Microporous TiO Research Articles

Zn and Ag Co-doped Anti-microbial TiO2 Coatings on Ti by Micro-arc Oxidation

Micro-porous TiO 2 coatings co-doped with Zn 2+ and Ag nanoparticles were fabricated on Ti by micro-arc oxidation (MAO) for 0.5, 1.5, 2 and 4 min, respectively. The evolutions of morphology and phase component of the coating as a function of processing time were investigated. The microstructure of the 2 min treated coating was further observed by transmission electron microscopy to explore the coating formation mechanism. The amounts of Ag and Zn released from the 2 min treated coating were measured and the antibacterial properties of the coatings against Staphylococcus aureus ( S. aureus ) were also investigated. The obtained results showed that with prolonged MAO time, the contents of Ag and Zn on the coating surfaces increased. All the coatings were micro-porous with pore diameters of 1–4 µm; however, some pores were blocked by deposits on the 4 min treated coating. The 2 min treated coating was composed of amorphous TiO 2 , anatase, rutile, ZnO, Zn 2 TiO 4 and homogenously distributed Ag nanoparticles. After immersion, Zn 2+ , Ag + , Ti 2+ and Ca 2+ were released from the coating and with the immersion time prolonged, the accumulated concentrations of these ions increased. After immersion for 36 weeks, the accumulated Zn 2+ and Ag + concentrations were 6.88 and 0.684 ppm, respectively, which are higher than the minimal inhibitory concentration but much lower than the cytotoxic concentration. Compared with polished Ti control, the coatings co-doped with Zn 2+ and Ag nanoparticles significantly inhibited the adhesions of S. aureus and reduced the amounts of planktonic bacteria in culture medium, indicating that the Zn and Ag co-doped TiO 2 could be a bio-adaptable coating for long-lasting anti-microbial performance.

Facile Synthesis and Active Photocatalysis of Mesoporous and Microporous TiO2 Nanoparticles

AbstractMorphology and crystalline‐phase control of titanium dioxide is a crucial issue in the study of photocatalytic activity. Here, we present a facile synthetic path combing the sol–gel method with solvothermal treatment to form hybrid mesoporous and microporous TiO2. The TiO2 precursor was obtained by the sol–gel method, and this was self‐assembled into mesopores and micropores by NH4F corrosiveness on the surface of TiO2 under hydrothermal conditions. Powder X‐ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), X‐ray photoelectron spectroscopy (XPS), N2 adsorption measurements, transmission electron microscopy (TEM) and Raman spectroscopy were used to characterise the titania powders. The results reveal that NH4F not only improved the formation of the crystallised anatase phase but also served as a corrosive agent modified on the surface of TiO2 precursors. Defective voids among these nanoparticles formed micropores by hydrothermal reaction of NH4F and TiO2 over a long time. When the NH4F concentration was 1.0 mol L−1, micropores became dominant,and few mesopores were obtained, and this results in a smaller average pore size. Thus, mesoporous and microporous structures were formed. Furthermore, these crystallised mesoporous and microporous anatase titania nanoparticles with uniform structure and high surface area have a higher photocatalytic activity for azo dye degradation under near UV irradiation.

Synthesis, characterization, and testing of supported Au catalysts prepared from atomically-tailored Au38(SC12H25)24clusters

Nearly monodispersed Au(38)(SC(12)H(25))(24) clusters (1.7 ± 0.2 nm) were synthesized using a modified Brust process while utilizing a "thiol etching" approach for the ligand exchange. HRTEM, MALDI, FTIR, and XAS analysis confirmed the formation of the 38-atom clusters in solution. This solution was used to impregnate a microporous TiO(2) support to give 0.7% Au(38)/TiO(2) catalyst. Subsequent drying in air and treatment with H(2)/He at 400 °C removed most of the sulfur ligands, and also increased the Au cluster size to 3.9 ± 0.96 nm. XPS and EXAFS analysis of this supported catalyst showed trace levels of residual sulfides, apparently located at the Au-TiO(2) interface. CO oxidation tests on these supported clusters show an activation energy and range of TOFs comparable to those reported by others. These results suggest that supported Au clusters of controllable size can be prepared with this thiol-ligated solution-based method, providing a new approach to the synthesis of these catalysts.

Microporous Ni-Doped TiO2 film Photocatalyst by Plasma Electrolytic Oxidation

Ni-doped TiO2 film catalysts were prepared by a plasma electrolytic oxidation (PEO) method and were mainly characterized by means of SEM, EDS, XRD, XPS, and DRS, respectively. The effects of Ni doping on the structure, composition and optical absorption property of the film catalysts were investigated along with their inherent relationships. The results show that the film catalyst is composed of anatase and rutile TiO2 with microporous structure. Doping Ni changes the phase composition and the lattice parameters (interplanar crystal spacing and cell volume) of the films. The optical absorption range of TiO2 film gradually expands and shifts to the red with increasing dosages. Both direct and indirect transition band gaps of the TiO2 films are deduced consequently. Moreover, the photocatalytic activity of the film catalysts for splitting Na2S+Na2SO3 solution into H2 is enhanced by doping with an appropriate amount of Ni. The as-prepared TiO2 film catalyst doping with 10 g/L of Ni(Ac)2 presents the highest photocatalytic reducing activity.

Solvent flux behavior and rejection characteristics of hydrophilic and hydrophobic mesoporous and microporous TiO 2 and ZrO 2 membranes

This paper describes solvent flux and rejection behavior of different hydrophilic TiO 2 membranes and a hydrophobic ZrO 2 membrane. Solvents and solutes used range from polar to non-polar. Additionally, the temperature effect on permeability and rejection of solutes through these membranes was examined. It was found that the solvent permeabilities through microporous hydrophilic membranes with MWCO 275 and 1400 Da do not obey the viscous flow transport mechanism, in contrast to the permeability through mesoporous TiO 2 membrane with MWCO 7000 Da. Decrease of the pore size increased deviation from the viscous flow mechanism. Obtained aqueous and polar solvent fluxes were high. This raises opportunities for industrial applications. Moreover, permeabilities of the non-polar solvents can be increased to acceptable levels by working at elevated temperatures through the mechanism of activated permeability. The hydrophobic membrane showed very high non-polar solvent fluxes and remarkably low water permeabilities. Here, no surface interactions can be considered, due to the lack of hydroxyl groups on a membrane surface. Thus, transport through this membrane is related with viscosity decrease at higher temperature and is closer to viscous behavior than for the hydrophilic membranes with similar pore sizes. Rejections of the solutes did not change with temperature and were high when the hydrophilic membranes were used. The non-polar solute bromothymol blue in toluene showed high rejections, unlike some other literature data. The hydrophobic membrane showed much higher fluxes, but rejections were lower than expected. The results of this study are representative for the ceramic nanofiltration membranes currently available on the market.

Dye-sensitized solar cells with a micro-porous TiO 2 electrode and gel polymer electrolytes prepared by in situ cross-link reaction

The ionic conductivities and performances of dye-sensitized solar cells (DSSCs) of gel polymer electrolytes (GPEs) prepared by in situ cross-link reaction with different cross-linkers were investigated. The poly(imidazole-co-butylmethacrylate)-based GPE containing the 1,2,4,5-tetrakis(bromomethyl)benzene (B4Br) cross-linker showed a higher ionic conductivity than that containing cross-linkers with a linear structure, due to the formation of micro-phase separation that resulted in an increase in ion transport paths in the GPE. Moreover, the co-adsorbent ((4-pyridylthio) acetic acid, PAA) co-adsorbed with N3 dye on the TiO 2 electrode not only reduced dye aggregation, but also reacted with the cross-linkers in the GPE at the TiO 2/GPE interface. A decrease in the charge transport resistance at the TiO 2/GPE interface was noted after forming the gel; thus the value of J SC significantly increased from 7.72 to 10.00 mA cm −2. In addition, in order to reduce the ionic diffusion resistance within the TiO 2 electrode, incorporation of monodispersed PMMA in the TiO 2 paste was considered. With the optimal weight ratio of PMMA/TiO 2 (w/w=3.75), the TiO 2 electrode exhibited larger pores (ca. 350 nm) uniformly distributed after sintering at 500 °C, and the ionic diffusion resistance within the TiO 2 film could significantly be reduced. The cell conversion efficiency increased from 3.61% to 5.81% under illumination of 100 mW cm −2, an improvement of ca. 55%.

Preillumination of TiO2 and Ta2O5 Photoactive Thin Films As a Tool to Tailor the Synthesis of Composite Materials

Illumination of TiO 2 thin films with UV light is known to induce the transformation of the surface of this material from partially hydrophobic into fully hydrophilic. The present work shows that this transformation is accompanied by other effects that may be used to control the synthesis of composite materials. For this purpose, TiO 2 and Ta 2O 5 transparent thin films with a columnar structure and open pores were prepared by electron evaporation at glancing angles. Transparent TiO 2 thin films with micropores (i.e., pores smaller than 2 nm) prepared by plasma enhanced chemical vapor deposition (PECVD) were also used. All these films became hydrophilic upon UV illumination. Rhodamine 6G and Rhodamine 800 dyes were irreversibly adsorbed within the columns of the TiO 2 and Ta 2O 5 thin films by immersion into a water solution of these molecules. Isolated and aggregated molecules of these two dyes were detected by visible absorption spectroscopy. The infiltration adsorption efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) in colloidal oxides. The infiltration experiments were repeated with columnar TiO 2 and Ta 2O 5 thin films that were subjected to preillumination with UV light. It was found that this treatment produced a modification in the type (isolated or aggregated) and amount of dye molecules incorporated into the pores. Moreover, the selective adsorption of a given dye in preilluminated areas of the films permitted the lithographic coloring of the films. Preillumination also controls the UV induced deposition of silver on the surface of the microporous TiO 2 thin films. It was found that the size distribution of the formed silver nanoparticles was dependent on the preillumination treatment and that a well-resolved surface plasmon resonance at around 500 nm was only monitored in the preilluminated films. A model is proposed to account for the effects induced by UV preillumination on the TiO 2 and Ta 2O 5 oxide surfaces. The possibilities of this type of light treatment for the tailored synthesis of nanocomposite thin films (i.e., dye-oxide, metal nanoparticles-oxide) are highlighted.

Preparation of porous rutile titania from ilmenite by mechanical activation and subsequent sulfuric acid leaching

Synthesis of porous titania via mechanical activation of natural ilmenite and subsequent simultaneous dissolution and hydrolysis in dilute solutions of sulfuric acid was investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), N 2 adsorption/desorption measurements, energy-dispersive X-ray spectrometry (EDX) and thermogravimetric analysis (TG). This is a novel template-free approach for synthesis of microporous, mesoporous and micro–mesoporous TiO 2 materials. Effects of sulfuric acid concentration and calcination temperature on physicochemical properties of the TiO 2 materials were examined systematically. The results show that both the factors considerably affected the porosity of the materials. In a 15% acid solution a microporous TiO 2 hydrolysate with BET surface area 109.3 m 2/g was prepared. With a 10% H 2SO 4, we obtained a more pure micro/mesopore TiO 2 hydrolysate with BET area of 257.6 m 2/g. Calcining the hydrolysate at ⩾500 °C led to the formation of a mesopore TiO 2. The mesoporous TiO 2 generated at 600 °C still has a BET area of 92.1 m 2/g. The high thermal stability is probably related to the presence of H 2SO 4 in the channel walls of hydrolysate. The XRD analysis indicated all the TiO 2 materials prepared in this study being rutile. The mechanism for formation of the porous rutile TiO 2 is mainly via in situ hydrolysis and precipitation of the dissolved titanium on the un-reacted ilmenite surface, where H 2SO 4 may play a very important role.

Preparation and optical characterization of transparent, microporous TiO 2 xerogel monoliths

This paper focuses on the sol–gel preparation and spectroscopic characterization of transparent and rare earth-doped TiO 2 monoliths, for further applications in luminescence. The preparation method was based on a sol–gel technique applied to titanium isopropoxide as the precursor. By controlling the hydrolysis of this precursor by the intermediate of an esterification reaction, and by also controlling the rate of drying, transparent TiO 2 xerogel monoliths were obtained at room temperature. The monoliths prepared in this manner were transparent to wavelengths between 400 and 1400 nm. They had a microporous texture, a specific surface area of ≈330 m 2 g −1 and they were partly X-ray amorphous. After heat treatment at 823 K for 6 h in air, the N 2 adsorption isotherm analysis indicated that a densification process occurred altogether with a phase transition from partly amorphous to anatase. The X-ray diffraction spectra indicated that the anatase crystals had a size in the range of the nm, while the UV transmission spectra kept the same characteristics as at room temperature.

Comparison of different thin film absorbers used in eta-solar cells

Alloying with mercury (Hg) has been used in electrodeposition as a means to reduce the bandgap of CdTe absorber films from 1.5 eV for CdTe to 1.07 eV for Cd x Hg 1− x Te (CMT). Alloy films have been incorporated as extremely thin absorbers in solar cells with the structure glass∣SnO 2∣microporous–TiO 2∣CMT∣Au. The decrease in the CMT bandgap is expected to reduce the conduction band offset at the interface to TiO 2, which is 0.6 eV for the TiO 2∣CdTe interface. This high band offset was believed to be responsible for the low fill-factor observed in the J– V characteristics of the former interface. Lowering the band offset is expected to lead to higher fill-factor values. Our results show that using a CMT as absorber gives place to both higher quantum efficiencies and a spectral response spectrum extended towards longer wavelengths, but not to a fill-factor enhancement.

Tests in controlled atmosphere on new optical gas sensing layers based on TiO 2/metal-phthalocyanines hybrid system

Chemical sensors based on surface plasmon resonance (SPR) measurements have been proposed in various applications ranging from biomedical and environmental monitoring to industrial process control. It is widely gaining recognition as a valuable tool to investigate gas sensing interactions. In this work, surface plasmon resonance studies in angular modulation have been used to characterise response in the presence of NO 2 toxic gas of thin TiO 2 porous films containing different types of metal-phthalocyanines. The hybrid thin films were prepared using sol–gel technique. Low temperature annealing of the films (80 °C) ensured the formation of microporous TiO 2 backbone and the preservation of phthalocyanine. Optical parameters of the active layers in dry air were calculated by using the SPR measurements and information about their variation in the presence of different concentrations of toxic gas was obtained.

TEM and X-ray diffraction investigation of the structural characteristics of the microporous oxide film formed on polycrystalline Ti

The microporous TiO 2 layer in the vicinity of the Ti–TiO 2 interface is formed by a great amount of tiny crystallites. Bigger anatase and rutile crystals stand in the outer region of the oxide. The orientation of a proportion of the TiO 2 crystals is influenced by the underlying textured Ti substrate.

Co-sensitization of microporous TiO 2 electrodes with dye molecules and quantum-sized semiconductor particles

The microporous titanium dioxide (TiO 2) film has been prepared on a conducting glass substrate. A seven-fold enhancement in energy conversion efficiency of the dye-sensitized solar cell was achieved by pre-depositing a closely packed TiO 2 thin film on the surface of the conducting glass. Moreover, FeS 2 particles were coated on TiO 2 electrode by chemical reaction of iron pentacarbonyl with sulfur in xylene. Both atomic force microscope (AFM) and photoelectric studies suggest that the FeS 2 quantum-sized particles play a dominate role in the photoelectric conversion of FeS 2/TiO 2 electrode, while the FeS 2 large particles have less or even no contribution to the photo-current. Furthermore, the TiO 2 electrode has been co-modified with phthalocyanine dye molecules and quantum-sized semiconductor particles. Co-sensitization of the TiO 2 electrode with CdSe particles and ZnTCPc dye molecules not only extends the photoresponse of CdSe/TiO 2 electrode further into red region, but also improve the quantum efficiency of photoelectric conversion. We believe that such a co-sensitization technique should be of general importance in designing novel solar energy conversion devices.

Microporous TiO 2 membranes with a cut off

Microporous TiO 2 membranes were developed by a polymeric sol–gel technique on top of a specially designed tubular ceramic multi-layer support. The microporosity of the membrane is 28% and depends strongly on the amorphous state of the TiO 2. N 2-sorption measurements indicated cylindrical pores with a mean diameter of 0.9 nm which was confirmed by filtration tests using molecular weight standards. The membrane has a cut off of 480 Da and a pure water flux of 20 l/(m 2 h bar). Salt retention depends on the pH and the salt concentration. At a pH above 5.8, the retention of sulphate ions is more than 90%.

Surface modification and photosensitisation of TiO 2 nanocrystalline films with ascorbic acid

Semi-transparent microporous TiO 2 films on SnO 2-coated conductive glass were prepared by applying a sol–gel process. Surface topography analysis was conducted with atomic force microscopy, which revealed a highly textured and rough surface, possessing a high capacity for adsorption of a diverse variety of compounds. Surface modification of the films with ascorbic acid results in the formation of a stable, coloured surface complex which red shifts the absorption threshold of TiO 2, enhancing utilisation of the solar spectrum. Upon illumination in a liquid electrochemical cell, ascorbic acid injects electrons into the conduction band of the semiconductor, giving rise to electrical current. The incident-photon-to-current efficiency presents a maximum at 415 nm (5.29%).

Semiconductor growth on porous substrates

We have studied different growth techniques for the deposition of compound semiconductors on highly structured and porous substrates. The idea behind these studies is the preparation of transparent spatially-distributed semiconductor heterojunctions. We used n-type nano- and microporous TiO 2 films of several micrometers thickness as substrates, and CuI and CuSCN as the growing p-type semiconductors. CuI was deposited by electrodeposition of Cu on the TiO 2 and subsequent iodation from the gas phase. Our results indicate that such two-step processes do not lend themselves to a complete filling of the porous structure. The second process studied uses a single-step electrodeposition process to deposit CuSCN from a solution of CuSCN + complexes. Here the results indicate that a complete filling of the substrate void volume is easily achieved and a compact two-phase film with intimate contact between the two phases can be prepared. Under suitable conditions, the substrate can be filled to a degree of 100±3% with excellent, rectifying electrical contact between the growing material and the substrate.

Photosensitization of TiO 2 semiconductor with porphyrin

Zn-tetrasulfophenylporphyin (ZnTSPP), stable colloidal TiO 2 and a transparent microporous TiO 2 electrode have been prepared. The interaction of ZnTSPP with colloidal TiO 2 was studied by absorption and fluorescence spectroscopy, the apparent association constant for the association between ZnTSPP and TiO 2 nanoparticles is about 1.6 × 10 4 M −1. ZnTSPP adsorbed on colloidal TiO 2 can participate in the sensitization process by injecting electrons from its excited states into the conduction band of TiO 2. Upon excitation of its absorption band, 90% of the fluorescence emission of ZnTSPP could be quenched by colloidal TiO 2 and the maximum of incident photon to current efficiency is 51.3% at 427 nm with a 10 μm thick TiO 2 film sensitised by ZnTSPP.

Influence of molecular aggregation and orientation on the photoelectric properties of tetrasulfonated gallium phthalocyanine self-assembled on a microporous TiO 2 electrode

The photoelectric conversion and surface photovoltage spectrum (SPS) of tetrasulfonated gallium phthalocyanine (GaTsPc) molecules self-assembled on a microporous titanium dioxide (TiO 2) electrode are reported. For comparison, the SPS of the GaTsPc sublimed film deposited at 10°C is also presented. The GaTsPc molecule exists mainly in the aggregated form on the microporous TiO 2 electrode and in the sublimed film. The photocurrent action spectrum and SPS have shown that only the absorption of the GaTsPc monomers leads to a photocurrent or photovoltage while GaTsPc cofacial aggregates do not generate a photocurrent and photovoltage. This is attributed to a perpendicular or titled orientation of the molecular planes in the GaTsPc molecular aggregates on the microporous TiO 2 electrode.

The photovoltaic study of co-sensitized microporous TiO 2 electrode with porphyrin and phthalocyanine molecules

A TiO 2 microporous electrode is modified simultaneously with porphyrin dye molecules and phthalocyanine dye molecules by chemical adsorption. Since porphyrin and phthalocyanine dye have a different spectral region for absorption of visible light, the TiO 2 electrode modified with these two dyes could more effectively absorb visible light. Experimental results show that the sensitization of TiO 2 electrode with porphyrin and phthalocyanine dyes effectively extends the optical absorption spectrum and photocurrent spectrum into a wider visible range and exhibits a significant improvement of photoresponse compared to the of a single dye modified electrode.

Preparation and Characterization of Microporous TiO<sub>2</sub>-Membranes

Preparation and Characterization of Microporous TiO<sub>2</sub>-Membranes