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See detailSynthesis by the sol-gel process of visible light sensitive-TiO2 for the degradation of pollutants and microorganisms
Tasseroul, Ludivine ULg; Lambert, Stéphanie ULg; Páez Martínez, Carlos ULg et al

in Récents Progrès en Génie des Procédés, Lavoisier Technique et Documentation, Volume 101, 6 p. (CD-ROM) (2011, November 29)

To stabilize the TiO2-dye interaction, free metal tetra(4-carboxyphenyl)porphyrin and nickel tetra(4-carboxyphenyl)porphyrin were introduced into the TiO2 matrix by cogelation rather than by grafting. DR ... [more ▼]

To stabilize the TiO2-dye interaction, free metal tetra(4-carboxyphenyl)porphyrin and nickel tetra(4-carboxyphenyl)porphyrin were introduced into the TiO2 matrix by cogelation rather than by grafting. DR and FT-IR spectroscopies were performed to establish the interaction between porphyrins and TiO2. Cristallinity and specific surface area were performed by XRD and nitrogen adsorption-desorption measurements. The photoactivity of doped-TiO2 xerogels was evaluated for p-nitrophenol and Escherichia coli degradation. Under visible light, the samples allowed the degradation of 40% of p-nitrophenol in 6 h and the elimination of 108 CFU/mL of E. coli in 48 h. [less ▲]

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See detailHighly efficient organic/inorganic titania xerogels for photocatalysis applications
Bodson, Céline ULg; Bied, Catherine; Páez Martínez, Carlos ULg et al

Poster (2011)

TiO2 heterogeneous photocatalysis is an attractive technique for the complete destruction of undesirable contaminants either in aqueous or gaseous phase by using solar or artificial light illumination ... [more ▼]

TiO2 heterogeneous photocatalysis is an attractive technique for the complete destruction of undesirable contaminants either in aqueous or gaseous phase by using solar or artificial light illumination. The main drawback of TiO2 is that it can be activated only by UV light because of its large band gap (3.20 eV for anatase). Thus, it would be interesting to sensitize TiO2 to the whole visible region by doping with non-metal atoms such as phosphorus. Furthermore, it was found that the P-doped species could significantly increase the specific surface area of the materials, which consequently exhibit a higher content of surface hydroxyl groups. Upon band gap excitation of TiO2, the photoinduced electrons and positively charged holes can reduce and oxidize the species adsorbed on the TiO2 particles. The high degree of recombination between photogenerated electrons and holes is a major rate-limiting factor controlling the photocatalytic efficiency. Attempts to increase the titania efficiency have been made by doping P-doped TiO2 with metals, such as Ag. In the present study, a sol-gel method is developed to synthesize P-doped TiO2 and P/Ag-codoped xerogels by a cogelation method [1] based on the hydrolysis and the condensation of Ti(OC3H7)4 in the presence of a phosphoryled compound able to complex silver: NH2-(CH2)2-NH-(CH2)2-P(O)-(OC2H5)2, EDAP), in various alcohols. These xerogels are dried at 150°C under vacuum for 24 h, and calcined under air for 5 h at 350°C, 450°C, 550°C and 650°C. The resulting materials were characterized by ICP-AES, TG-DSC, TEM, XRD, nitrogen adsorption-desorption isotherms, FT-IR and diffuse reflectance measurements in the UV/Vis region. To measure the photoactivity of these new hybrid organic/inorganic titania xerogels, all these samples were tested for the degradation of p-nitrophenol under visible light. The titanium, phosphorus and silver contents in xerogels were confirmed by ICP-AES. As expected, theoretical and actual Ti/P molar ratio and Ag contents in xerogels are similar and then after washing with THF for 48 h. These results allow to conclude that EDAP and Ag are well incorporated within the TiO2 matrix: EDAP is anchored in the titania matrix by complexation and cogelation with TTIP [2], whereas silver, first incorporated by complexation through the ethylenediamine fragment of EDAP, is present in the xerogels in the form of nanoparticles. It was found that the phosphor-doped species could significantly increase the surface area of the materials. [2] It is noteworthy that the porosity of these materials is not affected by the addition of silver acetate during the synthesis, a very slight decrease of the specific surface area being observed in all cases. The organic/inorganic hybrid titania materials display very high photocatalytic efficiencies in the degradation of p-nitrophenol compared to pure titania. Deeper investigations concerning the structure of these materials should enable a better understanding of the photocatalytic mechanisms involved with these hybrids and will soon be reported. 1. S. Lambert, K. Y. Tran, G. Arrachart, F. Noville, C. Henrist, C. Bied, J. J. E. Moreau, M. Wong Chi Man, B. Heinrichs, Micropor. Mesopor. Mater. 2008, 115, 609. 2. C.J.Bodson1, S.D. Lambert1, C. Alié1, X. Cattoën2, J-P. Pirard1, C. Bied2, M.Wong Chi Man2, B. Heinrichs1 ,Micropor. Mesopor. Mater. 2010, 134,157 [less ▲]

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See detailSynthesis by sol-gel process of visible light sensitive-TiO2 for the degradation of pollutants and microorganisms
Tasseroul, Ludivine ULg; Lambert, Stéphanie ULg; Páez Martínez, Carlos ULg et al

Poster (2011)

Since the discovery of photocatalytic decomposition of water on TiO2 electrodes by Fujishima and Honda [1], heterogenous photocatalysis has been widely studied for environmental applications ... [more ▼]

Since the discovery of photocatalytic decomposition of water on TiO2 electrodes by Fujishima and Honda [1], heterogenous photocatalysis has been widely studied for environmental applications. Photocatalytic processes are new technologies for waste water treatment because new compounds (alkanes, pesticides, dyes, etc.) in effluents are not readily degraded by the conventional treatments [2]. Oxidative processes can completely destroy organic pollutants [3] or microorganisms (bacteria, viruses, fungi, etc.) [4,5]. At this moment, the commercial Degussa P25 is the mostly used photocatalyst. Nevertheless, it requires UV light to be activated, that is why scientists try to activate TiO2 under visible light. The aim of this study is to synthesize photocatalysts activated by visible light and to evaluate their activity for the degradation of pollutants and microorganisms. The sol-gel process allows the direct introduction of visible light sensitive species like porphyrins inside the TiO2 matrix during the synthesis [6]. Two tetracarboxyphenyl porphyrins are synthesized for the sensitization of TiO2 to visible light : the metal free tetracarboxyphenyl porphyrin and the nickel tetracarboxyphenyl porphyrin. These porphyrins are characterized by 1H NMR, FT-IR and UV/Vis spectroscopies. They are introduced during the sol-gel synthesis of TiO2 matrix. Diffuse reflectance and FT-IR spectroscopies are used to ensure that porphyrins are incorporated inside the matrix of TiO2. Indeed, characteristic porphyrins peaks appear on spectra. The cristallinity and specific surfaces of catalysts are also determined by XRD and nitrogen adsorption-desorption measurements respectively. The depolluting efficiency of photocatalysts is evaluated for the degradation in water of p-nitrophenol, which is listed as one of the 114 organic pollutants by the Environmental Protection Agency in the US. After 6 h under visible light, 40 % of p-nitrophenol are degraded with some catalysts. The activity is influenced by i) the presence of porphyrins : the photoactivity increases with the amount of porphyrins ; ii) the nature of porphyrins : nickel porphyrins are more active than free metal porphyrins ; and iii) the crystallinity of catalysts : amorphous catalysts are less active than crystallized samples. The photocatalysts with the highest degradation rating of dyes will be selected for the degradation in water of Escherichia coli and Lactobacillus acidophilus. [1] A. Fujishima, K. Honda, Nature 238, 37-38 (1972) [2] P. Gogate, A. Pandit, Advances in Environmental Research 8, 501-551 (2004). [3] D. Chen, A. Ray, Water Research 32, 3223-3234 (1998) [4] R. Watts, S. Kong, M. Orr, G. Miller, B. Henry, Water Research 29, 95-100 (1995). [5] J. Hong, M. Otaki, Journal of Bioscience and Bioengineering 101, 185-189 (2006). [6] C. Wang, J. Li, G. Mele, G.M. Yang, F.-X. Zhang, L. Palmisano, G. Vasapollo, Applied catalysis 78, 218-226 (2007). [less ▲]

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See detailUnpredictable photocatalytic ability of H2-reduced rutile-TiO2 xerogel in the degradation of dye-pollutants under UV and visible light irradiation
Páez Martínez, Carlos ULg; Lambert, Stéphanie ULg; Poelman, Dirk et al

Poster (2011)

Photocatalytic degradation of organic and inorganic pollutants on the TiO2 semiconductor has been extensively studied as a way to solve environmental problems relating to wastewater and polluted air ... [more ▼]

Photocatalytic degradation of organic and inorganic pollutants on the TiO2 semiconductor has been extensively studied as a way to solve environmental problems relating to wastewater and polluted air. Anatase and rutile are the most commonly used crystalline structures of TiO2, with anatase showing a higher photocatalytic activity attributed to its higher specific surface area and its favourable band gap energy (Eg). However, its high band gap (Eg = 3.2 eV) implies the use of UV light (lambda ≤ 380 nm) to inject electrons into the conduction band (TiO2(e-CB)) and to leave holes in the valence band (TiO2(h+VB)). Although the low band gap energy of rutile-TiO2 (Eg = 3.02 eV) allows rutile to potentially absorb more solar energy than anatase, the anatase-to-rutile phase transition leads to the collapse of the TiO2 specific surface area, which may result in a decrease in the photocatalytic activity of rutile. Low specific surface area and therefore poor absorption properties lead to strong limitations in exploring the photo-efficiency of rutile. Nevertheless, rutile has been proved to be comparable to anatase in its photoelectrochemical properties when used in dye-sensitized solar cells. In the present study, a new process for the reduction of rutile-TiO2 xerogel under hydrogen flow was developed to enhance the photocatalytic activity of TiO2 materials synthesized by the sol-gel process. So a series of H2-reduced TiO2 xerogels of low specific surface area was prepared by hydrolysis and condensation of tetraisopropoxy titanium(IV) in 2-methoxyethanol. The gels were dried under vacuum, calcined in air at different temperatures (400°C, 500°C and 700°C) and finally reduced in H2 at 400 °C. The materials were characterized by X-ray diffraction, transmission electron microscopy (TEM), FT-IR spectroscopy and UV/Visible diffuse reflectance spectroscopy. The texture was determined by nitrogen adsorption-desorption measurements. The effects of the calcination/reduction treatments on the adsorption of methylene blue (MB) in aqueous solution and on the photocatalytic degradation of MB and crystal violet (CV) under UV and visible light irradiation were also evaluated. Results showed predictable modifications in the physico-chemical properties caused by the annealing of TiO2 xerogel at high calcination temperature (700 °C), such as a total anatase-to-rutile phase transition and a considerable loss of specific surface area from 260 to 2 m2 g-1. However, the higher degree of reduction exhibited by the rutile-TiO2 lattice led to unpredictable photocatalytic activity for the dye conversion under UV and visible light irradiation: the loss of specific surface area of the rutile-TiO2 sample was compensated by the increase in the affinity of this sample for the dye. Under UV light irradiation, the rutile-TiO2 xerogel obtained after a calcination at 700 °C showed a similar level of photoactivity as the one obtained with anatase-TiO2 xerogels obtained by calcination at 400 °C and 500 °C. Under visible light, unlike anatase-TiO2 xerogels, the rutile-TiO2 xerogel showed a higher dye photoconversion rate per external surface area (40 times higher) than the commercial TiO2 Degussa P25. [less ▲]

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See detailStudy of photocatalytic decomposition of hydrogen peroxide over ramsdellite-MnO2 by O2-pressure monitoring
Páez Martínez, Carlos ULg; Liquet, Dimitri ULg; Calberg, Cédric ULg et al

in Catalysis Communications (2011), 15

The catalytic and photocatalytic activities of ramsdellite type manganese oxide, R-MnO2 were studied from the initial rate of decomposition of H2O2 in aqueous solution. The kinetic study was followed by ... [more ▼]

The catalytic and photocatalytic activities of ramsdellite type manganese oxide, R-MnO2 were studied from the initial rate of decomposition of H2O2 in aqueous solution. The kinetic study was followed by the production of O2 via gas pressure monitoring (O2-monitored method), in the dark and under visible light irradiation (λ≥400 nm), at 20 °C. Experimental data showed that the rate of H2O2 decomposition, under visible light irradiation and in the dark, obeys the first order kinetic law.While in the dark the H2O2 decomposition rate bymass unit was around 6.88 mmol g−1 s−1, under visible light irradiation theH2O2 decomposition rate achieved a maximal value of 15.13 mmol g−1 s−1. The increase in the H2O2 decomposition, by effect of the visible light, was observed in ranges of catalyst concentrations from 16 to 374 mg L−1. These results reflect the potential of R-MnO2 as a photoactive catalyst, being a consequence of presumed photoreduction of Mn4+centers. [less ▲]

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See detailImprovement in the methylene blue adsorption capacity and photocatalytic activity of H2-reduced rutile-TiO2 caused by Ni(II)porphyrin preadsorption
Páez Martínez, Carlos ULg; Lambert, Stéphanie ULg; Poelman, Dirk et al

in Applied Catalysis B : Environmental (2011), 106

H2-reduced rutile-TiO2 xerogel (Ti-700), obtained via the sol–gel process, was found to strongly adsorb the Ni(II)-5,10,15,20-tetrakis(4-carboxyphenyl)-porphyrin (NiTCPP) from a methanolic solution ... [more ▼]

H2-reduced rutile-TiO2 xerogel (Ti-700), obtained via the sol–gel process, was found to strongly adsorb the Ni(II)-5,10,15,20-tetrakis(4-carboxyphenyl)-porphyrin (NiTCPP) from a methanolic solution, despite its very low specific surface area (SBET ≈ 2 m2 g−1). UV/vis spectroscopy analysis showed that after calcination at 700 ◦C and reduction under H2 flow at 400 ◦C, the TiO2-xerogel increased its NiTCPP-adsorption capacity by surface area unit by up to 120 times. The effect of the porphyrin presence in the catalytic performances of TiO2-xerogels was studied through three kinetics models: (i) the pseudo-first-order kinetic model; (ii) the pseudo-second-order kinetic model, which are used to describe the adsorption rate based on the adsorption capacity of the catalysts; and (iii) the Langmuir–Hinshelwood kinetic model which is used to describe the photocatalytic degradation rate of methylene blue (MB). A significant improvement in the efficiency of Ti-700 was observed after the porphyrin-adsorption process (NiTCPP/Ti-700): MB-adsorption capacity at equilibrium and the apparent MB-photoconversion constant, kapp, of NiTCPP/Ti-700 were both up to 2 times higher than those observed for the Ti-700. [less ▲]

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See detailActivated-carbon-xerogel/TiO2-P25 composite photocatalysts with high activity for the degradation of p-nitrophenol
Páez Martínez, Carlos ULg; Contreras, María; Olivera-Fuentes, Claudio et al

Poster (2010, July)

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See detailAg-and SiO2-doped porous TiO2 with enhanced thermal stability
Braconnier, Benoît ULg; Páez Martínez, Carlos ULg; Lambert, Stéphanie ULg et al

in Microporous and Mesoporous Materials (2009), 122

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See detailDécomposition photocatalytique de polluants et de micro-organismes dans l'eau
Heinrichs, Benoît ULg; Pirard, Jean-Paul ULg; Lambert, Stéphanie ULg et al

E-print/Working paper (2008)

Dans le cadre de la réutilisation des eaux usées et de l’accès limité à l’eau potable dans certaines régions du globe, de nouvelles techniques de désinfection nécessitant de faibles consommations ... [more ▼]

Dans le cadre de la réutilisation des eaux usées et de l’accès limité à l’eau potable dans certaines régions du globe, de nouvelles techniques de désinfection nécessitant de faibles consommations d’énergie sont étudiées. Cette eau n’est pas toujours potable et contient des polluants qui induisent des mutations génétiques pouvant conduire au développement de cancers ou encore des micro-organismes pathogènes causant des maladies graves. Depuis la découverte des propriétés de photodégradation oxydante du dioxyde de titane (TiO2), la photocatalyse hétérogène est utilisée pour l’élimination des polluants environnementaux et des micro-organismes. [less ▲]

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