Biochar-Reinforced Alginate-Guar Gum Hydrogels: Composition-Dependent Swelling and Sorption of Cadmium Ions and...

This study focuses on the development of bio-based composite hydrogels (HGs) from an alginate/guar gum matrix reinforced with biochar (BC) and cross-linked with Ca²⁺ ions for the removal of inorganic and organic pollutants. The effects of polymer ratio, cross-linker concentration, and BC incorporation on swelling and sorption toward Cd(II) ions and diuron herbicide were systematically investigated. The Fourier transform infrared (FTIR) spectroscopy confirmed successful network formation and cross-linking. The swelling ratio of BC-filled HGs varied from 20 to 177 g g^-1, depending on composition. Increasing guar content, Ca²⁺ concentration, and BC loading reduced swelling and Cd(II) uptake. The HGs exhibited pH-responsive behavior, with swelling increasing at higher pH values. The effect of electrolyte concentration on swelling shifted from a monotonic decrease at low cross-linker concentrations to a nonmonotonic swelling behavior at high concentrations. Increasing guar fraction extended the time needed to reach swelling equilibrium. The highest Cd(II) sorption capacity (150 mg g^-1) was observed for pure alginate HG, while BC incorporation enhanced diuron uptake (from 3.1 to 4.1 mg g^-1). The opposite pH-dependent sorption trends for Cd(II) and diuron suggested distinct binding mechanisms. Low desorption rates confirmed strong affinity, highlighting the potential of these tunable, sustainable composites for environmental remediation.