Design and fabrication of exfoliated Mg/Al layered double hydroxides on biochar support

Tailored design and fabrication of biochar-based adsorbents with high porosity and well dispersion is a critical process for enhancing their environmental applications. To elucidate the material structure-performance relationship, this study synthesized and compared corn straw biochar-supported Mg/Al layered double hydroxides composites (LDHs-BCs) using conventional co-precipitation or aqueous miscible organic solvent treatment (AMOST) methods under various pyrolysis temperatures (350, 550, 750, and 950 °C) and metal loadings (5 and 15 wt%). The comprehensive surface characterization demonstrated enlarged interlayer spacing, increased specific surface area, and smaller crystal size of LDHs as well as lowered intensities of O-containing functional groups in LDHs-BCs. These results suggested that, in comparison to conventional co-precipitation method, AMOST method can serve as a simple, cost-effective, and robust method to induce exfoliation, higher dispersion, and more stable attachment of LDHs on the biochar surface. The Langmuir adsorption isotherms further demonstrated that the AMOST-derived composites prepared at higher temperatures (i.e., 750 and 950 °C) and lower metal loading (i.e., 5 wt%) exhibited superior contaminant removal capacities (280.7–286.2 mg PO43−/g and 92.5–94.7 mg Cu(II)/g at pH 5.0–6.0). The synergistic effect was attributed to coupled functionalization of LDHs and biochar under customized synthesis conditions. These results provide valuable insights into fabricating high-performance and environmentally friendly LDHs-BCs for green remediation and sustainable development.