Photoelectrochemical solar cell properties of heteropolytungstic acid-incorporated TiO2 nanodisc thin films

Thin film of heteropolytungstic acid (HPA)-incorporated TiO₂ nanodisc was fabricated, and its photovoltaic performances were observed as a function of irradiation wavelength from 400 nm to 750 nm. Its incident photon-to-current efficiency (IPCE) was determined to be 18.6% around 500 nm, with energy conversion efficiency of 6.9%, which were observed to be further enhanced to 23% and 9%, respectively, by adsorption of ruthenium or porphyrin dyes. Complementary electron transports from both HPA and dyes to TiO₂ nanodisc seems to avoid most of the backward electron or hole transfer reactions to enhance the photoelectrochemical efficiencies of dye-sensitized solar cells.     

Photoelectrochemical properties of MoO2 thin films

Thin MoO₂ films were electrodeposited on a selenium pre-deposited SnO₂|glass plate. The photoelectrochemical properties of MoO₂ films were investigated in 0.1 M Na₂SO₄ solution by the ultraviolet–visible spectrophotometry, linear sweep voltammetry, and altering current impedance measurement techniques. It was found that under illumination with the incident light of λ?=?366 nm, the photo response of the MoO₂|SnO₂|glass electrode resulted from the MoO₂ layer, while the SnO₂ layer served as a sink for photogenerated charge carriers. The MoO₂ film exhibited n-type conductivity. A schematic band structure diagram of MoO₂ in 0.1 M Na₂SO₄ solution was constructed. The flat band potential (E _fb), the donor concentration (N _D), the photogeneration current efficiency depended on MoO₂ film thickness. The [Fe(CN)₆]^4?/3? redox PEC cell with MoO₂|SnO₂|glass plate as a photoanode was constructed. Power output characteristics such as the open circuit voltage (V _OC), short circuit current (I _SC), the fill factor (FF), and the light-to-electrical conversion efficiency (η) were determined. The maximum light-to-electrical conversion efficiency exhibited by the PEC cell was 0.94 %.     

Photoelectrochemical properties of thin films on titanium obtained by thermal,electrochemical, or sol-gel method

Journal of Solid State Electrochemistry - The photosensitivity of the titanium dioxide films on titanium substrate formed by the electrochemical, thermal, or sol-gel method was compared under the...     

Self-stabilization of aqueous suspensions of alumina nanoparticles obtained by electrical explosion

The particle-size distribution, electrooptical potential, and acid properties of the surface of Al₂O₃ nanoparticles in aqueous media were studied by dynamic light scattering, electroacoustic spectral analysis, and potentiometric titration. The nanopowder with the mean particle size 22 nm was obtained by the oxidation of aluminum wire in the vapor phase using electrical explosion in oxygen-argon mixture. In spite of the presence of aggregates, aqueous suspensions of nanoparticles, as distinct from suspensions of micropowders, are stable without the addition of special stabilizers because of the spontaneous formation of a double electrical layer on their surface, the electrokinetic potential of which is positive and exceeds 30 mV. The most probable reason for electrostatic self-stabilization of suspensions of nanopowders is the adsorption of Al ions formed in the hydrolysis of aluminum nitrates, small amounts of which are produced in electrical discharges during preparation.     

Optical, electrical and dielectric properties of TiO2-SiO2 films prepared by a cost effective sol-gel process

Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (100) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200°C for their possible use in optoelectronic applications.     

Photoelectrochemical properties of TiO2 photocatalyst and its applications for environmental purification

In view of the situation that environmental issues become more serious day by day, recent studies on practical applications of TiO₂ photocatalysis for environmental purification are reviewed. Although the fundamental aspects and the mechanisms of TiO₂ photocatalysis have recently become quite well understood, effective photocatalytic environmental purifier, especially water purifier, could not be developed to the stage of real industrial technology. The removal rate of gaseous or aqueous contaminants is influenced by numerous parameters; UV light intensity, substrate concentration, O₂ partial pressure, humidity, substrate type, and so on. Moreover, TiO₂ photocatalyst essentially has a difficulty in decomposition of large amount of contaminants or refractory chemicals. As the solutions of these problems, combination with other processes such as advanced oxidation processes and improvement of the design of photocatalytic environmental purification systems are described. During the past several years, the strategies for effective design of the system are well discussed and evaluated. The reactor design for air- or water-purification can be classified into two main strategies: (1) enlargement of reactive surface area and (2) improvement of mass transfer. Based on these insights, very recent achievements for development of photocatalytic environmental purification system with our contribution in each aspect and future research directions are reviewed.     

Photoelectrochemical properties of Fe2O3-Nb2O5 films prepared by sol-gel method

Fe2O3-Nb2O5 coating films of various Nb/(Fe + Nb) mole ratios were prepared on nesa silica glass substrates from Fe(NO3)3.9H2O - NbCl5 - CH3(CH2)2CH2OH - CH3COOH solutions by the sol-gel method. The photoanodic properties were studied in a three-electrode cell with an aqueous buffer solution of pH = 7 as the supporting electrolyte. The crystalline phases identified were alpha-Fe2O3 (Nb/(Fe + Nb) = 0), alpha-Fe2O3 + FeNbO4 (Nb/(Fe + Nb) = 0.25), FeNbO4 (Nb/(Fe + Nb) = 0.5), FeNbO4 + Nb2O5 (Nb/(Fe + Nb) = 0.75), and Nb2O5 (Nb/(Fe + Nb) = 1). When the Nb/(Fe + Nb) mole ratio increased from 0 to 0.25, the crystalline phases changed from alpha-Fe2O3 to alpha-Fe2O3 + FeNbO4, the photoanodic current under white light illumination increased, and the photoanodic current under monochromatized light illumination increased in both visible and ultraviolet regions. When the Nb/(Fe + Nb) ratio increased over 0.25, the crystalline phases changed to FeNbO4, FeNbO4 + Nb2O5, or Nb2O5, and the photoanodic current decreased. The sample consisting of alpha-Fe2O3 and FeNbO4 (Nb/(Fe + Nb) = 0.25) exhibited photoresponse extending to 600 nm and an IPCE of 18% at a wavelength of 325 nm.     

Influence of sputter power on structural and electrical properties of TiO2 films for Al/TiO2/Si gate capacitors

Titanium dioxide (TiO₂) thin films were deposited onto p‐Si substrates held at room temperature by reactive Direct Current (DC) magnetron sputtering at various sputter powers in the range 80–200 W. The as‐deposited TiO₂ films were annealed at a temperature of 1023 K. The post‐annealed films were characterized for crystallographic structure, chemical binding configuration, surface morphology and optical absorption. The electrical and dielectric properties of Al/TiO₂/p‐Si structure were determined from the capacitance–voltage and current–voltage characteristics. X‐ray diffraction studies confirmed that the as‐deposited films were amorphous in nature. After post‐annealing at 1023 K, the films formed at lower powers exhibited anatase phase, where as those deposited at sputter powers > 160 W showed the mixed anatase and rutile phases of TiO₂. The surface morphology of the films varied significantly with the increase of sputter power. The electrical and dielectric properties on the air‐annealed Al/TiO₂/p‐Si structures were studied. The effect of sputter power on the electrical and dielectric characteristics of the structure of Al/TiO₂/p‐Si (metal‐insulator‐semiconductor) was systematically investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Photoelectrochemical behavior of Nb-doped TiO2 electrodes

The photoelectrochemical behavior of degenerate Nb-doped TiO2 (Ti(1-x)Nb(x)O2: x = 0, 0.01, 0.03, 0.06, 0.1) electrodes prepared by pulsed laser deposition on LaAlO3 (LAO) and SrTiO3 (STO) was examined, revealing that an increase in Nb concentration causes a significant decay of titania photoactivity. One reason for such behavior may be a Burstein-Moss effect, which leads to a blue shift of the spectral limit of photoactivity. Another reason typical for metal-doped photocatalysts is the increase of the efficiency of charge carrier recombination.     

Electrochromic properties of sputtered TiO2 thin films

TiO₂ thin films were deposited on ITO/Glass substrates by the rf magnetron sputtering in this study. The electrochromic properties of TiO₂ films were investigated using cyclic voltammograms (CV), which were carried out on TiO₂ films immersed in an electrolyte of 1 M LiClO₄ in propylene carbonate (PC). As- deposited TiO₂ thin film was amorphous, while the films post-annealed at 300~600°C contained crystallized anatase and rutile. With the increase of the annealing temperature, the surface roughness of film increased from 1.232 nm to 1.950 nm. Experimental results reveal that the processing parameters of TiO₂ thin films will influence the electrochromic properties such as transmittance, ion-storage capacity, inserted charge, optical density change, coloration efficiency and insertion coefficient.     

TiO2 films by sol-gel spin-coating deposition with microbial antiadhesion properties

Intensive use of antibiotics induced adaptations in bacteria, which developed antibiotic resistance. This is becoming a serious health problem, particularly in the hospital, food industry, or public transport. It is also important to produce surfaces that not only are bactericidal but also prevent adhesion and the consequent biofilm formation, which can make the bacteria resistant to conventional disinfection methods. In this work, a simple and inexpensive method to obtain surfaces TiO₂ film coated has been realized to prevent attachment and bacterial proliferation on surfaces. The synthesis and deposition procedure has been finalized to the realization of a uniform coating, whose physical, morphological, and structural features are suitable to inhibit the proliferation of the bacteria and in particular the adhesion of the biofilm. The suitability of the obtained coating has been attested by RBS, X-ray diffraction (XRD), SEM, UV-vis, and Raman techniques. The obtained coatings were homogeneous anatase titania films with an excellent adherence to the substrate and a transmittivity higher than 80% in the visible region. The results show that the TiO₂ films considerably reduce microbial contamination on the surface (~98% reduction) feature that makes this coating suitable for antibacterial applications.     

卟啉衍生物敏化纳米TiO2多孔膜电极的光电性质研究

采用中位-四[邻-(3-磺酸基丙氨基)苯基]卟啉(TArP1)和中位-四[对-(3-磺酸基丙氨基)苯基]卟啉(TArP2)分别对纳米TiO2多孔膜电极进行敏化。对两种敏化电极进行了UV-V is光谱测试,结果表明,TiO2与TArP2的作用比与TArP1的作用强。在相同浸泡条件下,TiO2电极吸附TArP2的量大于吸附TArP1的量。将两种敏化电极分别组装成光电化学电池,从光电化学电池的I-V曲线计算TArP2敏化的光电化学电池的总光电转换效率(η)为0.15%,而TArP1敏化的光电化学电池的η为0.09%。     

Tuning the optical properties of mesoporous TiO2 films by nanoscale engineering

The optical properties of spin-coated titanium dioxide films have been tuned by introducing mesoscale pores into the inorganic matrix. Differently sized pores were templated using Pluronic triblock copolymers as surfactants in the sol-gel precursor solutions and adjusted by varying the process parameters, such as the polymer concentration, annealing temperature, and time. The change in refractive index observed for different mesoporous anatase films annealed at 350, 400, or 450 °C directly correlates with changes in the pore size. Additionally, the index of refraction is influenced by the film thickness and the density of pores within the films. The band gap of these films is blue-shifted, presumably due to stress the introduction of pores exerts on the inorganic matrix. This study focused on elucidating the effect different templating materials (Pluronic F127 and P123) have on the pore size of the final mesoporous titania film and on understanding the relation of varying the polymer concentration (taking P123 as an example) in the sol-gel solution to the pore density and size in the resultant titania film. Titania thin film samples or corresponding titanium dioxide powders were characterized by X-ray diffraction, cross-section transmission electron microscopy, nitrogen adsorption, ellipsometery, UV/vis spectrometry, and other techniques to understand the interplay between mesoporosity and optical properties.     

纳米TiO2电极的特殊光电化学响应

应用涂膜法、电沉积法和溶胶-凝胶法制备纳米TiO2电极.实验发现,纳米TiO2具有特殊的光电化学响应,其光电流~电位变化出现光电流峰,这一特殊的光电化学性质乃与纳米半导体电极的纳米结构及其特殊的光诱导氧化还原反应机理密切相关.     

Photoelectrochemical processes on TiO2 electrodes sensitized by lead selenide nanoparticles

The effect of spectral sensitization of photoelectrochemical processes on the surfaces of mesoporous TiO₂ modified by electrochemically deposited PbSe nanoparticles has been observed.     

The photocatalytic properties of amorphous TiO2 composite films deposited by magnetron sputtering

The preparation of amorphous TiO₂ film coupled with various metal-oxide semiconductors and their photocatalytic activities evaluated by photo-degradation of methylene blue and rhodamine B aqueous solution are briefly reviewed. The proposed photoreaction mechanism of the amorphous composite semiconductor and the differences between amorphous TiO₂-based films and crystalline TiO₂ photocatalytic materials in terms of preparation and usage are addressed. The inactive intrinsic amorphous TiO₂ film coupled with various metal oxides were found to gain high photocatalytic activity. These dopants induce forming new energy levels in the band gap of TiO₂ to enhance the charge separation of the photoinduced electrons and holes and extend the light absorption of TiO₂-based photocatalytic films into the visible region. In addition, two different effects of coupling metal oxides have been proved: the introduction of oxides of W, Cr, V, Ag, and Mo can significantly increase the photo-reactivity of amorphous TiO₂ film, while the combination of oxides of Zr, Sn, Sb, Cu, Ta, Fe, and Ni cannot affect the inactivity of pure amorphous TiO₂ film.     

Structural and optical properties of TiO2 thin films prepared by spin coating

Transparent semiconducting thin films of titanium oxide (TiO₂) were deposited on glass substrates by the sol–gel method and spin-coating technique. The physical properties of the prepared films were studied as a function of the number of spun-cast layers. The microstructure and surface morphology of the TiO₂ films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), with respect to the film thickness. The XRD analysis reveals that the films are polycrystalline with an anatase crystal structure and a preferred grain orientation in the (101) direction. The morphological properties were investigated by AFM, which shows a porous morphology structure for the films. The optical properties of the films were characterized by UV–Visible spectrophotometry, which shows that the films are highly transparent in the visible region and their transparency is slightly influenced by the film thickness, with an average value above 80 %. The dependence of the refractive index (n), extinction coefficient (k), and absorption coefficient (α) of the films on the wavelength was investigated. A shift in the optical band gap energy of the films from 3.75 to 3.54 eV, as a function of the film thickness, has been observed.     

TiO2光电化学电池催化氧化甲基红

以钛基TiO₂薄膜为光阳极，研究了光电化学电池中阳极光催化降解偶氮染料甲基红的动力学. 结果表明，短接光电化学电池分隔了光催化过程的阴、阳极反应，有利于抑制光生载流子的复合，提高光催化氧化速率. 相同实验条件下短路光电流越大，则甲基红降解速率越高. 在基底和TiO₂薄膜之间夹层SnO₂得到组装电极Ti/SnO₂/TiO₂，进一步提高了光生载流子的分离效率；同时采用电化学阻抗谱（EIS）评价了电极的光催化性能.