1,722,105 research outputs found
Pure and modified TiO2 photocatalysts and their environmental applications
No full textSemiconductor photocatalysis is a process that harnesses light energy in chemical conversions. In particular, its applications to environmental remediation have been intensively investigated. The characteristics of TiO2, the most popular photocatalyst, is briefly described and selected studies on the degradation/conversion of various recalcitrant pollutants using pure and modified TiO2 photocatalysts, which were carried out in this group, are reviewed. Photocatalytic reactions are multi-phasic and take place at interfaces of not only water/TiO2 and air/TiO2 but also solid/TiO2. Examples of photocatalytic reactions of various organic and inorganic substrates that are converted through the photocatalytic oxidation or reduction are introduced. TiO2 has been modified in various ways to improve its photocatalytic activity. Surface modifications of TiO2 that include surface platinization, surface fluorination, and surface charge alteration are discussed and their applications to pollutants degradation are also described in detail.X11141sciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Singlet-Oxygen Generation in Alkaline Periodate Solution
No full textA nonphotochemical generation of singlet oxygen COD Using potassium periodate (KIO4) in alkaline condition (pH > 8) was investigated for selective oxidation of aqueous organic pollutants. The generation of O-1(2) was initiated by the spontaneous reaction between IO4- and hydroxyl ions, along with a stoichiometric conversion of IO4- to iodate (IO3-). The reactivity of in-situ-generated O-1(2) was monitored by using furfuryl alcohol (FFA) as a model substrate. The formation of O-1(2) in the KIO4/KOH system was experimentally confirmed using electron spin resonance (ESR) measurements in corroboration with quenching studies using azide as a selective O-1(2) scavenger. The reaction in the KIO4/KOH solution in both oxic and anoxic conditions initiated the generation of superoxide ion as a precursor of the singlet oxygen (confirmed by using superoxide scavengers), and the presence of molecular oxygen was not required as a precursor of O-1(2). Although hydrogen peroxide had no direct influence on the FFA oxidation process, the presence of natural organic matter, such as humic and fulvic acids, enhanced the oxidation efficiency. Using the oxidation of simple organic diols as model compounds, the enhanced O-1(2) formation is attributed to perio date-mediated oxidation of vicinal hydroxyl groups present in humic and fulvic constituent moieties. The efficient and simple generation of O-1(2) using the KIO4/KOH system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral and near-alkaline conditions.112113sciescopu
TiO2 Nanotubes with Open Channels as Deactivation-Resistant Photocatalyst for the Degradation of Volatile Organic Compounds
No full textWe synthesized ordered TiO2 nanotubes (TNT) and compared their photocatalytic activity with that of TiO2 nanoparticles (TNP) film during the repeated cycles of photocatalytic degradation of gaseous toluene and acetaldehyde to test the durability of TNT as an air-purifying photocatalyst. The photocatalytic activity of TNT showed only moderate reduction after the five cycles of toluene degradation, whereas TNP underwent rapid deactivation as the photocatalysis cycles were repeated. Dynamic SIMS analysis showed that carbonaceous deposits were formed on the surface of TNP during the photocatalytic degradation of toluene, which implies that the photocatalyst deactivation should be ascribed to the accumulation of recalcitrant degradation intermediates (carbonaceous residues). In more oxidizing atmosphere (100% O-2 under which less carbonaceous residues should form), the photocatalytic activity of TNP still decreased with repeating cycles of toluene degradation, whereas TNT showed no sign of deactivation. Because TNT has a highly ordered open channel structure, O-2 molecules can be more easily supplied to the active sites with less mass transfer limitation, which subsequently hinders the accumulation of carbonaceous residues on TNT surface. Contrary to the case of toluene degradation, both TNT and TNP did not exhibit any significant deactivation during the photocatalytic degradation of acetaldehyde, because the generation of recalcitrant intermediates from acetaldehyde degradation is insignificant. The structural characteristics of TNT is highly advantageous in preventing the catalyst deactivation during the photocatalytic degradation of aromatic compounds.116545sciescopu
Effect of the anchoring group (carboxylate vs phosphonate) in Ru-complex-sensitized TiO2 on hydrogen production under visible light
No full textWe synthesized six Ru-bipyridyl complexes having di-, tetra-, and hexacarboxylate (C2, C4, and C6) and di-, tetra-, and hexaphosphonate (P2, P4, and P6) as the anchoring group, prepared six different sensitized TiO2 samples by using them, and then systematically tested their visible light reactivity for hydrogen production in aqueous suspension (with EDTA as an electron donor) under lambda > 420 nm illumination. The properties and efficiencies of C- and P-complexes as a sensitizer depended on the number and kind of anchoring groups in very different ways. The adsorption of P-complexes on TiO2 is strong enough not to be hampered by the presence of competing adsorbates (EDTA), whereas that of C-complexes is significantly inhibited. As a result, P-TiO2 exhibited much higher activity for the hydrogen production than C-TiO2, although the visible light absorbing capabilities are comparable among C- and P-complexes. Among the six sensitizers, P2 was the most active one for the H-2 production. The hydrogen production activities of C-TiO2 and P-TiO2 depended on the concentration of sensitizers and electron donors in different ways as well. How the sensitizing activity for hydrogen production is influenced by the anchoring group and the experimental conditions was investigated and discussed in detail. It is also notable that the effects of the anchoring group on the sensitized production of hydrogen were drastically different from those on the dye-sensitized solar cell we recently reported for the same set of six sensitizers.X11129125sciescopu
Photocatalytic oxidation of arsenite in TiO2 suspension: Kinetics and mechanisms
No full textArsenite [As(III)] and arsenate [As(V)] are highly toxic aquatic contaminants Since arsenite is more mobile in natural waters and less efficiently removed in adsorption/coagulation processes than arsenate the oxidation of arsenite to arsenate is desirable in water treatment We performed the photocatalytic oxidation of arsenite in aqueous TiO2 suspension and investigated the effects of pH dissolved oxygen humic acid (HA) and ferric ions on the kinetics and mechanisms of arsenite oxidation Arsenite oxidation in UV illuminated TiO2 suspension was highly efficient in the presence of dissolved oxygen Homogeneous photooxidation of arsenite in the absence of TiO2 was negligibly slow Since the addition of excess tert butyl alcohol (OH radical scavenger) did not reduce the rate of arsenite oxidation the OH radicals should not be responsible for As(III) oxidation The addition of HA increased both arsenite oxidation and H2O2 production at pH 3 under illumination which could be ascribed to the enhanced superoxide generation through sensitization We propose that the superoxide is the main oxidant of arsenite in the TiO2/UV process The addition of ferric ions also significantly enhanced the arsenite photooxidation In this case the addition of tert butyl alcohol reduced the arsenite oxidation rate which implied that the OH radical mediated oxidation path was operative in the presence of ferric ions Since both Fe3+ and HA that were often found with the arsenic in groundwater were beneficial to the photocatalytic oxidation of arsenite the TiO2/UV process could be a viable pretreatment method This can be as simple as exposing the arsenic polluted water in a TiO2 coated trough to sunlight.X11284276sciescopu
Charge-transfer surface complex of EDTA-TiO2 and its effect on photocatalysis under visible light
No full textWe investigated the formation of surface complex between TiO2 and common electron donors (methanol. formic acid, acetic acid, triethanolamine and EDTA) that can absorb visible light through ligand-to-metal charge transfer (LMCT) mechanism. The visible light activity of TiO2-EDTA complex was outstanding among all tested TiO2-substrate complexes. The complexation of EDTA on TiO2 induced a visible light absorption up to 550 nm and exhibited a marked visible light activity for both the reductive conversion of Cr(VI) and the production of H-2. The optimal concentration of EDTA was 100 mu M for the reduction of Cr(VI) but much higher (10 mM) for the production of H-2. The EDTA-adsorbed TiO2 electrode also generated a significant level of photocurrent under visible light irradiation. The LMCT-excited electrons (in TiO2 conduction band) are subsequently transferred to electron acceptors such as Cr(VI) and protons. The degradation of EDTA on TiO2 under visible light was significant only in the presence of Cr(VI) that should scavenge electrons with inhibiting the recombination. The surface CT-complex formation between TiO2 and EDTA was significantly inhibited when the surface of TiO2 was fluorinated. The isoelectric point of TiO2 particles suspended in water was gradually shifted to lower pH values with increasing the concentration of EDTA, which supported the formation of surface complex between TiO2 and EDTA anions. The FT-IR spectra of TiO2-EDTA complex showed a band centered at 1409 cm(-1), which is ascribed to the carboxylate group complexed with TiO2 surface. The complex IR band was diminished upon fluorinating the surface of TiO2. The fact that common electron donors like EDTA can form CT-complexes on the surface of TiO2 and contribute to the visible light activity should be recognized in assessing and understanding the overall photocatalytic activity. (C) 2010 Elsevier B.V. All rights reserved.X119387sciescopu
Nitric acid uptake and decomposition on black carbon (soot) surfaces: Its implications for the upper troposphere and lower stratosphere
No full textThe uptake and decomposition of HNO3 on black carbon (soot) surfaces were investigated in order to evaluate the proposal that HNO3 decomposition on aircraft-generated soot aerosols may alter the NOx/NOy partitioning in the upper troposphere and lower stratosphere. The experimental measurements were performed by using a fast flow-tube reactor coupled to a quadrupole mass spectrometer. Black carbon samples used as surrogate material for aircraft soot in this study included Degussa FW2 tan amorphous carbon black comprising medium oxides), graphite, hexane soot, and kerosene soot. The measurements of uptake were performed by varying P(HNO3) in the range of 5 x 10(-7) to 5 x 10(-4) Ton. at 220 and 295 K. The results are summarized as follows. Significant HNO3 decomposition was observed on FW2 at 295 K with P(HNO3) greater than or equal to 1 x 10(-4) Ton, while it did not occur at 220 K. Similar HNO3 decomposition behavior on graphite was also observed under the condition of P(HNO3) greater than or equal to 10(-4) Ton and T = 295 K, although the extent of the decomposition was much smaller than that on FW2. The decomposition of HNO3 on soot produced NO, NO2, H2O, oxidized soot surface, and some unidentified volatile products. To explain the observed decomposition behavior at higher partial pressures of HNO3, a bimolecular HNO3 decomposition mechanism on soot surfaces was proposed. However, HNO3 immediately decomposed on an FW2 surface at 503 K even at lower partial pressure (similar to 10(-6) Ton). On flame-deposited hexane and kerosene soot film, no HNO3 decomposition was observed up to P(HNO3) = 5 x 10-4 Ton. Moreover, the uptake and desorption of HNO3 were reversible at 295 K and irreversible at 230 K. Adsorbed HNO3 molecules on hexane soot film were saturated to a monolayer coverage at P(HNO3) similar to 2 x 10(-4) Torr according to Langmuir adsorption isotherm; further increase in P(HNO3) resulted in multilayer adsorption. Under the experimental conditions (P(HNO3) = 5 x 10(-7) Ton and T = 220 K), the uptake of HNO3 was found to involve purely physical adsorption without showing any sign of irreversible decomposition over all black carbon samples. Subsequent heating of the sample following the uptake at 220 K desorbed most of the adsorbed HNO3 molecules. Physical adsorption of HNO3 was found to take place on the surface of concentrated H2SO4-coated soot at 230 K, but decomposition of HNO3 took place at 296 K. Finally, the present results suggest that the HNO3 decomposition on soot aerosols through a direct gas-solid interaction, which was proposed as a possible NOy-reactivation mechanism in the atmospheric modeling of upper troposphere and lower stratosphere, should be dismissed.X1152sciescopu
TiO(2) modified with both phosphate and platinum and its photocatalytic activities
No full textA new hybrid modification method of TiO2 photocatalyst was developed and investigated. TiO2 modified with both phosphates and platinum nanoparticles on its surface (P-TiO2/Pt) was prepared by a simple two-step method using phosphoric acid (as phosphate source) and chloroplatinic acid (as platinum source). The coexistence of phosphate and platinum on the surface of TiO2 was confirmed by X-ray photoelectron spectroscopy and transmission electron micrography. P-TiO2/Pt showed a significantly higher photocatalytic activity than any of bare TiO2, P-TiO2, and Pt/TiO2 for the degradation of phenolic compounds (4-chlorophenol; bisphenol A; 2,4-dichlorophenoxyacetic acid (2,4-D)). In particular, P-TiO2/Pt minimized the production of toxic intermediate (2,4-dichlorophenol) during the photocatalytic degradation of 2,4-D. In accordance with the higher photocatalytic activities of P-TiO2/Pt, both the production of OH radicals and the photocurrent collection in the suspension were markedly enhanced upon the simultaneous platinization and phosphation of TiO2. The two surface species acted synergically to enhance the photocatalytic activity. The surface phosphation that should replace the surface hydroxyl groups on TiO2 favors the formation of unbound OH radicals instead of surface-bound OH radicals while the surface platinization accelerates the electron transfer with retarding the charge recombination. The phosphation of TiO2 was stable over a wide range of pH due to the strong chemical bonding of phosphate on TiO2 whereas the surface fluorination of TiO2, which can be similarly compared with the phosphation in its photocatalytic effect, is active only at acidic pH. P-TiO2/Pt showed a higher photocatalytic activity than Pt/TiO2 for the degradation of 2,4-D even at pH 11, under which condition the effect of surface fluorination of Pt/TiO2 completely disappeared. (C) 2011 Elsevier B.V. All rights reserved.X114747sciescopu
- …
