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WO3 is a known photocatalytic metal oxide frequently studied for its depollution properties. However, it suffers from a high recombination rate of the photogenerated electron/holes pair that is detrimental to its performance. In this paper, we present a new chemical method to decorate WO3 nanoleaves (NLs) with a complementary metal oxide (ZnWO4) in order to improve the photocatalytic performance of the composite material for the abatement of 400 ppb NO2 under mild UV exposure. Our strategy was to synthesize WO3·2H2O nanoleaves, then, to expose them, in water-free organic solution, to an organometallic precursor of Zn(Cy)2. A structural water molecule from WO3·2H2O spontaneously decomposes Zn(Cy)2 and induces the formation of the ZnO@WO3·H2O nanocomposite. The material was characterized by electronic microscopy (SEM, TEM), TGA, XRD, Raman and solid NMR spectroscopies. A simple thermal treatment under air at 500 °C affords the ZnWO4@WO3 nanocomposite. The resulting material, additionally decorated with 1% wt. Au, presents a remarkable increase (+166%) in the photocatalytic abatement of NO2 under UV compared to the pristine WO3 NLs. This synthesis method paves the way to the versatile preparation of a wide range of MOx@WO3 nanocomposites (MOx = metal oxide).

International audience; This study compares the (nitrogen oxides) NOx photocatalytic degradation performance of the commercial bare semiconductors, titanium dioxide (TiO2 P25) and zinc oxide (ZnO), with that of the homemade gold (Au)-decorated semiconductors, Au/TiO2 and Au/ZnO (1 wt% Au). A plasmonic absorption band was observed at 550 nm for Au/TiO2 and around 700 nm for Au/ZnO. Aqueous dispersions based on these oxides were sprayed on mortar surfaces. The results revealed that Au/ZnO had a high NO degradation capability, comparable to that of TiO2 P25, and the best selectivity towards the formation of nitrates instead of NO2. The Au decoration clearly improved the photocatalytic response of ZnO, notably by avoiding the production of NO2. This positive effect was attributed to the better charge carrier separation and higher OH• production induced by the presence of Au. To the best of our knowledge, this was the first study on Au/ZnO used for NO photocatalytic degradation.

International audience

“Almost real-life” experiments of abatement of a pollutant, actually nitrogen monoxide, were carried out in a 10-m3 chamber, the walls of which were covered with plasterboard samples, themselves coated with a photocatalytic dispersion. The experimental protocol consisted in first injecting NO polluted air into the chamber to a certain level, then maintaining a steady level of pollution by tuning the flow rate to balance the leaks and, finally, illuminating the chamber. In a first stage of analysis, a three-flow (injection, leakage and renewal flows) model was used in order to characterize the leakage flow rate. This model was based on the difference of NO concentration between the interior and the exterior rather than on a pressure difference. A two-parameter empirical law was specially formulated for this purpose. In a second stage, the photocatalytic phenomenon was described by a four-flow model completing the previous one, the fourth flow being associated with the photocatalytic oxidation of NO. This flow was described by a rate law derived from the Langmuir-Hinshelwood (L-H) law, which was generalized to the experimental chamber. The parameters K (adsorption constant) and k (abatement kinetics constant) of the rate law were identified using a standardized lab-scale reactor. The equations, integrated by finite differences, fitted the experimental results correctly. The “diffusive zone thickness” was introduced as the thickness of the air layer potentially concerned by the photocatalysis and was quantified. This first attempt to model photocatalysis on a large scale was promising. However, further research work is needed to enable the model to take more parameters into account.

International audience; itanium metal is widely used in the aeronautical sector for its specific properties and corrosion resistance. The design of titanium workpieces is based on chemical milling: a fast, precise, low cost technique popular in the aerospace industry. Material is removed from selected areas of a part by immersing it in a strong chemical reagent. This process produces shallow cavities on plates and sheets or removes shallow layers of materials from large aircraft components to optimize the strength/weight ratio. However, it leads to large volumes of wasted acid baths, which are harmful to the environment and have to be sent to an approved waste facility. The objective of this paper is to highlight a cleaner production process based on the circular economy concept, i.e. reduce, reuse and recycle to limit environmental pollution and operating costs. Waste from chemical milling baths used in the design of titanium parts was recovered with the aim of synthesizing titanium dioxide and using it for air depollution applications. The waste consisted of hexafluorotitanate compounds. Various processing techniques to synthesize titanium dioxide from hexafluorotitanate compounds were tested and resulted in powders having different physicochemical characteristics. The synthesis parameters studied were the nature of the decomplexing agent, the dehydration temperature and the heating period. Photocatalytic coatings were then formulated on the basis of the synthesized powders. They were applied to a mortar surface to evaluate their efficiency to degrade nitric oxide under two UV lighting intensities, 5 and 20 W/m2. Depending on the synthesis process conditions, the concentration and crystal form of titanium dioxide particles varied, leading to more or less efficient photocatalytic coatings. The proportions of anatase and rutile phases in the synthesized powders were between 3 and 13%, and 5 and 30%, respectively. Concerning the particle size distribution, the variations observed were dependent on the D-values. D10% was quite similar for all powders. However, D50% and D90% differed by a factor of two for some powders, notably because of the presence of impurities or remaining decomplexing agent particles. NO degradation varied depending on the photocatalytic dispersions and could reach 7% under an irradiation of 20 W/m2. This article highlights the possible valorization of a massive industrial waste for specific applications provided that the conditions of processing techniques are optimized.

This paper deals with the degradation of NO by photocatalytic oxidation using TiO2-based coatings. Tests are conducted at a laboratory scale through an experimental setup inspired from ISO 22197-1 standard. Various parameters are explored to evaluate their influence on photocatalysis efficiency: TiO2 dry matter content applied to the surface, nature of the substrate, and illumination conditions (UV and visible light). This article points out the different behaviors between three kinds of substrates which are common building materials: normalized mortar, denser mortar, and commercial wood. The illumination conditions are of great importance in the photocatalytic process with experiments under UV light showing the best results. However, a significant decrease in NO concentration under visible light is also observed provided that the TiO2 dry matter content on the surface is high enough. The nature of the substrate plays an important role in the photocatalytic activity with rougher substrates being more efficient to degrade NO. However, limiting the roughness of the substrate seems to be of utmost interest to obtain the highest exposed surface area and thus the optimal photocatalytic efficiency. A higher roughness promotes the surface contact between TiO2 and NO but does not necessarily increase the photochemical oxidation.

International audience; Indoor air is contaminated by numerous pollutants, which impact human health, comfort and productivity. These pollutants have various indoor sources such as building materials, furniture, combustion appliances or tobacco smoke. However, the pollution also comes from outside. In urban area, nitrogen oxides (NOx) emitted into the atmosphere can reach alarming levels. These traffic-related pollutants, which seriously impact the global environment and human health, can infiltrate inside buildings. Therefore, limiting the amount of breathable NOx in outdoor and indoor environments is an important priority for the modern society. The photocatalytic process has attracted particular attention in the last two decades and has proved to be efficient to reduce the concentration of NOx. However, further work has to be conducted to assess its efficiency in real indoor environments. The purpose of this paper was to report on the indoor air quality in an open space office in Manchester, UK. Focus was made on nitric oxide (NO) and nitrogen dioxide (NO2). The indoor concentrations of both gases were monitored from 14 January 2019 to 7 April 2019. During this period, a photocatalytic coating was applied to a part of the indoor wall. The influence of this coating on the level of NOx was assessed by comparing the indoor concentrations before and after the application. An attention was paid to the correlation between outdoor and indoor pollution and to the effect of other parameters such as temperature, humidity, pressure and O3 concentration. The results showed that the photocatalytic process led to a decrease in the NOx concentration. The likelihood to find concentrations above 35 ppb for NO and 7.5 ppb for NO2 was clearly reduced after the coating application.

Corrosion of steel in reinforced concrete structures is a recurrent problem affecting civil engineering structures and costing the world billions of dollars per year. This physical phenomenon mainly results from chloride ingress or concrete carbonation. Corrosion can be diagnosed through a nondestructive method such as half-cell potential measurements. The present paper studies this method on a reinforced concrete wall containing eighteen unconnected steel bars and subjected to chloride-induced macrocell corrosion. Three corrosion systems with different configurations of connections between the steel bars are generated, involving three different anode-to-cathode surface ratios. Then, half-cell potential variations are observed versus macrocell corrosion current. The results lead to a critical discussion regarding the physical relevance of the usual potential threshold method to detect corroding rebars in reinforced concrete structures. In addition, the experiments demonstrate that electrical continuity between reinforcing steel bars is not necessary to get meaningful information about the macrocell corrosion system. At last, the paper show that the electric field (potential gradient) relative to a macrocell corrosion system may be measured by connecting the measurement system (reference electrode + voltmeter) to any electrochemical system in electrolytic contact with the concrete.

WOS:000400765900008; International audience; This paper investigates a new test method to assess the photocatalytic activity of plasterboards coated with a TiO2 dispersion under real-world conditions. The degradation of nitrogen oxides NO (x) (NO and NO2) is studied and the photocatalytic efficiency under UV illumination is evaluated in a 10-m(3) room after a constant gas injection. Two ultrafine TiO2 dispersions are used: 0.85% TiO2 and 5% TiO2, and three types of gas are tested: an NO/NO2 mixture (8/8 mol-ppm), NO (45 mol-ppm) and NO2 (45 mol-ppm). The test method presented here is midway between laboratory and real-scale procedures and allows better control of the experimental parameters than a real field experiment. Testing a mixture of NO and NO2 is a way to get closer to real-world conditions as air is polluted by various gases. This study focuses on the degradation of NO and NO2 under UV illumination when two types of TiO2 dispersions are used and highlights the difference in behaviour between these two molecules in terms of photocatalytic degradation. The results show that photocatalytic activity does not appear to be efficient to degrade NO2 molecules. Another mechanism seems to be responsible for the reduction of the concentration of NO2, namely adsorption. Encouraging results are obtained with NO molecules, which can be degraded by photocatalysis. The degradation observed is even greater with the more concentrated TiO2 dispersion.

WOS:000373963700024; International audience; The objective of this study is to develop testing methods of asphalt release agent (ARA) performance and the degree to which they may damage the asphalt. The testing of ARA performance demonstrated their ability to reduce the adhesion between the asphalt and the surface of steel (asphalt tools, truck bedsaEuro broken vertical bar) by the asphalt slide test, which provided two indicators for quantifying performance. The testing of the their damage to asphalt consisted of the measurement of the degree to which the compacted asphalt is damaged by the ARA including CBR resistance, indirect-tensile strength and bitumen degradation testing, the latter also serving as a test to find the most effective bitumen remover (BR). For asphalt degradation, the indirect tensile strength test provided more consistent results than CBR resistance.

International audience; This article deals with the degradation of NO present in the air by means of a photocatalytic oxidation process based on TiO2 nanoparticles incorporated in a polymer-matrix-based coating. The experimental set-up consisted of a flow type reactor adapted from the ISO 22197-1 standard. NO2 in the gas phase, and nitrate ions adsorbed on the photocatalytic surface were detected as finals products. Various parameters influencing the NO degradation efficiency were studied: the coating composition, the substrate nature, the initial concentration of NO, the polluted air flow rate and the humidity. Compared to glass, the use of mortar as the substrate enhanced the photocatalytic performance of coatings by reducing the generation of gaseous NO2 as a by-product.

Aesthetics of external concrete walls can be altered in various constructions by fast developing algae and it is useful to propose technical solutions to prevent this problem. Laboratory tests are thus necessary, on the one hand to accelerate the growth of algae on concrete and, on the other, to quantify such growths. The first part of this article was dedicated to the description of two growth tests. This second part presents the advantages and drawbacks of three complementary techniques used to analyze the colonized areas. Two methods are non-destructive and estimate either the area covered, using image analysis, or the density of algae, which directly influences the stain intensity, by spectrophotometry. The third method is destructive and is based on the measurement of chlorophyll a. It is used to obtain information on the state of vitality of the algae on the colonized surface.

WOS:000333782100017; International audience; Building materials are regularly affected by the growth of microalgae. The consequences are mainly aesthetic but the colonization can cause biodeterioration of the material in the most extreme cases. This study investigates two building material treatments that can potentially inhibit or slow down such growth: photocatalytic coatings and water repellent treatments. The efficiency of these treatments in terms of biological growth inhibition was tested on the algae species Graesiella emersonii. Algal growth on building materials was investigated using two accelerated tests simulating different types of humidification (water capillary ascent and water run-off) under different lighting conditions. Mortars treated with photocatalytic coating or with water repellent were studied. The algal growth on the mortar surface was evaluated using image analysis (area covered and intensity of fouling). No slow down of the biological growth kinetics could be attributed to photocatalytic substrates. However, for mortars impregnated with a water-repellent preparation, algal growth slowed significantly under water run-off and even stopped under water capillary ascent. (C) 2014 Elsevier Ltd. All rights reserved.

WOS:000328713000018; International audience; Photocatalytic coatings intended for building materials were formulated using TiO2 nanoparticles incorporated in a polymer-matrix-based coating. Their air purification performance levels were assessed on a VOC (volatile organic compound) mixture representative of atmospheric pollution (benzene, toluene, ethylbenzene and xylenes, or BTEX). Experiments were performed using a flow type reactor adapted from the ISO 22197-3 standard under UV-A illumination (6 W m(-2)) at different ranges of inlet concentration (260-2600 ppbV of BTEX), relative humidity (RH: 0-90%) and flow rate (0.1-1.5 L min(-1)). Analysis was conducted by using an automated thermal desorption technique coupled to a GC-FID instrument. At low initial concentrations of pollutants, increasing humidity had a negative impact on the degradation of BTEX. In this case, the reaction was limited by the competition between pollutant and water at the absorptive sites. At higher initial concentrations of pollutant, the conversion of the pollutants increased with the increase in air humidity to an optimum value beyond which the conversion of pollutants decreased. The reaction may have been limited by a lack of hydroxyl radical at the low humidity level while, at higher humidity, competition at the absorptive sites limited pollutant removal. (C) 2013 Elsevier Ltd. All rights reserved.

International audience; This study concerns the assessment of non-coated concrete surfaces in civil engineering structures and buildings. Imaging is used as an objective tool for evaluation of the surfaces. Because images of surfaces taken under different conditions of illumination are difficult to compare, this paper presents a method suggested by the building firm GTM Construction and the laboratory LMDC for obtaining images of luminance L∗ simulated for one standard illuminant (D65). Concrete surfaces can be qualified with respect to uniformity of tint and distribution of surface bubbles. The process described is based on image analysis. Not only can the results be compared with current standards, but the method also gives access to additional, accurate information such as the distribution of defects and the size of surface bubbles. This method is already applied on building sites for experts’ assessments and in the laboratory for the study of the parameters influencing surface quality.

The PhD thesis "Exploratory studies dedicated to computer-assisted corrosion diagnosis of civil engineering structures" deals with the phenomenology and modeling of corrosion of structural steel. The safety, societal and environmental impact of aging infrastructures makes this theme a major economic issue for the development of any country. The proposed developments focus mainly on the corrosion of reinforcements in reinforced concrete. The corrosion of buried metallic structures is also addressed concerning the problems related to galvanic couplings induced by the heterogeneity of soils and stray currents. The usual methods of investigation (measurements of steel potential, concrete resistivity or polarization resistance), combined with empirical hypotheses established by experience, lead to interpretations that are often uncertain or have only a qualitative value. The ambition of this thesis, motivated by the issues at stake, is to show how a better understanding of the physics of corrosion, combined with the power of finite element calculation, allows the construction of elaborate and robust models, useful for a quantified and reliable diagnosis and/or prognosis. The thesis is abundantly illustrated by real or numerical case studies and supported by original laboratory tests. In order to improve the understanding of the phenomena prevailing in the corrosion process, the key concepts of thermodynamics and electrochemical kinetics are recalled and contextualized. The assembly of different physical, chemical and electrochemical laws allows the elaboration of an advanced modeling approach, integrating in particular the diffusion of oxygen to the reinforcement in an unsaturated context, but also the production and precipitation of corrosion products and their influence on the dynamic equilibrium of a corrosion system. This modeling approach, necessarily three-dimensional or at least two-dimensional, gives rise to a transcription in a finite element calculation code. It is first applied to the numerical study of a first typical case of corrosion: a reinforced concrete pile partially submerged in the sea. The influence of the role of oxygen (availability and diffusion) on the dissolution kinetics of the steel and on the nature of the corrosion products formed is studied in particular. In order to illustrate the effective contribution of 3D modeling in the process of corrosion diagnosis, a real case study is proposed concerning a buried steel structure, in this case sheet piles used to support the abutments of a freeway overpass, located near a pipe buried under cathodic protection. Measurements carried out in-situ but also in the laboratory from judiciously chosen samples are used to feed the calculation model. The numerical model thus constructed, qualified as a digital twin, makes it possible to highlight the existence of stray currents circulating in the structure, but also the risk of galvanic corrosion induced by the heterogeneity of the soil. The electrochemical digital twin is then a powerful tool for estimating the kinetics and the corrosion facies of the structure and making a prognosis in terms of service life. Within a concrete structure, the presence of chlorides is associated with various effects, notably associated with the local electric field. If this phenomenon is ignored, the interpretation of field data, for example potential maps, can lead to a biased diagnosis. This thesis addresses the question of corrosion initiation.[...]; La thèse "Études exploratoires dédiées au diagnostic de corrosion assisté par ordinateur des structures de génie civil" traite de la phénoménologie et de la modélisation de la corrosion de l'acier de construction. Le poids sécuritaire, sociétal, environnemental du vieillissement des infrastructures fait de ce thème un enjeu économique majeur de développement de tout pays. Les développements proposés portent principalement sur la corrosion des armatures dans le béton armé. La corrosion des structures métalliques enterrées est également adressée concernant les problématiques relatives aux couplages galvaniques induits par l'hétérogénéité des sols et aux courants vagabonds. Les méthodes d'investigation usuelles (mesures de potentiel des aciers, de résistivité du béton ou de résistance de polarisation), jointes à des hypothèses empiriques consacrées par l'usage, conduisent à des interprétations souvent incertaines ou n'ayant qu'une valeur qualitative. L'ambition de cette thèse, motivée par les enjeux évoqués, est de montrer comment une meilleure compréhension de la physique de la corrosion, conjuguée à la puissance du calcul aux éléments finis, permet de construire des modèles élaborés et robustes, utiles pour poser un diagnostic et/ou un pronostic quantifié et fiable. La thèse est abondamment illustrée par des études de cas réels ou numériques et étayée par des essais originaux conduits en laboratoire. Afin d'améliorer la compréhension des phénomènes prévalant dans le processus de corrosion, les concepts-clés de thermodynamique et de cinétique électrochimique sont rappelés et contextualisés. L'assemblage de différentes lois physiques, chimiques et électrochimiques permet d'élaborer une approche de modélisation avancée, intégrant notamment la diffusion du dioxygène jusqu'aux armatures en contexte insaturé, mais aussi la production et la précipitation des produits de la corrosion et leur influence sur l'équilibre dynamique d'un système de corrosion. Cette approche de modélisation, nécessairement tridimensionnelle ou a minima bidimensionnelle, donne lieu à une transcription dans un code de calcul par éléments finis. Elle est appliquée dans un premier temps à l'étude numérique d'un premier cas typique de corrosion : pile en béton armé partiellement immergée en mer. L'influence du rôle du dioxygène (disponibilité et diffusion) sur la cinétique de dissolution de l'acier et sur la nature des produits de corrosion formés est notamment étudiée. Afin d'illustrer l'apport effectif de la modélisation 3D dans le processus de diagnostic de la corrosion, une étude de cas réelle est proposée concernant un ouvrage métallique enterré, en l'occurrence des palplanches servant au soutènement des culées d'un passage supérieur d'autoroute, situées à proximité d'une conduite enterrée sous protection cathodique. Des mesures effectuées in-situ mais aussi en laboratoire à partir d'échantillons judicieusement choisis, permettent d'alimenter le modèle de calcul. Le modèle numérique ainsi construit, qualifié de jumeau numérique, permet de mettre en évidence l'existence de courants vagabonds circulant dans la structure, mais également le risque de corrosion galvanique induit par l'hétérogénéité du sol. Le jumeau numérique électrochimique constitue alors un outil puissant pour estimer la cinétique et le faciès de corrosion de l'ouvrage et poser un pronostic en termes de durée de vie. [...]