Visible Light-induced Photocatalytic Activity Research Articles

Facile synthesis of nanostructured BiOI microspheres with high visible light-induced photocatalytic activity

Self-assembled three-dimensional BiOI microspheres composed of nanoplatelets were synthesized at low temperature using ethanol–water mixed solvent as reaction media and NH3·H2O as pH adjustment. The as-prepared BiOI was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, and nitrogen sorption. The possible formation mechanism for the architectures was discussed. It was found that mixed solvent and alkali play key roles in the formation of BiOI microspheres. The photocatalytic activity of the as-prepared sample was evaluated by degradation of phenol in aqueous solution under visible light irradiation. The BiOI microspheres show much higher photocatalytic activity than the random BiOI platelets. The total organic carbon measurement after the degradation process indicated that phenol was effectively mineralized over the BiOI microspheres. In addition, the BiOI microspheres are stable during the reaction and can be used repeatedly. The high catalytic performance of the BiOI microspheres comes from their narrow band gap, high surface area and high surface-to-volume ratio.

Efficient Photocatalytic Activity of PZT/TiO2 Heterojunction under Visible Light Irradiation

A Pb(Zr0.52Ti0.48)O3/TiO2 composite photocatalyst with nanostructured heterojunction was prepared by a simple sol−gel method. The catalyst was characterized by powder X-ray diffraction, nitrogen adsorption−desorption, transmission electron microscopy, UV−vis diffuse reflectance spectroscopy, electrochemistry technology, and spin-trapping electron paramagnetic resonance. The visible light-induced photocatalytic activities were evaluated by decomposing ethylene in gas phase. The result showed that the prepared composite catalyst exhibited efficient photocatalytic activities with high photochemical stability under visible light irradiation. Moreover, it also showed excellent photocatalytic performance under UV light or simulated sunlight irradiation. On the basis of the measurement of flatband potentials of the samples and the detection of active oxygen species (such as O2•− and OH•), a visible light-induced photocatalytic degradation mechanism of ethylene on PZT/TiO2 was proposed.

Photo-reductive decolorization of an azo dye by natural sphalerite: Case study of a new type of visible light-sensitized photocatalyst

Natural sphalerite, which represents a new class of mineral-based catalyst, was characterized and investigated for photo-reduction of an azo dye methyl orange (MO) under visible light. After 2 h of visible light irradiation, a complete decolorization of the MO solution was achieved. The degradation rate was related to the pH conditions. Spectra from FT-IR analysis indicate an initial adsorption of MO to sphalerite via its sulfonate group. Further reduction of the adsorbed MO by sphalerite under light irradiation led to the destruction of the azo structure, as indicated by the results from UV–vis, FT-IR and ESI-MS analyses. The visible light-induced photocatalytic reductive activity of natural sphalerite was mainly attributed to the distribution of foreign metal atoms in its crystal lattice, which reduces the intrinsic bandgap of sphalerite and also broadens its spectra responding range. In addition, the high conduction band potential of natural sphalerite may also enhance the photo-reduction of MO.

Visible light-induced photocatalytic activity of delafossite AgMO2 (M = Al, Ga, In) prepared via a hydrothermal method

Delafossite-structured oxides AgMO2 (M=Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO2>AgGaO2>AgAlO2. The relative high photocatalytic activity of AgInO2 can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO2 was proposed and its stability was also investigated.

Synthesis of C,N,S-tridoped mesoporous titania with enhanced visible light-induced photocatalytic activity

C,N,S-tridoped mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating method using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectra (DRS), N 2 adsorption–desorption measurements (BET) and Fourier transform infrared spectroscopy (FT-IR). The photocatalytic activity was evaluated by the photocatalytic degradation of Reactive Brilliant Red X-3B in aqueous solution. The results showed that the prepared titania was mesoporous structured and exhibited stronger absorption in the visible light region with red shift in the absorption edge. The prepared C,N,S-tridoped mesoporous titanias showed high photocatalytic activity under visible light irradiation. The high activity can be attributed to the synergetic effects of large surface area, red shift in absorption edge, strong absorption in visible light region and mixed phase structures of the C,N,S-tridoped mesoporous titania.

A simple route for the preparation of Eu, N-codoped TiO 2 nanoparticles with enhanced visible light-induced photocatalytic activity

A simple route has been developed for the synthesis of europium, nitrogen-codoped titania photocatalysts under mild conditions (i.e., low temperature, ⩽348 K, and ambient pressure). The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectra (DRS) analyses. The results showed that the codoped photocatalyst with a spheroidal shape exhibited a smaller size than the undoped titania. The transformation from anatase to rutile was suppressed by doping with Eu and N atoms. Furthermore, the absorbance spectra of Eu, N-codoped TiO 2 exhibited a significant red shift to the visible region. The photocatalytic activity of Eu, N-codoped TiO 2 was evaluated by photodegradation of the dye reactive brilliant red X-3B under visible light. This codoped sample exhibited enhanced photocatalytic activity compared to N-doped TiO 2, pure TiO 2, and P25.

Enhanced Photocatalytic Degradation of RhB Driven by Visible Light-Induced MMCT of Ti(IV)−O−Fe(II) Formed in Fe-Doped SrTiO3

It is important to reveal the origin of the visible light-induced photocatalytic activity of transition metal-doped SrTiO3 in which an isolated energy level is created by the dopant in the forbidden band gap. In this particle, the photocatalytic and photophysical properties of pure SrTiO3 and Fe-doped SrTiO3 were investigated comparatively. The Fe-doped SrTiO3 has been shown to have a much higher photocatalytic activity than pure SrTiO3 for the degradation of RhB under visible light irradiation. It was showed that doping Fe into SrTiO3 exhibited an absorption extending up to the visible region in the optical absorption spectrum and established the TiIV−O−FeII heterobimetallic linkages in the host. Difference diffuse reflectance spectra revealed that the absorption in the visible region is partly attributed to the metal-to-metal charge-transfer (MMCT) excitation of TiIV−O−FeII linkage formed in the Fe-doped SrTiO3. The visible light excitation of TiIV−O−FeII linkage was demonstrated to be the cause of the enhanced degradation of RhB. Furthermore, it was noted that the TiIV−O−FeII linkages only onto and nearest the surface of the Fe-doped SrTiO3 behavior as active sites for the visible light-induced photocatalysis.

N-doped TiO 2 coatings grown by atmospheric pressure MOCVD for visible light-induced photocatalytic activity

N-doped TiO 2 films were deposited by atmospheric pressure CVD from titanium tetra-isopropoxide (TTIP) and N 2H 4 as reactive gas in the temperature range 400–500 °C on various substrates. The films grown at 400 °C are amorphous and exhibit a compact structure and a smooth surface morphology. Increasing the deposition temperature first leads to the crystallization in the anatase structure (temperature range 410–450 °C) and then to the formation of rutile, so that an anatase-rutile mixture is observed in the temperature range 450–500 °C. Correlation between the structure, the morphology, optical properties, hydrophilicity and photocatalytic activity of the thin films both under UV and VIS light are presented and discussed in relation with deposition conditions.

The role of nitrogen doping on the development of visible light-induced photocatalytic activity in thin TiO 2 films grown on glass by chemical vapour deposition

A brief review of the findings of a range of studies aimed at describing the influence of the N-doping of TiO 2 thin films and particles on possible visible light-induced photoactivity is presented. By way of a new approach to the direct growth of N-doped TiO 2 thin films, the physical and photochemical effects of the addition of ammonia during atmospheric chemical vapour deposition (CVD) growth of TiO 2 are described. It is found that the addition of ammonia to the CVD reactive gas mixture causes a dramatic change in film morphology and a reduction in growth rates. In addition, it is found that although we have clear evidence for the incorporation of β-substitutional N atoms within the growing film, there is no evidence of any appreciable photocatalytic activity of the doped TiO 2 films when irradiated with visible light. In fact the degradation in film morphology results in a decrease in conventional UV-induced photoactivity as compared to that for an undoped film. These findings are discussed in terms of the findings of other studies of N-doped TiO 2 films that have been reported.

Synthesis and photochemical properties of HTaWO6/ (Pt, TiO2) nanocomposite under visible light irradiation

A new layered nanocomposite, HTaWO6/(Pt, TiO2) was synthesized using n-type semi-conductor HTaWO6 as a host material. HTaWO6 and HTaWO6/TiO2were white, while both HTaWO6/Pt and HTaWO6/(Pt, TiO2) were yellow. The yellow color might be attributed to H1-xTaWO6-x/2 formed by the photo-induced phase transformation promoted by Pt. Although HTaWO6/Pt showed absorption in visible light region (λ > 400 nm), the hydrogen evolution activity was negligibly small. On the other hand HTaWO6/(Pt, TiO2) showed excellent photocatalytic activities even under visible light irradiation. The sample containing rutile type titania such as TiO2(P-25) also showed hydrogen evolution activity, but the activity was smaller than that of HTaWO6/(Pt, TiO2). These results suggested that rutile type titania, which can be excited by visible light of wavelength less than 413 nm, played an important role in the visible light-induced photocatalytic activity. The improvement of the hydrogen evolution activity of rutile type titania by intercalating into HTaWO6/Pt may be due to the depression of the recombination of photoinduced electrons and holes by the heterogeneous electron transfer from rutile type TiO2 to HTaWO6/Pt.