Comparison between P25 and anatase-based TiO_2 quasi-solid state dye sensitized solar cells

Pure anatase TiO2 films have been made via hydration of titanium isopropoxide using a sol-gel tech- nique, while mixed TiO2 films which contained both anatase and rutile TiO2 were made from commercial P25 powder. Quasi-solid state dye-sensitized solar cells were fabricated with these two kinds of mesoporous films and a comparison study was carried out. The result showed that the open-circuit photovoltages (Voc) for both kinds of cells were essentially the same, whereas the short-circuit photo- currents (Isc) of the anatase-based cells were about 33% higher than that of the P25-based cells. The highest photocurrent intensity of the anatase-based cell was 6.12 mA/cm2 and that of the P25-based cell was 4.60 mA/cm2. Under an illumination with the light intensity of 30 mW/cm2, the corresponding en- ergy conversion efficiency was measured to be 7.07% and 6.89% for anatase-based cells and P25-based cells, respectively.     

Silicon field emission arrays coated with CN<Subscript>x</Subscript> thin films

Arrays of silicon micro-tips were made by etching the p-type (1 0 0) silicon wafers which had SiO₂ masks with alkaline solution. The density of the micro-tips is 2×10⁴ cm⁻². The Scanning Electron Microscope (SEM) photos showed that the tips in these arrays are uniform and orderly. The CN_x thin film, with the thickness of 1.27 μm was deposited on the silicon micro-tip arrays by using the middle frequency magnetron sputtering technology. The SEM photos showed that the films on the tips are smoothly without particles. Keeping the sharpness of the tips will benefit the properties of field emission. The X-ray photoelectron spectrum (XPS) showed that carbon, nitrogen and oxygen are the three major elements in the surfaces of the films. The percents of them are C: 69.5%, N: 12.6% and O: 17.9%. The silicon arrays coated with CN_x thin films had shown a good field emission characterization. The emission current intensity reached 3.2 mA/cm² at 32.8 V/μm, so it can be put into use. The result showed that the silicon arrays coated with CN_x thin films are likely to be good field emission cathode. The preparation and the characterization of the samples were discussed in detail. Foundation item: Supported by the National Natural Science Foundation of China (19975035) Biography: Chen Ming an (1978-), male, Ph. D candidate, research direction: novel functional materials film and ion beam modification of materials.     

Preparation of Zn-doped TiO2 nanotubes electrode and its application in pentachlorophenol photoelectrocatalytic degradation

Zn-doped titanium oxide （TiO2） nanotubes electrode was prepared on a titanium plate by direct anodic oxidation and immersing method in sequence. Field emission scanning electron microscopy （FESEM） showed that the Zn-doped TiO2 nanotubes were well aligned and organized into high density uniform arrays with diameter ranging from 50 to 90 nm. The length and the thickness were about 200 and 15 nm respectively. TiO2 anatase phase was identified by X-ray diffraction （XRD）. X-ray photoelectronspectroscopy （XPS） indicated that Zn ions were mainly located on the surface of TiO2 nanotubes in form of ZnO clusters. Compared with TiO2 nanotubes electrode, about 20 nm red shift in the spectrum of UV-vis absorption was observed. The degradation of pentachlorophenol （PCP） in aqueous solution under the same condition （initial concentration of PCP： 20 mg/L; concentration of Na2SO4：0.01 mol/L and pH： 7.03） was carried out using Zn-doped TiO2 nanotubes electrode and TiO2 nanotubes electrode. The degradation rates of PCP using Zn-doped TiO2 nanotubes electrode were found to be twice and 5.8 times as high as that using TiO2 nanotubes electrode by UV radiation （400 μw/cm^2） and visible light radiation （4500 μw/cm^2）, respectively. 73.5% of PCP was removed using Zn-doped TiO2 nanotubes electrode against 45.5% removed using TiO2 nanotubes electrode in 120 min under UV radiation. While under visible light radiation, the degradation efficiency of PCP was 18.4% using Zn-doped TiO2 nanotubes electrode against 3.2% using TiO2 nanotubes electrode in 120 min. The optimum concentration of Zn doping was found to be 0.909%. The PCP degradation efficiencies of the 10 repeated experiments by Zn-doped TiO2 nanotubes electrode were rather stable with the deviation within 3.0%.     

Photovoltaic properties of MEH-PPV/TiO2 nanocomposites

Photovoltaic properties of photodiodes based on nano-TiO2 and poly[2-methoxy,5-（2＇-ethlhexyloxy）-p-phenylenevinylene] （MEH-PPV） composites are investigated. By comparing composite devices with the same weight of TiO2 （nanoparticles and nanotubes）：MEH-PPV, it was found that the device with TiO2 nanotubes exhibited better performance. By further optimizing the weight radio of TiO2 nanotubes： MEH-PPV, we gained the device with a short circuit current density of 9.27μA/cm^2 with a light intensity of 16.7mW/cm^2 at the 500 nm wavelength, the highest open-circuit voltage of 1.1V, and a photosensitivity of 332 at reverse bias of -0.6V. The photosensitivity is improved by a factor of 33 compared with the undoped MEH-PPV device.     

Visible light photocatalytic decoloration of methylene blue on novel N-doped TiO2

Novel N-doped TiO2 (denoted as N-NTA600) was prepared by treating nanotube titanic acid (NTA) in NH3 flow. Its visible light photocatalytic activity,evaluated by decoloration reaction of methylene blue,is higher than that of N-P25(600) prepared by treatment of P25-TiO2 in the same condition. It is suggested that the origin of visible-light photocatalytic activity is single-electron-trapped oxygen vacancy (Vo·) modified by chemisorbed NO.     

Fluorescence and sensitization performance of phenylene-vinylene-substituted polythiophene

A new kind of polythiophene derivative, Poly(3-{2-[4-(2-ethylhexyloxy)-phenyl]-vinyl}-2,2′-bithiophene) (PTh), was applied in dye-sensitized solar cell to extend the light response of nanocrystalline TiO2 electrode. UV-vis absorption and fluorescence spectra were employed to investigate the interaction of PTh with nanocrystalline TiO2. The absorption coefficient of the PTh was high in visible part of spec- trum, and the fluorescence emission of the PTh can be efficiently quenched by TiO2 nanoparticles ow- i...     

Micro-arc oxidization fabrication and ethanol sensing performance of Fe-doped TiO<Subscript>2</Subscript> thin films

In-situ pure TiO₂ and Fe-doped TiO₂ thin films were synthesized on Ti plates via the micro-arc oxidation (MAO) technique. The as-fabricated anatase TiO₂ thin film-based conductometric sensors were employed to measure the gas sensitivity to ethanol. The results showed that Fe ions could be easily introduced into the MAO-TiO₂ thin films by adding precursor K₄(FeCN)₆·3H₂O into the Na₃PO₄ electrolyte. The amount of doped Fe ions increased almost linearly with the concentration of K₄(FeCN)₆·3H₂O increasing, eventually affecting the ethanol sensing performances of TiO₂ thin films. It was found that the enhanced sensor signals obtained had an optimal concentration of Fe dopant (1.28at%), by which the maximal gas sensor signal to 1000 ppm ethanol was estimated to be 7.91 at 275°C. The response time was generally reduced by doped Fe ions, which could be ascribed to the increase of oxygen vacancies caused by Fe³⁺ substituting for Ti⁴⁺.     

Performances improvement of eosin Y sensitized solar cells by modifying TiO2 electrode with silane-coupling reagent

Chemical fixing of xanthene dye （eosin Y） on the surface of TiO2 electrode was carried out by modifying the electrode with silane-coupling reagent to obtain stable dye-sensitized TiO2 electrode. Such silane modification can not only evidently enhance the stability of dye-sensitized TiO2 electrode but also improve the energy conversion efficiency of the assembled cells by increasing short-circuit photocurrent （Jsc） and open-circuit photovoltage （Voc）. It was found that the improvements of cell performances differ depending on the composition of the electrolyte. The optimum cell of the cell performance was achieved in the electrolyte with 0.5 mol/L TBAI/0.05 mol/L 12/EC：PC（3：1 w/w）, yielding Jsc of 4.69 mA. cm-2, Voc of 0,595 V, fill factor （FF） of 0.64 and ηof 1,78%, Different spectroscopic techniques including UV-Vis spectra, fluorescence spectra, EIS and dark current measurements were employed to derive reasonable analysis and explanations.     

Preparation of nano-crystal N-Zn/TiO<Subscript>2</Subscript> anode films and the effects of co-sensitization on the performance of dye-sensitized solar cells

A nano-crystal N-Zn/TiO₂ anode film was prepared using a combined technology. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry characterizations showed that the two elements N and Zn were doped into nano-crystal TiO₂ successfully. This resulted in a strong redshift in the UV-Visible spectrum. UV-Visible measurements showed that the light absorption of N719 and P3OT were complementary and covered the entire visible region. This led to a high utilization of visible light. Solar cells based on the N-Zn/TiO₂ anode film were co-sensitized using P3OT and N719. The cells have a short-circuit current density of 7.91 mA/cm², an open-circuit photovoltage of 0.659 V, and a photoelectric conversion efficiency of 2.64%. Also, the relationship among the N-Zn/TiO₂-film anode’s electric structure, the dye’s LUMO, electrochemical impedance, and photoelectric conversion efficiency are discussed in the paper.     

TiO<Subscript>2</Subscript>@MgO core-shell film: Fabrication and application to dye-sensitized solar cells

In this study,TiO2@MgO core-shell film was obtained by using a simple chemical bath deposition method to coat a thin MgO film around TiO2 nanoparticles. The core-shell configuration was characterized by X-ray diffractometer (XRD),scanning elec-tron microscopy (SEM),energy dispersive X-ray spectroscopy (EDX),and high-resolution transmission electron microscopy (HRTEM). Lattice fringes were observed for the TiO2 particles,and the MgO shell showed an amorphous structure,revealing a clear distinction between the core and shell materials. Applying the core-shell film as photoanode to the dye-sensitized solar cells (DSSCs),it shows a superior performance compared to the pure TiO2 electrode. Under the illumination of simulated sunlight (75 mW-cm-2),the short circuit photocurrent (Jsc),the open circuit photovoltage (Voc),and the fill factor (fF) are 8.80 mA-cm-2,646 mV,and 0.69,respectively,and the conversion efficiency (η) in-creased by 21.8% (from 4.32% to 5.26%) when dipping for opti-mum condition.     

Fabrication of visible-light responsive S-F-codoped TiO<Subscript>2</Subscript> nanotubes

Fabrication and S-F-codoping of TiO2 nanotubes were carried out by a one-step electrochemical anodization process to extend the photoresponse of TiO2 to the visible-light region. The prepared samples were annealed in air and detected by SEM, XRD, XPS and UV-vis DRS spectrophotometer. The results showed that the average tube diameter of the nanotubes was 150 nm and the average tube length was 400 nm. The doped TiO2 nanotubes exhibited strong absorption in visible-light region. Photoelectrocatalytic degradation efficiency of 4-CP over S-F-codoped TiO2 nanotubes was 39.7% higher than that of only-F-doped sample. Moreover, sulfur and fluorine codoped into substitutional sites of TiO2 had been proven to be indispensable for strong response and high photocatalytic activity under visible light, as assessed by XPS.     

Preparation of porous nanoparticle TiO2 films for flexible dye-sensitized solar cells

A TiO2 paste was prepared by mixing commercial TiO2 (P25), ethanol, distilled water and a small amount of Ti (IV) tetrai-sopropoxide (TTIP), following by a hydrothermal treatment. Before hydrothermal treatment, a stirring for 48 h can prevent cracking TiO2 films. TTIP significantly promote the chemical connection between TiO2 particles and its adherence to the substrate, the TTIP amount of 6 mol% is suitable. UV irradiation can remove some impurities and water from the TiO2 film with an optimal time of 2 h. Transmission electron microscopy, X-ray diffraction, scanning electron microscopy and photovoltaic tests are charac- terized and measured. Shortcircuit current density, open-circuit voltage, fill factor and photoelectric conversion efficiencies for the fabricated flexible dye-sensitized solar cell are 7.20 mA cm-2, 0.769 V, 0.686 and 3.84%, respectively, under irradiation with a simulated solar light of 100 mW cm-2.     

Modification of TiO2 nanotubes arrays by CdS and their photoelectrocatalytic hydrogen generation properties

In order to realize hydrogen generation under visible light, novel CdS/TiO2 nanotubes arrays are developed by electrochemical anodizaUon of Ti in 0.15 mol/L NHTF ＋ 0.08 mol/L H2C2O4 electrolyte. The diameter of the nanotube is 80-100 nm and the length is approximately 550 nm. The CdS nano-particles are deposited on the TiO2 nanotubes arrays by chemical bath deposition （CBD） in the ammonia-thiourea system. A 300 W Xe lamp is used as the light source, CdS/TiO2 nanotube arrays are used as the photoanode with the application of 1.0 V bath voltage, and 0.1 mol/L Na2S ＋ 0.04 mol/L Na2SO3 solution is used as the electrolyte, then the rate of photoelectrocatalytic hydrogen generation is 245.4 μL/（h·cm^2）. This opens new perspectives for photoelectrocatalytic hydrogen generation by using CdS/TiO2 nanotubes arrays.     

Nitric oxide suppresses stomatal opening by inhibiting inward-rectifying K<Stack><Subscript>in</Subscript><Superscript>+</Superscript></Stack> channels in <Emphasis Type="Italic">Arabidopsis</Emphasis> guard cells

We explore nitric oxide （NO） effect on K^＋in, channels in Arabidopsis guard cells. We observed NO inhibited K^＋in, currents when Ca^2＋ chelator EGTA （Ethylene glycol-bis（2-aminoethylether）-N,N,N′,N;tetraacetic acid） was not added in the pipette solution; K^＋in currents were not sensitive to NO when cytosolic Ca^2＋ was chelated by EGTA. NO inhibited the Arabidopsis stomatal opening, but when EGTA was added in the bath solution, inhibition effect of NO on stomatal opening vanished. Thus, it implies that NO elevates cytosolic Ca^2＋ by activating plasma membrane Ca^2＋ channels firstly, then inactivates K^＋in, chartnels, resulting in stomatal opening suppressed subsequently.     

Compression behavior and equation of state of Ni77P23 amorphous alloy

The compression behavior of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using insitu high pressure energy dispersive X-ray diffraction with a syn- chrotron radiation source. The equation of state is determined by fitting the experimental data accord- ing to Birch-Murnaghan equation: -ΔV/V0=0.08606P-3.2×10-4P2 5.7×10-6P3. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa.     

Giant magneto-optical faraday effect of nanometer Fe-In<Subscript>2</Subscript>O<Subscript>3</Subscript> granular films

The giant magneto-optical Faraday effect of nanometer ferromagnetic metal-semiconductor matrix Fe-ln2O3 granular films prepared by the radio frequency sputtering are studied. The result shows that the Faraday rotation angle θF value of the granular film samples with Fe volume fraction x = 35% is of the order of 10^5（°）/cm at room temperature. Temperature dependence of the Faraday rotation angle θF of Fe0.35（In2O3）0.65 granular films shows that θF value below 10 K increases rapidly with the decrease of the temperature, and when T= 4.2 K, θF value is 106（°）/cm. Through the study of the dependence of low field susceptibility on temperature and the hysteresis loops at different temperatures, it has been found that when the temperature decreases to a critical point Tp = 10 K, the transformation of state from ferro-agnetic to spin-glass-like occurs in Fe0.35（In2O3）0.65 granular films. The remarkable increase of the Faraday rotation angle θF value of Fe0.35（In2O3）0.65 granular films below 10 K seems to arise from the sp-d exchange interaction of the granular film samples in the spin-glass-like state.     

TiO2-based building materials: Above and beyond traditional applications

In the 1910s, TiO₂ began to be used in building materials as pigments and opacifier due to its excellent optical property. Since the photocatalytic property of TiO₂ was observed in 1972, its application field was expanded to air cleaning and sterilization. Thereafter, people added TiO₂ into building materials to develop novel and facile building materials. These materials were widely used for air cleaning, sterilization, self-cleaning, anti-fogging, decoration, and building cooling. The combination of building and other functions can serve simultaneously. Although TiO₂-based building materials have bright prospects, some aspects such as improving the stability and enhancing photoactive performance of the materials are of importance for future research. Supported by the National High Technology Research and Development Program (“863” Program) of China (Grant No. 2007AA061402), Chinese Key Technology Research and Development Program of the Eleventh Five-year Plan (Grant No. 2006BAJ02A08), Hangzhou Science & Technology Development Program (Grant No. 20061133B27) and Research Fund for the Doctoral Program of Higher Education (Grant No. 20070335197)     

Preparation and luminescence characteristics of Sr3SiO5：Eu^2＋ phosphor for white LED

The Sr3SiO5：Eu^2＋ phosphor was synthesized by high temperature solid-state reaction. The emission spectrum of Sr3SiO5：Eu^2＋ shows two bands centered at 487 and 575 nm, which well agree with the theoretic values of emission spectrum. The excitation spectrum for 575 nm emission center has several excitation bands at 365, 418, 458 and 473 nm. And the results show that the emission spectrum of Sr3SiO5：Eu^2＋ is influenced by the Eu^2＋ concentration. The relative emission spectra of the white-emitting InGaN-based YAG：Ce^3＋ LED and Sr3SiO5：Eu^2＋ LED were investigated. The results show that the color development of InGaN-based Sr3SiO5：Eu^2＋ is better than that of InGaN-based YAG：Ce^3＋, and the CIE chromaticity of InGaN-based Sr3SiO5：Eu^2＋ is （x=0.348, y=0.326）.     

Investigation of the cross-reaction mechanism of C<Subscript>6</Subscript>H<Subscript>5</Subscript>F-HNO<Subscript>2</Subscript> aqueous solution irradiated at 355 nm by transient absorbance spectrum technique

The transient absorption spectrum technique was employed to investigate the cross-reaction mechanism of C6H5F-HNO2 aqueous solution irradiated at 355 nm. The characteristic and the kinetic parameters of transient species were also detected. Hydroxyl radical derived from the photolysis of HNO2 was added to monofluorobenzene with a second-order rate constant of （5.83±0.17）×10^9 L·mol^-1·s^-1 to form an adduct, C6H5F…OH, which was able to react with HNO2 as the main reaction pathway with a rate constant of （8.3±0.1）×10^7 L·mol^-1·s^-1. The C6F6…OH adduct can also be decayed by elimination of H2O to yield monofluorophenyl radical C6H4F-. By GC-MS technique, the final products were identified to be monofluorophenol, nitro-monofluorobenzene, nitro-monofluorophenol and para-fluorobiphenyl.     

I-V andC-V properties of TiO2 thin film by pulsed-laser reactive deposition

TiO-2 thin films have bee deposited on p-Si(111) substrates by pulsed-laser ablation of metallic Ti target in the O-3 ambient. The current-voltage and capacitance-voltage of the Al/TiO-2/Si capacitors are measured. The results show that the dielectric constant of thin film after being annealed at 700℃ is found to be 46, and the border trap density and the interface state density at the TiO-2/p-Si interface are 1.8×10 12 cm -2 and 2×10 12 eV -1·cm -2, respectively. The conduction mechanisms of as-deposited films are also discussed.