In this work, beta-cyclodextrin–chitosan modified walnut shell biochars (β-CCWB) were synthesized as a low-cost adsorbent for the removal of heavy metal Cr(VI) from aqueous solutions. Batch sorption experiments were carried out to investigate the adsorption characteristic of β-CCWB. The experimental data fitted a pseudo-second order equation and Freundlich isotherm model, and the optimum adsorption of the modified biochar was observed at pH 2.0 with an adsorption capacity of 206 mg g⁻¹. Thermodynamic analysis showed that the adsorption process was spontaneous and endothermic. The removal efficiency of Cr(VI) by β-CCWB (about 93%) was higher than that by the pristine biochar (about 27%). Characteristic analysis indicated that amino and carboxyl groups were the major functional groups for Cr(VI) sorption, and implied that the electrostatic attraction of Cr(VI) to the positively charged biochar surface, reduction of Cr(VI) to Cr(III) ions and the complexation between Cr(III) ions and β-CCWB functional groups were responsible for Cr(VI) removal mechanism in this research. Furthermore, the environmentally friendly and low-cost β-CCWB could be applied as a potential effective adsorbent to remediate Cr(VI) contamination from aqueous solution.

Three biochars converted from water hyacinth biomass at 300, 450, and 600 °C were used to investigate the adsorption properties of Cd²⁺ and Pb²⁺.

A biochar supported calcined-Mg/Al layered double hydroxides composite (CLDHs/BC) was synthesized by a one-pot slow pyrolysis of LDHs preloaded bagasse biomass. Multiple characterizations of the product illustrated that the calcined-Mg/Al layered double hydroxides (CLDHs) were successfully coated onto the biochar in slow pyrolysis of pre-treated biomass. The as-synthesized CLDHs/BC could efficiently remove antibiotic tetracycline from aqueous solutions. The coating of CLDHs significantly increased the adsorption ability of biochar, and CLDHs/BC exhibited more than 2 times higher adsorption capacity than that of the pristine biochar (BC) in the tested pH range. The maximum adsorption capacity of CLDHs/BC for tetracycline was 1118.12 mg/g at 318 K. The experimental results suggested that the interaction with LDHs on biochar played a dominant role in tetracycline adsorption, accompanied with π–π interaction and hydrogen bond. This study provides a feasible and simple approach for the preparation of high-performance material for antibiotics contaminated wastewater treatment in a cost-effective way.