Insights into the removal of Cd and Pb from aqueous solutions by NaOH–EtOH-modified biochar
Tong Cai, Huihui Du, Xiaoli Liu, Baiqing Tie, Zhaoxia Zeng
Abstract
The enhancement of surface functional groups on biochar is essential to improving its toxic metals adsorption capacity. In this study, we used two solutions: NaOH(aq) and NaOH dissolved in absolute ethanol (C2H5OH) to dope the surface of powdered oiltea camellia shell. Then, the shells were pyrolyzed at 500 °C for 120 min to obtain NaOH-modified biochar (SBC), NaOH–C2H5OH-modified biochar (EBC), and the undoped sample (BC). After modification, the special surface area, O-containing functional groups, especially C=C were improved. The specific surface area of EBC and SBC (91.76 and 56.83 m2g−1, respectively) were superior to that of the BC (36.98 m2g−1). With NaOH–C2H5OH, more C=C groups were introduced via elimination reaction, enhancing its adsorption properties. EBC consistently showed higher adsorption efficiency than BC for Cd(II) and Pb(II). Moreover, the spectroscopic analysis revealed that Cd(II)-π, Pb(II)-π interactions were the predominant mechanisms for the toxic metals’ collection on the EBC, each contributing 75.45% and 58.60%, respectively. Besides, the O-functional groups onto EBC surface bonded easily to Pb(II) than Cd(II) in the mixture solution. Therefore, EBC produced in the NaOH–C2H5OH system, as efficient and cost-effective biochar, is promising for toxic metals adsorption.