Removal of Cr(VI) from aqueous solutions using polyamidoamine dendrimer-modified biochar

In this study, a novel set of polyamidoamine (PAMAM) dendrimer-modified biochar adsorbents (BC-G1, BC-G2, and BC-G3) were fabricated using the "graft onto" method. The results showed that the modified biochar adsorbents, with the inclusion of amine functional groups, exhibited higher Cr(VI) removal efficiency compared with the original biochar at pH 2. The adsorption capacity of biochar adsorbents was in the following order: BC-G2 > BC-G1 > BC-G3, with maximum adsorption capacity of 120.77, 101.52, and 40.98 mg/g at 30 degrees C, respectively. The effects of cations Cu(II), Cd(II), Mn(II), Ca(II), and K(I) or anions (Cl-, NO3-, and HPO42-) in wastewater on the adsorption of Cr(VI) were insignificant, except for SO42-. The adsorption process of all biochar materials for removing Cr(VI) was well described using the pseudo-second-order kinetics model and Langmuir adsorption isotherm model. The Cr(VI) adsorption was primarily based on the chemical adsorption of a single molecular layer, accompanied by electrostatic interaction, reduction, and surface complexation. In addition, the adsorbents could be regenerated using a 0.2 M NaOH solution, and the adsorption capacity of the BC-G2 remains high for four adsorption-desorption cycles. Therefore, PAMAM dendrimer-based biochar adsorbent (BC-G2) can effectively remove Cr(VI) from wastewater.