Efficient Interfacial Charge Transfer Research Articles

Nanometric TiO 2 as NBBs for functional organic-inorganic hybrids with efficient interfacial charge transfer

Nanometric TiO 2 as NBBs for functional organic-inorganic hybrids with efficient interfacial charge transfer

Dual‐Phase Titanate/Anatase with Nitrogen Doping for Enhanced Degradation of Organic Dye under Visible Light

The need for environmental remediation processes on a large scale is becoming ever more urgent, especially in anticipation of the increasing demand (and potential shortage) of potable water supplies for a growing world population. Among the armory of advanced oxidation technologies (AOTs), photocatalytic (solar-light-driven) processes are particularly attractive, and photocatalysts have a well-demonstrated potential to mineralize harmful organic substances in air and water and even to act as regenerable adsorbents for toxic heavy metal ions, some of these being recovered as photodeposited metals. [1] Although anatase TiO2 remains the most popular photocatalyst due to high catalytic activity and chemical stability, there are some drawbacks associated with it. The activity is confined to UV-light stimulation, representing just a few percent of the solar-power spectrum. In this respect, much research has been done in modifying the bandgap of the material to extend the absorption into the visible-light region. [2] In addition, the adsorptive properties of TiO2 are not ideal either. [3] Since photoreactions take place at or near the catalyst surface, surface adsorption is critical for efficient interfacial charge transfer to and from the target molecules. In contrast, titanate materials have recently been identified as superior adsorbents for, for example, organic dyes and heavy metal ions. [4] The crystal structure consists of layers of TiO6 octahedra in edge connectivity with protons or alkali metal ions localized between the layers. [5] Various one-dimensional structures, including nano

Photocatalytic mineralisation of organic compounds: a comparison of flame-made TiO2 catalysts

A comparative photocatalytic analysis was carried out on TiO2 made in a Flame Spray Pyrolysis (FSP) process and flame-made Degussa P25. Both have similar crystallinity, phase composition, phase segregation and a non-porous surface. Hence comparison was made based on their difference in specific surface area, organic adsorption and the amount of OH• generated upon illumination. The photocatalytic activity tests were carried out using the following series of organic compounds: sucrose, glucose, fructose, maleic acid, glyoxylic acid, oxalic acid, isobutyric acid, phenol and methanol. FSP-made TiO2 outperformed P25 for saccharides mineralisation, while for phenol and methanol mineralisation P25 was better than FSP-made TiO2. Similar mineralisation rates were observed for both FSP-made and P25 TiO2 for the mineralisation of carboxylic acids. This shows that the relative performance of the photocatalysts depends on the type of organic compounds to be degraded. The high surface area and possibly a more efficient interfacial charge transfer of FSP-made TiO2 provided an efficient pathway for saccharides mineralisation. As for phenol and methanol, the mineralisation rates were higher when using P25 due to the greater amount of OH• radicals generated by this photocatalyst. The fast mineralisation rates of carboxylic acids made degradation of these organic compounds to be less affected by the TiO2 photocatalyst properties and conditions tested in this work.

Direct (one-step) synthesis of [formula omitted] and [formula omitted] nanoparticles for photocatalytic mineralisation of sucrose

TiO 2 and Pt / TiO 2 nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that resulted in mostly anatase (69–85 wt%) powders with controlled specific surface area and crystallite size. These particles resulted in shorter half-lives for sucrose photomineralisation, up to 50% lower than Degussa P25. Co-precipitation of Pt on TiO 2 during FSP increased the rutile content and slightly increased the specific surface area. Close control over Pt deposit size during this process was possible by varying the Pt concentration in the feed precursor. The dispersion of the Pt was high, 45–77% (at 4.0–0.1 atom% Pt) and corresponded to metal deposit size of 2.5–1.4 nm, respectively. An optimum photocatalytic activity was observed at 0.5 atom% Pt loading. At low Pt loading (0.1 atom% Pt), the activity was lower than that of FSP-made TiO 2 since the high photocurrent density of the Pt deposits increased the electron-hole recombination. The deposit size was also too small to establish sufficient electrical contact for efficient interfacial charge transfer between the photocatalysts and sucrose. Additional studies on the photocatalytic mineralisation of sucrose under oxygen enriched conditions reaffirmed the postulation that both FSP-made TiO 2 and improved Pt / TiO 2 photocatalysts favoured a reductive pathway which was different and faster than the pathway followed when using Degussa P25 TiO 2 . The intricate relationship between photocatalyst characteristics and its performance is highlighted.

Catalytic hydrogen evolution properties of nickel-doped tungsten disulfide

The dark and photocatalytic properties of Ni-doped WS{sub 2} supported on SiO{sub 2} were investigated. Adding Ni increases the dark catalytic hydrogen evolution activity of WS{sub 2}. With separate particles of CdS on SiO{sub 2} to photosensitize WS{sub 2}/SiO{sub 2}, the photocatalytic hydrogen evolution activity of Ni-doped WS{sub 2} maximizes at intermediate Ni loading levels. With fluorescein as a sensitizer, the addition of Ni lowers the activity of WS{sub 2}. The authors interpret the results in terms of a model in which Ni on the surface of WS{sub 2} plays an important role in controlling the surface geometric and electronic properties of the substrate and thereby the efficiency of interfacial energy and charge transfer.

Charge Transfer across Organic Photoconductor/Insulating Liquid Interfaces. Part II: Metal Free Phthalocyanine/Dodecane Containing Electron Donor/Acceptor Molecules

AbstractThe phenomenon of charge transfer through the metal free Phthalocyanine/Dodecane interface has been investigated using a transient technique. It is reported that the photoinjected charge, interfacial charge transfer efficiency and overall quantum yield are mainly controlled by the presence of foreign molecules in Dodecane. The effect of about 30 different molecules (electron donor/acceptor) on the relevant parameters is presented. The results are discussed qualitatively and an attempt has been made to correlate the results to the relevant molecular parameters.

Charge Transfer across Organic Photoconductor/Insulating Liquid Interface. Part I: Metal Free Phthalocyanine/Alkanes

AbstractIn order to understand the decisive step in the photoelectrophoretic image formation i. e. the charge exchange between inert and photosensitive particles, we report in part I of a series of papers the charge transfer across metal free x‐Phthalocyanine/Octane and Dodecane interfaces. The electron injection from the photoconductor into the organic liquid as a function of intensity and wavelength of light, and electric field has been studied using a transient measurement technique. It was found that oxygen is the most dominant species in alkanes which is responsible for the negative charge transfer from the photoconductor into the alkanes. The values of the interfacial charge transfer efficiency and quantum yield have been calculated from experimental data and were found to be in agreement with the previous results. The photoinjected charge follows the absorption spectrum of x‐Phthalocyanine qualitatively and was found to be dependent on the electric field and the intensity of light.