Purification of pesticide-rich wastewater 2,6-dichlorophenol in solar photo-oxidation reactor with visible light

2,6-Dichlorophenol (2,6-DCP), a compound used for synthesizing medical and pharmaceutical agents, is highly toxic and potentially carcinogenic. Advanced oxidation has been used for the cleavage of strong bonds in 2,6-DCP, giving a reliable and practical option compared with the conventional wastewater treatment systems. Hence, this study focused on the application of a solar photo-oxidation process to treat herbicides wastewater containing 2,6-DCP. Bismuth chloride was combined with biochar to maintain the dual benefits of 2,6-DCP adsorption and degradation concomitantly. The O–Bi–O and Bi–O bonds were successfully detected in the synthesized Bi ₁₂ O ₁₇ Cl ₂ , whereas the synergetic effect between Bi ₁₂ O ₁₇ Cl ₂ and biochar was validated by increasing the carbon-based functional groups, reducing particle size (14–32 nm), and creating more active sites of the composite. The initial 2,6-DCP concentration of 122 mg/L was reduced to 17 mg/L (86.0% removal efficiency) within 6 h of photodegradation at a pH of 2.3 and a catalyst dosage of 100 mg/L. Concurrently, the phenol concentration in the aqueous solution increased from 4.7 to 32.4 mg/L, respectively. Reusing the photocatalytic reactions three times by the biochar/Bi ₁₂ O ₁₇ Cl ₂ composite reduced the 2,6-DCP removal efficiency by only 7.7%. Biochar exhibited an adsorption energy of -14.8 kJ/mol to capture 2,6-DCP, and it accumulated photo-excited electrons that react with adsorbed oxygen and/or dissolved oxygen to generate super oxygen radicals (•O ₂ ⁻ ). Super hydroxyl radicals (•OH) could also be generated from the positive holes (h ⁺ ) in the valence band of Bi ₁₂ O ₁₇ Cl ₂ . These radicals could cleave C–Cl bonds of 2,6-DCP, generating Cl ⁻ ions, dechlorinated product 2-CP, and phenols. The treatment of wastewater containing 2,6-DCP by the proposed biochar-based photocatalyst could cost 10.3 USD/m ³ .