Search

A study is undertaken of the effect of fluorinating two TiO catalysts, both with the same surface area but one composed only of pure anatase phase (SA) and the other of mixed anatase and rutile phases (P25), on the degradation of phenol, formic acid and aniline. The catalysts were characterised by FTIR, BET, EDAXs, SEM, XRD and DRS-UV–vis studies. The method used for synthesis of the F-P25 and F-SA resulted in fluorinated catalysts with properties different to those of other fluorinated catalysts reported in the bibliography. The results obtained show that, unlike other studies in which the formation of free hydroxyl radicals ([rad]OH) was enhanced with the fluorinated catalysts, in the F-P25 and F-SA catalysts it was the formation of surface hydroxyl radicals ([rad]OH) which was significantly enhanced. In this way, the F-P25 and F-SA catalysts gave rise to higher degradation rate constants of phenol (k), aniline (k) and formic acid (k) than the P25 and SA catalysts., We are grateful for the financial support of the Spanish Ministry of Economy and Competitiveness through the projects CTQ2015-64664-C2-1-P and the Spanish Ministry of Science and Innovation for the UNLP10-3E-726 infrastructure, co-financed with ERDF funds. D. Garzón Sousa would like to thank the University of La Palmas de Gran Canaria for its funding through its PhD Grant Program and Wiâm El-Alami would also like to thank the UNetBA Erasmus Program for its funding through a mobility grant.

The photodegradation of imazaquin, [2-(4,5-dihydro-4-methyl-4-(methylethyl)-5-oxo-1-imidazol-2-yl]-3-quinolinecarboxylic acid (CAS RN: [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , an herbicide belonging to the family of imidazolinone, was investigated using steady-state irradiation in aqueous solutions at different pH values, different wavelengths and different oxygen concentrations. Using spectrometry techniques (UV–vis and fluorescence), p K a values for the ground state, p K a ( S 0 ) , and for the lowest excited singlet state p K a ( S 1 ) , were found to be 3.6 and 7.5, respectively. The degradation of imazaquin appeared to be more effective at pH > p K a ( S 0 ) and in the absence of oxygen. The use of laser flash photolysis has shown the presence of a triplet state in the region from 320 to 550 nm with a maximum centred at 380 nm. By comparing the quenching rate constant, k q , obtained from the quenching of the triplet state by molecular oxygen ( k q = 9.31 × 10 8 mol −1 L s −1 ) and from the Stern–Volmer relation ( k q = 1.13 × 10 8 mol −1 L s −1 ), we deduced that the singlet state also seems to play a role in the photodegradation process. According to the experimental results, it has been found that imazaquin is a rather stable molecule in the dark or at low pH. In pure water, imazaquin degrades slowly and the photodegradation leads to the formation of four photoproducts. Three photoproducts were tentatively identified by HPLC–MS analyses and another one was proposed by taking into account the literature.