Preparation of rice straw-derived biochar for efficient cadmium removal by modification of oxygen-containing functional groups

In order to enhance the adsorption capacity of cadmium (Cd) ion from aqueous solution, the rice straw-derived biochar (BC800) was modified by a mixture of HNO3 and H2O2 (MHH) with equal volume. Several elemental, chemical and structural characterization methods were used to determine the characteristics of biochars. Batch adsorption experiments were carried out concerning the influences of contact time, initial pH value, and initial concentration. The results indicated that the modified biochar (BCM) was more effective in removing Cd2+ from water than BC800. For 550 mg L-1 Cd2+ concentration solution, the adsorption capacity of 93.2 mg g(-1) was observed for BCM, which was much higher than that of BC800 (69.3 mg g(-1)). The BCM had a significant increase of acidic functional groups with a rate of 101.6% and the component carboxyl, lacton and phenol groups increased by 124.1%, 293% and 1113% respectively, while the specific surface area increased about 22.0%, compared with BC800. The pseudo-second-order model provided high correlation coefficients for BCM, speculating chemisorption of the Cd2+ onto biochars. Therefore, the rice straw-based biochar treated by MHH is considered to be an efficient adsorbent for Cd2+ removal from aqueous solution, especially for high concentrations of cadmium solution. (C) 2018 Published by Elsevier B.V.