Constructing anion traps on biomass-based aerogels for efficient TcO4−/ReO4− removal

Abstract

The long half-life and high environmental mobility of TcO₄⁻ make its effective capture from nuclear wastewater both critical and challenging. This study developed a cationic polymer aerogel based on the biomass material chitosan (CTS) for the highly efficient removal of TcO₄⁻/ReO₄⁻. This approach involves the crosslinking of chitosan and polyethyleneimine via a Schiff base reaction, followed by the formation of quaternary ammonium sites on the aerogels using a quaternization agent. The quaternary sites serve as specific anion traps, which creates a hydrophobic microenvironment that facilitates selective TcO₄⁻/ReO₄⁻ capture. Experimental results demonstrate that the aerogel exhibits high ReO₄⁻ adsorption capacity (713 mg/g) and excellent selectivity, with removal rates of 62.93 %, 71.16 %, and 75.71 % in the presence of 500 times the concentration of NO₃⁻, SO₄²⁻, and PO₄³⁻, respectively. Additionally, the aerogel achieves an 83.4 % ReO₄⁻ removal rate from simulated Hanford wastewater. This material has a high removal rate for TcO₄⁻/ReO₄⁻ over a broad pH range. Characterization techniques, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), have demonstrated the effective adsorption of ReO₄⁻ ions within aerogel channels. The aerogel's anion traps, combined with its distinctive porous channel structure, offer exceptional adsorption capabilities, surpassing most macroscopic plastic adsorbents and numerous powdered high-porosity materials.