Significant role of UV and carbonate radical on the degradation of oxytetracycline in UV-AOPs: Kinetics and mechanism

Abstract

Carbonate radical (CO3(•-)), a selective oxidant, reacts readily with electron-rich compounds through electron transfer and/or hydrogen abstraction. In this study, the role of CO3(•-) in degrading oxytetracycline (OTC) by UV only, UV/H2O2 and UV/persulfate (UV/PS) advanced oxidation processes (AOPs) in the presence of HCO3(-) or CO3(2-) was investigated. For UV only process, the presence of photosensitizers, i.e., nitrate (NO3(-)) and natural organic matter (NOM), had different impacts on OTC degradation, i.e., an enhancing effect by NO3(-) due to the generation of HO(•) and a slight inhibiting effect by NOM possibly due to a light scattering effect. Differently for UV/H2O2 and UV/PS processes, the presence of NO3(-) hardly influenced the destruction of OTC. Generation of CO3(•-) presented a positive role on OTC degradation by UV/NO3(-)/HCO3(-). Such influence was also observed in the two studied AOPs in the presence of both bicarbonate and other natural water constituents. When various natural water samples from different sources were used as reaction matrices, UV only and UV/H2O2 showed an inhibiting effect while UV/PS demonstrated a comparable or even promoting effect in OTC decomposition. After elucidating the potential contribution of UV direct photolysis via excited state OTC* at an elevated reaction pH condition, putative OTC transformation byproducts via CO3(•-) reaction were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Five different reaction pathways were subsequently proposed, including hydroxylation (+16 Da), quinonization (+14 Da), demethylation (-14 Da), decarbonylation (-28 Da) and dehydration (-18 Da). The significant role of UV at high pH and CO3(•-) on OTC removal from contaminated water was therefore demonstrated both kinetically and mechanistically.

Direct fabrication of lamellar self-supporting Co3O4/N/C peroxymonosulfate activation catalysts for effective aniline degradation

“…Advanced oxidation processes based on Å OH or Å O 2 À have been commonly used in the degradation of persistent organic pollutants in water. For example, lots of technologies have been applied to generate Å OH or Å O 2 À radicals for aniline degradation including Fenton process [6,7], photocatalysis [8][9][10], catalytic wet oxidation [11][12][13], ozonation [14][15][16] and electrochemical oxidation [17][18][19][20]. However, these technologies have several limitations such as metal leaching, low pH rang (3)(4), excessive sludge production, and the high hydrogen peroxide transportation cost [1,4].…”

The effect of anions on decolorization of textile azo dye Reactive Orange 16 with UV/H2O2 process

“….... (7) .... (8) Effect of inorganic anions Many inorganic anions, such as CO 3 2-, HCO 3 -, NO 3 -, SO 4 2-, Cl -, could be present in textile effluents and hence significantly influence the removal of organic pollutants with AOP processes [14][15][16]. Among all anions, the influence of carbonate and bicarbonate are the most investigated ones, since they can be present in a significant amount both in surface waters and in wastewaters.…”

“…The overall reaction of nitrate photolysis can be presented by the reaction (11) . (14) Furthermore, it is reported that nitrite anions are very efficient • OH radicals scavengers (k = 1x10 10 M -1 s -1 ), unlike nitrates which are not so efficient (k < 1.0 x 10 5 M -1 s -1 ), and hence can negatively affect UV/H 2 O 2 treatments, particularly in the nitrate rich water (reactions (15) and (16) Decolorisation of RO16 dye by UV/H 2 O 2 process was conducted in the presence of 10, 50, and 100 mmol L -1 of nitrate. As shown in Fig 3. about 98% of 50 mg dm -3 RO16 dye was decolorized in the absence of nitrate, while in the presence of 10, 50, and 100 mmol L -1 of the nitrate the obtained percentage of decolorisation after 20 min of irradiation was 98%, 95%, and 85%, respectively.…”

Advanced oxidation processes for antibiotics removal in aqueous environment

“…In practical application, water quality and cost should be considered to determine initial pH. CO in UV/PS system was presented [7]. Different from the inhibition of …”

“…However, it would inhibit the processes without UV or involving oxidants [4,7]. The inhibition mechanism of phosphates is (1) radical scavenging; (2) forming precipitate with metal ions, which covers the surface of catalyst.…”