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

Highlights

•	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.

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 $\mathrm{\Delta }{\text{G}}^{\mathrm{\Theta }}$ (< 0 kJ mol⁻¹), $\mathrm{\Delta }{\text{H}}^{\mathrm{\Theta }}$ (− 2.199 kJ mol⁻¹), $\mathrm{\Delta }{\text{S}}^{\mathrm{\Theta }}$ (− 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.

Funding

Natural Science Foundation of Guangdong Province, China(2022A1515010333); 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)