Elevated efficiency in tartrazine removal from wastewater through boron-doped biochar: enhanced adsorption and persulfate activation

Abstract

Boron-doped biochar (B-BC) was synthesized by pyrolysis using solid waste of sorghum straw as raw material. The specific surface area of B-BC increased significantly by 2.38 times compared to that of pure BC. This enhancement allowed B-BC (0.3 g L⁻¹) to achieve complete adsorption of 10 mg L⁻¹ tartrazine (TTZ) within 40 min. Moreover, acidic conditions were more favorable for TTZ adsorption, achieving complete removal of TTZ in only 15 min at a pH of 3.0. Interestingly, the adsorption rate of TTZ by B-BC in the presence of 0.05 M Cl⁻ was approximately 2.12 times higher than that in the absence of Cl⁻. When other background electrolytes were present, excluding PO₄³⁻, complete adsorption of TTZ could also be achieved within 60 min. Thermodynamic analysis and DFT calculations described the parameters of B-BC for TTZ adsorption, including $\Delta {\text{G}}^{\Theta }$ (< 0 kJ mol⁻¹), $\Delta {\text{H}}^{\Theta }$ (− 2.199 kJ mol⁻¹), $\Delta {\text{S}}^{\Theta }$ (− 6.068 J mol⁻¹ K⁻¹), and the adsorption energy (E_ads = − 0.6919 eV), indicating a tendency towards a spontaneous adsorption process. Moreover, the strong electron transfer ability of B-BC and the oxygen-containing groups promoted the activation of PDS and generation of active substances such as ¹O₂, O₂^•−, and SO₄^•−, thereby degrading TTZ into products with lower biological toxicity. When the added PDS was only 0.1 mM, the degradation rate constant of TTZ could reach 0.1481 min⁻¹. Furthermore, boron doping enhanced the stability of biochar, enabling the complete removal of 10 mg L⁻¹ TTZ even after recycling and regeneration. In summary, this study offers a practical solution for the resource utilization of solid waste sorghum straw and the treatment of TTZ-polluted wastewater.

Highlight

•	Boron doping significantly increased the specific surface area of biochar by 2.38 times.
•	B-BC exhibited complete adsorption of TTZ in only 15 min at a pH of 3.0.
•	Addition of 0.05 M Cl− increased the adsorption rate of TTZ on B-BC by 1.12 times.
•	Free radicals and nonradicals contributed to TTZ degradation in B-BC/PDS system.
•	Degradation products of TTZ displayed reduced toxicity to typical aquatic organisms.

Funding

Natural Science Foundation of Guangdong Province, China(2023A1515030162)

Guangdong Basic and Applied Basic Research Foundation(2022A1515140122)

National Natural Science Foundation of China(42377245)

Guangdong Foundation for Program of Science and Technology Research, China(2023B1212060044)