Simultaneous removal of dyes and Cr(VI) by phosphoric acid–activated biochar: Adsorption performance and cytotoxicity assessment

In this study, biochar was produced from phosphoric acid (H 3 PO 4 )-activated biomass (forest logging residues and oak), and the adsorption characteristics of multi-pollutants (methylene blue, rhodamine B, and Cr(VI)) on the biochar were analyzed. In addition, cytotoxicity assessments for human hepatocarcinoma cells and embryonic kidney cells were performed using biochar leachates obtained before and after the adsorption experiments to evaluate the effects on human cells. In the XRD patterns and FTIR spectra of H 3 PO 4 -activated biochar, peaks corresponding to P-O-P bonds, HO-P = O bonds, and P = O bonds were observed, indicating that H 3 PO 4 related functional groups were successfully introduced into the biochar. The specific surface area of H 3 PO 4 -activated biochar increased compared to untreated biochar, reaching 1369.50 m 2 /g in forest logging residues and 1563.90 m 2 /g in oak, respectively, and the pore size decreased to less than 2 nm. As a result of multi-pollutants adsorption on the biochar, the removal efficiency improved in H 3 PO 4 -activated biochar for both species. In particular, H 3 PO 4 -activated biochar derived from forest logging residues showed high removal rates for all types of pollutants under the tested conditions. The adsorption of multi-pollutants on H 3 PO 4 -activated biochar is driven by a combination of physical adsorption, pore-filling, electrostatic forces, π-π interactions, and Cr(VI) reduction. Additionally, the biochar demonstrated high removal rates over a wide pH range and maintained significant reusability for up to three cycles. As a result of the cytotoxicity assessment, no significant cytotoxicity was observed in the biochar leachate after adsorption of multi-pollutants.