A Review of Pectin-Based Material for Applications in Water Treatment

Abstract

Climate change and water are inseparably connected. Extreme weather events cause water to become more scarce, polluted, and erratic than ever. Therefore, we urgently need to develop solutions to reduce water contamination. This review intends to demonstrate that pectin-based materials are an excellent route to detect and mitigate pollutants from water, with several benefits. Pectin is a biodegradable polymer, extractable from vegetables, and contains several hydroxyl and carboxyl groups that can easily interact with the contaminant ions. In addition, pectin-based materials can be prepared in different forms (films, hydrogels, or beads) and cross-linked with several agents to change their molecular structure. Consequently, the pectin-based adsorbents can be tuned to remove diverse pollutants. Here, we will summarize the existing water remediation technologies highlighting adsorption as the ideal method. Then, the focus will be on the chemical structure of pectin and, from a historical perspective, on its structure after applying different cross-linking methods. Finally, we will review the application of pectin as an adsorbent of water pollutants considering the pectin of low degree methoxylation.

Keywords: adsorption; cross-linking; low methoxylation degree; pectin; pollution; remediation; structural models; wastewater.

Figure 1

Common examples of emerging contaminants in water.

Figure 2

Publications in pectin water remediation for 1970–2022. Data are the number of hits of a search for publication titles containing the keywords “pectin” and “adsorption” using the Web of Science.

Figure 3

(a) Representation of pectin structure. Pectin has different polysaccharides (homogalacturonan, xylogalacturonan, apiogalacturonan, rhamnogalacturonan II, and rhamnogalacturonan I, as shown in the figure). (b) The schematic representation of the poly(galacturonic) acid chain indicates the Carbon 6 and galacturonic acid units with different functional groups at Carbon 6.

Figure 4

Schematic representation of calcium cross-linking in pectin or alginate [147].

Figure 5

Ca²⁺ binding to alginate in multi-steps is shown schematically for the (a) Short-chain alginate and (b) Long-chain alginate, respectively. R stands for the Ca²⁺ to the guluronate residue feeding ratio [119].

Figure 6

Cartoon representing the evolution of Ca²⁺ cross-linking of LM pectin and its final structure [159].

Figure 7

Suggested network scheme for calcium and zinc pectate complexes at R = 0 (pectin alone) and R = 0.44. Figure extracted from reference [160].