Preparation and performances of mesoporous TiO2 film photocatalyst supported on stainless steel

Mesoporous TiO₂ film photocatalysts supported on stainless steel substrates were prepared using the sol–gel method with Ti(OC₄H₉)₄ as a precursor and poly ethylene glycol (PEG) as a structure-directing agent. Mesoporous TiO₂ film with a pore diameter of about 15 nm was obtained with the addition of PEG (molecular WEIGHT =400). The pore diameter of TiO₂film was varied with molecular weight of PEG additive. The structure-directing process was also discussed. Mesoscopically ordered inorganic/polymer composites were believed to form during the process. Compared to conventional TiO₂ film photocatalyst, the mesoporous TiO₂ film showed a good performance for the photo degradation of rhodamine B (RB) solution irradiated with UV light of 365 nm. The photo degradation constant of rhodamine B for mesoporous TiO₂ film photocatalyst can arrive at 22 times of that for conventional TiO₂ film photocatalyst. Also an excellent performance for the degradation of gaseous formaldehyde with mesoporous film photocatalyst was obtained. The photo degradation rate of gaseous formaldehyde for mesoporous TiO₂ film photocatalyst can arrive at six times of that for conventional TiO₂ film photocatalyst.     

The synthesis of Ag-doped mesoporous TiO2

Ag-doped mesoporous titanium oxide was prepared using non-ionic surfactants and easily handled titanium precursors, under mild reaction conditions. The structure of these materials was determined as a function of the concentration of the Ag dopant and calcination temperature. In contrast to the stabilizing effect of Cd-doping on mesoporous TiO₂, Ag doping was found to significantly destabilize the mesoporous structure.     

Synthesis of thermally stable mesoporous TiO2 and investigation of its photocatalytic activity

The effects of heat treatment, dopant type and thickness of sol layer, on the formation and stability of ordered TiO₂ mesostructure were investigated. Higher ageing temperature facilitates the separation of organic phase and inorganic phase, while thinner sol layer facilitates the formation of homogeneous system and improves the mesostructural order of TiO₂. Lanthanum dopant, which is more electropositive than Ti, can improve the thermal stability of mesostructure by enhancing the strength of Ti–O bond. On the contrary, Fe and Pd dopants, which are more electronegative than Ti, decrease the thermal stability of mesostructure. Furthermore, La doped mesoporous TiO₂ shows high activity in the photocatalytic degradation of Rhodamine B under the irradiation of visible light.     

Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO2 from mesoporous precursors

Si-doped and rare earth-doped TiO₂ with large specific surface area were prepared by the hydrothermal method and sol–gel route, respectively, using C₁₈H₃₇NH₂ as template. The samples were characterized by XRD, FT-IR, low-temperature N₂ adsorption–desorption measurement, XPS and solid state UV–vis diffuse reflectance spectroscopy. The pore size for Si-doped TiO₂ exhibits both mesoporous and microporous distribution, and that for rare earth-doped TiO₂ exhibits a sharp and narrow distribution in microporous range. The photocatalytic activities were investigated with the degradation of phenol as probe reaction. Compared with pure TiO₂, the conversion of phenol and selectivity to CO₂ increases when adding rare earth elements, and the substitution of Si for Ti in an appropriate range also increases the conversion of phenol.     

Photodegradation of aromatic pollutants in water over TiO2 supported on molecular sieves

TiO₂ was supported on porous materials, including NaY and Na-mordenite zeolites, as well as mesoporous MCM-41 molecular sieve by using impregnation method with organic solvents. The products were characterized with powder XRD, BET surface area measurement, TEM, IR, Raman and UV–VIS spectroscopies. The supported TiO₂ was crystallized in anatase structure and the intensity of its X-ray diffraction peaks increased with TiO₂ loading. In contrast, the total surface area of the supported catalyst decreased with TiO₂ loading. A blue shift of the absorption edge in the UV–VIS spectra was observed when TiO₂ particle size decreased, a phenomenon corresponding to the particle size quantization effect. For photodegradation of aromatic pollutants in water, the activity was found strongly influenced by the chemical nature of the pollutant and the surface property of the support. For volatile pollutants such as benzene and chlorobenzenes, molecular sieve supports facilitated the photodegradation reaction by providing high surface area for adsorption. Moreover, there is an optimal loading of TiO₂ to achieve the best photocatalytic activity on various supports. The supports in contrast did not show positive contribution in degradation of hydrophilic pollutants such as phenol.     

Photocatalytic activity of TiO2/ZSM-5 composites in the presence of SO4 ion

TiO₂/ZSM-5 composites were prepared from SiO₂ of rice husk ash and TiO₂ sol from hydrolyzed TiOSO₄ salt. The combined effect of these two materials greatly enhanced the photocatalytic decolorization of methylene blue dye solution. The instant decolorization of the dye solution in the dark by the composite, TiO₂/ZSM-5 (wt ratio 1:1), resulted from the combination of the adsorption by ZSM-5 zeolite and TiO₂ nano-particles, and of Na₂SO₄ salt adhering to the composite surface. As a strong flocculating agent, the SO₄²⁻ ion caused the precipitation of the dye onto the composite surface which consequently enhanced the photocatalytic decolorization of the dye under UV irradiation. The composite, TiO₂/ZSM-5 (wt ratio 1:5), completely decolorized the methylene blue dye in 2.5 h, giving an equivalent performance to that of TiO₂, P-25 powder.     

水基纳米TiO_2路径制备有序介孔TiO_2-SiO_2及其可见光催化性能

在多巴胺修饰的水基TiO_2纳米微粒(TiO_2NPs)悬浮液中,以正硅酸乙酯为硅源,十六烷基三甲基溴化铵为模板剂,分别采用碱性水热方法或酸性溶胶-凝胶方法,制备了有序介孔TiO_2-SiO_2(TiO_2NPs/MCM-41或TiO_2NPs/SBA-3)。采用XRD、TEM、ICP和N2吸附-脱附实验对样品进行表征。结果表明,制备的介孔TiO_2-SiO_2在TiO_2高负载质量分数(23.98%TiO_2NPs/MCM-41、17.27%TiO_2NPs/SBA-3)时,仍能保持长程有序的介孔氧化硅结构。TiO_2NPs随机地嵌入在有序介孔氧化硅孔道所组成的网络结构中。在可见光下催化甲基橙降解反应中,反应时间120 min时,在P25上甲基橙相对浓度降为57%,在TiO_2NPs/MCM-41上降为33%,而在TiO_2NPs/SBA-3上降为5.7%。     

Selective formation of CH3OH in the photocatalytic reduction of CO2 with H2O on titanium oxides highly dispersed within zeolites and mesoporous molecular sieves

Highly dispersed titanium oxide catalysts have been prepared within zeolite cavities as well as in the zeolite framework and utilized as photocatalysts for the reduction of CO₂ with H₂O to produce CH₄ and CH₃OH at 328 K. In situ photoluminescence, ESR, diffuse reflectance absorption and XAFS investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species play a significant role in the reduction of CO₂ with H₂O with a high selectivity for the formation of CH₃OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH₄, being similar to reactions on the powdered TiO₂ catalysts. Ti-mesoporous molecular sieves exhibit high photocatalytic reactivity for the formation of CH₃OH, its reactivity being much higher than the powdered TiO₂ catalysts. The addition of Pt onto the highly dispersed titanium oxide catalysts promotes the charge separation which leads to an increase in the formation of CH₄ in place of CH₃OH formation.     

Combined TiO2/SiO2 mesoporous photocatalysts with location and phase controllable TiO2 nanoparticles

Combined TiO₂/SiO₂ mesoporous materials were prepared by deposition of TiO₂ nanoparticles synthesised via the acid-catalysed sol–gel method. In the first synthesis step a titania solution is prepared, by dissolving titaniumtetraisopropoxide in nitric acid. The influences of the initial titaniumtetraisopropoxide concentration and the temperature of dissolving on the final structural properties were investigated. In the second step of the synthesis, the titania nanoparticles were deposited on a silica support. Here, the influence of the temperature during deposition was studied. The depositions were carried out on two different mesoporous silica supports, SBA-15 and MCF, leading to substantial differences in the catalytic and structural properties. The samples were analysed with N₂-sorption, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) to obtain structural information, determining the amount of titania, the crystal phase and the location of the titania particles on the mesoporous material (inside or outside the mesoporous channels). The structural differences of the support strongly determine the location of the nanoparticles and the subsequent photocatalytic activity towards the degradation of rhodamine 6G in aqueous solution under UV irradiation.     

Excellent antimicrobial properties of mesoporous anatase TiO2 and Ag/TiO2 composite films

Optically transparent, crack-free, mesoporous anatase TiO₂ thin films were fabricated. The Ag/TiO₂ composite films were prepared by incorporating Ag in the pores of TiO₂ films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N₂ adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli (E. coli) as a model. The as-prepared mesoporous TiO₂ films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO₂ spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.     

Synthesis, characterization and photocatalytic activity of N-doped TiO2 modified by platinum chloride

Structures and photocatalytic performance of N-doped TiO₂ modified by platinum chloride (PtCl_x/N-TiO₂) was investigated. It was found that the PtCl_x/N-TiO₂ forms anatase structure of TiO₂ involving nitrogen, chloride species and platinum ions (+IV) as major species, and it exhibits higher photocatalytic activity than either N-TiO₂ or PtCl_x/TiO₂ for the decomposition of acetic acid or acetaldehyde in aqueous solutions under visible light irradiation (λ > 420 nm). An enhancement of the photocatalytic activity on PtCl_x/N-TiO₂ has been proposed as a Z-scheme mechanism for charge separation between platinum chloride and N-TiO₂.     

Development of the efficient TiO2 photocatalyst in photoassisted selective catalytic reduction of NO with NH3

Photoassisted selective catalytic reduction (photo-SCR) of NO with NH₃ in the presence of O₂ takes place at room temperature over TiO₂ photocatalyst. From the results of photo-SCR reaction over various TiO₂, we found that JRC-TIO-11 exhibited the best activity. The reaction activity correlated to the amount of acid sites of TiO₂, but did not depend on the specific surface area and crystal diameter. The mixture of rutile and anatase shows higher activity than any of the corresponding TiO₂ single phase catalyst.     

The entrapment of UO2 in mesoporous MCM-41 and MCM-48 molecular sieves

A method based on direct template-ion-exchange was employed for the entrapment of UO₂²⁺ ions in MCM-41 and MCM-48 molecular sieves via swapping of cetyltrimethylammonium cations present in the mesoporous channels by the UO₂²⁺ ions in an aqueous solution. The samples were characterized by XRD, FT-IR, and ICP-AES techniques. The entrapment of UO₂²⁺ ions is facilitated by the large pore size vis-a-vis the high surfactant content in the as-synthesized host materials. A higher loading of UO₂²⁺ ions was achieved in MCM-48 as compared to MCM-41, which could be attributed to its three-dimensional pore system and higher surfactant-to-silica ratio. FT-IR results provide an evidence of a strong binding of UO₂²⁺ groups with the defect silica sites of mesoporous molecular sieves.     

Purification/deodorization of indoor air and gaseous effluents by TiO2 photocatalysis

Our objective was to further assess the capabilities of TiO₂ to purify/deodorize indoor air and industrial gaseous effluents. Using a laboratory photoreactor including a lamp emitting around 365 nm and a TiO₂-coated fiber glass mesh, we first determined that the removal rate of three very different pollutants (CO, n-octane, pyridine) was 5–10 μmol per Wh consumed by the lamp for 50–2000 ppmv concentrations and 25–50 l h⁻¹ flow rates (dry air or O₂). We inferred that this order of magnitude allows, by use of a reasonable-size apparatus, the abatement of pollutants in constantly renewed indoor air, except CO and CH₄ that are too concentrated. Using a TiO₂ photocatalysis-based individual air purifier prototype, we showed, through distinctive analytical measurements, that the average concentrations of benzene, toluene and xylenes were indeed reduced by a factor of 2–3 in an ordinary non-airtight room. We also showed that O₃ addition in O₂ very markedly increases the mineralization percentage of n-octane, under otherwise identical conditions, in the laboratory photoreactor without photoexcitation of O₃; this property of O₃ can expand the application field of photocatalytic air purification in industry, at least in some cases.     

Characterization and photocatalytic activity in aqueous medium of TiO2 and Ag-TiO2 coatings on quartz

In the present study, TiO₂ and Ag-TiO₂ catalysts have been supported in the form of thin layers by a dip-coating procedure on quartz substrate. The resulting materials have been characterized by SEM/EDX, XRD, XPS and UV-vis absorption spectroscopy. The immobilized catalysts were tested in the photocatalytic degradation of malic acid. For this reaction, the presence of metallic silver does not produce an intrinsic increase in photocatalytic activity in comparison with pure titania. The apparent increase observed in activity is principally due to the increase in the exposed surface due to the textural characteristics of the Ag-TiO₂ layer in comparison with TiO₂. In addition, the presence of metallic silver always produces an increase in activity in comparison with oxidized Ag⁺ ions. This can be explained by the increase in the electron-hole pair-separation efficiency induced by trapping of electrons by metallic silver.     

Features of the transformation of Hg by heterogeneous photocatalysis over TiO2

UV/TiO₂ photocatalysis of 0.5 mM mercuric aqueous solutions has been analyzed starting from Hg(NO₃)₂, Hg(ClO₄)₂ and HgCl₂ at different pH (3, 7 and 11) and in the presence or absence of oxygen. Profiles of Hg^II concentration with time were characterized by a relatively rapid initial conversion followed by a decrease or an arrest of the rate, the shape of profiles changing with the conditions. Conversions at 60 min and initial quantum efficiencies have been found dependent on the initial conditions and type of mercuric salt. The faster transformation took place at pH 11 for all salts. A good transformation yield is observed also for HgCl₂, which behaves differently to the other two salts, at pH 3 under nitrogen and pH 7 (N₂ or O₂). Inhibition by oxygen was observed in acid and neutral media but not at basic pH. When the conversion was 50% or more, pale or dark gray solids were deposited on the catalyst, identified as mixtures of Hg⁰, HgO or Hg₂Cl₂. A unique kinetic scheme could not be defined, which seemed to depend on the nature of the mercury salt, the ambient conditions and the type of deposit. Implications of the application of the technique to real systems are discussed.     

Photocatalytic degradation of organic compounds diluted in water using visible light-responsive metal ion-implanted TiO2 catalysts: Fe ion-implanted TiO2

The application of metal ion-implantation method has been made to improve the electronic properties of the TiO₂ photocatalyst to realize the utilization of visible light. The photocatalytic properties of these unique TiO₂ photocatalysts for the purification of water have been investigated. By the metal ion-implantation method, metal ions (Fe⁺, Mn⁺, V⁺, etc.) are accelerated enough to have the high kinetic energy (150 keV) and can be implanted into the bulk of TiO₂. TiO₂ photocatalysts which can absorb visible light and work as a photocatalyst efficiently under visible light irradiation were successfully prepared using this advanced technique. The UV-Vis absorption spectra of these metal ion-implanted TiO₂ photocatalysts were found to shift toward visible light regions depending on the amount and the kind of metal ions implanted. They were found to exhibit an effective photocatalytic reactivity for the liquid-phase degradation of 2-propanol diluted in water at 295 K under visible light (λ>450 nm) irradiation. The investigation using XAFS analysis suggested that the substitution of Ti ions in TiO₂ lattice with implanted metal ions is important to modify TiO₂ to be able to adsorb visible light.     

Preparations and photocatalytic properties of magnetically separable nitrogen-doped TiO2 supported on nickel ferrite

A magnetically separable nitrogen-doped photocatalyst TiO_2−xN_x/SiO₂/NiFe₂O₄ (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO₂/NiFe₂O₄ (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO_2−xN_x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO₂/NiFe₂O₄ (SN) nanoparticles adhere to the surface of TiO_2−xN_x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO₂ coating round the surface of NiFe₂O₄ nanoparticles prevents effectively the injection of charges from TiO₂ particles to NiFe₂O₄, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity.     

Anatase TiO2-pillared hexaniobate mesoporous nanocomposite with enhanced photocatalytic activity

Mesoporous anatase TiO₂-pillared hexaniobate has been successfully prepared by an exfoliation-restacking route. The resulting nanocomposite was characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, thermogravimetric analysis, UV-Vis spectroscopy and N₂ adsorption-desorption measurements. It was reveal that the obtained material has a gallery height of about 2 nm, a specific surface area of about 170 m²/g and a wide pore size distribution with two extrema at about 2 and 3 nm. The mesoporous material exhibits an enhanced photocatalytic activity in the degradation of acid red G under ultraviolet light irradiation, attributed to its high surface area, mesoporosity and the electronic coupling between the host and the guest components. A photoexcitation model in the semiconductor-semiconductor pillared photocatalyst was proposed based on the results of XPS and UV-Vis.     

TiO2-SiO2 and V2O5/TiO2-SiO2 catalyst: Physico-chemical characteristics and catalytic behavior in selective catalytic reduction of NO by NH3

TiO₂-SiO₂ with various compositions prepared by the coprecipitation method and vanadia loaded on TiO₂-SiO₂ were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH₃ and in the undesired oxidation of SO₂ to SO₃, using BET, XRD, XPS, NH₃-TPD, acidity measurement by the titration method and activity test. TiO₂-SiO₂, compared with pure TiO₂, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V₂O₅. The SCR activity and N₂ selectivity are found to be more excellent over vanadia loaded on TiO₂-SiO₂ with 10–20 mol% of SiO₂ than over that on pure TiO₂, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH₃ adsorbed on the catalysts. With increasing SiO₂ content, the remarkable activity decrease in the oxidation of SO₂ to SO₃, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V⁴⁺ on TiO₂-SiO₂, while V⁵⁺ exists on TiO₂, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO₂-SiO₂ with low SiO₂ content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO_x activity but also the low SO₂ oxidation performance.