Study on the Performance of N-Doped Biochar for Removing Pb, Cu, and Crfrom Water

In this study, N-doped straw biochar(N-BC) was prepared using urea for the removal of Pb, Cu, and Cr from water. SEM, FT-IR, XRD, and XPS characterization analyses demonstrated the successful loading of N onto the biochar. The adsorption performance of the N-doped biochar was evaluated by orthogonal and single-factor experiments. The results showed that the magnitude of the effect on the adsorption of the three heavy metals was consistent with initial pH > dosing > pyrolysis temperature. In addition, the optimum initial pH for the adsorption of Pb, Cu, and Cr was 5, 6, and 2, respectively. Compared to the single biochar, the adsorption of Pb, Cu, and Cr by N-doped biochar increased from 6.33, 4.25, and 3.78 mg/g to 30.2, 16.28, and 14.53 mg/g. The adsorption of Pb, Cu, and Cr followed quasi-secondary kinetics and the Langmuir model. Mechanistic studies showed that the adsorption mechanism of N-doped biochar for Cu and Pb involved surface adsorption, cation-π bonding, and complexation, while that for Cr included electrostatic attraction and reduction. The reusability and excellent adsorption properties of the surface N-doped biochar from cycling experiments indicate that biochar is a good material for the removal of heavy metals from water.