In this study, the iron-based metal–organic framework MIL-53(Fe) was successfully prepared by a solvent method and used as a photocatalyst for the efficient degradation of DDBAC under visible light. The morphology, structure and photocatalytic properties of MIL-53(Fe) were investigated by SEM, XRD, XPS and UV–vis DRS characterization methods. The optimum conditions for the degradation of DD pathways of DDBAC were analyzed in combination with DFT calculations. Based on molecular orbital theory and free radical quenching experiments, it was demonstrated that hydroxyl radicals were the main contributors in the oxidative degradation of DDBAC. The toxicity of DDBAC and its intermediates was evaluated by culturing Chlorella vulgaris, and the results showed that the Vis/MIL-53(Fe)/H 2 O 2 system was capable of solution detoxification.
Min-Yong Lee,Wen-Long Wang,Qian-Yuan Wu,Nan Huang,Zi-Bin Xu,Hong-Ying Hu
Dodecyl dimethyl benzyl ammonium chloride (DDBAC), a non-oxidizing biocide, is commonly used in municipal wastewater reverse osmosis system. It has been used also as an ingredient in fabric softeners, disinfectants, detergents, phase transfer agent and numerous personal skin care products. In this study, the DDBAC degradation efficiency achieved using UV and persulfate (PS) oxidation processes was investigated. Substantial synergistic effects on DDBAC degradation were found when UV and PS oxidation processes were combined. During the UV/PS process, UV photolysis and reactions with radical species accounted for 42.7% and 57.3%, respectively, of DDBAC degradation. The OH and SO 4 − radicals accounted for 4.6% and 52.7%, respectively, of DDBAC degradation. The calculated k OH,DDBAC and k SO 4 - ,DDBAC rate constants were (1.45 ± 0.16) × 10 9 and (1.51 ± 0.02) × 10 9 M −1 s −1 , respectively. The k obs rate constant for DDBAC degradation increased from 0.047 to 0.150 min −1 when the PS dose was increased from 0.05 to 1.45 mM. The presence of natural organic matter (NOM), HCO 3 − /CO 3 2− , and NO 3 − adversely affected DDBAC degradation. Five main intermediates were identified by high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry. The proposed DDBAC degradation pathway involves benzyl-nitrogen bond cleavage (or subtraction of hydrogen from the alkyl chain), demethylation, hydroxylation, and hydrogen subtraction. UV/PS treatment decreased the acute toxicity of the DDBAC solution in less than 15 min. However, the residual toxicity indicated that toxic oxidation transformation products were formed when DDBAC was treated using the UV/PS process.
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