Counterion Effects in Metal Hybrid Biopolymer Materials for Sulfate Adsorption: An Experimental and Computational Study AITranslate

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DOI：https://doi.org/10.1021/acsapm.1c00706

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Modification of biomaterials is an active research area in materials and environmental science, where the controlled removal of sulfate is a key goal toward achieving global water security in regions with saline aquifers. In this study, biopolymer-based ternary metal composites (TMCs) were prepared that contain alginate/chitosan/Al(III) with variable counterions: chloride (C), nitrate (N), and sulfate (S), denoted as TMC-C, TMC-N, and TMC-S, respectively. The structure and physicochemical properties of the TMCs were characterized by spectroscopy (NMR, FT-IR, Raman, and XPS) and other complementary methods (thermal gravimetry, potentiometry, and zeta potential) to gain insights on the role of counterion effects related to the adsorption properties of TMCs with inorganic and organic anions in aqueous media. Both equilibrium and dynamic adsorption properties of the TMCs were evaluated with inorganic sulfate (Na2SO4) and two types of anionic organic dyes (methyl orange, MO,; and reactive black-5, RB5) at pH 7 and 295 K. A computational study was carried out to evaluate the structural features of the TMCs related to the coordination of sulfate with the TMC-N system. The charge state of the TMCs for the various counterion systems was estimated according to the pHPZC (5.0 to 5.9) and zeta potential (+8.31 to +35.7 mV) of the composites in aqueous media. The presence of variable counterions (chloride, nitrate, and sulfate) revealed the effects on the equilibrium and kinetic uptake of sodium sulfate and RB5. The Sips isotherm model for sulfate adsorption revealed a value of Qe from 87 to 120 mg/g, which depends on the counterion. The uptake of RB5 (Qm = 77 to 208 mg/g) by the TMCs varied over a wider range due to the role of secondary biopolymer adsorption sites. The incorporation of switchable counterions in TMCs offer a low-cost and bottom-up approach for the design of tailored biopolymer adsorbents with tunable anion uptake properties toward organic and inorganic anions in aqueous media.