Sustainable Construction of Heterocyclic 1,2,3-Triazoles by Strict Click [3+2] Cycloaddition Reactions Between Azides and Alkynes on Copper/Carbon in Water

1,4-Disubstituted-1,2,3-triazoles, considered as an important and useful class of heterocycles with potential applications in material science and biology, have been prepared in an efficient and selective manner by copper on carbon-catalyzed [3+2] cycloaddition reactions of azides and alkynes (CuAAC) in water under strict click chemistry conditions. Copper(I) catalysts heterogenized onto commercially activated carbon materials (Cu-CC) and on another carbon material produced from vegetable biomass using Argan nut shells (Cu-CANS) were found to be versatile catalytic sources for sustainable CuAAC. These copper on carbon supports were prepared and fully characterized by using two types of activated carbons that exhibit different porosity and specific surface. The delineation of the nature of the catalytic copper species and the role of the carbon support in the CuAAC were addressed. These heterogeneous copper on carbon catalysts were recovered and reused until ten catalytic runs without any noticeable loss of activity

Toluene, Methanol and Benzaldehyde removal from gas streams by adsorption onto natural clay and faujasite-Y type Zeolite

A great number of pollution problems come as a result of the emission of Volatile Organic Compounds (VOCs) into the environment and their control becomes a serious challenge for the global chemical industry. Adsorption is a widely used technique for the removal of VOCs due to its high efficiency, low cost, and convenient operation. In this study, the feasibility to use a locally available clay, as adsorbent material to control VOCs emissions is evaluated. Natural clay is characterised by different physical-chemical methods and adsorptive interaction features between VOCs and natural clay are identified. Toluene (T), methanol (M) and benzaldehyde (B) are used here as representatives of three different kinds of VOCs. Adsorption isotherms onto natural clay and faujasite-Y type zeolite (Fau Y) are obtained at room temperature. According to Langmuir model data, maximum adsorption capacities (qm) of Fez natural clay and zeolite toward methanol (M), toluene (T) and benzaldehyde (B) at 300 K are 8, 0.89 and 3.1 mmol g-1, and 15, 1.91 and 13.9 mmol g-1 respectively. In addition, the effect of temperature on the adsorption of toluene onto natural clay is evaluated in the range from 300 to 323K. An increase on temperature reduces the adsorption capacity of natural clay toward toluene, indicating that an exothermic physical adsorption process takes place. The enthalpy of adsorption of toluene onto Fez natural clay was found to be -54 kJ mol-1. A preliminary cost analysis shows that natural clay could be used as an alternative low cost adsorbent in the control of VOCs from contaminated gas streams with a cost of US$0.02 kg-1 compared to Fau Y zeolite with US$ 10 kg-1

Photochemical transformation of flufenamic acid by artificial sunlight in aqueous solutions

International audienceIn the present article, we have studied the photochemical behavior of a common non-steroidal anti-inflammatory drug (NSAIDs) namely flufenamic acid (FLUA) in aqueous solution. The absorption spectrum of such compound shows a significant absorption beyond 290 nm and the photochemical irradiation within the range 300–450 nm leads to its complete transformation in roughly 6 h. The quantum yield of FLUA transformation measured at 290 and 310 nm was evaluated to about 1.1 × 10−4 without any significant effect of the excitation wavelength. The degradation process was inhibited in acidic solutions owing to the sharp increment in the absorption of FLUA in the wavelength region between 300 and 350 nm. The quantum yield was estimated to 1.2 × 10−4 at pH 7. The effect of oxygen on the photochemical behavior of FLUA has also been investigated. The obtained results clearly indicate that oxygen is not significantly involved in the photochemical degradation process. The phototransformation of the flufenamic acid appears to occur through one pathway that involves the photohydrolysis of trifluoromethyl group, and thus leads to the formation of one specific photoproduct, namely 2,3′-imino-dibenzoic acid. This result was confirmed by the formation of the fluoride ions after irradiation during the irradiation of flufenamic acid. A mechanistic scheme for such transformation of flufenamic acid was proposed

Highly efficient photodegradation of the pesticide metolcarb induced by Fe complexes

International audienceHere we show the efficient photoinduced degradation of the pesticide metolcarb, in less than 400 min, using iron(III) aquacomplexes and 365 nm light. The degradation is mainly due to the formation of hydroxyl radical. It was complete when molecular oxygen was present. The analytical study gives evidence for the primary formation of several byproducts formed from 1) the scission of the O-C bond, 2) the hydroxylation of the aromatic moiety and 3) the attack of the two methyl groups. Under prolonged irradiation and in aerated solutions, efficient mineralization was evidenced by the study of total organic carbon evolution as a function of irradiation time

Photochemical behaviour of triclosan in aqueous solutions: Kinetic and analytical studies

International audienceThe mechanism of the direct photolysis of the anti-microbial triclosan in aqueous solutions was investigated by using steady state and laser flash photolysis. Quantum yields were determined for the disappearance of triclosan and formation of chloride anions in steady state irradiations in the absence and in the presence of oxygen as well as a function of pH. The photoreactivity was found to be efficient with the anionic form and in the absence of oxygen. Following laser flash photolysis (226 nm), three transients were found (triclosan triplet state, solvated electron and phenoxyl radical). Several primary and secondary stable photoproducts were elucidated by means of LC/MS/MS data. They were found to arise from four main photochemical processes: isomerisation, cyclization (leading to the formation of dioxin derivatives), dimerisation of the phenolic moiety and hydrolysis. The ionic chromatography showed that the loss of chloride anion in triclosan phototransformation represents an important degradation pathway. The formation of oligomeric products was also observed for prolonged irradiation time. A detailed mechanism for the formation of the primary products is proposed and discussed. The very important photocyclization reaction is more likely involving the triplet state pathway and the homolytic dissociation of the ether bridge occurs from the singlet excited state pathway

Photocatalytic degradation of metsulfuron methyl in aqueous solution by decatungstate anions

International audienceThe degradation of the pesticide metsulfuron methyl was studied in aqueous solutions by using decatungstate anion, W10O324−, as a photocatalyst. An electron transfer process involving the highly oxidizing features of the decatungstate excited state, namely W10O324−*, was clearly observed. The degradation led to the oxidation of the pollutant and the formation of the decatungstate reduced species, i.e. W10O325−. In aerated as well as in oxygen-saturated solutions, the system was found to operate in a photocatalytic way with the formation of superoxide anion and the regeneration of the starting decatungstate species. The phototransformation of the pesticide metsulfuron methyl appeared to occur through three different reaction pathways involving the three main parts of the chemical structure: the aromatic ring, the sulfonylurea bridge and to a less extent the methoxy group of the triazine moiety. Under continuous excitation a partial mineralization of metsulfuron methyl was observed owing to the presence of the triazine structure. A mechanistic scheme for complete degradation of metsulfuron methyl is proposed

Phototransformation of triclosan in the presence of TiO2 in aqueous suspension: Mechanistic approach.

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Three Dimensionally Ordered Macroporous Layered Double Hydroxides : Preparation by Templated Impregnation/ Coprecipitation and Pattern Stability upon Calcination.

International audienceThree dimensionally ordered macroporous layered double hydroxides (3-DOM LDH) have been synthesized using sacrificial polystyrene (PS) colloidal crystal templates impregnated by divalent and trivalent metal salts. LDH spatially confined coprecipitation occurs during soaking in NaOH solution, and the PS template is subsequently removed by dissolution to preserve the hydroxyl structure. This synthetic process can be applied to a wide range of LDH compositions (M11: Mg, Ni, Co, Zn and MIII: Al, Cr). On the basis of XRD, SEM, TEM, chemical analysis, nitrogen adsorption, XAS experiments, and TGA, structural, textural, and thermal properties of these new nanostructured LDH particles are described. In particular, the study shows that both macro- and mesoporosity can be present and that the macroporosity is maintained after calcination at temperatures as high as 800 °C, giving rise to the presence of macroporous metal and mixed metal oxides. The photocatalytic activity experiments indicate that decatungstate intercalated into the 3-DOM LDH exhibits a higher photocatalytic activity for the photodegradation of 2,6-dimethylphenol than the decatungstate intercalated into the standard coprecipitated LDH parent material