copyright 2020, Elsevier.) (C) The effect of SL/CMCS PEC hydrogels composition on Pb(II) sorption (Reprinted with permission from Ref. [74]. Copyright 2020, Elsevier.) (D) The effect of competing ions on Pb(II) sorption by the SL/CMCS PEC hydrogels (SL/CMCS = 6/4) (Reprinted with permission from Ref. [74]. Copyright 2020, Elsevier.) (E) Reusability efficiency in Pb(II) successive sorption/desorption cycles by the SL/CMCS PEC hydrogels (SL/CMCS = 6/4) (Reprinted with permission from Ref. [74]. Copyright 2020, Elsevier.).

Figure 6

(A) The principle of CMC/PAAm semi-IPN hydrogel preparation, sorption of Cu(II) ions, synthesis of CuNPs, and catalytic reduction of 4-NP to 4-AP (Reprinted with permission from Ref. [79]. Copyright 2019 Elsevier.) (B) Comparison between Cu(II), Pb(II), and Cd(II) ions sorption by CMC/PAAm semi-IPN hydrogels in mono- and multi-component systems Reprinted with permission from Ref. [79]. Copyright 2019 Elsevier.) (C) UV–vis adsorption spectra of 4-NP solution in the presence of CuNPs-loaded CMC/PAAm semi-IPN hydrogel and NaBH₄ Reprinted with permission from Ref. [79]. Copyright 2019 Elsevier.) (D) Selective HMIs removal by lignin/CS/PAAm IPN hydrogel at different initial concentrations (Reprinted with permission from ref. [82]. Copyright 2022 Elsevier).

Figure 7

(A) The preparation strategy of CS/PEI/PEI and CS/PEI/PDMAEMA TN sponges (Adapted with permission from ref. [39]. Copyright 2021 Elsevier.) (B) The influence of interfering anions on the phosphate sorption by CS/PEI/PEI and CS/PEI/PDMAEMA TN sponges (Reprinted with permission from ref. [39]. Copyright 2021 Elsevier.) (C) Phosphate sorption/desorption cycles CS/PEI/PEI and CS/PEI/PDMAEMA TN sponges (Reprinted with permission from ref. [39]. Copyright 2021 Elsevier.).

Figure 8

(A) The effect of contact time on Cu(II) sorbed amount by CS/PAN-g-St composite beads differing by St source and hydrolysis (Reprinted with permission from Ref. [106]. Copyright 2022 Elsevier.) (B) Cu(II) removal performance by CS/PAN-g-St (from rice) composite cryobeads in successive sorption/desorption cycles (Reprinted with permission from Ref. [106]. Copyright 2022 Elsevier. (C) Effect of pH on selective removal of U(VI) by the sulfonate modified CS/Arabic gum biosorbent in the presence of competitive HMIs (Reprinted with permission from Ref. [107]. Copyright 2022 Elsevier.) (D) Illustration with the cyclic Cu(II) sorption, CO₂-mediated desorption, and regeneration of P(AA-co-DMAEMA)/CS aerogels (Reprinted with permission from ref. [108]). (E) Cu(II) sorption/CO₂-mediated desorption performance of P(AA-co-DMAEMA)/CS aerogels (Reprinted with permission from ref. [108]).

Figure 9

SEM micrographs of CEL/CS aerogels prepared at 1 wt.% (A) and 2 wt.% (B) CS solution. (C) Optical image of CEL/CS aerogel prepared at 1 wt.% CS solution featuring its ultralightweight property. (D) Reusability performance and optical images after pollutants sorption and desorption of CEL/CS aerogel (abbreviated with CE/CSA-1 and CE/CSA-2, the number identifying the concentration of CS solution), as well as of control CEL (CEA) and CS (CSA) aerogels. The breakthrough curves of CR sorption in column experiments by the CEL/CS aerogel prepared at 1 wt.% CS solution as a function of (E) flow rate, (F) sorbent mass and (G) pollutant concentration. (Reprinted with permission from Ref. [109]. Copyright 2023 Elsevier.)

Figure 10

SEM micrographs of hollow CMC/PEI beads (A and B) and their reusability performance in the removal of Cr(VI) (C) and phosphate (D) (Reprinted with permission from Ref. [122]. Copyright 2021 Elsevier.) (E) Breakthrough curves (with Thomas model fitting profiles) for bisphenol A and Cr(VI) sorption onto CTAB-modified CMC/sugarcane baggase composite in monocomponent solution and in mixture, and (F) photographs at different time intervals of the column during bisphenol A and Cr(VI) sorption (Reprinted with permission from Ref. [131]. Copyright 2022 Elsevier.) Pb(II) and Cr(VI) ions sorption by PVA/ALG and PVA/ALG/CS composite hydrogels, respectively, from real wastewater (G), their reusability performance (H) and illustration of the possible interactions between Cr(VI) ions and PVA/ALG/CS hydrogels (I) (Reprinted with permission from Ref. [111]. Copyright 2022 Elsevier.)

Figure 11

(A) Optical images of CS-CPL and CS_EDTA-CPL beads and illustration of functional groups (-NH₂, -OH, and EDTA) available to interact with HMIs. (B) Breakthrough curve of Cd(II), Ni(II), Pb(II), Zn(II), and Co(II) ions sorption (from their mixture) on CS_EDTA-CPL beads. (C) SEM micrographs of CS-CPL and CSEDTA-CPL beads before and after interaction with a equimolar mixture of Cd(II), Ni(II), Pb(II), Zn(II), and Co(II) ions. (D) EDX mapping and elemental analysis of the CS-CPL and CS_EDTA-CPL bead surface after interaction with a mixture containing Cd(II), Ni(II), Pb(II), Zn(II), and Co(II) ions. (E) Potential interaction mechanism between the CS_EDTA-CPL composite cryobeads and HMIs (Reprinted from Ref. [29]).

Figure 12

Influence of co-existing ions on phosphate uptake (A), sustainability upon consecutive sorption/desorption cycles (B), and the possible phosphate removal mechanism (C) by PVA/ALG/palygorskite composite beads (Reprinted with permission from Ref. [165]. Copyright 2023 Elsevier.)

Figure 13

Illustration summarizing the types of polysaccharide-based composite hydrogels and their application in wastewater treatment from a sustainability perspective.