Fabrication,characterization and photoelectrochemical performance of chromium-sensitized titania nanotubes as efficient photoanodes for solar water splitting

Chromium-sensitized titanium dioxide nanotubes (CTNT) with high photocatalytic activity were prepared by a chemical bath deposition technique. The resulting films were characterized by SEM, EDX, and XRD. Results showed that the fabricated films have the ordered nanotubes with diameter of 90–140 nm, wall thickness of 20–50 nm, and tube lengths in the range of 24 μm. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare titanium dioxide nanotubes (TNT). The photoelectrochemical performance was examined under light irradiation in 1 M NaOH electrolyte. Photoelectrochemical characterization shows that chromium sensitizing efficiently enhances the photocatalytic water splitting performance of CTNT composite. The sample (C3TNT) exhibited better photocatalytic activity than the TNT and CTNT fabricated using other chromium concentrations. This inexpensive photoanodes prepared free of noble metals showed enhanced high photocurrent density with good stability and is a highly promising photoanode for solar hydrogen production.     

Nitrogen-doped TiO2 from TiN and its visible light photoelectrochemical properties

Homogeneous titanium nitride (TiN) thin film was produced by simple electrophoreic deposition process on Ti substrate in an aqueous suspension of nanosized TiN powder. Nitrogen-doped titanium dioxide (TiO_2−xN_x) was synthesized by oxidative annealing the resulted TiN thin film in air. Photoelectrochemical measurements demonstrated visible light photoresponse for the electrode of annealed electrophoreic deposited TiN samples. It is found that the synthesized TiO_2−xN_x electrode showed higher photo potential under white and visible light illumination than the pure TiO₂ electrode. The photocurrent under visible light illumination was also observed, which increased with the increase of deposition time of TiN thin films.     

Easy Room Temperature Synthesis of High Surface Area Anatase Nanowires with Different Morphologies

Anatase nanowires were synthesized in solution by using a simple mixing of titanium diisopropoxide bis(acetylacetonate), lactic acid and sodium hydroxide at room temperature. We discuss effects of reaction parameters and post treatment (annealing) on the nanowire morphology, surface area, and crystallinity, as well as the competing morphology directing effects of lactic acid and sodium hydroxide. Then the room temperature nanowires were directly grown onto fluoride doped tin oxide (FTO) glass to form photoanodes. Photoelectrochemical measurements of the different nanowires were performed and compared to conventional nanowires produced by high temperature synthesis. Clearly the nanowires introduced in this work show a significant increase in the maximum photocurrent, compared to classic hydrothermal nanowire layers.     

Photosensitization and the photocurrent switching effect in nanocrystalline titanium dioxide functionalized with iron(II) complexes: a comparative study

Selected iron(II) complexes (ferrocene, ferrocenylboronic acid, hexacyanoferrate(II)) have been used as photosensitizers of titanium dioxide. Various types of electronic interactions between the surface complex and the semiconducting support are reflected in different yields of photocurrent generated upon visible-light irradiation and different efficiencies of the photosensitization effect. The studied systems, showing the photocurrent switching upon changes of electrode potential and energy of photons (the PEPS effect), are good models of simple photoelectrochemical logic devices. The mechanism of photosensitization and photocurrent switching is discussed with respect to the type of surface-complex-support interaction. Quantum-mechanical calculations support the proposed mechanisms.     

Determination of titanium dioxide in foods using inductively coupled plasma optical emission spectrometry

Titanium dioxide is a common food additive of increasing interest in dietary intake studies and dietary exclusion studies. Food labelling for titanium dioxide is imprecise so a method was developed for its rapid determination in foods using acid digestion and inductively coupled plasma optical emission spectrometry (ICPOES). Twenty-five foods thought to contain titanium dioxide were obtained. Based on preliminary digestion studies, samples (500 mg) were digested in 18 mol l-1 H2SO4 at 250 degrees C for 1 h and then diluted to 5.9 mol l-1 H2SO4 before determination of titanium by ICPOES at 336.121 nm. Emission intensity was suppressed by H2SO4 so standards were matched for acid concentration. Titanium dioxide embedded in gelatine was used to assess accuracy. A standard reference material of known titanium concentration and six foods of known titanium dioxide content were used as external reference materials. Limits of detection were 2-7.5 ppb, depending on spectral integration times, and the signal was linear up to 5 ppm. Results for all control samples were in good agreement with the expected values. Twelve of the foods contained detectable titanium, ranging from 0.001 to 0.782% by weight, but only eight indicated this on their labels, four being exempt under food labelling regulations. Based on food portion sizes, an individual's daily intake of titanium dioxide could exceed 200 mg from just one of these products. This method may facilitate future studies on titanium dioxide intake, given the present limitations of food labelling.     

New Insight into the Synthesis and Biological Activity of the Polymeric Materials Consisting of Folic Acid and β‐Cyclodextrin

This work presents a very new look at folate targeting and is focused on synthesizing and assessing the biological activity of folic acid‐targeted drug delivery materials based on β‐cyclodextrin. Both folic acid and β‐cyclodextrin have been covalently conjugated to branched polyethylenimine as the polymeric vector. Host–guest inclusion of folic acid into a β‐cyclodextrin cavity, demonstrated by means of the spectroscopic methods (2‐D NMR, IR, UV–Vis), is found to be of crucial importance for biological activity of nanotherapeutics. This paper describes the very first example of the versatile synthetic approach to create the polymeric biosystems, where folic acid activity is not limited by the inclusion phenomenon. Cytotoxicity of the obtained polymeric materials against Lewis lung carcinoma cells is determined by neutral red uptake assay. Folate receptor‐binding studies reveal that the developed synthetic approach enables full exploitation of the potential of folic acid as a targeting ligand.     

Folic acid‐polyamine‐β‐cyclodextrin for targeted delivery of scutellarin to cancer cells

The efficient tumor targeting drug carrier was designed by bioconjugation of folic acid to β‐cyclodextrin through a polyamine cationic spacer. The characterization and inclusion complexation behavior of the inclusion complex of hydrophobic drug scutellarin with folic acid‐polyamine‐β‐cyclodextrin were investigated in both solution and solid state by means of phase‐solubility, nuclear magnetic resonance, X‐ray power diffraction, thermal gravimetric analysis, and scanning electron microscopy. Besides, the solubilization efficiency and antitumor activity of the inclusion complex were tested by saturated solution and MTT (Thiazole blue) method. Solubility and antitumor activity studies showed higher solubilizing ability and antitumor activity of the inclusion complex in comparison to free scutellarin. The folic acid‐polyamine‐β‐cyclodextrin that is presented may be promising active tumor‐targeting carrier candidates via folate mediation. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Photovoltaic Properties of Boron β‐Ketoiminate Dyes Forming a Linear Donor‐π‐Acceptor Structure

Organoboron complexes are of interest as chromophores for dye sensitizers owing to their light‐harvesting and carrier‐transporting properties. In this study, compounds containing boron β‐ketoiminate (BKI) as a chromophore were synthesized and used as dye sensitizers in dye‐sensitized solar cells. The new dyes were orange or red crystals and showed maximum absorptions in the 410–450 nm wavelength region on titanium dioxide substrates. These electrodes exhibited maximum efficiencies of over 80% in incident photon‐to‐current conversion efficiency spectra, suggesting that the continuous process of light absorption‐excitation‐electron injection was effectively performed. Open‐circuit photovoltages were relatively high owing to the large dipole moments of the BKI dyes with a linear molecular structure. Thus, a maximum power conversion efficiency of 5.3% was successfully observed. Comparison of BKI dyes with boron β‐diketonate dyes revealed certain differences in solution stability, spectral properties, and photovoltaic characteristics.     

光电化学型半导体生物传感器

光电化学型半导体生物传感器是一种利用半导体的光电特性来检测与光生电流或光生电压相关的待测物质浓度及生化过程参数的分析新技术。随着新兴半导体功能材料及相关加工技术的不断涌现,光电化学型半导体生物传感器已在微型化、集成化、多点及多参数测量方面显现出优势、有望在复杂体系中实现在线高灵敏、快速测定,在生物、医药、环境监测、食品等领域显示出广阔的应用前景。本文主要介绍了光电化学型半导体传感器的基本原理、特点及近几年的研究进展,并对其发展前景做了展望。     

Efficient Photoelectrochemical Reduction of Carbon Dioxide to Formic Acid: A Functionalized Ionic Liquid as an Absorbent and Electrolyte

Photoelectrochemical (PEC) reduction of carbon dioxide (CO₂) is a potential method for production of fuels and chemicals from a C1 feedstock accumulated in the atmosphere. However, the low solubility of CO₂ in water, and complicated processes associated with capture and conversion, render CO₂ conversion inefficient. A new concept is proposed in which a PEC system is used to capture and convert CO₂ into formic acid. The process is assisted by an ionic liquid (1‐aminopropyl‐3‐methylimidazolium bromide) aqueous solution, which functions as an absorbent and electrolyte at ambient temperature and pressure. Within this PEC reduction strategy, the ionic liquid plays a critical role in promoting the conversion of CO₂ to formic acid and suppressing the reduction of H₂O to H₂. At an applied voltage of 1.7 V, the Faradaic efficiency for formic acid production is as high as 94.1 % and the electro‐to‐chemical efficiency is 86.2 %.     

Photoelectrochemical behavior of nanostructured WO3 thin-film electrodes: The oxidation of formic acid.

Nanostructured tungsten trioxide thin-film electrodes are prepared on conducting glass substrates by either potentiostatic electrodeposition from aqueous solutions of peroxotungstic acid or direct deposition of WO3 slurries. Once treated thermally in air at 450 degrees C, the electrodes are found to be composed of monoclinic WO3 grains with a particle size around 30-40 nm. The photoelectrochemical behavior of these electrodes in 1 M HClO4 apparently reveals a low degree of electron-hole recombination. Upon addition of formic acid, the electrode showed the current multiplication phenomenon together with a shift of the photocurrent onset potential toward less positive values. Photoelectrochemical experiments devised on the basis of a kinetic model reported recently [I. Mora-Seró, T. Lana-Villarreal, J. Bisquert, A. Pitarch, R. Gómez, P. Salvador, J. Phys. Chem. B 2005, 109, 3371] showed that an interfacial mechanism of inelastic, direct hole transfer takes place in the photooxidation of formic acid. This behavior is attributed to the tendency of formic acid molecules to be specifically adsorbed on the WO3 nanoparticles, as evidenced by attenuated total reflection infrared spectroscopy.     

Controlled Aqueous Growth of Hematite Nanoplate Arrays Directly on Transparent Conductive Substrates and Their Photoelectrochemical Properties

Two‐dimensional (2D) hematite nanoplate arrays were synthesized directly on fluorine‐doped tin oxide (FTO)‐coated glass by using a facile and novel hydrothermal method. High‐temperature annealing retained the morphology of the nanoplate arrays while simultaneously introducing porosity. The thickness and length of the nanoplates could be tailored by adjusting the precursor composition. Photoelectrochemical (PEC) measurements showed that the photocurrent generated with bare hematite nanoplate photoelectrode under backside illumination was about four times of that under frontside illumination in the entire bias range used, which suggested that slow electron transport was a limiting factor for its PEC performance. Upon Sn doping and Co‐Pi co‐catalyst addition, the photocurrent increased significantly owing to the enhancement of electron conductivity and oxidation kinetics. Electrochemical impedance spectroscopy (EIS) measurements were conducted to understand the surface properties of the nanoplate arrays. Since this strategy is simple, cost‐effective, and highly reproducible, it provides exciting opportunities for the large‐scale growth of porous 2D metal oxide photoelectrodes for a variety of photoelectrochemical and photocatalytic applications.     

Lithium Incorporation into Titanium Dioxide Films from a Propylene Carbonate Solution: A Photoelectrochemical Study

Photoelectrochemical behavior of thin-film TiO₂ electrodes produced by chemical and electrochemical oxidation of a titanium substrate is studied at potentials corresponding to the domain of active incorporation/extraction of lithium in an LiClO₄ solution in propylene carbonate (1.0 V <; E <; 2.5 V vs. Li/Li⁺) and the inert domain (2.6 V <; E <; 3.6 V). Spectral and current–voltage characteristics are obtained for the photocurrent of TiO₂- and Li _x TiO₂-electrodes, which show n-semiconductor properties, in particular, generate an anodic (hole) photocurrent under illumination. The disappearance of the anodic photocurrent and the onset of a small cathodic photocurrent correlate with the beginning of active incorporation of lithium into the source oxide. The photosensitivity of intercalate Li _x TiO₂ in the studied domain of spectrum is low and decreases with increasing lithium concentration. A photoeffect is discovered in the long-wave domain of spectrum beyond the limits of intrinsic absorption of a solid. The photocurrent is described by a characteristic exponential spectral curve.     

Modification of TiO2 Microporous Electrode with Chemical Bath Deposited Quantum-Size CdSe Particles

The transparent titanium dioxide (TiO₂) electrodes have been modified with cadmium selenite (CdSe) particles by means of chemical deposition method. The sensitization of TiO₂ electrode with CdSe particles extends both the optical absorption spectrum and photocurrent action spectrum into the visible region. Furthermore, compared with CdSe bulk materials, a blue shift up to 0.24 eV in both absorption spectrum and photocurrent action spectrum of CdSe/TiO₂ electrode was observed and explained in terms of quantum-size effect.     

PHOTOVOLTAGE AND PHOTOCURRENT AT TETRAPHENYLPORPHYRIN AND ZINC TETRAPHENYLPORPHYRIN ELECTRODES IN ACIDIC SOLUTIONS

Abstract— Photoelectrochemical properties of tetraphenylporphyrin and zinc tetraphenylporphyrin spread on a platinum plate were investigated in acidic solutions containing a variety of electroactive species. It was found that the photovoltage measured in 0.5 M sulfuric acid solutions depended strongly on the redox potential of the electroactive species; species having a redox potential of around 1.0 V vs NHE (such as oxygen and dichromate ions) generated the largest photovoltage. A similar dependency was also observed in the photocurrent, although a little ambiguous. These phenomena are discussed from a point of semiconductor electrochemistry. The magnitude of the photocurrent was found to be influenced by solution pH, suggesting that protonation of the porphyrin film surface plays an important role in the charge transfer process.     

TiO2‐modified Carbon Paste Electrode as a Sensor for the Assay of Weak Organic Acids/Bases and Complex Matrix Samples

The construction, general performance characteristics and analytical application of a titanium dioxide–modified carbon paste electrode sensitive to hydrogen ions, based on incorporation of titanium dioxide in a carbon paste matrix, is described. The proposed electrochemical sensor exhibits a linear response in the pH range from 2 to 10, at 25 °C, with a sub‐Nernstian slope. The value of a slope is in a direct correlation with the electrode composition – the optimum content of a titanium dioxide in carbon paste is 30 %. Titanium dioxide‐modified carbon paste electrode shows fast response time and reproducibility, confirmed by different compounds determination in both, individual and complex material, namely, in synthetic and real samples. Besides, the electrode shows high selectivity in the presence of the alkali and the alkaline earth ions as Na⁺, K⁺, Ca²⁺ or Mg²⁺. The standard deviation of the investigated acids (acetic, oxalic, 5‐sulfosalicylic, p‐toluensulfonic acid, and amino acid‐glycine) and bases (N,N′‐diphenylguanidine and collidine) is less than 1.3 %. The obtained data are compared with those obtained by using a conventional glass pH‐electrode under the same experimental conditions and indicate a high correlation between them.     

Photoelectrochemical oxidation behavior of methanol on highly ordered TiO2 nanotube array electrodes

The highly ordered titanium dioxide nanotube array (HOTDNA) electrodes were prepared in hydrofluoric acid solution by electrochemical anodic oxidation technique on a pure titanium sheet. The HOTDNA electrodes were characterized by X-ray diffraction, SEM microscopy, and UV–vis spectra. It has shown high density, well ordered and uniform titanium dioxide nanotube array film covered on these electrodes and the TiO₂ structure depending on the heating condition, the anatase phase of TiO₂ appeared when heating to 500 °C. The photoelectrochemical characteristics of methanol in 0.5 M Na₂SO₄ on the HOTDNA electrodes were investigated. The cyclic voltammetry, photocurrent-time and open-circuit photopotential response of methanol on the HOTDNA electrode were represented and significant photogenerated current was observed upon illumination in the UV regions with the light of 253.7 nm central wavelength. The effect of variables such as light intensity, applied potential, and methanol concentration on the photoelectrochemical response was investigated. It was found that the photocurrent was greatly influenced by these factors.     

Light-driven OR and XOR programmable chemical logic gates

Photoelectrodes made of nanocrystalline titanium dioxide modified with various pentacyanoferrates exhibit unique photoelectrochemical properties; photocurrent direction can be switched from anodic to cathodic and vice versa upon changes in photoelectrode potential and incident light wavelength (PhotoElectrochemical Photocurrent Switching, PEPS effect). At certain potentials, anodic photocurrent generated upon UV irradiation has the same intensity as the cathodic photocurrent generated upon visible irradiation. Under these conditions, simultaneous irradiation with UV and visible light results in compensation of anodic and cathodic photocurrents, and zero net photocurrent is observed. This process can be used for construction of unique light-driven chemical logic gates.     

Photoelectrochemical Scanning Droplet Cell Microscopy (PE‐SDCM)

Principles of localised photoelectrochemistry are summarised and an experimental approach is described that allows the performance of the most important photoelectrochemical experiments within a diameter of 100 μm. Various light sources, such as a continuum emitter with a monochromator, LEDs, and lasers are coupled into a multi‐mode fibre to illuminate a small spot that is wetted by the electrolyte from a capillary. Reference electrode, counter electrode, and optical fibre are installed in the capillary system. The performance of this system is demonstrated by photocurrent measurements on n‐doped Si and p‐doped Si as model substrates. A thickness‐graded aluminium thin film for partial shadowing on Si proves the applicability for material library investigations in combinatorial materials science. Further experiments demonstrate the possibility of electrical light chopping as well as impedance spectroscopy with subsequent Mott–Schottky analysis for the determination of charge‐carrier concentration and type, flat‐band potential, and inversion layer formation. Photoelectrochemical scanning droplet cell microscopy (PE‐SDCM) is an extremely versatile tool for the screening of water splitting photoelectrodes, the characterisation of photocatalysts, and high throughput characterisation of microgram amounts of new solar cell materials.     

An Investigation into the Optimum Thickness of Titanium Dioxide Thin Films Synthesized by Using Atmospheric Pressure Chemical Vapour Deposition for Use in Photocatalytic Water Oxidation

Twenty eight films of titanium dioxide of varying thickness were synthesised by using atmospheric pressure chemical vapour deposition (CVD) of titanium(IV) chloride and ethyl acetate onto glass and titanium substrates. Fixed reaction conditions at a substrate temperature of 660 °C were used for all depositions, with varying deposition times of 5–60 seconds used to control the thickness of the samples. A sacrificial electron acceptor system composed of alkaline sodium persulfate was used to determine the rate at which these films could photo‐oxidise water in the presence of 365 nm light. The results of this work showed that the optimum thickness for CVD films on titanium substrates for the purposes of water oxidation was ≈200 nm, and that a platinum coating on the reverse of such samples leads to a five‐fold increase in the observed rate of water oxidation.