Microwave photocatalysis II: novel continuous‐flow microwave photocatalytic experimental set‐up with titania‐coated mercury electrodeless discharge lamps

BACKGROUND: A continuous‐flow microwave photocatalytic reactor was set up consisting of a glass tube equipped with microwave powered mercury electrodeless discharge lamps (EDLs) coated with thin films of nanoporous titanium(IV) oxide. The effect of operational parameters on photocatalytic degradation of aqueous mono‐chloroacetic acid (MCAA) by a TiO₂/UV/MW process was investigated. RESULTS: Studies were carried out at a relatively high concentration of MCAA (0.1 mol L^?1), and revealed that reaction temperature and light intensity of the EDLs depend inversely on the flow rate, but that the 366 nm line intensity of EDL is directly proportional to the reaction temperature. The photodegradation of MCAA was enhanced by heating and significantly enhanced by air bubbling of the reaction mixture in the glass reservoir at laboratory temperature. The photocatalytic efficiency increased with the number of titania‐coated EDLs inserted in the glass tube reactor. CONCLUSIONS: It was found that the operational parameters (i.e. flow rate, reaction temperature, number of titania‐coated EDLs, and air bubbling) had important effects on degradation efficiency. The photocatalytic degradation of MCAA on thin films of titanium(IV) oxide in the continuous‐flow microwave photoreactor can be enhanced in the TiO₂/UV/MW system. Copyright © 2009 Society of Chemical Industry     

Self-cleaning performance of sol–gel-derived TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> double-layer thin films

The self-cleaning properties of the TiO₂/SiO₂ double-layer films prepared by sol–gel method were investigated. Thin films were prepared by spin coating onto glass and then thermally treated at different temperatures, and characterized using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and UV–visible spectroscopy. The cross-sectional structure of the films was observed by FESEM. The surface roughness of the films was characterized by AFM. The root mean square surface roughness of the thin films was below 2 nm, which should enhance their optical transparency. The photo-induced hydrophilicity of the films was evaluated by water contact angle measurement in air. The photocatalytic activity of the films was studied by the photocatalytic degradation of methylene blue under UV light irradiations. The TiO₂/SiO₂ double-layer thin films are plausibly applicable to developing self-cleaning materials in various applications such as windows, solar panels, cement, and paints.     

ZnO薄膜光催化降解苯酚实验

采用溶胶-凝胶法分别在普通玻璃和石英玻璃基底上制备出性能优良的ZnO薄膜,并通过XRD、AFM和UV-V is吸收光谱对薄膜进行表征,进一步研究了不同波长紫外光照射、不同基底及不同退火温度对薄膜光催化性能的影响。实验结果表明,以石英为基底,退火温度为400℃的ZnO薄膜具有更好的光催化氧化能力,并且实现了催化剂的固载,便于回收再利用,催化效果显著。     

Poly(O‐methoxyaniline) thin films: Cyclic voltammetry study

Electrochemical polymerization of poly(O‐methoxyaniline) (POMA) thin films was carried out under cyclic voltammetric conditions. The cyclic voltammograms (CV) of the POMA films in the presence and absence of monomer in the aqueous solution of 1M H₂SO₄ were studied. The electrochemical degradation of the POMA films was investigated by cyclic voltammetry and UV‐visible spectroscopy. It was observed that the rate of degradation is strongly dependent on the applied potential. UV‐visible spectroscopy revealed no significant chemical modification or phase change from the degradation. The temperature dependence of the voltammetric response of the POMA films in the aqueous solution of 1M H₂SO₄ was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3009–3015, 1999     

Nanocrystalline ZnO Thin Film Synthesis Using Glycerol in Aqueous Polymeric Precursor Processing

Synthesis of high-quality ZnO thin films via simple and cost effective processing technique is a major challenge. In this work, the preparation of nanocrystalline ZnO thin films by a novel polymeric precursor processing using glycerol as chelating agent is presented. The process has advantages of being cost-effective and environment friendly. ZnO thin films were prepared by a single spin-coating deposition of aqueous polymeric precursor prepared with zinc nitrate [Zn(NO₃)₂] and glycerol as chelating agent. The thermal decomposition of polymeric precursors was studied by thermogravimetric analysis and Fourier transform infrared (FTIR) spectroscopy. Annealing of these films were performed over the range of 300°–600°C, and the effect of annealing on the degree of crystallization, surface morphology, crystallite size, and optical properties was investigated. X-ray diffraction analysis shows that the thin films are polycrystalline with wurtzite structure. The thin films are 80% dense, have crack free microstructure, and transparency of >85% in the visible region. These films exhibit absorption edge at 375 nm. On measuring at room temperature, the optical band gap energy of ZnO thin films, annealed at 450° and 600°C, was determined to be 3.295 and 3.267 eV. Room temperature photoluminescence spectra of these films show strong UV emission and a broad yellow-green emission in the range 525–600 nm. The intensity of UV emission peak increases with increase in annealing temperature that is attributed to an improvement in crystallinity.     

Fe~(3+)掺杂TiO_2薄膜材料的制备与光催化性能研究

以载玻片为基材,通过溶胶-凝胶技术制备Fe3+离子掺杂的TiO2薄膜。采用甲基橙作为目标降解物,研究Fe3+掺杂薄膜的光催化活性,采用X-射线衍射、扫描电镜和紫外-可见光吸收谱等技术对薄膜相关特征进行了表征。研究表明,当Fe/Ti物质量比为0.25%时,光催化活性最高。经500℃焙烧2h制备TiO2薄膜具有锐钛矿结构,TiO2粒子大小均匀,有孔隙结构。掺杂Fe3+使薄膜TiO2粒子减小,孔隙率增加,而粒子粒径分布不均匀增加,且吸收强度增加吸收边有一定的红移。     

微接触印刷术制备强发光有机荧光材料阵列

许多共轭的有机发光体在溶液中具有很高的发光性，但是当把它们制备成薄膜时发光就会变弱，但是利用微接触印刷术将有机荧光分子印刷到硅基片上形成有序微米阵列，得到的阵列的荧光强度非常强，是薄膜强度的几倍，同时研究了阵列尺寸与荧光强度之间的关系。     

Surface hydrophilization of two polyester films by atmospheric-pressure plasma and ultraviolet excimer light exposures

Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) films were treated with an atmospheric-pressure plasma (APP) jet and a 172-nm ultraviolet (UV) excimer light in air. The advancing and receding water contact angles on both films decreased after the treatments, especially after APP treatment. After the treatments, the hydrophobic recovery was observed and almost diminished within a week. The dispersive component of the surface free energy of the two polyester films did not change due to the APP and UV exposure, whereas the acid–base component drastically increased after the treatments. The X-ray photoelectron spectroscopy results showed that the polyester film surfaces were oxidized by the treatments. From the AFM images, the topographical change on the film surfaces due to the treatments was clearly observed. It was found that the APP treatment of the PET film prevented the deposition of particulate soils in air due to the decrease in the contact area between the film and the soil particle. Furthermore, the soil release in the aqueous solutions was promoted as a result of the hydrophilization of the polyester films due to the APP treatment.     

Effect of structural defects,surface roughness on sensing properties of Al doped ZnO thin films deposited by chemical spray pyrolysis technique

In this article, the gas sensing properties of Al-doped ZnO thin films have been reported where the nanocrystalline ZnO based thin films were well deposited by a simple and inexpensive ‘chemical spray pyrolysis (CSP)’ technique. Films have been found to be uniform, pinhole free and well adherent to the substrate. The morphology, structures, and surface roughness of the deposited Al-doped ZnO thin films were studied by various types of characterization techniques. In addition, the authors have observed that the sensor response and selectivity towards CO gas is improved by the Al doping at a low operating temperature. XRD results showed that the obtained films are nanocrystalline in nature with hexagonal wurtzite phase. Further, the annealed films were used for detection of CO in the air and maximum response was observed at 175 °C. The improvement in sensor response of Al-doped ZnO thin films to CO gas attributed to the defect chemistry, crystallite size and surface roughness.     

A comparative study of copper electrodeposition and photoelectrodeposition on boron doped diamond

Copper (Cu) electrodeposition and photoelectrodeposition on highly boron-doped diamond films (BDD) were investigated, at two different pH solutions. Cu particles were deposited in the potentiostat mode and under UV irradiation. The as-grown as well as the Cu modified BDD films were characterized by Raman Spectroscopy and Scanning Electron Microscopy. The copper photocatalytic deposition on BDD was discussed taking into account the influence of the photogenerated electrons for photoelectrodeposition process at both acid and neutral pH solutions. Under UV irradiation, the copper deposits presented higher density and uniformity all over the crystal faces when compared with those without UV irradiation. This behavior may be attributed to BDD semiconductor character due to its photogenerated electrons which enhanced the copper reduction reaction.     

A comparative study of gamma and ultraviolet radiation on gelatin film with 2-ethylhexyl acrylate

Gelatin films were prepared from gelatin granules in an aqueous medium by casting. Tensile strength (TS) and elongation at break (Eb%) of the films were found to be 29.2?MPa and 4.9%, respectively. Gelatin films were irradiated under gamma and UV radiation with different doses. Gamma treated gelatin films showed higher TS and Eb% over untreated ones, and even higher than that of the UV treated films. A series of gelatin solutions (formulations) was prepared by blending varying percentages (2–10% by wt) of 2-ethylhexyl acrylate (EHA) and then the films were prepared. Some EHA-blended gelatin films were irradiated under gamma radiation at various doses (50–500?krad) and other films were cured under UV radiation at different intensities (10–30 UV passes). EHA-blended?+?gamma treated gelatin films showed the highest mechanical properties than that of the EHA-blended?+?UV treated films. The degradation properties present in the soil were determined for the pure and treated films. It was observed that EHA-blended?+?gamma treated gelatin film degrades more than that of the EHA-blended?+?UV treated films.     

Effect of simulated low earth orbit radiation on polyimides (UV degradation study)

UV degradation of polyimide films in air and vacuum were studied using UV-visible, ESR, FTIR, and XPS spectroscopies. The UV-visible spectra of polyimide films showed a blue shift in the absorption compared to Kapton. This behavior was attributed to the presence of bulky groups and kinks along the polymer chains which disrupt the formation of a charge-transfer complex. The UV-visible spectra showed also that UV irradiation of polyimides result extensively in surface degradation, leaving the bulk of the polymer intact. ESR spectra of polyimides irradiated in vacuum revealed the formation of stable carbon-centered radicals which give a singlet ESR spectrum, while polyimides irradiated in air produced an asymmetric signal shifted to a lower magnetic field, with a higher g value and line width. This signal was attributed to oxygen-centered radicals of peroxy and/or alkoxy type. The rate of radical formation in air was twofold higher than for vacuum irradiation and reached a plateau after a short time. This suggests a continuous depletion of radicals on the surface via an ablative degradation process. FTIR, XPS, and weight loss studies supported this postulate. An XPS study of the surface indicated a substantial increase in the surface oxidation after irradiation in air. The sharp increase in the C? O binding energy peak relative to the C? C peak was believed to be associated with an aromatic ring-opening reaction. © 1995 John Wiley & Sons, Inc.     

液相沉积法制备光催化TiO2／SiO2复合薄膜及其表征

通过液相沉积法在较低的温度下制备了TiO2／SiO2复合薄膜，利用UV-Vis、XRD和SEM等表征手段对薄膜的透明性、物相和表面形貌进行了表征；并在紫外光照下，通过薄膜对罗丹明B水溶液的光催化降解实验，评价了沉积薄膜的光催化活性。实验结果表明，在室温下制备的液相沉积膜具有较好的光催化活性。     

Ionomeric poly(urethane semicarbazides) with azobenzene groups in the main chain – studies on photoswitching behaviour and mechanical properties

Poly(urethane semicarbazide) anionomers containing azobenzene chromophores in the main chain were prepared by chain extending the isocyanate terminated prepolymers with chromophoric dihydrazide. Variations were done with respect to the hard segment content and the nature of the diisocyanate and the effect of the variations on the thermal, mechanical properties and wettability were studied. The polymers in solution showed reversible photoisomerization behaviour evinced by UV/vis spectroscopy in which irradiation of polymer solutions with UV light was observed as a decrease in intensity of absorbance corresponding to trans-form and increase in the absorbance of cis-form. The back relaxation took place in the presence of visible light. Photoswitching or the wettability of the films induced by the reversible cis–trans isomerization of the azobenzene chromophores was experimentally shown from water contact angle measurements. Irradiation of the films with 365 nm light effected a decrease in the water contact angle. X-ray diffraction results indicated dense arrangement of crystallized hard segments in compositions containing higher hard segment content. Thermal stability up to 300 °C was exhibited by the polymers as shown by thermogravimetric analysis and the phase separated morphology was confirmed by dynamic mechanical analysis. Tensile strength measurements showed that the films with increasing hard segment content exhibited increasing tensile strength and modulus but decreasing values of elongation.     

Enhanced visible-light catalytic activity of Au nanoparticles loaded c-axis oriented Bi2VO5.5 porous thin films

Au nanoparticles loaded c-axis oriented Bi₂VO_5.5 (BVO) porous thin films were prepared by using a simple spin-coating technique. The porous structures were formed through the hydrolysis of bismuth nitrate, Bi(NO₃)₃, one of the raw materials for synthesizing the BVO precursor solutions. The optimal photocatalytic rate of the porous thin film is three times more than that of pure BVO thin film. The enhancement of photocatalytic activity can be attributed to the Schottky barrier in the intimate interface between Au nanoparticles and BVO grains and the increase of absorption of light caused by surface plasmon resonance effect of gold nanoparticles. The possible degradation mechanism of Au–BVO-Methylene Blue system has been discussed based on the energy band structure and further trapping experiments. This study provides a simple method to prepare bismuth-containing oxide porous thin films without any pore-forming reagents, and the results suggest that the Au nanoparticles loaded BVO thin film is a promising candidate material for water or air treatment.     

Surface characterization of Au–ZnO nanowire films

Au–ZnO nanowire films have been synthesized by annealing Zn foils coated with a thin layer of gold. An X-ray diffraction study found that the synthesized ZnO consists mainly of a hexagonal wurtzite structure along with a small amount of AuZn₃ phase. Scanning electron images showed that the ZnO wires extend to several microns in length. X-ray photoelectron spectroscopy studies confirmed the oxidation states of Au and Zn. An asymmetric O 1s peak indicates the presence of oxygen in an oxide layer and O–H groups on the films surfaces. Photoluminescence (PL) spectra showed different visible peaks for pre-annealed films, while for annealed films an UV peak appeared. In addition, the PL analysis showed that the overall intensity of photoluminescence decreased significantly after the films were annealed. Raman spectroscopy results also indicated that the crystalline quality of the films improved with annealing. This could be attributed to a decrease in oxygen vacancies and/or absorption of O–H groups on the surface of ZnO film. The highly hydrophilic surface with a water contact angle of ∼155° was obtained after annealing in air.     

ZnO薄膜的制备及光催化性能研究

采用溶胶 凝胶法在石英玻璃基底上制备出性能优良的ZnO薄膜。并通过XRD、AFM和UV VIS吸收光谱对薄膜的结构及形貌进行表征,研究了降解温度、苯酚溶液的初始浓度和空气流量对ZnO薄膜光催化性能的影响,ZnO薄膜光催化降解苯酚的最佳条件：降解温度25～45 ℃,空气流量40 mL·min^－1。起始浓度越低,降解效果越显著,同时实现了ZnO薄膜催化剂的固载,催化效果显著。同时研究了ZnO薄膜催化剂的固载。固载后的ZnO薄膜催化剂催化效果显著,且便于回收利用。     

Time-resolved photoluminescence study of low-energy emission mechanisms in oligofluorene and polyfluorene films

We report time-resolved photoluminescence (PL) spectroscopy study of solutions and thin films of pure penta-fluorenes with varying alkyl side-chain structures. While no low-energy green emissions were observed in solutions, spin-cast and vacuum dried initial films exhibited low-energy emission in time-delayed PL spectra, centered at 490 nm, whose intensity varied strongly with the side-chain structure. In comparison, the films annealed at 170 °C in air showed nearly identical low-energy emission in time-delayed PL spectra, centered at 520 nm, regardless of the side-chain structures. Therefore, our experimental results obtained for pure penta-fluorenes provided clear evidence that the mechanism of the green emission of oligofluorene and polyfluorene films includes both the intermolecular aggregate/excimer formation, emitted around 490 nm, and fluorenone-type chemical defects, emitted around 520 nm.     

Synthesis and optical and thermal properties of poly[methyl(2,9‐diphenyl‐ 7,8‐benzophenanthryl)silylene‐co‐1,4‐bis(methylphenylsilyl)phenylene]

Poly[methyl(2,9‐diphenyl‐7,8‐benzophenanthryl)silylene‐co‐1,4‐bis(methylphenylsilyl)phenylene] (PMBS‐co‐BSP) was synthesized by the condensation reaction of dichloromethyl(2,9‐diphenyl‐7,8‐benzophenanthryl)silane and 1,4‐bis(chloromethylphenylsilyl)benzene with sodium in toluene. Optical and thermal behavior of the polymer was investigated. Because of the introduction of substituted benzophenanthryl groups into the Si atoms of the polymer, the UV absorption wavelength of the PMBS‐co‐BSP red‐shifted significantly in the UV region, and a strong photoluminescence band was observed in the visible region other than the near‐UV photoluminescence typical of normal polysilane. The photochemical behavior was examined both in solution and in thin film by fluorescence and UV spectroscopy. Irradiation of the PMBS‐co‐BSP with a low‐pressure mercury lamp in solution resulted in homolytic scission of silicone–silicone bonds; the fluorescence emission intensities decreased gradually with increasing UV irradiation time and the maximum emission wavelength blue‐shifted significantly. Irradiation of thin solid films of the PMBS‐co‐BSP in air led to the formation of photoproducts containing Si? OH and Si? O? Si groups. The PMBS‐co‐BSP began to weigh less at about 300 °C and the weight loss of the polymer at 700 °C was calculated to be 75% of the initial weight in N₂. Copyright © 2006 Society of Chemical Industry     

Enhanced photocatalytic activity of highly transparent superhydrophilic doped TiO2 thin films for improving the self-cleaning property of solar panel covers

Undoped and metal doped nanocrystalline TiO₂ transparent thin films were synthesized on glass substrates via sol-gel/dip-coating method. TiO₂ thin film coatings can be applied to the surfaces of solar panels to impart self-cleaning properties to them. The structural and optical properties of few nanometer-thick films were characterized by XRD, SEM, CA, AFM, XPS, and UV–Vis spectrophotometry techniques. The stoichiometric TiO₂ films crystallized in anatase phase, with a particle size of ～100 nm, which were uniformly distributed on the surface. The prepared films with a roughness of ～1–5 nm, increased the hydrophilicity of the glass surface. Reducing the amount of Ti precursor (X) favored the improvement of film quality. To improve the photocatalytic activity of the TiO₂ thin film, it was doped with Ni, Cd, Mo, Bi and Sr metal ions. The effect of metal doping on the photocatalytic activity of the films was investigated using the degradation process of methylene blue (MB) dye as the model contaminant. Among the prepared coatings, the Sr–TiO₂ film showed the highest efficiency for MB degradation. It increased the dye degradation efficiency of the films under both UV and Vis lights. The kinetic investigations also showed that the degradation of MB by TiO₂ and M ? TiO₂ films obeyed the pseudo-first order kinetics.