Application of vacuum-ultraviolet (VUV) for phenolic homologues removal in humic acid solution: Efficiency, pathway and DFT calculation

• Published in: Journal of hazardous materials 2020-02, Vol.384, p.121464-121464, Article 121464
• Main Authors: Cao, Ting-ting, Tie-fu, Xu, Zhao, Mu-nan, Xu, Jiang, Cui, Chong-wei
• Format: Article
• Language: English
• Subjects: Benzoic acid (BA); Humic acid (HA); Phenolic homologues; Simulative natural water; Vacuum-ultraviolet (VUV)
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.121464

[Display omitted] •The removal rate of the six phenolic homologues exhibited discrepancy under the VUV system in different water matrix.•Carboxy group of HA was the main reason to restrain the removal of phenolic homologues.•The de-nitration rate of PNP was superior to the de-chlorination rate of OCP under VUV system. Vacuum-ultraviolet (VUV) photo-initiated oxidation of phenolic homologues in simulative natural water were investigated, including phenol, o-dihydroxybenzene (ODB), m-dihydroxybenzene (MDB), p-dihydroxybenzene (PDB), paranitrophenol (PNP) and o-chlorophenol (OCP). Results showed the phenolic homologues removal rate reached at least 90% in pure water, which was dependent on temperature, pH, concentration of HA, and functional group of HA. Experimental results indicated that 0.2 mg/L HA might be a critical point. Additionally, the rate constant of the six phenolic homologues reduced by 76.85%, 77.81%, 71.91%, 79.15%, and 55.69%, respectively in the MDB solution, and 79.73%, 82.80%, 95.36%, 80.38%, and 92.64%, respectively in the benzoic acid (BA) solution, compared to the rate constant in pure water. Moreover, quantum chemistry calculation indicated that the variances between phenolic compounds in removal rate were attributed to the substituent on the benzene ring. And, to some extent, the carboxy group of HA was supposed to arose the suppression for phenolic homologues removal rate. Mechanism involved phenolic homologues degradation using vacuum-ultraviolet (VUV) was summarized, where it underwent the formation of quinone structures, ring opening, short-chain organic acid, even eventually the transformation into NO3− and Cl− of PNP and OCP.