Influence of Dye Content on the Conduction Band Edge of Titania in the Steam‐treated Dye‐dispersing Titania Electrodes

The titania and dye‐dispersing titania electrodes were prepared by a nitric acid‐catalyzed sol‐gel process. The dye‐dispersing titania contains the dye molecules dispersed on the surface of the individual nanosized titania particles. The photo‐cyclic voltammetry (Photo‐CV) and photoelectric measurements of the dye‐dispersing titania electrodes were conducted to clarify the factors changing the conduction band edge of the titania and the open‐circuit voltage (V_oc) of the electrodes. The remaining nitrate ions caused a negative shift of conduction band edge of the titania of the dye‐dispersing titania. The conduction band edge of the titania was shifted in a negative direction in the electrode containing a greater amount of the dye. These results are due to the adsorption of nitrate ions and the dye‐titania complex formation on the titania particle surface. The effect of the dye‐titania complex formation on the shift in the titania conduction band edge was greater than that of the adsorption of nitrate ions due to strong interaction between the dye and titania through the carboxylate and quinone‐like groups of the dye. The shift in the titania conduction band edge corresponded to the change in the V_oc value.     

Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein‐Dispersing Sol–Gel Titania Films

Fluorescein‐dispersing titania gel films were prepared by the acid‐catalyzed sol–gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid–base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate‐like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye–titania complex. This result indicated that the dianion form was the most favorable for formation of the dye–titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye–titania complex formation played an important role in the electron injection from the dye to the titania conduction band.     

柔性TiO2纳米管薄膜电极的制备及其光电性能

采用水热合成法制备出TiO₂纳米管,通过XRD、TEM和氮气等温吸附-脱附仪等测试手段对TiO₂纳米管进行了表征.用烧结的TiO₂纳米管和P25粉末混合制成薄膜电极,并研究了薄膜电极的表面形貌、染料吸附量和光电性能.研究表明,加入TiO₂纳米管可以制备出机械稳定的薄膜;掺杂TiO₂纳米管的含量越多,薄膜电极的染料吸附量越大;掺杂5%烧结纳米管粉末的薄膜电极的光电性能最好,其短路电流可达3.25mA,光电转换效率达到1.67%.     

Morphology and dispersion control of titania–silica monolith with macro–meso pore system

Macroporous gels with bicontinuous morphology in micrometer range were prepared in a titania?Csilica system containing 5 and 7.6 mass?% titania using tetraethoxysilane and four kinds of Ti precursors, two titanium alkoxides, titanium chloride and titanium sulfate, under coexistence of poly(ethylene glycol) (PEG) with an average molecular weight of 20,000. In all the systems with different Ti precursors, the addition of PEG induced phase separation, and the macroporous morphology was formed when the transitional structure of phase separation was frozen-in by sol?Cgel transition of inorganic components. However, we can see large differences in phase separation tendency and Ti dispersion in silica network depending on the Ti precursors used. When titanium alkoxides were added into pure silica sol?Cgel system, phase separation tendency largely decreased, so that low temperature reaction was necessary for macropore formation. When we used titanium salts, on the other hand, phase separation tendency does not change much from pure silica system. The difference has been tentatively attributed to the difference in the mixing level of Ti in silica network. Although titania tended to aggregate when titanium alkoxides were used as precursors, Ti could be well dispersed in silica gel matrix when acetylacetone was added in the alkoxide system or when titanium salts were used as Ti precursors.     

Photosensitization of Nanocrystalline TiO2 Electrode Modified with C60 Carboxylic Acid Derivatives

C₆₀ carboxylic acid derivatives can be readily adsorbed on the surface of nanocrystalline TiO₂ film. The C₆₀ carboxylic acids adsorbed on nanocrystalline TiO₂ films act as charge‐transfer sensitizer. The electron transport from TiO₂ to the C₆₀ derivatives results in the generation of the cathodic photocurrent. The short‐circuit photocurrent of a C₆₀ tetracarboxylic acid is 0.45 μA/cm² under 464 nm light illumination. The photoelectric behaviour of ITO electrodes modified by the same C₆₀ carboxylic acids is different from that of the modified TiO₂ electrodes, and shows anodic photocurrent.     

Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO₂) nano-photocatalysts, with different phases, prepared using a modified sol?Cgel process were employed in the degradation of rhodamine at 10?mg?L^?1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450?°C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K _app) of 0.023?min^?1. The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024?min^?1 for 450, 500, 550 and 600?°C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017?min^?1, which is similar to that of the commercial titania.     

Photoelectrochemical application of hollow titania film

In this study, hollow titania film (HTF) was prepared by a sol–gel spin-coating technique using titania coated nano carbon spheres as precursor suspension. The carbon spheres were synthesized by hydrothermal method using glucose as precursor. Photoelectrochemical property of HTF was examined by anodic photocurrent response, and results showed that the photocurrent of HTF was nearly twice as that of compact titania film (CTF). The photocatalytic and photoelectrochemical applications were investigated by using HTF or CTF as photoanodes for X-3B degradation under UV irradiation. Results showed that photocatalytic and photoelectrochemical activity of HTF enhanced a lot compared to CTF.     

Electronic band structure of titania semiconductor nanosheets revealed by electrochemical and photoelectrochemical studies

Electrochemical and photoelectrochemical studies were conducted on self-assembled multilayer films of titania nanosheets on a conductive ITO substrate. Cyclic voltammogram (CV) curves indicated that the titania nanosheet electrode underwent insertion/extraction of Li(+) ions into/from the nanosheet galleries, associated with reduction/oxidation of Ti(4+)/Ti(3+). These processes accompanied reversible changes in UV-vis absorption of the titania nanosheet electrodes. Applying a negative bias of -1.3 V (vs Ag/Ag(+)) and lower brought about absorption reduction where the wavelength is shorter than 323 nm, and vice versa, indicating a flat-band potential of (approximately) -1.3 V and a band gap energy of 3.84 eV. Photocurrents were generated from the titania nanosheet electrodes under a positive bias. The onset potential for photocurrent generation from the titania nanosheet electrodes was around -1.27 V, and the band gap energy estimated from the photocurrent action spectra was 3.82 eV, in excellent agreement with the values obtained from the spectroelectrochemical data. The lack of difference in the band gap energies for titania nanosheet electrodes with different numbers of layers suggests that a nanosheet is electronically isolated in multilayer assemblies without affecting the electronic state of neighboring nanosheets. Similar measurements on the anatase-type TiO(2) electrode revealed that the lower edge of the conduction band for the titania nanosheet is approximately 0.1 V higher than that for anatase, while the upper edge of the valence band is 0.5 V lower.     

Study on photoconductivity of dye-polymer-based solid-state thin film

In this article, we describe a solid-state photoelectrochemical cell for light detection. Safranine-T dye mixed with polyvinyl alcohol (PVA) solution was deposited on a conducting and transparent indium-tin-oxide (ITO)-coated glass that was used as one electrode and another ITO-coated glass as the counterelectrode. A solid polymeric electrolyte consisting of polyethylene oxide-ammonium perchlorate-ethylene carbonate and propylene carbonate with suitable weight ratio was prepared and sandwiched between these two ITO-coated glass electrodes, which were separated by a Teflon spacer about 50 μm thick. The cell was biased with a direct current source to make the dye and PVA-coated ITO as the anode and the other ITO as the cathode. On illumination by a tungsten lamp, from the cathode side, the change of photocurrent was measured. The dark current-voltage characteristics and the growth and decay of the photocurrent for steady and pulsed illumination were studied.     

Covalent immobilization of a fluorescent pH-sensitive naphthalimide dye in sol–gel films

A pH indicator dye was covalently linked to inorganic?Corganic hybrid sol?Cgel layers via its carboxyl function by the formation of an amide bond. For this, the dye was activated by 2-succinimido-1,1,3,3-tetramethyluronium tetrafluoroborate and linked to N-(3-(trimethoxysilyl)propyl)-ethylendiamine. Different ratios of tetraethoxy-silane, diisobutyldimethoxysilane and 3-glycidoxypropyltrimethoxysilane were evaluated to tailor the performance of the sensing material. Fluorescence spectroscopy of the optimised sensor layers with a molar ratio of organically modified siloxane to tetraethoxysilane of 25.9 and of dye/amino groups of 1.16, showed a reversible fluorescence signal increase of 117?% upon protonation, and a pk _a 6.5. The signal changes were caused by photoinduced electron transfer between the methylpiperazine moiety and the naphthalimide fluorophore, its efficiency being modulated by protonation of the methylpiperazine nitrogen. The influence of parameters such as synthesis, dip-coating process and heat-treatment on the performance of the sensor layers was investigated. Optimum signal changes were obtained when heating the sol?Cgel structure up to 170?°C.     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

Photoelectrochemical properties of alternating multilayer films composed of titania nanosheets and Zn porphyrin

Alternating multilayer films composed of titania nanosheets and Zn porphyrins were prepared by use of a previously reported Langmuir-Blodgett film-transfer method in order to fabricate photoelectrochemical devices. Closely packed titania nanosheet monolayers on indium tin oxide (ITO), mica, and quartz surfaces strongly adsorbed cationic [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrinatozinc]4+ (ZnTMPyP4+) by electrostatic interactions. The alternating deposition process afforded nanometer-scale multilayer films with the following structure: solid surface/(titania nanosheet/ZnTMPyP4+)n (n is the number of layers). The multilayer films were characterized by various physical measurements, including AFM, XRD, and UV-visible spectra. The visible-light irradiation of this multilayer film on an ITO electrode in the presence of triethanolamine as an electron donor yielded an anodic photocurrent. The action spectrum was consistent with the absorption spectrum of ZnTMPyP4+, which indicates that the photoexcitation of ZnTMPyP4+ is responsible for the photocurrent generation. However, the photocurrent density decreased with an increasing number of layers, which indicates that the harvesting of photoexcited electrons vertically through the titania nanosheets in the ITO/(titania nanosheet/ZnTMPyP4+)n structure was not efficient. To overcome this problem, the use of a lateral interlayer connection to all of the titania nanosheets with Ag paste was examined. As a result, a dramatic improvement in the photocurrent density was obtained. Thus, for efficient photocurrent generation with the titania nanosheet-ZnTMPyP4+ composite material, the lateral connection to all of the titania nanosheet layers is effective.     

Cold Deposition as a Novel Procedure for the Preparation of Titania Sol‐Gel: A Development of a High Sensitive Electrochemical Method for Determination of Cu(II) in the Presence of Arsenic(III)

Titania sol‐gel modified gold electrode (TSGMGE) was prepared with the usage of a new proposed cold deposition method at ?10 °C. Scanning electron microscope (SEM) operating at 30 kV was used to obtain micrographs of unmodified and modified electrodes. The obtained results showed that this procedure yields a sol‐gel with high porosity in comparison to conventional methods. The modified Au electrode was fabricated by trapping the L‐glutamine in titania sol‐gel at low temperatures to preparation of a new titania sol‐gel glutamine modified gold electrode (TSGGMGE). The possibility determination of traces of Cu(II) in the presence of As(III) was investigated using proposed electrode. Under the optimized conditions, copper was accumulated at ?0.35 V (vs. Ag/AgCl) for 40 s in 0.1 M acetate buffer (pH 4.0) in the presence of different amounts of arsenic. Two dynamic linear responses with good reproducibility were observed for copper ions in the concentration range of 1 × 10^?6 ?4 × 10^?4 M and 4 × 10^?8 ?6 × 10^?7 M.     

Sol-Gel Formation of ITO Thin Film from a Sol Including ITO Powder

Recently, low temperature synthesis of ITO thin film of low resistivity is desired in the field of LCD (Liquid Crystalline Display) production. This paper describes the results of experiment to produce ITO thin film from a sol containing crystalline ITO particles and alkoxides of In and Sn. Crystallization temperature of ITO thin film obtained from the sol mixed with ITO powder was lower than that of ITO from the sol without ITO powder. Furthermore, the resistivity of the former ITO thin film was lower than that of the latter. It was assumed that these results were attributed to the promotion effect of ITO crystalline particles to crystalize the amorphous ITO gel at lower temperature. This low temperature crystallization effect plays an important role in enhancing the crystallinity and electric conductivity of ITO thin film from sol-gel process.     

Synthesis, structure and some properties of zirconium phosphate/oxide support compositions

Deposited zirconium phosphate samples on the base of silica and titania have been prepared using the sol?Cgel and mechanochemical methods. Porous structure, phase composition, and electrokinetic parameters have been studied by means of nitrogen adsorption?Cdesorption, XRD, DTA-TG, FTIR, electrophoresis, and potentiometric titration. The compositions possess varied parameters of porous structure, structure of deposited phase, and electrokinetic properties depending on support nature and synthesis conditions.     

Water based sol–gel methods used for Bi-222 thermoelectrics preparation

Three different water based sol?Cgel methods were compared in the synthesis of Bi₂Sr₂Co_1.8O_x thermoelectric ceramics. We chose methods that can stabilize a Bi³⁺ ion while solution and gel are formed: chelating method using combination of ethylenediamintetraacetic acid (EDTA) and triethanolamine (TEA) chelating agents and, further, synthesis using two different water soluble polymers??polyacrylamide or polyethylenimin. In each sol?Cgel process, we tested two gel decomposition atmospheres. The gels were decomposed either in air or in inert atmosphere (followed by treatment in pure oxygen). Additionally, a sample synthesized by solid state reaction was used for comparison with the sol?Cgel prepared samples. The grain size of precursors and also their phase composition were determined for methods used and different gels decomposition atmospheres. The sintered final samples did not differ in phase composition; on the other hand, they vary in volume density and microstructure. The differences were reflected in electric transport measurement (the temperature dependence of Seebeck coefficient, resistivity and thermal conductivity). The use of EDTA/TEA or PEI methods led to the samples with improved thermoelectric parameters in comparison to the solid state sample.     

Fabrication of highly efficient dye-sensitized solar cell and CO2 reduction photocatalyst using TiO2 nanoparticles prepared by spin coating-assisted sol–gel method

A sol?Cgel method was applied for fabrication of nanocrystalline anatase TiO₂ thin films on ITO glass substrates and followed by rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). TiO₂ nanoparticles were characterized by X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) and the absorption of dye on the TiO₂ electrode was shown by UV?Cvis spectroscopy. By controlling different parameters including numbers of coated layers, the gap between two electrodes, sensitization time, and light source power, TiO₂-based solar cells with high efficiency was achieved. The results show that a five time spin-coated TiO₂ electrode with applying sealant and sensitization time of 24?h in N3 dye under illumination of 100?W?cm^?2 tungsten lamp give the optimum power conversion efficiency (??) of 6.61%. The increases in thickness of TiO₂ films by increasing the numbers of coated layers can improve adsorption of the N3 dye through TiO₂ layers to increase the open-circuit voltage (V _oc). However, short-circuit photocurrents (J _sc) of DSSCs with a one-coated layer of TiO₂ films are smaller than those of DSSCs with five-coated layer of TiO₂ films. It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films. Also, this electrode was employed to photoreduce CO₂ with H₂O under tungsten lamp as light source.     

Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.     

Highly Efficient and Stable Palladium Nanoparticles Supported on an Ionic Liquid Silica Sol?Gel Modified Electrode

A carbon ionic liquid electrode modified with a thin layer of silica sol? gel containing phosphinite ionic liquid was prepared for deposition of palladium nanoparticles. Palladium nanoparticles were formed easily by simple contact of the modified electrode with palladium chloride solution. The novel material overcomes the shortcomings of conventionally modified electrodes with a thin layer of silica sol? gel, due to the existence of ionic liquid in silica matrix. A crack‐free sol? gel matrix was obtained and also, the uniform porous structure of the ionic liquid‐sol? gel matrix resulted in a fast mass transport and increased ionic conductivity. The electrode exhibits high electrocatalytic effects towards hydrazine and ascorbic acid. It is very stable against repetitive cycling in the applied potential window.     

Synthesis monolithic copper-based aerogel with polyacrylic acid as template

Copper-based monolithic aerogel was prepared by sol?Cgel method with inorganic salt as precursor, the polyacrylic acid as template and the propylene oxide as gelation agent. The as-prepared aerogel was calcined at 400?°C to remove the organic substances and obtain crystalline copper-oxide nanostructured materials (tenorite, JCPDS File No. 00-045-0937). The aerogels?? structural properties were characterized by the field emission scanning electron microscopy, the high resolution transmission electron microscopy, the X-ray diffraction (XRD), and the Brunauer-Emmett-Teller methods. The results indicate that the as-prepared copper-based aerogel shows a typical three-dimensional porous structure with a large surface areas about 587?m²/g. The XRD patterns show that the as-prepared copper-based aerogel belongs to amorphous materials. The phase transition from the amorphous to crystalline copper oxide occurs at 400?°C.