Removal of gaseous toluene by using TiO<Subscript>2</Subscript> film doped of Ru-dye/Pt in a pilot scale photoreactor

The photodegradation efficiency (PE) of gaseous toluene was investigated by using titanium dioxide (TiO₂) film doped of ruthenium (Ru)-dye/platinum (Pt) in a 3,600 L pilot reactor. Ru-dye was applied as a sensitizer to enhance PE of toluene in both UV and visible wavelength range since its major peaks are 225 nm, 325 nm, 375 nm, and 525 nm. PE by using Pt/TiO₂ was more enhanced since Pt plays a role as an electron trapper in UV light range. The 3.2 μm thickness of TiO₂ film was optimized for the highest PE. The highest PE was 75%, 85%, and 90% by TiO₂, Pt/TiO₂, and Ru-dye/Pt/TiO₂ film, respectively.     

Effect of CdS contents on H<Subscript>2</Subscript> production from Pt-(CdS/TiO<Subscript>2</Subscript>) film-typed photocatalysts

Pt-(CdS/TiO₂) film-typed photocatalysts are prepared with a doctor-blade method followed by a chemical bath deposition (CBD) process, and the films are characterized by UV-vis spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy. The film-typed structure is composed of photocatalysts and Pt metal part on a FTO substrate without additional electric device, so it is relatively simpler than the conventional photoelectrochemical cell. CdS quantum dots are introduced as a sensitizer for visible light response. Amounts of CdS quantum dots on TiO₂ surface are increased with increasing CBD cycles, but they start to aggregate after certain CdS concentration due to oversaturation phenomenon. This high CdS content induces high electron losses, and therefore it reduces amounts of hydrogen production. As a result, there is a saturation point of CdS content at Cd/Ti ratio of 0.197, and the amounts of evolved hydrogen are 5.407 μmol/cm²·h at this photocatalyst formulation.     

Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Optical properties of Pt-TiO<Subscript>2</Subscript> catalyst and photocatalytic activities for benzene decomposition

In order to improve the photocatalytic decomposition activity of benzene, which has been regarded as a typical volatile organic compound in air, TiO₂ catalysts modified with metals (Pt, Cu, and Fe) were prepared and tested. Certain correlations between the photocatalytic activities and the optical properties of those catalysts were also found and discussed by using UV-visible spectroscopy and a photoluminescence spectroscopy. Among the metal impregnated TiO₂, the Pt impregnated TiO₂ showed the best activity and it was even better than that of P-25 which is widely used in commercial applications. For the various metal impregnated TiO₂ samples, certain proportional relationships were found between the observed photoluminescence values and photocatalytic activities. On the other hand, in UV-visible spectra for metal impregnated TiO₂ samples, the transmittance value was reduced depending upon the loading of metals. It was thought that photocatalytic activity increases from initial reaction state because the number of photoexcited electrons, which exist at Pt surface augment due to the band gap energy change of Pt and TiO₂ by sintering and light energy-absorbed electrons excited easily to conduction. In conclusion, it was confirmed that the enhanced photocatalytic activity for high metal loading on TiO₂ is related with the high concentration of excited electrons, which could be monitored through UV-visible spectra.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Photocatalytic Generation of H<Subscript>2</Subscript> Gas from Neat Ethanol over Pt/TiO<Subscript>2</Subscript> Nanotube Catalysts

TiO₂ nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H₂ gas (C₂H₅OHC₃CHO +H₂). It was found that the ability to produce H₂, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO₂ catalysts with TiO₂ nanotubes washed with diluted H₂SO₄ solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H₂O, acetaldehyde was the major liquid phase product.     

The role of TiO<Subscript>2</Subscript> layers deposited on YSZ on the electrochemical promotion of C<Subscript>2</Subscript>H<Subscript>4</Subscript> oxidation on Pt

The electrochemical promotion of Pt/YSZ and Pt/TiO₂/YSZ catalyst-electrodes has been investigated for the model reaction of C₂H₄ oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375 °C. It has been found that the presence of a dispersed TiO₂ thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO₂. This significantly enhanced EPOC effect via the addition of TiO₂ suggests that the presence of the porous TiO₂ layer enhances the transport of promoting O²⁻ species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO₂ porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO₂ layer which results to enhanced O²⁻ transport to the Pt surface via a self-driven electrochemical promotion O²⁻ transport mechanism.     

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO<Subscript>2</Subscript> nanofibers in a TiO<Subscript>2</Subscript> film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO₂ nanofiber [TN] and Ag-doped TiO₂ nanofiber [ATN] have been extended to be included in TiO₂ films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO₂ photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO₂ films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.     

Photocatalytic Activity of a TiO<Subscript>2</Subscript> Photocatalyst Doped with C<Superscript>4+</Superscript> and S<Superscript>4+</Superscript> Ions Having a Rutile Phase Under Visible Light

C⁴⁺ and S⁴⁺-codoped titanium dioxide (TiO₂) having a rutile phase was prepared. By doping C⁴⁺ and S⁴⁺ ions into a TiO₂ lattice, the absorption edge of rutile TiO₂ powder was largely shifted from 400 to 700 nm. 2-Methylpyridine and methyleneblue were photocatalytically oxidized at high efficiency on C⁴⁺ and S⁴⁺-doped TiO₂ under visible light at a wavelength longer than 5 nm.     

The Effects of Co-Sensitization and Electronic Structure of Nanocrystalline N/TiO<Subscript>2</Subscript> Anode on the Performance of Dye-Sensitized Solar Cells

N/TiO₂ nanocrystalline film anodes were obtained by doping nonmetallic element N which could change the LUMO of anode. This paper also studied the match between the LUMO energy lever of N/TiO₂ anode and the dye, which led to the easy injection of electron from the excited state of dye molecule to the conduction band of semiconductor, and thus improved the photoelectric conversion efficiency and reduced the impedance of solar cells. The solar cell based on N/TiO₂ anode film co-sensitized by P3HT (poly(3-hexylthiophene))/N719(RuL2(NCS)2:2TBA (L = 2,2′-bipyridyl-4,4′-dicarboxylic acid)), the absorption region of which covered the entire visible region in solar cells, showed a short-circuit current density of 6.88 mA cm⁻², an open-circuit voltage of 0.616 V, and a photoelectric conversion efficiency of 2.34%.     

On the Photomagnetic Properties of the Binuclear Spin Crossover Complexes {[Fe(bt)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)} and {[Fe(bpym)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)}

Infrared and visible light irradiation effects on the spin state of iron(II) ions have been investigated in the binuclear molecules {[Fe(bt)(NCSe)₂]₂(bpym)} (4) and {[Fe(bpym)(NCSe)₂]₂(bpym)} (2). For compound 2 we could observe LIESST and partial reverse-LIESST effects under visible and infrared light irradiation, respectively. Compound 4 exhibits a wavelength-selective photoconversion at 10 K from the low spin (LS–LS) ground state of the binuclear molecule to the metastable high spin (HS–HS) state under visible (785 or 532 nm) light irradiation or to the metastable HS–LS state under infrared (1,342 nm) light irradiation. In addition we also observed the reverse (HS–HS → HS–LS) and the cascade (LS–LS → HS–LS → HS–HS) photoconversions as well. These phenomena lead to complex and original photomagnetic behaviour due to the intramolecular magnetic coupling. This article is dedicated to Professor Didier Astruc in honor of his scientific achievements, with friendship and sincere respect.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

The Synthesis and Photocatalytic Properties of Nitrogen Doped TiO<Subscript>2</Subscript> Films Prepared Using the AC-PLD Method

Synthesis of N doped TiO₂ films were conducted by the atmospheric controlled pulsed laser deposition (AC-PLD) method to generate visible light active photocatalytic films. In this method, the anion doped TiO₂ films were synthesized on a quartz substrate by the irradiation of a pulsed Nd:YAG laser on a TiO₂ target in the presence of gaseous nitrogen containing reagents at reduced pressure. For nitrogen doping, the use of CH₃CN was found to be more effective than the use of NH₃. The visible light absorption properties of the films were very sensitive to the CH₃CN partial pressure during ablation. When using CH₃CN, nitrogen and an equal quantity of carbon was uniformly doped into the TiO₂ films. The resultant films showed better catalytic performance than those which were either un-doped or doped using NH₃. The formation of nitrogen doped TiO₂ is discussed by relating experimental results to thermodynamic considerations. It is also suggested that stronger reducing agents such as carbon are required for doping nitrogen into TiO₂ films.     

Nanoporous TiO<Subscript>2</Subscript> film electrode for electrocatalytic reduction of 2-pyridineethanol in ionic liquids

Nanoporous TiO₂ having enhanced surface area was synthesized by sol–gel method. On the nanoporous TiO₂ film electrode, electrocatalytic reduction of the 2-pyridineethanol in the ionic liquid electrolyte of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF₄) was investigated by cyclic voltammetry (CV). It was found that the indirect electroreduction of 2-pyridineethanol produced 2-piperidinoethanol by Ti(IV)/Ti(III) redox system on the nanoporous TiO₂ film surface. The current of cathodic reduction peak increased along with the increase of reactant concentration. The electrode reaction mechanism is called catalytic (EC′) mechanism.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite oxide and its photocatalytic degradation of rhodamine B

The composite semiconductor photocatalyst TiO₂/SiO₂ was prepared by template-hydrothermal method using carbon spheres as the template. The structural and optical properties of TiO₂/SiO₂ were characterized by XRD, SEM, BET, UV–Vis DRS, TG-DTA, PL techniques. The formation of hydroxyl radical on the surface of TiO₂/SiO₂ was studied with terephthalic acid as the probe molecule, combined with fluorescence technique. The results showed that the specific surface area of TiO₂/SiO₂ composite was 327.9 m²/g, and the specific surface area of TiO₂/SiO₂ was larger than that of pure TiO₂. Photocatalytic degradation of rhodamine B showed that TiO₂/SiO₂ composite oxide under visible light illumination 40 min, the degradation rate was 98.6 % and the degradation rate of pure TiO₂ was only 11.9 %. The apparent first-order rate constant of TiO₂/SiO₂ was 33 times that of pure TiO₂ and more than 6 times that of P25 when the molar ratio of Ti to Si was 1:1 under visible light irradiation. Moreover, it’s also as much as 5 times that of pure TiO₂ and is more than 1 times that of P25 under UV light irradiation 25 min. Based on the experimental results, ^·O₂ ^? and h⁺ were suggested to be the major active species which was responsible for the degradation reaction. The increased photocatalytic activity of TiO₂/SiO₂ may be mainly attributed to effectively suppressing the recombination of hole/electron pairs. After the photocatalyst TiO₂/SiO₂ was reused 5 times, the degradation rate of rhodamine B could reach 89.2 % under visible light irradiation. Moreover, The composite semiconductor photocatalyst TiO₂/SiO₂ was selective towards the degradation of rhodamine B.     

Thermal and neutron shielding properties of <Superscript>10</Superscript>B<Subscript>2</Subscript>O<Subscript>3</Subscript>/polyimide hybrid materials

In this study, ¹⁰B₂O₃/polyimide (PI) hybrid materials were synthesized with the aim to improve their thermal stability and neutron shielding properties. 3,3′-Diaminodiphenyl sulfone (DADPS) reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) and mixed with amine functionalized ¹⁰B₂O₃ to prepare a series of poly (amic acid), meanwhile, corresponding PIs were obtained via the thermal imidization procedures. The morphologies and structures of the prepared hybrid materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The thermooxidative and flame retardancy properties of the PI films were examined by thermogravimetric analysis (TGA) and limiting oxygen ındex (LOI). The experimental results showed that as the amount of functionalized ¹⁰B₂O₃ was increased, flame retardant properties of the hybrid films were increased. Hybrid materials were also irradiated with thermal neutrons. The neutron shielding properties increasing depends on the amount and the distribution of the ¹⁰B isotope.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Photocatalytic Water Splitting on Visible Light-responsive TiO2 Thin Films Prepared by a RF Magnetron Sputtering Deposition Method

The development of visible light-responsive TiO₂ (Vis-TiO₂) thin films has been achieved by applying a radio-frequency magnetron sputtering deposition (RF-MS) method. Pt-loaded Vis-TiO₂ thin films act as photocatalysts to decompose water involving sacrificial reagent such as methanol or silver nitrate even under visible light (λ ≧ 420 nm) irradiation. It was also found that Pt-loaded Vis-TiO₂ thin films decompose pure water into H₂ and O₂ stoichiometrically under light irradiation of wavelengths longer than 390 nm. Vis-TiO₂ thin films exhibit columnar structures perpendicular to the substrate and a declined composition of the O/Ti ratio from the surface (O/Ti = 2.00) to bottom (O/Ti = 1.93). This unique structure (anisotropic structure) of Vis-TiO₂ can be considered an important factor in the modification of the electronic properties of Vis-TiO₂ thin films, enabling the absorption of visible light. Furthermore, the effect of the Pt loadings on the photocatalytic activity of the TiO₂ thin films was investigated and the optimum Pt loading was determined to be 21 μ g/cm² as Pt metal     

Electrochemical polymerization and characterization of a poly(azulene)-TiO<Subscript>2</Subscript> nanoparticle composite film

A poly(azulene)-TiO₂ composite film (PAz-TiO₂) was synthesized electrochemically by oxidation of azulene in an electrolyte medium containing TiO₂ nanoparticles. Polymerization was performed under magnetic stirring in an acetonitrile solution containing tetrabutylammonium hexafluorophosphate as the electrolyte salt. Influence of the concentration of TiO₂ in the reaction suspension on the electrochemical and optical properties and on the structure of the composite films was studied by cyclic voltammetry, ex situ Raman and FTIR reflection spectroscopy and in situ UV–vis and FTIR spectroelectrochemical techniques. Morphology of the composite films was studied by Scanning Electron Microscopy and the amount and distribution of the TiO₂ nanoparticles within the polymeric matrix by Inductively Coupled Plasma Mass Spectrometry with laser ablation. Addition of TiO₂ in the reaction suspension had a small catalytic activity for the polymerization of Az. Inclusion of TiO₂ nanoparticles in PAz did not affect the voltammetric behavior or the chemical structure of the formed polymer films. However, a different chain conformation and morphology of the film was formed when synthesized in presence of TiO₂ compared to the plain PAz film. It was also found that the film morphology was more homogeneous when the concentration of TiO₂ was ≥10 mM in the polymerization solution than films polymerized without any TiO₂.     

Efficient Photocatalytic Decomposition of Glucose,Starch, and Cellulose to CO<Subscript>2</Subscript> Using a Mesoporous Semiconductor Thin Film

Abstract  

UV light-activated highly efficient photocatalytic decomposition of aqueous glucose and polysaccharides (starch and cellulose) to CO₂ was successfully achieved by using a mesoporous TiO₂ thin film coated on a fluorine-doped transparent conductive glass (FTO). The external quantum efficiency (η) of 0.08 (=8%) was obtained for glucose photodecomposition at neutral pH based on the total incident UV light, and the internal quantum efficiency (η′) was 8 (=800%) based on the photon that was effective for activating the reactant, demonstrating that the major decomposition mechanism is dark auto-oxidation of the activated reactant by O₂. Glucose gave η′ values of 19 at pH 12 and 25 at pH 2 demonstrating that when a glucose molecule was once activated by one photon, the molecule can undergo auto-oxidative decomposition to CO₂ at these pH under dark. Water-soluble starch was also photodecomposed completely to CO₂ with estimated η′ value of 8.6. Water-soluble carboxymethyl cellulose (CMC) also underwent decomposition to CO₂ with similar efficiency of η′ = 5. Solid state cellulose powders could be photodecomposed to CO₂ by sandwiching them between FTO-coated TiO₂ thin films.