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Abstract: Chemometric optimization tools were employed, such as experimental design and response surface methodology (RSM) to assess the efficiency of two advanced oxidation processes (AOPs): homogeneous Fenton (FeII/H2O2) and heterogeneous (TiO2) photocatalysis for the degradation of the artificial sweetener sucralose. The aqueous samples were irradiated under a variety of experimental conditions (pH, light intensity) and with different amounts of H2O2, Fe(II), TiO2. The use of RSM allowed fitting the optimal values of the parameters leading to the degradation of the contaminant. Also, a single polynomial expression modeling the reaction was obtained for both AOPs. The intermediates formed during the photocatalytic and photo-Fenton process were investigated and characterized by means of HPLC/HRMS. The photocatalysed transformation of sucralose proceeds through the formation of few (eight) products, involving four different pathways: hydroxylation of the molecule, oxidation of the alcohol function, dechlorination and the cleavage of glycoside bond. All the identified intermediates were easily degraded and within four hours of irradiation complete mineralization was achieved. A comparison with Photo-Fenton reaction was also reported. In addition Microtox bioassay (Vibrio fischeri) was employed in evaluating the ecotoxicity of solutions treated by heterogeneous photocatalysis. Results clearly demonstrate the efficiency of the photocatalytic process in the detoxification of the irradiated solutions. [Copyright &y& Elsevier]

Abstract: The present paper deals with the photocatalytic transformation of HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[γ]-2-benzopyran, trade name Galaxolide), under simulated solar irradiation using titanium dioxide as a photocatalyst. The investigation has involved a study of HHCB decomposition under a variety of experimental conditions, the identification of intermediate compounds, as well as the assessment of mineralization. A fully nested experimental design was applied to study the effect of various matrices (i.e. distilled water, surface water and wastewater) as well as the initial HHCB concentration on the variation of the photocatalytic efficiency. GC/MS and LC/MS were brought to bear in assessing the temporal course of the photocatalyzed process. A first pathway involves the hydroxylation, that is confined to the benzopyran moiety. Another route proceeds through the detachment of the hexamethylpentacycle moiety, with the formation of the ketoderivative. A parallel transformation involves benzopyran moiety with the ring cleavage. All the identified transformation products are degraded themselves until 2h of irradiation, while complete mineralization is achieved until 8h. [ABSTRACT FROM AUTHOR]

Abstract: Diclofenac (2-[2′,6′-(dichlorophenyl)amino]phenylacetic acid) is a non-steroidal anti-inflammatory drug used to treat inflammatory and painful diseases of rheumatic and non-rheumatic origin. The present work deals with the photocatalytic transformation of diclofenac, under simulated solar irradiation using titania suspensions as catalyst, to assess the decomposition of the pharmaceutical compound, to identify intermediates, as well as to elucidate some mechanistic details of the degradation. The variation of TiO2 amount and initial diclofenac concentration on the reaction rate, were systematically investigated. The use of the response surface methodology allowed to fit the optimal values of the parameters leading to the degradation of the pollutant. Also, a single polynomial expression modeling the reaction was obtained. Photomineralization of the substrate in terms of chlorine ions release was rather a quick process (within 1h), while the amino moiety is mainly transformed into NH4 + and in a lesser extend into NO3 − ions. Evolution of CO2 (loss of TOC) was found to occur within 2h of irradiation. LC/MS was brought to bear in assessing the temporal course of the photocatalyzed process. Based on our findings a tentative degradation pathway is proposed for the photocatalytic degradation of diclofenac based on the formation of hydroxy-derivatives before the complete mineralization of the starting molecule. In addition Microtox bioassay (Vibrio fischeri) was employed in evaluating the ecotoxicity of solutions treated by photocatalysis. Results clearly demonstrate the efficiency of the photocatalytic process in the detoxification of the irradiated solution. [Copyright &y& Elsevier]

In the present study reduced graphene oxide—TiO 2 composites were synthesized at two different ratios (1:10 and 1:5) through a hydrothermal method using graphene oxide and commercial P25 as starting materials. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET surface area and ultraviolet–visible (UV–vis) absorption spectroscopy were employed to investigate the morphology and properties of the produced composites. The photocatalytic performance of TiO 2 –rGO catalysts was evaluated under artificial solar light and visible light in distilled water, as well as, different surface waters (at natural pH) with respect to risperidone (antipsychotic drug) degradation. Irrespectively of the irradiated aqueous matrix, the photocatalytic efficiency of the tested composite materials under simulated solar light and visible light irradiation was higher compared to bare TiO 2 –P25 (reference catalyst). The identification of intermediate compounds, the assessment of mineralization and the evaluation of toxicity were performed as well. LC/HRMS was brought to bear in assessing the temporal course of the photocatalyzed process. Along with risperidone decomposition, the formation of twenty intermediate compounds (TPs) occurred in the presence of TiO 2 . Irradiation of risperidone in the presence of the hybrid material resulted in the identification of thirty-four TPs. The transformation of risperidone progressed through the formation of compounds more harmful than the drug itself, as assessed by the measurement of acute toxicity, evaluated using the Vibrio fischeri bacteria test. When employing TiO 2 –rGO, all the identified transformation products were quicker degraded compared to TiO 2 –P25. At the same time both the reduction of toxicity and mineralization were faster achieved than with bare TiO 2 –P25. [ABSTRACT FROM AUTHOR]

Abstract: In order to exploit the efficiency of titania suspensions in photocatalysis for the degradation of the herbicide flufenacet, chemometric optimization tools were employed, such as response surface methodology and experimental design. The aqueous samples were irradiated under a variety of experimental conditions with different amounts of catalyst (TiO2), electron acceptor (H2O2) as well as pH. Results indicated that the degradation efficiency of the herbicide in the experimental domain investigated was mainly affected by the concentration of H2O2, followed by TiO2, pH, as well as their interaction effects. Additionally, the phototransformation products formed during the photocatalytic process were investigated and characterized by means of HPLC/HRMS. The photocatalysed transformation of flufenacet proceeds through the formation of thirty-two (32) products, involving reactions of mono- and di-hydroxylation, dealkylation, detachment of the thiadiazole ring, defluorination on the benzene ring followed by the detachment of the latter ring. The thiadiazole ring appears to be involved in the process to a lesser extent and only as a secondary path. The measurement of acute toxicity, evaluated using the Vibrio fischeri bacteria test, showed that the transformation of flufenacet proceeds through the formation of compounds more toxic than the parent molecule. Although the identified intermediates were easily degraded and within two hours of irradiation were completely disappeared, mineralization was much slower and complete formation of CO2 and inorganic constituents was only achieved after 24h of irradiation. [Copyright &y& Elsevier]

Abstract: Central composite design (CCD) based on response surface methodology (RSM) was employed in the present study in combination with “profiling and desirability function” to evaluate the effects of main variables (TiO2, H2O2, and light intensity) affecting 4-methylbenzylidene camphor (4-MBC) photocatalytic degradation and for optimization of the process. Besides statistical optimization of the UV filter decomposition, the investigation involved a study of the identification of intermediate compounds, mineralization, as well as toxicity evaluation. The transformation of 4-MBC proceeds through: (i) demethylation of the bridged structure; (ii) hydroxylation of the methylbenzylidene moiety; (iii) bihydroxylation/demethylation reaction. Even if all the identified compounds are degraded themselves within 30min, the complete carbon mineralization is only achieved after 24h of irradiation. Toxicity assays using Vibrio fischeri, have shown that 4-MBC intermediates exhibit acute toxicity. [Copyright &y& Elsevier]