A new methodology to assess the performance of AOPs in complex samples: Application to the degradation of phenolic compounds by O3 and O3/UV-A-Vis

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Degradation characteristics of refractory organic matter in naproxen pharmaceutical secondary effluent using vacuum ultraviolet-ozone treatment

Vacuum ultraviolet-ozone (VUV-O3) treatment was found to be superior to ultraviolet-ozone (UV-O3) treatment in terms of ozone utilization and hydroxyl radicals (·OH) generation when used to treat the secondary effluent (SE) from a naproxen pharmaceutical plant. VUV-O3 treatment was beneficial in terms of decolorization (100%), chemical oxygen demand removal (43.29%), and total organic carbon removal (54.81%). The VUV-O3 process was applicable over a wide pH range, and the presence of various anions had no significant influence on the oxidation efficiency. After treatment, the genotoxicity, unsaturation degree, and polarity of the SE decreased. In addition, the oxidation sensitivities of the fluorescent organic compounds were ranked as follows: humic acid-like > tyrosine-like > fulvic acid-like > tryptophan-like Moreover, the VUV-O3 process effectively converted refractory organic matter (molecular weights, MW > 2000 Da) into short-chain molecules with low MWs. The removal efficiency of dissolved organic matter (DOM) was 63.27%, and 77.27% of the DOM was found to be reactive to VUV-O3 oxidation. The unsaturation, polarity, and compositional complexity of the DOM decreased after VUV-O3 treatment. Finally, it was deduced that the direct O3 oxidation,·OH, O2·- and 1O2 played a role in the VUV-O3 oxidation process.

Fluorescence Spectroscopy and Chemometrics: A Simple and Easy Way for the Monitoring of Fluoroquinolone Mixture Degradation

In this work, fluorescence excitation-emission matrices (EEMs), in combination with the chemometric tool and parallel factor analysis (PARAFAC), have been proposed as an unexplored methodology to follow the removal of the fluorescent contaminants of emerging concern, fluoroquinolones (FQs). Ofloxacin, enrofloxacin, and sarafloxacin were degraded by different advanced oxidation processes employing simulated sunlight (hν): photolysis, H₂O₂/hν, and photo-Fenton. All experiments were performed in ultrapure water at three different pH values: 2.8, 5.0, and 7.0. With the obvious advantage of multivariate analysis methods, EEM-PARAFAC allowed the monitoring of degradation from the overall substances (original and formed ones) through simultaneous, rapid, and cost-efficient fluorescence spectroscopy determinations. A five-component model was found to best fit the experimental data, allowing us to (i) describe the decay of the fluorescence signals of the three parent pollutants, (ii) follow the kinetics profile of FQ-like byproducts with similar EEM fingerprints than the original FQs, and (iii) observe the formation of two families of reaction intermediates with completely different EEMs. Results were finally correlated with high pressure liquid chromatography, total organic carbon, and toxicity tests on Escherichia coli, showing good agreement with all the studied techniques.

Flexible Carbon-Fiber/Semimetal Bi Nanosheet Arrays as Separable and Recyclable Plasmonic Photocatalysts and Photoelectrocatalysts

In this work, we prepared flexible carbon-fiber/semimetal Bi nanosheet arrays from solvothermal-synthesized carbon-fiber/Bi₂O₂CO₃ nanosheet arrays via a reductive calcination process. The flexible carbon-fiber/semimetal Bi nanosheet arrays can function as photocatalysts and photoelectrocatalysts for 2,4-dinitorphenol oxidation. Compared with carbon-fiber/Bi₂O₂CO₃ nanosheet arrays, the newly designed flexible carbon-fiber/semimetal Bi nanosheet arrays show enhanced ultraviolet-visible (UV-vis) light absorption efficiency and photocurrent, photocatalytic, and photoelectrocatalytic activities. Photocatalytic analyses indicate that the surface plasmon resonance (SPR) of semimetal Bi occurs under solar-simulated light irradiation during the photocatalytic process. The carbon-fiber traps the hot electrons exerted from the SPR of semimetal Bi and creates holes in the semimetal Bi nanosheets, which boosts the photocatalytic activity of the carbon fiber through plasmonic sensitization. Both photocatalytic experiments and density functional theory (DFT) calculations indicate that the electrons transferred to the carbon fiber and the holes created in semimetal Bi contribute to the formation of •O₂^- and •OH, respectively. The synergistic effect between electrocatalysis and photocatalysis under the solar-simulated light results in almost complete degradation of 2,4-dinitorphenol during the photoelectrocatalytic process. This work realizes a non-noble-metal plasmonic catalyst and provides a new avenue for the commercialization of photocatalysis and photoelectrocatalysis using the separable and recyclable carbon-fiber/semimetal Bi nanosheet arrays in the environment-related field.

Monitoring photolysis and (solar photo)-Fenton of enrofloxacin by a methodology involving EEM-PARAFAC and bioassays: Role of pH and water matrix

The degradation of enrofloxacin (ENR) by direct photolysis, Fenton and solar photo-Fenton processes has been studied in different water matrices, such as ultra-pure water (MQ), tap water (TW) and highly saline water (SW). Reactions have been conducted at initial pH 2.8 and 5.0. At pH = 2.8, HPLC analyses showed a fast removal of ENR by (solar photo)-Fenton treatments in all studied water matrices, whereas a 40% removal was observed after 120 min of photolysis. However, TOC measurements showed that only solar photo-Fenton was able to produce significant mineralization (80% after 120 min of treatment); differences between ENR removal and mineralization can be attributed to the release of important amounts of reaction by-products. Excitation-emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) were employed to gain further insight into the nature of these by-products and their time-course profile, obtaining a 5-component model. EEM-PARAFAC results indicated that photolysis is not able to produce important changes in the fluoroquinolone structure, in sharp contrast with (solar photo)-Fenton, where decrease of the components associated with fluoroquinolone core was observed. Agar diffusion tests employing E. coli and S, aureus showed that the antibiotic activity decreased in parallel with the destruction of the fluoroquinolone core.

Investigations on Ozone-Based and UV/US-Assisted Synergistic Digestion Methods for the Determination of Total Dissolved Nitrogen in Waters

Over the past two decades, the alkaline persulfate oxidation (PO) with thermal and/or ultraviolet (UV) assisted digestion method has been widely used for digestion of nitrogen containing compounds (N-compounds) in water quality routine analysis in laboratory or on-line analysis, due to its simple principle, high conversion rate, high percent recovery, low-cost. However, this digestion method still has some inevitable problems such as complex operations, high contamination potential, batch N blanks, higher reaction temperature (120–124 °C) and time-consuming (30–60 min). In this study, ozone (O3) was selected as the oxidant for digestion of N-compounds through analysis and comparison firstly. Secondly, we proposed and compared the UV and/or ultrasound (US) combined with ozone (UV/O3, US/O3 and UV/US/O3) synergistic digestion methods based on O3 with sole O3 oxidation method on digestion efficiency (digestion time and conversion rate) of standard N-compounds. Simultaneously, the influence of reaction temperature, pH of water sample, concentration of O3 and mass flow rate, UV intensity, US frequency and power on digestion efficiency were investigated, and then the optimum parameters for digestion system were obtained. Experimental results indicated that UV radiation can effectively induce and promote the decomposition and photolysis of O3 in water to generate hydroxyl radicals (•OH), while US can promote the diffusion and dissolution of O3 in water and intensify the gas-liquid mass transfer process for the reaction system. Meanwhile, results showed that the UV/US/O3 synergistic digestion method had the best digestion efficiency under the optimum conditions: water sample volume, 10 mL; pH of water sample, 11; O3 mass flow rate, 3200 mg/h; reaction temperature, 30 °C; digestion time, 25 min; UV lamp power, 18 W; distance between UV lamp and reactor, 2 cm; US frequency, 20 kHz; US power, 75 W. The conversion rate (CR) of synthetic wastewater samples varied from 99.6% to 101.4% for total dissolved nitrogen (TDN) in the range of 1.0~4.0 mg/L. The UV/US/O3 synergistic digestion method would be an effective and potential alternative for digestion of N-compounds in water quality routine analysis in laboratory or on-line analysis.