Quaternization of lignin hydrochar integrated with vertically oriented alginate aerogel toward ReO4- removal: Performance and mechanism.

Herein, an emerging vertically oriented alginate aerogel composites (QLHC@A aerogel) was constructed by combining the mild ionic crosslinking technique with directed freeze-casting to achieve adsorptive removal of ReO4- (the chemical analogue of TcO4-). The lignin hydrochar in aerogel composites served as a bridge connecting quaternary ammonium groups to fabricate functional addition, among the PDDA-modified lignin hydrochar investigated, QLHC100 exhibited the best adsorption performance, up to 212.95 mg/g, while the regular lamellar structure and good hydrophilic property of alginate-based aerogel allowed rapid diffusion of ReO4- anion in water. When the usage amount of QLHC100 powder became 0.8 g, the optimal ReO4- removal efficiency of QLHC@A aerogel reached 188.90 mg/g at pH 4, 0.1 g/L and 303 K. Batch adsorption experiments also validate that the ReO4- adsorption process was mightily pH-dependent behavior, and adsorption behavior fitted both the pseudo-second-order kinetic model and the Langmuir isothermal model well. Meanwhile, QLHC@A aerogel had a high adsorption selectivity, excellent chemical tolerance, and good reuse performance. Based on various characterization techniques and DFT calculation result, the adsorption mechanism of ReO4- on QLHC@A aerogel is mainly dominated by electrostatic adsorption and strong affinity between quaternary ammonium groups and ReO4-. Significantly, this strategy can be expanded to include high-performance aerogel composites for the remediation of nuclear effluent contaminated with TcO4-.