Tunning the defects in lignin-derived-carbon and trimetallic layered double hydroxides composites (LDH@LDC) for efficient removal of U(VI) and Cr (VI) in aquatic environment

Utilizing different absorbents to remove heavy metals from aquatic environment has been extensively investigated because of its simple operation, good reusability, and low cost. The removal efficiency of these adsorbents, nevertheless, need to be further enhanced to meet the practical requirement. In this study, we demonstrate defect engineering as an effective approach to enhance the performance of biochar-based composites for U(VI) and Cr (VI) removal. Lignin derived carbon and Ca/Fe/Al-trimetallic layered double hydroxide composites (LDH@LDC) is prepared by hydrothermal method. Defects are introduced into the LDH layer by H2 plasma treatment. The obtained defective LDH@LDC exhibits outstanding removal efficiency for U(VI) (267.65 mg/g at pH = 5.0, T = 308.15 K, CInitial = 30 mg/L), which is much higher than LDH@LDC as-prep (190.47 mg/g at pH = 5.0, T = 308.15 K, CInitial = 30 mg/L). Similar defect-induced enhancement is observed for the removal of Cr(VI). The thermodynamic and kinetic studies of the removal process, as well as the surface analyze suggest that the removal mechanism of U(VI) and Cr(VI) by the as-prepared and plasma-treated LDH@LDC were both dominated by ion exchange. The plasma treatment introduces defects into the LDH layer, which effectively promote the ion exchange between the LDH layer and the heavy metal in the aquatic environment, leading to strongly enhanced removal performance. This study clarifies the critical role of defects in heavy metal removal process and provides a new pathway of designing high performance absorbents for water remediation.