Role of pH on photolytic and photocatalytic degradation of antibiotic oxytetracycline in aqueous solution under visible/solar light: Kinetics and mechanism studies

Abstract

In this study, the photochemical degradation of the antibiotic oxytetracycline (OTC) at different pH values was investigated in aqueous solution under visible and solar light irradiation. Particular emphasis was given to the kinetics and mechanism during the photolytic and photocatalytic degradation of OTC. A comparative study of the photolysis of OTC under solar light, with different initial concentrations and in the presence of scavengers of reactive oxygen species (ROS), revealed a self-photosensitization pathway with evidence of singlet oxygen generation at pH 8.5 and 11.0 during OTC photolysis. The three-dimensional fluorescence spectra of OTC at different pH values demonstrate that OTC only exhibits significant emission spectra at pH 8.5 and 11.0. The change of the internal electrostatic force between the electron withdrawing group and the dehydrogenation moiety of OTC as a function of solution pH values was proposed as a critical factor influencing the energy states and observed reaction pathways of OTC under light irradiation. Moreover, the mechanism of photochemical degradation of OTC was investigated with nitrogen and fluorine doped titanium dioxide (NF-TiO 2 ) film at different pH values under visible and solar light in the presence of tert-butyl alcohol (TBA), sodium azide (NaN 3 ), potassium iodine (KI) and catalase as scavengers. Five pathways, including direct photolytic degradation, UV/vis light-induced photocatalytic oxidation and reduction, and visible light-induced self-photosensitized oxidation and reduction, were proposed and verified during the photocatalytic degradation of OTC with NF-TiO 2 film.

Synthesis of Magnetic Sonophotocatalyst and its Enhanced Biodegradability of Organophosphate Pesticide

“…The solution pH is an important parameter because it determines the surface charge properties of the catalyst, the charge of the pollutant and the adsorption of the pollutant onto the catalyst surface. 25 The effect of pH on the sonophotocatalytic degradation of DDVP was investigated in the range of 5. . As shown in Figure 4, after 240 min of irradiation, the COD Cr removal efficiency of DDVP were 54.19%, 63.13%, 59.74% and 60.70% at pH values of 5.3, 7.3, 9.1 and 10.3, respectively.…”

“…A desired concentration of DDVP was prepared by dissolving the 12 L of dechlorinated tap water aerated for 40 min at room temperature (19)(20)(21)(22)(23)(24)(25) o C). Then, the catalyst was added to the above DDVP solution.…”

Process enhancement at near neutral pH of a homogeneous photo-Fenton reaction using ferricarboxylate complexes: Application to oxytetracycline degradation

“…The decreasing reaction rates at pH 4.1, pH = 5.0 and pH = 6.0 experiments, 8.6 ± 0.5, 6.3 ± 0.2 and 2.3 ± 0.1 L -1 kJ, respectively, appear to reflect this relationship between the molar fractions of the referred iron-oxalate complexes and their respective quantum yields. On the other hand, the positive influence of increasing solution pH on OTC degradation by means of its solar/visible light absorption properties, as described by Zhao et al [43], did not seem to play a significant role in this process. Considering these results, the working pH of 5.0 was chosen for the subsequent set of experiments, since no extra dosage of oxalic acid was needed to obtain a satisfactory 49% mineralization of the initial DOC content, OTC was no longer for unadjusted pH0 and controlled pH0 = 5.0, respectively.…”

Assessment of solar driven TiO2-assisted photocatalysis efficiency on amoxicillin degradation

“…However, according to Fig. 6b,the 1O2 reactive species also plays an important role in AMX self-photosensitization under UV/visible solar light, as reported by Zhao et al (2013).…”