Kinetics and Mechanism of Aniline and Chloroanilines Degradation Photocatalyzed by Halloysite-TiO2 and Halloysite-Fe2O3 Nanocomposites

Carbon, hydrogen, nitrogen and chlorine isotope fractionation during 3-chloroaniline transformation in aqueous environments by direct photolysis, TiO2 photocatalysis and hydrolysis

This study investigates carbon, hydrogen, nitrogen and chlorine isotope fractionation during the transformation of 3-chloroaniline (3-CA) via direct photolysis, TiO2 photocatalytic degradation at neutral condition and hydrolysis at pH 3, pH 7 and pH 11. Direct photolysis and ∙OH reaction (UV/H2O2) showed similar inverse isotope fractionation (ε) for carbon (1.9 ± 0.4 ‰ and 1.9 ± 0.6 ‰), for hydrogen (6.9 ± 1.6 ‰ and 5.0 ± 2.6 ‰), and inverse chlorine (13.9 ± 3.8 ‰ and 11.9 ± 2.9 ‰) and no nitrogen isotope fractionation, respectively. In contrast, significantly different normal carbon (-0.5 ± 0.1 ‰), inverse hydrogen (6.6 ± 1.5 ‰), and normal nitrogen (-0.8 ± 0.2 ‰) and inverse chlorine (5.2 ± 3.7 ‰) isotope fractionations were observed for the photocatalysis of 3-CA by TiO2 indicating a different degradation pathway as expected from ∙OH. For hydrolysis, inverse carbon (0.7 ± 0.3 ‰) and hydrogen (12.5 ± 3.3 ‰) isotope fractionation have been found at pH 3 while a normal carbon isotope fractionation was observed at pH 7 (-0.9 ± 0.3 ‰) and pH 11 (-1.3 ± 0.4 ‰), respectively. The correlation of 2H and 13C, 15N and 13C, and 37Cl and 13C isotope fractionation (Λ) allowed to distinguish direct photodegradation (ΛHC = -4.6 ± 1.7 (ΛHC-YORK=-5.2 ± 1.0) and ΛCl-C = 8.7 ± 0.9 (ΛCl-C-YORK=8.0 ± 0.3)), UV/H2O2 oxidation (ΛHC = -4.7 ± 1.0 (ΛHC-YORK=-4.5 ± 0.6) and ΛCl-C = 6.7 ± 0.8 (ΛCl-C-YORK=7.0 ± 1.0)), UV/TiO2 photocatalysis (ΛHC = -9.2 ± 3.1 (ΛHC-YORK=-9.3 ± 1.4), ΛCl-C = -10.2 ± 1.5 (ΛCl-C-YORK=-12.4 ± 1.7) and ΛNC -2.2 ± 0.3 (ΛNC-YORK=-2.3 ± 0.4)) and the modes of hydrolysis (ΛHC = 15.2 ± 5.3 (ΛHC-YORK=17.9 ± 2.9) and ΛCl-C = 0.9 ± 0.2 (ΛCl-C-YORK=1.1 ± 0.1) at pH 3) of 3-CA. The results were mechanistically interpreted highlighting the potential of CSIA to elucidate chemical oxidation and hydrolysis mechanisms of 3-CA.

Competitive photooxidation of small colorless organics controlled by oxygen vacancies under visible light

Visible-light photooxidation sensitized by surface attachment of small colorless organics on semiconductor photocatalysts has emerged as an economical method for photocatalytic synthesis or degradation. In particular, heteroatom (X = N and Cl)-containing substrates could undergo either C-N coupling or dechlorination degradation via sensitizing TiO2, but the mechanism in conducting the competitive visible-light sensitized photooxidations is still vague. Herein, the visible-light photooxidation of colorless 4-chlorobenzene-1,2-diamine (o-CAN) on TiO2 was revealed, contributing to selective C-N coupling rather than dechlorination. Oxygen vacancies (OVs) were in situ generated on the TiO2 surface, which could be dominant in weakening the Cl-Ti adsorption of o-CAN and regulating the activation of O2 for selective C-N coupling. The C-N coupling product, functionalized as the sensitizer, further promoted the visible-light photooxidation upon N-Ti and Cl-Ti coordination. This process was then confirmed by on-line mass spectrometric analysis, and the intermediates as well as their kinetics were determined. Thereby, theoretical calculations were employed to verify the roles of OVs in competitive photooxidation and lowering the energy barriers as well. Based on the comprehensive characterizations of both the catalysts and intermediates, this work has provided insights into competitive photooxidations under visible light.

Plasma treatment of sulfamethoxazole contaminated water: Intermediate products, toxicity assessment and potential agricultural reuse

The increasing global water demand has prompted the reuse of treated wastewater. However, the persistence of organic micropollutants in inefficiently treated effluents can have detrimental effects depending on the scope of the reclaimed water usage. One example is the presence of sulfamethoxazole, a widely used antibiotic whose interference with the folate synthesis pathway negatively affects plants and microorganisms. The goal of this study is to assess the suitability of a non-thermal plasma-ozonation technique for the removal of the organic pollutant and reduction of its herbicidal effect. Fast sulfamethoxazole degradation was achieved with apparent reaction rate constants in the range 0.21-0.49 min-1, depending on the initial concentration. The highest energy yield (64.5 g/kWh at 50 % removal) exceeds the values reported thus far in plasma degradation experiments. During treatment, 38 degradation intermediates were detected and identified, of which only 9 are still present after 60 min. The main reactive species that contribute to the degradation of sulfamethoxazole and its intermediate products were hydroxyl radicals and ozone, which led to the formation of several hydroxylated compounds, ring opening and fragmentation. The herbicidal effect of the target compound was eliminated with its removal, showing that the remanent intermediates do not retain phytotoxic properties.

[Cu(C3H3N3S3)3] Adsorption onto ZnTiO3/TiO2 for Coordination-Complex Sensitized Photochemical Applications

Currently, the design of highly efficient materials for photochemical applications remains a challenge. In this study, an efficient semiconductor was prepared, based on a coordination complex (Cu-TTC) of Cu(I) and trithiocyanuric acid on ZnTiO₃/TiO₂ (ZTO/TO). The Cu-TTC/ZTO/TO composite was prepared by the solvothermal method at room temperature. The structural, optical, and electrochemical characteristics, as well as the photocatalytic performance of the composite, were experimentally and computationally studied. The results show that the Cu-TTC/ZTO/TO composite efficiently extended its photoresponse in the visible region of the electromagnetic spectrum. The electrochemistry of the proposed tautomeric architecture (s-Cu-TTC) clearly reveals the presence of metal–ligand charge-transfer (MLCT) and π → π* excitations. The maximum methylene blue (MB) dye photodegradation efficiency of 95% in aqueous solutions was achieved under the illumination of simulated solar light. Finally, computational calculations based on the Density Functional Theory (DFT) method were performed to determine the electronic properties of the s-Cu-TTC tautomeric structure and clarify the adsorption mechanism of this complex on the surface (101) of both ZnTiO₃ and TiO₂ oxides. The results obtained allow us to suggest that the Cu-TTC complex is an effective charge carrier and that the Cu-TTC/ZTO/TO composite can be used efficiently for photochemical applications.