Non-titania photocatalyst BiVO4 was supported on SiO2-coated Fe3O4 particles in order to solve the problems of photocatalyst recovery and reuse. The prepared photocatalyst BiVO4/SiO2/Fe3O4 (BiVO4/SFN) was proved to be nano-sized (less than 10 nm) by TEM characterization. The superparamagnetism of BiVO4/SFN was confirmed by a vibrating sample magnetometer (VSM). The photocatalyst can be easily separated experimentally by an external magnetic field in lab. XRD analysis proved the dominant existence of BiVO4 crystals. The magnetic photocatalyst BiVO4/SFN showed high photoactivity for methylene blue (MB) decolorization under visible light above 400 nm (72.1%) and a lower activity (21.8%) was observed under line spectra at 420 nm. MB was almost not degraded by P25 titania at 420 nm. The reusability experiment under visible light irradiation also demonstrated the potential application of magnetic photocatalyst in water and wastewater treatment.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen doping was recently shown to extend the absorptivity of TiO2 photocatalysts into the visible. We find that N-doped TiO2 materials fail, however, to catalyze the oxidation of HCOO- into CO2•-, or of NH3OH+ into NO3-, under visible illumination. By N-doping anatase at ambient or high temperature according to the literature we obtained yellow powders A and H, respectively, that absorb up to 520 nm. Aqueous H suspensions (pH 6, 1 atm O2) photocatalyze the oxidation of HCOO- into CO2•- radicals at λ 330 nm, but the quantum yield of CO2•- formation at λ > 400 nm remains below 2 × 10-5 and is probably zero. A is similarly inert toward HCOO- in the visible region and, moreover, unstable in the UV range. Thus, the holes generated on N-doped TiO2 by visible photons are unable to oxidize HCOO- either by direct means or via intermediate species produced in the oxidation of water or the catalyst. Reports of the bleaching of methylene blue (MB) on N-doped TiO2, which may proceed by direct oxidative or reductive photocatalytic pathways and also by indirect photocatalysis (i.e., induced by light absorbed by MB rather than by the catalyst) even under aerobic conditions are, therefore, rather uninformative about the title issue.
The Journal of Physical Chemistry B 11/2004; 108(45):17269-17273. DOI:10.1021/jp0467090 · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A kind of loaded photocatalyst of TiO2/γ-Fe2O3 (TF) that can photodegrade organic pollutants in the dispersion system effectively and can be recycled easily by a magnetic field is reported in this paper. The structural features of TF catalyst sintered at different temperatures (in the range 200–900 °C) have been investigated by X-ray diffraction, atomic force microscope and transmission electron microscope studies. Phase composition and crystallinity change with the increasing sintering temperature of the specimens. The TF photocatalyst is composed of two parts: (1) TiO2 shell used for photocatalysis; (2) γ-Fe2O3 core for separation by the magnetic field. Due to the strong light absorption by γ-Fe2O3, when the amount of the loaded TiO2 content was under 30% in the catalyst, the photocatalytic activity of TF was significantly lower than that of the pure TiO2. On the other hand, the photocatalytic activity of TF reduced to a large extent at high sintering temperature (900 °C) owing to the presence of inactive (Fe2TiO5) pseudobrokite phase. The sample sintered at 500 °C showed the highest activity for the degradation of aqueous solution of acridine dye.
[Show abstract][Hide abstract] ABSTRACT: Magnetic iron oxide–titania photocatalysts (Fe3O4–TiO2) were prepared using a coating technique in which the photoactive titanium dioxide was deposited onto the surface of a magnetic iron oxide core. These particles had a core–shell structure. The prepared particles were heat treated at high temperature in order to transform the amorphous titanium dioxide into a photoactive crystalline phase. The heat treatment temperature and duration were varied, and the correlation between the heat treatment and the observed photoactivities was investigated. An increase in the applied heat treatment, either by increasing the temperature or increasing the heat treatment duration, led to a decrease in the activities of the catalyst particles. A decrease in surface area due to sintering, along with the diffusion of Fe ions into the titanium dioxide coating are seen as contributing factors to the decline in photoactivity which accompanied an increase in the heat treatment. Differential scanning calorimetry analysis (DSC) results confirmed that the presence of the iron oxide core did not have an effect on the phase transformation of titania under the experimental conditions investigated. In this study we also present surface charge measurements which show that the surface of the particles became more positive as the heat treatment was increased. This is an indication of changing surface properties as heat treatment is applied. For single-phase TiO2 powders, this is postulated to be due to a decrease in the surface hydroxyl (OH) groups and/or residual organics (OR) groups. For the Fe3O4–TiO2 powders, in addition to the loss of OH and OR groups, the diffusion of the Fe into the titania shell is postulated to also play a role in the changing surface properties with applied heat treatment. Experiments aimed at reducing the duration of the heat treatment revealed that a heat treatment duration of 20 min at 450 °C was sufficient to transform amorphous titanium dioxide into a photoactive crystalline phase. This does not only minimise loss of surface hydroxyl groups but it also has the potential to limit the oxidation of the magnetic core, which occurs due to the porosity of the coating. This has practical implications in terms of separating the magnetic particles from the treated waste waters under the application of an external magnetic field. It also presents an opportunity to produce photoactive composite particles while limiting the interactions between the core and the shell during the heat treatment.
Materials Science and Engineering B 06/2002; 94(1-94):71-81. DOI:10.1016/S0921-5107(02)00085-5 · 2.17 Impact Factor
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