Article

Alumina/TiO2/hydroxyapatite interface nanostructure composite filters as efficient photocatalysts for the purification of air

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Abstract

Alumina/TiO2/Apatite interface nanostructure composite filters have been developed for air purification. It was shown that these filters can efficiently absorb and decompose organic species which are suspended in air. To prepare the filters, TiO2 nanopowder was dispersed in titanium sol in 30 and 70 g/L concentrations, and the prepared mixture was deposited on the porous alumina body by dip-coating. Then, the calcined nanostructure composite TiO2–TiO2 was soaked in a simulated physiological solution (SBF) at 37 °C. The surface morphology, surface area, crystalline structure and crystallite sizes of the films were investigated by SEM, EDS, BET, and XRD. The photocatalytic activity of the composite filters, as well as the effect of the TiO2 nanopowder concentration in the titania sol and soaking time in SBF were also evaluated through the degradation of nitrogen oxides (NOx ) as one of the dominant causes of air pollution in the car exhaust gases. SEM and XRD results showed that immersion in SBF forms a layer of carbonate-containing apatite on the TiO2 layer. The results showed that increasing nanopowder TiO2 concentration increases the NOx oxidation rate. The prepared alumina/TiO2/HA filter can be used to remove CO gas with the absorption mechanism, as an interesting CO degradation performance (about 95 %) was observed in the alumina/TiO2/HA filter after soaking into SBF for 20 days. However, it could not significantly alter the concentrations of other car exhaust pollutants (SO2 and Cx Hy ).

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... Several studies have focused on the use of the adsorption-photocatalytic coupling of the TiO 2 /HAP composite for the removal of gaseous pollutants (Azouani et al. 2010a;Azouani et al. 2010b;Azouani et al. 2007;Benmami et al. 2006). Thus, NO adsorption was observed by Nonami (2004), Mitsionis et al. (2011), andNasr-Esfahani andFekri (2012) in photocatalytic studies. However, the improvement of the gas-phase photocatalytic activity due to the presence of hydroxyapatite on the surface of TiO 2 is controversial; a negative or no effect can be observed with regard to the process procedure and the UV wavelengths used. ...
... Several studies have focused on the use of the adsorption-photocatalytic coupling of the TiO 2 /HAP composite for the removal of gaseous pollutants (Azouani et al. 2010a;Azouani et al. 2010b;Azouani et al. 2007;Benmami et al. 2006). Thus, NO adsorption was observed by Nonami (2004), Mitsionis et al. (2011), andNasr-Esfahani andFekri (2012) in photocatalytic studies. However, the improvement of the gas-phase photocatalytic activity due to the presence of hydroxyapatite on the surface of TiO 2 is controversial; a negative or no effect can be observed with regard to the process procedure and the UV wavelengths used. ...
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... Beside aforementioned applications, nano-hydroxyapatite bioceramic based composites are used as a filter aid for absorbing and decomposing automotive pollutant carbon monoxide and removal of fluoride through an ion-exchange mechanism [25,26]. Recently nano-hydroxyapatite is used in catalysis and protein separation; however, its many unrevealed applications are under investigation into various multidisciplinary teams of researchers [27,28,29]. ...
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In the developing area of modern nanobiotechnology, the research is being focused on enhancement of catalytic performance in terms of efficiency and stability of enzymes to fulfill the industrial demand. In the context of this interdisciplinary era, we isolated and identified alkaline protease producer Bacillus aryabhattai P1 by polyphasic approach and then followed one variable at a time approach to optimize protease production from P1. The modified components of fermentation medium (g/L) were wheat bran 10, soybean flour 10, yeast extract 5, NaCl 10, KH2PO4 1, K2HPO4 1 and MgSO4·7H2O 0.2 (pH 9). The optimum alkaline protease production from P1 was recorded 75 ± 3 U/mg at 35 °C and pH 9 after 96 h of fermentation period. Molecular weight of partially purified P1 alkaline protease was 26 KDa as revealed by SDS-PAGE. Calcium based nanoceramic material was prepared by wet chemical precipitation method and doped in native P1 protease for catalytic activity enhancement. Catalytic activity of modified P1 protease was attained by nanoactivator mediated modulation was more by 5.58 fold at pH 10 and 30 °C temperature. The nanoceramic material named as nanoactivator, with grain size of 40–60 nm was suitable to redesign the active site of P1 protease. Such types of modified proteases can be used in different nanobiotechnological applications.
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... Enamel, the hardest tissue in the human body, is a highly organized dental tissue, covering the outer layer of the tooth crown. It possesses unique mechanical and structural properties [29][30][31][32], relying on its high hydroxyapatite content, the arrangement of apatite crystals into enamel prisms, and finally, the alignment of these prisms in a picket-fence appearance in a tissue of high physical resilience and great hardness [33][34][35][36][37]. Ameloblasts, the enamel-forming cells, are specialized epithelial cells differentiating from the inner cells of the enamel organ [38]. ...
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... It was actually demonstrated -by electron spin resonance -that superoxide radicals ( O 2 À ) are the main active reactive oxygen species responsible for the photocatalytic degradation of NO x (Dong et al., 2015). It follows that NO was mainly oxidised by oxygen radicals (Giannakopoulou et al., 2012b;Nasr-Esfahani and Fekri, 2012). This demonstrates the much higher photocatalytic activity of the coated samples compared to that of the mixed samples, due to the preparation method. ...
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... Many other potential applications were reported basing to the absorptive properties of HAp. Those include absorption of CO (Nasr-Esfahani et al. 2012) and absorption of fluorine (Pandi et al. 2014). ...
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Pt-Rh/TiO2/Al2O3 was investigated as a NOx storage-reduction catalyst using lean-rich cycles. It was found to be highly effective for NOx reduction and highly resistant to SO2 and H2O. In the presence of 100ppm SO2 and 2.3% H2O, approximately 90% of NOx conversion was obtained at 250°C and a GHSV of 30,000h−1 after 5h lean-rich cyclic runs. A model NOx trap catalyst, Pt-Rh/BaO/Al2O3, was used for comparison. In the absence of SO2 and H2O, nearly complete removal of NOx was achieved. NOx conversion dropped to only 30% after SO2/H2O were introduced into the reactant gases at 300°C. With Pt-Rh/TiO2/Al2O3, over 70% NO conversion was still obtained at 400°C. Although, the BaO containing catalyst has much higher capacity for NOx than that containing TiO2, it is much more susceptible to SOx poisoning. In situ FT-IR spectra of the titania catalyst showed that nitrate species was the final adspecies (i.e. at the end of the lean phase) on the storage catalyst and its intensity was only slightly weakened in the presence of SO2 and H2O.
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Two types of photocatalytic films, macroporous TiO2-P25 (Degussa) composite films (PPMSGF-PEG) and macroporous TiO2 films (TiO2-PEG), have been synthesized by a P25-PEG modified sol–gel method and a PEG modified sol–gel method, respectively. The physicochemical properties, including thermal behavior, surface morphology, crystallinity, crystal size, specific surface area (BET), pore volume and adhesion on the stainless steel substrate, of the two types of films were investigated by TGA, SEM, XRD, Raman spectroscopy, HRTEM, N2 adsorption and the tape test. The photocatalytic activities of the films were compared using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant in water. It was found that adding 10g/L P25 in the sol can improve not only the amount of crystalline material immobilized on the support, but also the BET surface area and pore volume of the films calcined at temperatures between 500 and 600°C. N2 adsorption results suggested that the enhanced BET surface area and pore volume were due to the formation of large pores induced by the presence of P25 powders, which could help retain a relatively high pore volume during calcination at higher temperatures. The results on photocatalytic degradation of 4-CBA showed that the increase in photocatalytic activity caused by P25 powders reached maximum for PPMSGF-PEG calcined at 500°C, compared with that of TiO2-PEG film. The tape test showed that adding 10g/L P25 in the sol did not affect the critical calcination temperature (i.e., 500°C) at or above which excellent adhesion between the films and the stainless steel substrate can be maintained. This study proves that optimizing calcination temperature is still an important strategy for the preparation of macroporous TiO2-P25 composite films with enhanced photocatalytic activity and excellent adhesion on the stainless steel substrate.
Article
An artificial neural network (ANN) was built to analyze the decrease of nitrogen oxides relative to TiO2 powder photocatalytic efficiency. Experimental sets were considered to train and test ANN where it was possible to identify an optimized structure representing the correlations between experimental variables and NO and NOx efficiencies. Predicted results permitted to point out the role of exposed surface and powder mass.
Article
A simple sol−gel route has been developed for the preparation of mesoporous and nanocrystalline anatase thin layers. An anatase hydrosol was first synthesized at room temperature from acidic hydrolysis of titanium isopropoxide. The optimization of the synthesis parameters, including titanium concentration, HCl/Ti and H2O/Ti ratios, temperature, and aging time, enabled us to produce a clear sol with a very low HCl/Ti ratio (equal to 1). As a function of the further thermal treatment conditions, it was then possible to control the size of the anatase crystallites (from 5 to >10 nm) and the O/Ti stoichiometry (from 1.9 to 2.0). Ordered mesoporosity was obtained by using a triblock copolymer as the templating agent. Preliminary experiments evidenced the photocatalytic activity of the prepared layers.
Article
The new TiO2 photocatalytic filter supported by photo-induced activated hydroxyapatite (HAp Ca10(PO4)6(OH)2) was developed and the complete oxidation of acetaldehyde on the filter was investigated. The photocatalytic filter was fabricated by coating TiO2 and HAp on the porous ceramics body. In the decomposition of acetaldehyde using this composite filter, CO2 generation came to maximum at 20min after starting of UV (254nm) irradiation and the value was the stoichiometric to the complete oxidation. The rapid and complete oxidative decomposition of acetaldehyde can be achieved using the new photocatalytic composite filter in spite of the very small contact time, about 0.4s through the filter and one path method. This effect would not be explained alone by the absorption capacity of HAp for acetaldehyde. Synergic and composite effect of HAp followed by radical formation under light is maximum at 254nm.
Article
The evaporation-induced self-assembly method using a novel diblock (poly(ethylene-co-butylene)-b-poly(ethylene oxide)) copolymer (KLE) provides fully crystalline mesoporous layers of TiO2 exhibiting high thermal stability up to 700 °C, high photocatalytic activity in the decomposition of methyl stearate and facile transformation into a substantially stable superhydrophilic state by 1 mW/cm2 UV-illumination.
Article
Titanium dioxide (TiO2) coatings have been long considered as biocompatible interfaces to promote the physico-chemical bonding between the bone tissues and implant material (e.g., titanium and stainless steel). Monodispersed TiO2 (anatase, the low temperature polymorph of TiO2) microspheres, produced in the form of colloidal precipitates, were deposited on different substrates and apatite formation was induced on the resulted surface by immersing the coated substrates in simulated body fluid solution. Analytical and microstructural investigations, conducted by X-ray diffraction, energy depressive X-ray spectroscopy and scanning electron microscopy techniques, showed considerable higher rates of apatite formation, in vitro, on the anatase microspheres compared to the sol–gel-derived thin films of the same oxide. We concluded that the particular surface morphology of the packed TiO2 microspheres, promotes a faster apatite formation in vitro.
Article
A study of electrochemical Li insertion combined with structural and textural analysis enabled the identification and quantification of individual crystalline and amorphous phases in mesoporous TiO2 films prepared by the evaporation-induced self-assembly procedure. It was found that the properties of the amphiphilic block copolymers used as templates, namely those of a novel poly(ethylene-co-butylene)-b-poly(ethylene oxide) polymer (KLE) and commercial Pluronic P123 (HO(CH2CH2O)(20)(CH2CH(CH3)O)(70)(CH2CH2O)(20)H), decisively influence the physicochemical properties of the resulting films. The KLE-templated films possess a 3D cubic mesoporous structure and are practically amorphous when calcined at temperatures below 450 degrees C. but treatment at 550-700 degrees C provides a pure-phase (anatase), fully crystalline material with intact mesoporous architecture. The electrochemically determined fraction of crystalline anatase increases from 85 to 100 % for films calcined at 550 and 700 degrees C, respectively. In contrast, the films prepared using Pluronic P123, which also show a 3D cubic pore arrangement, exhibit almost 50 % crystallinity even at a calcination temperature of 400 degrees C, and their transformation into a fully crystalline material is accompanied by collapse of the mesoporous texture. Therefore, our study revealed the significance of using suitable block-copolymer templates for the generation of mesoporous metal oxide films. Coupling of both electrochemical and X-ray diffraction methods has shown to be highly advisable for the correct interpretation of structure properties, in particular the crystallinity, of such sol-gel derived films.
Article
The competition effect between water vapor and pollutants at ppb level for adsorption sites has been previously reported. It was found that at high humidity levels, the pollutant photodegradation rate reduced drastically. To improve the photodegradation of pollutants at ppb level and at high humidity levels, TiO2 is immobilized on an activated carbon (AC) filter. 200 ppb of nitrogen oxide (NO) and 20 ppb of benzene, toluene, ethylbenzene and o-xylene (BTEX) were chosen as target pollutants. Sensitivity analyses were conducted for NO and BTEX under different residence times and levels of humidity. Results showed that the combination of TiO2 and AC significantly increased NO and BTEX removals at short residence time and high humidity levels. TiO2 immobilized on AC filter was less affected by the increasing humidity levels. NO2, as an intermediate generated from the photodegradation of NO, was also successively suppressed from exiting the system. Deactivation from the photodegradation of NO was suppressed by immobilizing TiO2 on an activated carbon filter. The use of activated carbon acted as a local pollutant concentrator by adsorbing pollutants from the air stream and thereby diffused to the TiO2 for photodegradation.
Article
Titanium is the most commonly used metallic material in the manufacture of orthopedic implants, and hydroxyapatite (HA) is bioactive and biocompatible when used as bone substitutes. To achieve better biocompatibility and excellent mechanical performance of prostheses, HA coating is often fabricated on titanium surfaces. The present study used dip-coating techniques to fabricate HA coating of organic sol–gel of Ca(NO3)2·4H2O and PO(CH3)3 and inorganic sol of Ca(NO3)2·4H2O and (NH4)2·HPO4. Scanning electron microscopy (SEM) and grazing-incidence X-ray diffraction (XRD) have been used to characterize the morphology and the distributions of crystallite size and micro-strains of the coatings. After firing at 400 °C, the apatite structure of coatings on titanium began to appear. Warren–Averbach Fourier transfer analysis of the diffuse reflections indicated that the mean crystallite size increased and micro-strain decreased significantly with the rise in firing temperature. In the range of 400–600 °C, the effect of firing temperatures on mean crystallite size and micro-strain of both coatings was obvious. Precursor types of HA coating significantly affected the aggregating size of particles of nano-HA coatings, which were 25–40 nm for organic sol–gel and approximately 100 nm for inorganic sol. The morphology of interfaces between coating and titanium indicated thin nano-HA coatings with thickness 2 μm for organic sol–gel and 5 μm for inorganic sol were intact and homogenous. The effect of firing temperatures on aggregating size of particles of both coatings was not obvious.
Article
A novel method for the processing of sol–gel-derived titanium dioxide composites has been developed and investigated for the purpose of producing thick films and self-supported photocatalysts. The processing of the composite sol–gel (CSG) photocatalysts, prepared as “coating” and self-supported “bulk” bodies involved utilizing precalcined commercial titania (Degussa P-25 and Aremco) as filler mixed with the sol and then, heat treatment at relatively low temperature (up to 700 °C). The resulting photocatalyst exhibited relatively high surface area and enhanced mechanical stability and integrity. Scratch adhesion tests performed on the CSG photocatalysts showed very good mechanical integrity and scratch resistance of about 5–10 N, far greater than the 0–0.2 N observed for P-25 and Aremco photocatalysts. Photocatalytic activities of the developed composites were evaluated through the oxidation of a known and standard air contaminant trichloroethylene (TCE), which has been widely investigated by many researchers in the field of photocatalysis. The CSG photocatalysts coatings provided TCE removals ranging up to 90% of that provided by P-25. However, the better mechanical integrity offered by the CSG photocatalysts make them viable alternatives for commercial applications that require long term stability and good mechanical properties.
Article
In a previous paper [J. Mater. Sci. 38 (2003) 823] we have described the preparation and characterization of conventional alkoxide sol–gel derived TiO2 films [J. Mater. Sci. 23 (1988) 2259] and of TiO2 powder enriched alkoxide sol–gel derived films. The powder films were prepared on flat stainless steel substrates and on glass beads. These films were characterized for various parameters like particle size, crystal phase, pore size, thickness and mechanical properties. In our current study, the photocatalytic activities of these sol–gel derived TiO2 films were studied utilizing a quartz batch reactor. The quartz batch reactor was characterized for parameters like mixing, recycle, aeration and UV radiation flux, and the TiO2 coated substrates were used as the photocatalyst. The activities of the catalyst films were evaluated by measuring the degradation rate of 4-chlorobenzoic acid used as a model organic pollutant. Immobilized TiO2 powder films on stainless steel containing a mixture of anatase and rutile phases were found to be more effective than films that were substantially composed of anatase phase particles. The activity of glass beads coated with TiO2 powder was compared to the activity of commercially available TiO2 catalyst beads. While the activity of the commercially available TiO2 catalyst beads was higher there was significant attrition of the TiO2 catalyst film. The films on the glass beads possessed better mechanical properties than the commercial catalyst beads and their activity can be significantly improved by optimizing the film synthesis process parameters.
Article
Sulfur-containing compounds are well-known catalyst poisons. To evaluate the feasibility of photocatalytic technology for indoor air purification, a typical atmospheric SO2 concentration of 200 parts per billion (ppb) was selected. In order to further evaluate the impact of SO2 on the photocatalytic activity of other typical indoor air pollutants, SO2 was co-injected with 200 ppb NO and 20 ppb benzene, toluene, ethylbenzene, and o-xylene (BTEX) using TiO2 (P-25) as photocatalyst coated on a glass fiber filter. A concurrent photodegradation of SO2 with NO, SO2 with BTEX, and SO2 with NO and BTEX was also conducted. Results showed that no photodegradation of SO2 was found. However, the blank glass fiber filter adsorbed more than 75% of the SO2. The conversion of NO decreased by 8% and the generation of NO2 increased by 10% with the presence of SO2. A similar inhibition effect was found on the photodegradation of BTEX with the presence of SO2. The presence of SO2 decreased the conversion of BTEX by more than 10%. Ion chromatography analysis on the TiO2 glass fiber filter showed that sulfate ion was formed from the adsorption of SO2. The formation of sulfate ion inhibited the formation of nitrate ion, which increased the generation of NO2. It is suggested that the inhibition effect of SO2 is due to the sulfate ion competing with the pollutant for adsorption sites on TiO2. The promotion effect of NO on BTEX was also reduced by the presence of SO2.
Article
TiO2 photocatalysts film supported on glass plate was soaked in a pseudo body solution (PBS) containing excess phosphate ions. The surfaces were characterized by scanning electron microscopy, energy-dispersive spectroscopy, thin-film X-ray diffraction, and Fourier-transformed infrared methods. After soaking in the pseudo body solution for 1 day, a bone-like apatite layer was formed on the surface of the TiO2. The apatite layer was approximately 0.7 mm thick and made up of thin plate-like crystals. The haze values of dry and wet specimens were 28.47 and 9.51%, respectively. The apatite-coated TiO2 thin film could be used for antibacterial and environmental purification purposes.
Article
Photocatalytic oxidation (PCO) of nitric oxide (NO) over TiO2 catalyst was studied at source levels (5–60 ppm). The PCO process involves a series of oxidation steps by the OH radical: NO→HNO2→NO2→HNO3. The product NO2 can be collected in an adsorbent bed and either recycled back to the combustion chamber or recovered as nitric acid. The ratio of NO2− to NO3− from spent catalyst liquor drops with irradiation time until a steady state is reached. The reactions are limited by thermodynamic equilibrium after ∼12 s space time. The steady-state experimental data from space time and inlet concentration effects can be described with the Langmuir–Hinshelwood (L–H) kinetic model with R2=0.9208.
Article
UV and visible light photocatalytic removal of concentrated toluene (110 ppm) in the gas phase was performed in an annular flow-reactor on mesoporous anatase TiO2 supported WO3 photocatalysts. Depending on the template, hexagonal and cubic mesoporous TiO2 thin layers were obtained by dip-coating of an anatase sol onto slides of soda lime–silica glass, which was then mechanically removed. The coupling of low contents of WO3 (4 wt.%) with mesoporous anatase TiO2 led to high photocatalytic efficiency both using UV and visible light activation. The highly positive effect of WO3 on the toluene removal efficiency was attributed to a one-way and a two-way coupling phenomena depending on the photocatalyst nature and on the activation source. The hypothesis of a confinement effect of the reactants inside the mesoporous structure, based on an increase in their partial pressure on the active sites, was put forward to explain the high photocatalytic performances obtained under UV and visible light activation.
Article
Three type of photocatalytic composite films, MPC500SGF-MC, ANPSGF-MC and P25SGF-MC, have been synthesized by a modified sol-gel method using different particle size of TiO2 nanopowder MPC500, ANP and P25, respectively. Methyl cellulose (MC) was added as a template to the sol for stress reduction which improved not only the amount of crystalline material immobilized on the support, but also the nanosize of the films calcined at 500 degrees C. The physicochemical properties, including surface morphology, crystallinity, crystal size and adhesion on glass substrate, of the three types of films were investigated by SEM, XRD and the scratch test. The photocatalytic activities of the films were compared using methyl orange (MO) as a model organic contaminant in water. The results on photocatalytic degradation of MO showed that the increase in photocatalytic activity for P25SGF-MC, compared with that of MPC500SGF-MC and ANPSGF-MC composite films. The optimum degradation conditions of MO solution are determined. This study proves that particle size of starting TiO2 material is important for the preparation of nanostructured TiO2 composite film with enhanced photocatalytic activity and excellent adhesion on the glass substrate.
Article
Glasses in the system SiO(2)-CaO-P(2)O(5)-MgO were prepared by the sol-gel method. These glasses featured SiO(2) contents in the range 60-80 mol %, 4 mol % of P(2)O(5), and a CaO/MgO molar ratio of 4. Because of their composition and surface properties, all the glasses showed in vitro bioactivity, as evidenced by the formation of an apatite-like layer on their surface when soaked in an acellular medium with ionic composition similar to human blood plasma. An increase in the CaO content of the glasses also caused an increase in their porosity. Higher porosity facilitated the apatite nucleation on the sample surface during the first days of the in vitro test. On the other hand, those glasses with higher SiO(2) content also showed higher surface area values, as well as higher calcium phosphate layer growth rates. For longer soaking periods, the grown layer was analyzed, revealing a two-phase composition: apatite and whitlockite.
Article
The bandgap of solid-state TiO2 (3.2 eV) enables it to be a useful photocatalyst in the ultraviolet (lambda < 380 nm) region of the spectrum. A clean TiO2 surface in the presence of sunlight therefore enables the removal of harmful NOx gases from the atmosphere by oxidation to nitrates. These properties, in addition to the whiteness, relative cheapness and non-toxicity, make TiO2 ideal for the many de-NOX catalysts that are currently being commercially exploited both in the UK and Japan for concrete paving materials in inner cities. There is need, however, for further academic understanding of the surface reactions involved. Hence, we have used surface specific techniques, including X-ray photoelectron spectroscopy and Raman spectroscopy, to investigate the NOx adsorbate reaction at the TiO2 substrate surface.
Article
Although some types of TiO(2) powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO(2) coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO(2) surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO(2) coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO(2) surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO(2) with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO(2) coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.
Article
TiO2 loading on woven glass fabric is applied to treat nitrogen oxides (NOx) by photocatalytic oxidation (PCO). In this paper, the PCO behavior of NO at high concentrations was studied by PCO of NOx at source levels (20-168 ppm). The PCO efficiency reached 27% in this experiment, while the inlet NOx concentration was 168 ppm (147 ppm NO). The dependency of the reaction rate on several key influencing factors (relative humidity, space time, inlet concentration, oxygen percentage) was also studied. The results illustrate that the resulting hydroxyl radical and active oxide play an important role in the oxidation of NOx. The reactions are limited by the thermodynamic equilibrium after ca. 15s space time. A possible explanation for the catalyst deactivation is the accumulation of nitric acid and nitrous acid on the TiO2 surface during the PCO of NOx. However, the photocatalytic activity can be recovered with a simple heat treatment. The results from the study of the effect of the inlet concentration were described with the Langmuir-Hinshelwood model.
Article
An indoor car park was appropriately equipped in order to test the de-polluting efficiency of a TiO(2)-containing paint in an indoor polluted environment, under real scale configuration. Depollution tests were performed in an artificially closed area of the parking, which was polluted by a car exhaust during the testing period. The ceiling surface of the car park was covered with white acrylic TiO(2)-containing paint (PP), which was developed in the frame of the EU project 'PICADA' (Photocatalytic Innovative Coverings Application for Depollution Assessment). The closed area was fed with car exhaust gases. As soon as the system reached steady state, the UV lamps were turned on for 5h. The difference between the final and the initial steady state concentration indicates the removal of the pollutants due to both the photocatalytic paint and car emission reduction. Results showed a significant photocatalytic oxidation of NO(x) gases. The photocatalytic removal of NO and NO(2) was calculated to 19% and 20%, respectively, while the photocatalytic rate (microgm(-2)s(-1)) ranged between 0.05 and 0.13 for NO and between 0.09 and 0.16 for NO(2).
Article
Apatite (Ca5(PO4)3OH) has long been considered as an excellent biomaterial to promote bone repairs and implant. Apatite formation induced by negatively charged nanocrystalline TiO2 coatings soaked in simulated body fluid (SBF) was investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques, and factors affecting its formation such as pH, size of TiO2 particles and thickness of TiO2 coatings, were discussed in detail. Two different stages were clearly observed in the process of apatite precipitation, indicating two different kinetic processes. At the first stage, the calcium ions in SBF were initially attracted to the negatively charged TiO2 surface, and then the calcium titanate formed at the interface combined with phosphate ions, consequently forming apatite nuclei. After the nucleation, the calcium ions, phosphate ions and other minor ions (i.e. CO3(2-) and Mg2+) in supersaturated SBF deposited spontaneously on the original apatite coatings to form apatite precipitates. In terms of the in situ frequency shifts, the growth-rate constants of apatite (K1 and K2) were estimated, respectively, at two different stages, and the results were (1.96+/-0.14)x10(-3)s(-1) and (1.28+/-0.10)x10(-4)s(-1), respectively, in 1.5 SBF solution. It was found that the reaction rate at the first stage is obviously higher than that at the second stage.
Photocatalytic oxidation of NO x gases using TiO 2 : a surface spectroscopic approach
  • Jones Ng Ja Nicholson
  • Hallam
  • Kr
  • Allen
  • Gc
Dalton JS, Janes PA, Jones NG, Nicholson JA, Hallam KR, Allen GC (2002) Photocatalytic oxidation of NO x gases using TiO 2 : a surface spectroscopic approach. Environ Pollut 120:415