Comparison of adsorption behavior of Pb(II) by acid–alkali and chitosan modified biochar derived from kiwifruit branch

In this work, the kiwifruit branch, a kind of agricultural waste, was reused as a raw material to prepare biochar adsorbent for the removal of Pb(II) from aqueous solution. Then pristine biochar (BC) was further modified to form acid–alkali modified biochar (OBC) and chitosan modified biochar (CBC) to enhance adsorption efficiency toward Pb(II). Characterization experiments with SEM, FTIR and XRD suggested that surface functional groups and crystallization degree of OBC and CBC were all increased in comparison with BC. Batch sorption experiments showed that, compared with BC, the adsorption capacity of Pb(II) by OBC and CBC were improved by 19.57 and 8.37%, respectively. The pseudo-second-order model and the Freundlich model were better for describing the kinetics and isotherms for Pb(II) adsorption onto OBC and CBC, respectively. Accordingly, chemisorption on the heterogeneous adsorption surface played a dominant role in Pb(II) removal.