New insights into ball milling effects on MgAl-LDHs exfoliation on biochar support: A case study for cadmium adsorption

Ball milling (BM) as a solvent-free technology has been widely used to tailor the biochar-based adsorbents with high porosity and well dispersion for enhancing their environmental applications. In this study, the ball-milled layered double hydroxides (LDHs) biochar composite (B-LDHs-BC) was successfully fabricated with BM method for Cd(II) adsorption and the BM effects on the LDHs-BC structure-performance relationships were investigated. The solid-state characterization demonstrated the LDHs were successfully exfoliated by BM on the B-LDHs-BC surface which was identified by the enlarged basal spacing and reduced crystallite size of the LDHs. Although the BET surface area of B-LDHs-BC (226 m2/g) was slightly lower than the ball-milled BC, the B-LDHs-BC had more O-containing functional groups and higher adsorption capacity (119 mg/g). The kinetics experiments indicated that the Cd(II) removal by B-LDHs-BC was through both the physical and chemical adsorption processes, and the liquid membrane diffusion was the rate-controlling step. The positive BM effects mainly induced more abundant acidic functional groups and active adsorption sites, and thus enhanced Cd(II) performance of B-LDHs-BC. This work demonstrated a facile solvent-free method for production of the exfoliated LDHs modified BC composite, and also well illustrated the BM effects which can extend their practical use in environment.

Automated summary

Ball milling was used to fabricate a B-LDHs-BC composite with enhanced Cd(II) adsorption capacity, due to the exfoliation of LDHs on the BC surface. The BM effects induced more acidic functional groups and active adsorption sites, leading to improved performance of B-LDHs-BC in Cd(II) removal. This study demonstrated a solvent-free method for producing exfoliated LDHs modified BC composites, showing potential for practical applications in the environment.