Preparation and characterization of a novel graphene/biochar composite and its application as an adsorbent for Cd removal from aqueous solution

A novel graphene/biochar composite (BG composite) was synthesized by mixing graphene (Gr) onto feedstock biomass followed by slow pyrolysis. The composite was then tested for its sorption capacity of Cd from aqueous solutions. Structure and morphology analysis showed that graphene was coated on the biochar surface, resulting in a larger surface area, more functional groups, greater thermal stability, and higher removal efficiency of Cd in comparison to unmodified biochar. The sorption capacity of the BG composite for Cd was 1.26-2.36 times that of biochar. A pseudo second-order model adequately simulated sorption kinetics. The sorption isotherms were simulated well by Langmuir models, and calculated maximum Cd adsorption capacities did not change significantly with increasing temperature. Thermodynamic parameters showed that the sorption process of Cd onto the BG composite was feasible and spontaneous. The results of the adsorption experiments, as well as the characteristics of biochar, demonstrate that the process of Cd adsorption on BG composites is mainly physical adsorption accompanied by other chemical adsorption phenomena, such as complexation and ion exchange. This study highlights the use of a BG composite as a multifunctional adsorbent for the efficient, economic, and environmentally friendly treatment of pollutants.