Biochar-loaded nZVI/Ni bimetallic particles for hexavalent chromium removal from aqueous solution

The biochar-loaded nZVI/Ni bimetallic nanoparticles (BC@nZVI/Ni) was synthesized by liquid phase co-reduction method and evaluated for its potential Cr(VI) removal capacity. BC@nZVI/Ni had a good removal effect in a wide pH range (2.1-9.2). The removal efficiency reached 100% for 20 mg L−1 Cr(VI) at pH ≤ 3.1. The maximum adsorption capacity of 55.52 mg g−1 was obtained at 298 K. Its excellent removal performance was mainly attributed to the abundant surface functional groups of BC and its prevention effect on nZVI agglomeration, and the reduction effect of Ni(0) on Fe(II). The main mechanism of BC@nZVI/Ni for Cr(VI) removal was electrostatic attraction, ligand exchange, surface complexation, reduction and co-precipitation. The adsorption process fitted well with Freundlich and pseudo-second-order models. It was a spontaneous and endothermic process.