Efficient removal of Cr(VI) from aqueous solution by hydrochloric acid and polypyrrole co-modified sludge-based biochar

In this work, in view of the poor adsorption capacity of sludge-based biochar, a sludge-based biochar adsorbent co-modified with hydrochloric acid and polypyrrole (PPy/SBC-HCl) was prepared and used to remove Cr(VI) from aqueous solution. Its characterization of SEM, EDS, BET, XRD, FT-IR, and XPS show that the removal mechanism of Cr(VI) by PPy/SBC-HCl includes electrostatic adsorption, ion exchange, reduction, and complexation. The removal efficiency of Cr(VI) by PPy/SBC-HCl decreases with the increase of pH. The coexisting cations Ca2+ and Mg2+ have a slight negative effect on it, while the oxoacid anions have a great negative effect on it. The adsorption of Cr(VI) by PPy/SBC-HCl is a spontaneous endothermic process, which conforms to the pseudo-second-order adsorption kinetic model and the Freundlich adsorption isotherm model. The maximum adsorption capacity is 97.37 mg g−1 at pH 2.0 and temperature 298 K.