Carboxylate-functionalized polyoxo-titanium clusters for adsorption/solar photocatalytic synergistic tetracycline degradation

Adjusting the bandgap of polyoxo-titanium clusters (PTCs) to enhance their visible light catalytic performance is one of the effective strategies. Herein, three PTCs modified by organic carboxylic acid ligands with different conjugated systems were synthesized in one-step, [Ti₆(O₃P-Phen)₂(OiPr)₁₀(L)₂] (OiPr = isopropyl alcohol; L = benzimidazole dicarboxylic acid, Ti₆-BIDC; 4-chloromethyl benzoic acid = CMBA, Ti₆-CMBA; malonic acid = MA, Ti₆-MA), and were used as photocatalysts in the visible light catalytic degradation of tetracycline (50 mL, 50 mg L⁻¹). Ti₆-BIDC showed excellent catalytic activity and cycling stability in the degradation of tetracycline. Importantly, the degradation efficiency under real sunlight was 92.4%. The modification of carboxylic acid ligands significantly changed the photoelectric properties and specific surface area of the compounds. In addition, the results of active species trapping experiments demonstrated that the superoxide anion (˙O₂⁻) radical and hole (h⁺) played dominant roles in TC degradation. The intermediates and possible pathways of TC degradation were analyzed by LC-MS, and the toxicity of the degradation intermediates was evaluated by the Mung bean planting experiment and toxicity estimation software tool (T.E.S.T.). This is the first report on the application of PTCs in photocatalytic degradation of tetracycline, providing new ideas for the degradation of tetracycline.