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The performances of a laboratory PhotoCatalytic Oxidation (PCO) device were determined using a recirculation closed-loop pilot reactor. The closed-loop system was modeled by associating equations related to two ideal reactors: a perfectly mixed reservoir with a volume of VR = 0.42 m3 and a plug flow system corresponding to the PCO device with a volume of VP = 5.6 × 10−3 m3. The PCO device was composed of a pleated photocatalytic filter (1100 cm2) and two 18-W UVA fluorescent tubes. The Clean Air Delivery Rate (CADR) of the apparatus was measured under different operating conditions. The influence of three operating parameters was investigated: (i) light irradiance I from 0.10 to 2.0 mW·cm−2; (ii) air velocity v from 0.2 to 1.9 m·s−1; and (iii) initial toluene concentration C0 (200, 600, 1000 and 4700 ppbv). The results showed that the conditions needed to apply a first-order decay model to the experimental data (described in Part I) were fulfilled. The CADR values, ranging from 0.35 to 3.95 m3·h−1, were mainly dependent on the light irradiance intensity. A square root influence of the light irradiance was observed. Although the CADR of the PCO device inserted in the closed-loop reactor did not theoretically depend on the flow rate (see Part I), the experimental results did not enable the confirmation of this prediction. The initial concentration was also a parameter influencing the CADR, as well as the toluene degradation rate. The maximum degradation rate rmax ranged from 342 to 4894 ppbv/h. Finally, this study evidenced that a recirculation closed-loop pilot could be used to develop a reliable standard test method to assess the effectiveness of PCO devices.

This study demonstrated that a laboratory-scale recirculation closed-loop reactor can be an efficient technique for the determination of the Clean Air Delivery Rate (CADR) of PhotoCatalytic Oxidation (PCO) air purification devices. The recirculation closed-loop reactor was modeled by associating equations related to two ideal reactors: one is a perfectly mixed reservoir and the other is a plug flow system corresponding to the PCO device itself. Based on the assumption that the ratio between the residence time in the PCO device and the residence time in the reservoir τP/τR tends to 0, the model highlights that a lab closed-loop reactor can be a suitable technique for the determination of the efficiency of PCO devices. Moreover, if the single-pass removal efficiency is lower than 5% of the treated flow rate, the decrease in the pollutant concentration over time can be characterized by a first-order decay model in which the time constant is proportional to the CADR. The limits of the model are examined and reported in terms of operating conditions (experiment duration, ratio of residence times, and flow rate ranges).

Graphical abstract Highlights • Evaluation of photocatalytic oxidation (PCO) degradation of a mixture of three VOCs at ppb level. • Comparison of degradation with single initial compounds and with a mixture. • No significant influence in the degradation rate when compounds are in mixture. • No significant interactions between either VOC or intermediates at ppb level. • Oxygenated intermediated compounds are good indicators in photocatalytic systems performance. Abstract An investigation of the photocatalytic degradation of indoor air model pollutants: toluene, n -decane and trichloroethylene (TCE), as single contaminants and in a mixture is proposed. The degradation of these contaminants was performed in a continuous closed-loop reactor operating in recirculation mode. Degradations were conducted at ppb level concentrations and under humid conditions (RH = 50%) in order to be closer to real applications of photocatalytic oxidation (PCO) systems developed for indoor air quality improvement. Accurate analytical methods were developed to identify and quantify the majority of the potential formed intermediates. Kinetic constants and the time constant of degradation were obtained for the model pollutants. Under these conditions, the degradation of the three VOCs in a mixture did not really show a decrease in the kinetic rates. Toluene and decane degradations were slightly slowed down when they were in a mixture but no significant interference was demonstrated with TCE. The intermediates formed during the PCO of the mixture of VOCs were the same as those identified during single degradation, leading to the hypothesis of few interactions between them. Only the formation and degradation of secondary intermediates, mostly composed of aldehydes, were time delayed. The total VOC concentration may lead to a competitive adsorption that seemed more sensitive for the last formed oxygenated intermediates. This investigation points out the need to always monitor the last formed aldehyde intermediates. Monitoring acetaldehyde and formaldehyde enables an evaluation of the efficiency and a better design of future PCO systems for indoor applications. [ABSTRACT FROM AUTHOR]

The performances of a laboratory PhotoCatalytic Oxidation (PCO) device were determined using a recirculation closed-loop pilot reactor. The closed-loop system was modeled by associating equations related to two ideal reactors: a perfectly mixed reservoir with a volume of VR = 0.42 m3 and a plug flow system corresponding to the PCO device with a volume of VP = 5.6 Ø 10-3 m3. The PCO device was composed of a pleated photocatalytic filter (1100 cm2) and two 18-W UVA fluorescent tubes. The Clean Air Delivery Rate (CADR) of the apparatus was measured under different operating conditions. The influence of three operating parameters was investigated: (i) light irradiance I from 0.10 to 2.0 mW·cm-2; (ii) air velocity v from 0.2 to 1.9 m·s-1; and (iii) initial toluene concentration C0 (200, 600, 1000 and 4700 ppbv). The results showed that the conditions needed to apply a first-order decay model to the experimental data (described in Part I) were fulfilled. The CADR values, ranging from 0.35 to 3.95 m3·h-1, were mainly dependent on the light irradiance intensity. A square root influence of the light irradiance was observed. Although the CADR of the PCO device inserted in the closed-loop reactor did not theoretically depend on the flow rate (see Part I), the experimental results did not enable the confirmation of this prediction. The initial concentration was also a parameter influencing the CADR, as well as the toluene degradation rate. The maximum degradation rate rmax ranged from 342 to 4894 ppbv/h. Finally, this study evidenced that a recirculation closed-loop pilot could be used to develop a reliable standard test method to assess the effectiveness of PCO devices. [ABSTRACT FROM AUTHOR]

This study demonstrated that a laboratory-scale recirculation closed-loop reactor can be an efficient technique for the determination of the Clean Air Delivery Rate (CADR) of PhotoCatalytic Oxidation (PCO) air purification devices. The recirculation closed-loop reactor was modeled by associating equations related to two ideal reactors: one is a perfectly mixed reservoir and the other is a plug flow system corresponding to the PCO device itself. Based on the assumption that the ratio between the residence time in the PCO device and the residence time in the reservoir τP/τR tends to 0, the model highlights that a lab closed-loop reactor can be a suitable technique for the determination of the efficiency of PCO devices. Moreover, if the single-pass removal efficiency is lower than 5% of the treated flow rate, the decrease in the pollutant concentration over time can be characterized by a first-order decay model in which the time constant is proportional to the CADR. The limits of the model are examined and reported in terms of operating conditions (experiment duration, ratio of residence times, and flow rate ranges). [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of toluene in indoor air conditions was performed in a closed-loop multi-pass photocatalytic reactor using the Box-Behnken experimental design methodology. The objective of this work was to rigorously determine a kinetic model in order to understand the behavior of the reactor in real indoor air conditions and to relate the kinetic parameters to physical and chemical mechanisms. Three main parameters were studied: initial toluene concentration, light irradiance and air stream velocity. The experimental results were used to calculate the single-pass removal efficiency for different operating conditions and to establish a relationship between the single-pass removal efficiency, light irradiance and air stream velocity. This relationship was integrated into an overall reaction rate law based on the Langmuir-Hinshelwood mechanism. The kinetic model obtained was then validated for various experimental conditions. [ABSTRACT FROM AUTHOR]

The ability of nanostructured titanium materials developed in the FP7/EU collaborative Clean Water project to photocatalytically degrade pollutants was tested, using 17β-estradiol (E2) as the model compound. The photocatalytic degradation of E2 was carried out under simulated solar light (both the UV part (280–400 nm) and full spectrum (200 nm–30 μm)). The efficiency of the process was assessed using several indicators including the conversion yield, the mineralization yield, the formation of by-products and their endocrine disrupting effects. The newly synthesized catalysts significantly degraded E2 and their efficiency was found to depend on the irradiation wavelength range. Some of the intermediates formed during the photocatalytic treatment with ECT-1023t and Evonik P25 were identified and their estrogenic effect was evaluated in vivo using the ChgH-GFP transgenic medaka line. This analysis confirmed that in the structure of the identified by-products, the phenol group is not destroyed and that the estrogenic effect is still present in the corresponding solution. The persistence of the estrogenic effect after the photocatalytic treatment is hypothesized to be due to the presence of the phenol group in the by-products. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured titanium materials with high UV-visible activity were synthesized in the collaborative project Clean Water FP7. In this study, the efficiency of some of these catalysts to degrade endocrine disruptor compounds, using bisphenol A as the model compound, was evaluated. Titanium dioxide P25 (AEROXIDE® TiO2, Evonik Degussa) was used as the reference. The photocatalytic degradation was carried out under the UV part of a simulated solar light (280–400 nm) and under the full spectrum of a simulated solar light (200 nm-30 μm). Catalytic efficiency was assessed using several indicators such as the conversion yield, the mineralization yield, by-product formation and the endocrine disruption effect of by-products. The new synthesized catalysts exhibited a significant degradation of bisphenol A, with the so-called ECT-1023t being the most efficient. The intermediates formed during photocatalytic degradation experiments with ECT-1023t as catalyst were monitored and identified. The estrogenic effect of the intermediates was also evaluated in vivo using a ChgH-GFP transgenic medaka line. The results obtained show that the formation of intermediates is related to the nature of the catalyst and depends on the experimental conditions. Moreover, under simulated UV, in contrast with the results obtained using P25, the by-products formed with ECT-1023t as catalyst do not present an estrogenic effect. [Copyright &y& Elsevier]

Abstract: The use of photocatalysis to improve the biodegradability of an antibiotic compound, tetracycline (TC) was investigated. The toxicity of TC and its degradation products were also examined. The Sturm test was conducted to assess the biodegradability of by-products formed in the photocatalytic process. The toxicity of tetracycline and its by-products was evaluated using a dehydrogenase inhibition test, which showed a decrease in toxicity during photocatalysis. However, the Sturm test results indicated that, like tetracycline, the by-products are not biodegradable. Possible structures of these by-products were determined using liquid chromatography–electrospray ionization-tandem mass spectrometry (LC–ESI-MS/MS). It was found that, during the photocatalytic process, the TC aromatic ring is not opened and the structure of the identified by-products is quite similar to that of tetracycline. A reaction pathway is proposed. [Copyright &y& Elsevier]

This work focuses on the photocatalytic oxidation of gaseous methyl ethyl ketone chosen as a typical indoor air pollutant. Two types of TiO2 coatings were prepared and deposited on glass plates: one using the commercial Degussa P25 TiO2 and the other one by sol-gel method. The first objective of this study was to compare different ways of preparing thin films of sol-gel TiO2 coated on glass plates, taking into account their general aspect and their photocatalytic efficiency. Several parameters were tested, such as the stabilising agent, the glass type of the support, the number of coatings and the calcination temperature. One of the synthesised materials was then kept to carry out the following study. The study aimed to assess the influence of TiO2 coating types on the effect of water vapour. This was achieved by performing MEK photocatalytic degradation kinetics under two levels of humidity at a fixed temperature. Experimental results were then modelled by the Langmuir-Hinshelwood equation. The obtained parameters gave specific trends in function of the considered catalyst. The second part of this work was to identify MEK degradation byproducts during its photocatalytic oxidation. The main detected intermediate was acetaldehyde, followed by methyl formate. A MEK degradation pathway was then proposed. [ABSTRACT FROM AUTHOR]

Abstract: Four TiO2-based materials, named A, B, C and D, are used to investigate the influence of water vapor on the gas–solid adsorption and heterogeneous photocatalytic oxidation of gaseous methyl ethyl ketone (MEK). Two of the photocatalysts (A and B) are constituted of powdered TiO2 deposited onto two different supports (ordinary glass and non-woven cellulose fibers). The other ones (C and D) are composed of a thin film of TiO2 coated on glass substrates. The effect of water vapor on MEK initial conversion rates is studied for the four photocatalytic materials using the Langmuir–Hinshelwood model at the initial time. On the concentrations range where the model hypotheses are verified, adsorption constants K and kinetics constants k are calculated for experiments under both dry and humid atmosphere. When the relative humidity is increased, the evolution of these constants shows that water vapor acts differently depending on the form of deposited TiO2 (powder and film). [Copyright &y& Elsevier]

Gas--solid photocatalyzed oxidation of air contaminants is being explored more and more for possible application to decontamination, purification and deodorization of enclosed atmospheres. Indoor air is characterized by a huge number of pollutants at low concentrations. Volatile organic compounds (VOC) represent the main indoor air pollutants category, and are of great concern since some of them can act negatively on human health. Several treatments exist to reduce VOC concentrations in gaseous effluents, but photocatalytic oxidation appears to be the most appropriate regarding indoor air specific constraints. It is then necessary to develop photocatalysts, which can possibly be used in an application such as indoor airquality improvement. In the present work, three different TiO2-based materials were studied and compared for the photocatalytic oxidation of a typical pollutant of indoor air: methyl ethyl ketone. Kinetic studies were performed for each material in dry and humid air conditions, and the Langmuir--Hinshelwood model was satisfactorily applied in almost every case. A second approach consisted of determining methyl ethyl ketone degradation by-products. Acetaldehyde was found to be the main gaseous intermediate, and could be taken into account in the general Langmuir--Hinshelwood modeling. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation of two ketones, acetone, and 2-butanone, over TiO2-containing paper was studied under two different levels of relative humidity. Adsorption of these ketones on TiO2-containing paper is significantly affected by the presence of water vapor. Adsorption isotherms of both acetone and 2-butanone, under dry and humid atmosphere, can be satisfactory described using the Langmuir adsorption model for concentrations ranging from 0 to 6 g m-3. Kinetic data of the photocatalytic oxidation of these ketones are analyzed using the Langmuir–Hinshelwood model except for the photocatalytic oxidation of acetone in humid air conditions where adsorption was assumed to be the rate limiting step. In the case of acetone, photoactivity is greatly inhibited in presence of water vapor. On the other hand, it is showed that water vapor has little effect on 2-butanone photocatalytic degradation. The latter is just slightly improved in humid air conditions for initial 2-butanone concentrations upper than 2 g m-3. An explanation is given in term of adsorption affinity of the pollutants compared with competitive adsorption of water molecules with the ketones onto TiO2-containing paper. [Copyright &y& Elsevier]

Abstract: Nowadays, with the increase in the thermal insulation of buildings, indoor air quality (IAQ) has deteriorated, particularly because of the presence of volatile organic compounds (VOC). To improve IAQ, photocatalytic processes can be used. Photocatalytic reactions can be broken down into three steps: adsorption of pollutants, chemical reaction, and desorption of water, carbon dioxide and by-products. In this work, the accessibility of the pollutants to the reactive sites of a commercial TiO2-photocatalyst is studied. Firstly, adsorption mechanisms are investigated through toluene adsorption isotherms in batch reactors. In humid air conditions (relative humidity of 50% at 24°C), the classical adsorption models cannot be applied. Consequently, a new model, called the “Langmuir-multi”, is built. It fits the obtained experimental data properly. Adsorption equilibrium constants are calculated based on this new model. To understand adsorption mechanisms better, adsorption isotherms are also performed in dry air conditions with toluene and in humid air with acetone and heptane. It is observed that water vapor plays a major role. Secondly, photocatalytic reactions are carried out with toluene, acetone and heptane in humid air. The kinetic curves are well-represented by the Langmuir–Hinshelwood (L–H) equation so that reaction and equilibrium constants can be assessed. The L–H equilibrium constant appears to depend on the type of pollutant and on the affinity between the pollutant and the photocatalyst surface. No correlation is found between the equilibrium constant and light intensity. It is also shown that the calculated L–H equilibrium constants are not equal to those previously obtained in dark conditions and in batch reactors. [Copyright &y& Elsevier]

Highlights: [•] Decane batch photocatalytic abatement on the ppb range. [•] Simultaneous monitoring: (i) decane, (ii) reaction intermediate, and (iii) CO and CO2. [•] Reaction pathway of decane oxidation. [•] Light aldehydes firstly the main gaseous intermediates, then mineralized into CO2. [•] Intermediates and CO2 formations are maximized by 50% RH. [Copyright &y& Elsevier]

Abstract: This work reports the influence of the meso-structure of TiO2 films in the photocatalytic oxidation of methyl ethyl ketone. Five types of TiO2 films were prepared combining the sol–gel route with the Evaporation Induced Self-Assembly (EISA) method. Sols were prepared from titanium tetrachloride (TiCl4) using different types of pore generating agents. Films characterisation was performed by Fourier Transform Infrared Spectroscopy (FTIR), Grazing X-ray diffraction (GXRD), X-ray diffraction of small angle and Transmission Electron Microscopy (FE-SEM). Environmental Ellipsometric Porosimetry (EEP) studies were performed to obtain the adsorption/desorption isotherms and calculate porous size distribution, pore volume and specific surface area (S s) of the films. Kinetic of MEK photocatalytic oxidation data were modelled by Langmuir–Hinshelwood equation and the adsorption and kinetics constants (k and K) were calculated. Better results of MEK degradation were obtained for the Brij58 films deposited at relative humidity (RH) of 20% and 50%. The results are correlated with the porosity properties of the films. [Copyright &y& Elsevier]