Zinc oxide doped with copper and nitrogen exhibits photocatalytic antibacterial activity under light from common fluorescent tubes

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Projet BACZEREAU dans le cadre du 28ème appel ERA-Net CORNET « Collective Research Networking »

Due to global warming, more and more people are attracted by freshness of water in swimming pools but also in many other locations, including cities fountains, pounds… If the natural bathing area is located downstream of a wastewater treatment plant, a tertiary treatment of water is needed before disposal in rivers to respect the European Directive 2006/7/CE for surface water bathing area in term of microbiological water quality. According to this directive, intestinal Enterococcus must stay under 330 CFU/100 ml and Escherichia coli can’t overpass 900 CFU/100 ml in natural bathing waters. Currently, the most conventional and useful technology to reduce pathogens uses UVC lamps, no matter if they are low or medium pressure. The UV energy alters the DNA structure of the microorganism in a process called thymine dimerization. Despite the excellent results achieved by most of the UVC reactors, there are some technical and economic constraints: • To avoid inadequate disinfection during the heating phase, the UVC lamps must run continuously, which leads to high energy costs and a reduction in lifetime. • High operating costs of UVC devices due to the energy needs and to the price of UVC lamps (replacement every 12 months or after 12000 operating hours). • Frequent oversizing of the UVC dose due to quartz sleeves fouling, and/or scaling, the water transmittance and the suspended solid load. • Potential reactivation of microorganisms after UVC under visible light and/or in darkness. Recently, photocatalysis and photo-induced processes have proved being effective for disinfection based on their deactivation capacity on numerous bacterial strains. The aim of the project is to validate at pilot scale the effective and definitive disinfection performance of sol-gel photocatalytic reactor combined with UVA illumination as tertiary treatment of a waste water treatment plant or in closed circulating loops, taking advantage of killing germs by affecting their cell wall instead of DNA alterations

Nucleation phenomenon in silica xerogels and Pd/SiO2, Ag/SiO2, Cu/SiO2 cogelled catalysts

Pd/SiO2, Ag/SiO2 and Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino) propyltrimethoxysilane (EDAS). It appears that, in cogelled samples, the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica porous particles with a monodisperse microporous distribution. Xerogels without metal synthesized with EDAS and TEOS (C. Alie, R. Pirard, A. J. Lecloux, and J.-P. Pirard, J. Non-Cryst. Solids 289, 88 (2001)) verify this hypothesis of nucleation by EDAS

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. I. O-17 NMR study of the hydrolysis-condensation process

Low-density xerogels were synthesised by incorporation of an additive to base catalysed tetraethylorthosilicate (TEOS) alcogels directly during the preparation of the sol. The nucleation mechanism by the additive was established by experiments during sol-gel transition. O-17 NMR spectroscopy on TEOS-ethanol-water, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS)-ethanol-water and EDAS-TEOS-ethanol-water solutions shows that the hydrolysis-condensation of EDAS is much faster than that of TEOS. Consequently it can be assumed that EDAS forms nuclei, onto which TEOS condenses later to form the silica particles. (C) 2003 Elsevier Science B.V. All rights reserved

Projet BACZEREAU dans le cadre du 28ème appel ERA-Net CORNET « Collective Research Networking »

Due to global warming, more and more people are attracted by freshness of water in swimming pools but also in many other locations, including cities fountains, pounds… If the natural bathing area is located downstream of a wastewater treatment plant, a tertiary treatment of water is needed before disposal in rivers to respect the European Directive 2006/7/CE for surface water bathing area in term of microbiological water quality. According to this directive, intestinal Enterococcus must stay under 330 CFU/100 ml and Escherichia coli can’t overpass 900 CFU/100 ml in natural bathing waters. Currently, the most conventional and useful technology to reduce pathogens uses UVC lamps, no matter if they are low or medium pressure. The UV energy alters the DNA structure of the microorganism in a process called thymine dimerization. Despite the excellent results achieved by most of the UVC reactors, there are some technical and economic constraints: • To avoid inadequate disinfection during the heating phase, the UVC lamps must run continuously, which leads to high energy costs and a reduction in lifetime. • High operating costs of UVC devices due to the energy needs and to the price of UVC lamps (replacement every 12 months or after 12000 operating hours). • Frequent oversizing of the UVC dose due to quartz sleeves fouling, and/or scaling, the water transmittance and the suspended solid load. • Potential reactivation of microorganisms after UVC under visible light and/or in darkness. Recently, photocatalysis and photo-induced processes have proved being effective for disinfection based on their deactivation capacity on numerous bacterial strains (John J. Alvear-Daza, & Al., Solar Energy 171, pp 761–768, 2018). The aim of the project is to validate at pilot scale the effective and definitive disinfection performance of sol-gel photocatalytic reactor combined with UVA illumination as tertiary treatment of a waste water treatment plant or in closed circulating loops, taking advantage of killing germs by affecting their cell wall instead of DNA alterations

Characterization of porous texture of hyperporous materials by mercury porosimetry using densification equation

peer reviewedThe purpose of this paper is to propose a method of analyzing the mercury porosimetry data in the case of materials called hyperporous. This class of material does not undergo intrusion by mercury; instead, it shrinks under the mercury isostatic pressure and its density increases. The phenomenon is partially or completely irreversible. The proposed method enables computing the pore volume distribution as a function of the pore size in the same way as Washburn's method does in the case of mercury intrusion. (C) 2002 Elsevier Science B.V. All rights reserved

The role of the main silica precursor and the additive in the preparation, of low-density xerogels

peer reviewedThe incorporation of an additive during sol-gel synthesis reduces shinkage during ambient drying. The following additives have been studied: 3-,(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltriethoxysilane (AES) and 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) and the main silica precursors were tetraethylorthosilicate (TEOS) and tetrapropylorthosilicate (TPOS). When the additive contains methoxy groups (EDAS), it acts as a nucleation agent of the silica particles and exactly the same properties (pore volume, specific surface area, particle and aggregate size) are obtained whether the main reagent is TEOS or TPOS. The nucleation mechanism is based on the difference in reactivity between additive and main reagent. In case of nucleation by the additive, the nucleation agent fixes the properties whatever the main silica precursor is. When both the additive and the main reagent contain ethoxy groups (series AES-TEOS and EDAES-TEOS), there is no nucleation mechanism by the additive, and the silica particle size remains nearly constant. With less reactive main reagent (series AES-TPOS and EDAES-TPOS), pore volumes up to 17 cm(3)/g have been obtained with pore sizes up to nearly 10 pm and very big particles (similar to100 nm). The absence of nucleation by the additive for the couples AES-TPOS and EDAES-TPOS could be due to the fact that the difference in reactivity between ethoxy groups and propoxy groups is not sufficient to initiate the nucleation mechanism by the additive. In the absence of nucleation by the additive, the main reagent plays a role: highly porous materials with very large p. ores are prepared with TPOS. (C) 2002 Elsevier Science B.V. All rights reserved

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. II. Viscosity study of the sol-gel transition

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed by theological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive. the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations. (C) 2003 Elsevier Science B.V. All rights reserved

Mercury porosimetry: applicability of the buckling-intrusion mechanism to low-density xerogels

peer reviewedMineral materials can be either crushed or invaded by mercury during mercury porosimetry experiments. It has been shown here that many low-density xerogels exhibit the two volume variation mechanisms successively, compaction followed by intrusion. when submitted to mercury porosimetry and that a unimodal pore size distribution can be obtained by applying Pirard's collapse model below the pressure of transition P-1 and Washburn's intrusion theory above P-t. To confirm the validity of the use of the buckling law, one low-density xerogel was wrapped in a tight membrane (intrusion is prevented and the sample is crushed during the whole porosimetry experiment). The analysis of the mercury porosimetry data of the wrapped sample by the buckling law leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. The position of P-t is characteristic of the tested material: when submitted to mercury pressure. aerogels and low-density xerogels only collapse in case of very small aggregates whereas they are crushed and then intruded in case of larger silica aggregates. The fact that compacted slabs of monodisperse non-aggregated silica spheres (of the same size range as the xerogels and aerogels) show only intrusion during mercury porosimetry experiments implies that the particles need to be aggregated so that the compaction mechanism takes place. The position of the change of mechanism from crushing to intrusion is not directly related to the size of the elementary particles but is linked to the size of the aggregates of silica particles. (C) 2001 Elsevier Science B.V. All rights reserved