Insights into the removal of Cd and Pb from aqueous solutions by NaOH-EtOH-modified biochar

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 degrees 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 m(2)g-(1),z respectively) were superior to that of the BC (36.98 m(2)g(-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)-pi, Pb(II)-pi 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. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

Enhancing surface functional groups on biochar is crucial for improving its adsorption capacity towards toxic metals. The NaOH-C2H5OH modified biochar showed a higher specific surface area, more O-containing functional groups, and introduced more C=C groups, leading to enhanced adsorption properties, especially for Cd(II) and Pb(II). Spectroscopic analysis indicated that Cd(II)-pi and Pb(II)-pi interactions were the predominant mechanisms for the toxic metals' collection on the NaOH-C2H5OH modified biochar, with O-functional groups facilitating Pb(II) binding more effectively than Cd(II) in the mixture solution.