Porous photocatalytically active ZnO films obtained from ethylcellulose modified solutions by spray pyrolysis

Nanocrystalline porous ZnO films are deposited onto alumina foil substrates by polymer-modified spray pyrolysis of zinc nitrate and zinc acetate solutions. The dependence of the concentration of added ethylcellulose and the type of zinc precursor on both the photocatalytic properties and films morphologies is investigated. It is established that the addition of ethylcellulose as a modifier in the spray solution leads to the formation of a porous structure with crystallites sizes about 15 nm, when zinc acetate is used as precursor. These films show better photocatalytic activity for degradation of Malachite Green (MG) dye than the films obtained from zinc nitrate modified solution. The zinc nitrate films exhibit weaker activity for degradation of MG regardless of their smaller crystallite size (8–12 nm). This can be explained with their lower porosity than that of polymer-modified zinc acetate films. It is established that 450 °C is the limit temperature of treatment for the preparation of ZnO films with good photocatalytic activities. This photocatalytic activity in films shows a drop in the comparison to the films treated at lower temperature, due to decreasing of the pore number and deterioration of the surface morphology.     

Rapid electroplating of photocatalytically highly active TiO2-Zn nanocomposite films on steel

Nanocomposite films consisting of TiO₂ and Zn with thickness of 10–15 m (TiO₂-Zn) have been electrodeposited on steel plates by rapid plating from a ZnSO₄-based bath (I _d > 10 A dm^–2). Upon addition of NH₄NO₃ to the bath (<0.3 g L^–1), the uptake of TiO₂ in the film significantly increased. Glow discharge optical emission spectrometry clarified that TiO₂ particles were incorporated throughout the film and the loaded amount increased near the surface. The first-order rate constant (k/h^–1) for gas-phase CH₃CHO oxidation was employed as an indicator of the photocatalytic activity. The k value for the TiO₂-Zn film prepared at I _d = 12 A dm^–2 (0.20 h^–1) was comparable to that for the sample from a ZnCl₂-based bath at I _d = 4 A dm^–2 (0.27 h^–1). X-ray diffraction measurements indicated that a TiO₂-ZnO nanocomposite layer was generated on the surface by the heat treatment in air at 673 K for 6 h. Consequently, the photocatalytic activity was further improved (k = 0.29 h^–1); this effect was explained in terms of the synergy of TiO₂ and ZnO in photocatalysis.     

Synthesis and characterization of highly dispersed TiO2 nanocrystal colloids by microwave-assisted hydrothermal method

Anatase TiO₂ nanocrystal colloids with high dispersion and photocatalytic activity were rapidly synthesized from peroxo-titanium-acid precursor by microwave-assisted hydrothermal method within 30?min at low temperature (120–180?°C). The transmission electron microscopy results indicate that the as-prepared TiO₂ have a narrow particle size distribution (25–29?nm) and high dispersion. The crystal structure of all these products are pure anatase phase (XRD, Raman), and they show good crystallinity and large surface area (N₂ adsorption–desorption measurements BET). The results of the UV–Visible absorbance and Fourier transform infrared spectra indicate that the surface peroxo group Ti(O₂) still remains in TiO₂ nanoparticles prepared by microwave-assisted hydrothermal method at 120?°C, and this surface peroxo group can be decomposed effectively by drying at 140?°C. The photocatalytic activity of the as-prepared TiO₂ were evaluated by the degradation of reactive brilliant red X-3B, it is found that the as-prepared TiO₂ exhibited good photocatalytic performance. Moreover, the existence of surface peroxo group greatly suppressed the photocatalytic activity of the TiO₂ nanoparticles.     

Microemulsion-mediated hydrothermal synthesis of photocatalytic TiO2 powders

A reverse microemulsion-mediated hydrothermal route has been employed to synthesize photocatalytic titanium dioxide (TiO2) powders. Nano-crystalline monophasic anatase TiO2 powders were successfully prepared when the microemulsion-derived precursors were hydrothermally treated. The advantage of using this microemulsion mediated hydrothermal route is the significant reduction in reaction time and temperatures as compared with the conventional hydrothermal process. The oil/water emulsion ratio significantly affected the particle sizes of the obtained TiO2 powders. The specific surface area of TiO2 powders was increased with the oil/water ratio, thereby leading to enhanced photocatalytic activity of TiO2 powders. As the hydrothermal temperature was elevated, the morphology of the TiO2 particles changed from a rod-like shape into a polyhedral shape. The variation in microstructures decreased the specific surface area of the TiO2 powders and lowered the photocatalytic activity.     

水热法制备稀土掺杂TiO2薄膜及光催化降解性能研究

采用水热法,以载玻片为基片制备了稀土掺杂Ti O2薄膜。以紫外光区吸光度值为指标,确定最佳制备条件为:90℃保温2h,Ti(SO4)2溶液和尿素溶液摩尔比为10∶1,稀土掺杂量为1 mL0.5 mol/L稀土盐溶液,掺杂稀土镧Ti O2薄膜有较好的光吸收性能。利用X-射线粉末衍射法(XRD)、扫描电子显微镜(SEM)及电子能谱法(EDS)对Ti O2薄膜的结构及表面特性进行表征,结果表明制备的稀土掺杂Ti O2薄膜为锐钛矿型。以紫外灯为光源,降解率为指标,罗丹明B溶液降解为模型反应,考察稀土掺杂Ti O2薄膜光催化性能,结果表明,稀土掺杂Ti O2薄膜具有较高光催化活性且明显大于纯Ti O薄膜,该薄膜对罗丹明B的光催化降解率达87%以上。     

The influence of heat treatment parameters on pyrolysed TFA-derived YBCO films deposited by inkjet printing

An anhydrous TFA-derived YBa₂Cu₃O_7?δ precursor solution was deposited on all chemical solution deposition fully buffered metallic tape by means of electromagnetic drop-on-demand inkjet printing and pyrolysed in a flowing wet O₂ atmosphere. The influence of the annealing temperature and time, the gas flow rate and water vapour partial pressure on phase formation, and the morphology and superconducting performance of the resulting film, were investigated. It was found by scanning Hall probe magnetometry that reproducible superconducting films with a critical current density of 0.18 MA/cm² can be produced after annealing for 2 h at 728 °C, without metal substrate oxidation, in a flowing 200 ppm O₂ in Ar atmosphere with 31 mbar water vapour partial pressure.     

Solar photocatalytically active,engineered silver nanoparticle synthesis using aqueous extract of mesocarp of Cocos nucifera (Red Spicata Dwarf)

ABSTRACT

Silver nanoparticles synthesised using aqueous extract of Cocos nucifera (CN) mesocarp were evaluated for their photocatalytic activity under solar irradiation. The silver nanoparticles were synthesised by a green method of harnessing bioactive phytocomponents from the mesocarp of Cocos nucifera. Large-scale application of this process necessitates the manoeuvering of the process parameters for increasing the conversion of silver ions to nanoparticles. Process parameters influencing the morphological characteristics of silver nanoparticles such as precursor salt concentration and pH of the synthesis mixture were studied. The crystalline nanoparticles were characterised using UV-vis spectroscopy, XRD, FTIR, SEM and EDX analysis. CN extract and 5 mM silver nitrate solution at a ratio of 1:4 (v/v) in the synthesis mixture was found to be the optimum. Alkaline initial pH of the synthesis mixture was found to favour the synthesis of smaller sized monodispersed silver nanoparticles. Solar energy was harnessed for the photocatalytic degradation of Malachite green dye using silver nanoparticles obtained through the green synthesis method. Overall process aims at utilisation of naturally available resource for the synthesis of silver nanoparticles as well as the degradation of dyes using these nanoparticles, making it useful in the treatment of wastewater.     

Deposition at low substrate temperatures of high-quality TiO2 films by radical beam-assisted evaporation

We deposited high-quality TiO(2) films by an oxygen-radical beam-assisted evaporation (RBE) method at a lower substrate temperature (Ts) than that for a TiO(2) film deposited by conventional thermal evaporation (TE) with neutral-oxygen gas. The films were then evaluated in terms of refractive index, shift of wavelength of a peak in the reflection curve, and absorption coefficient. The TiO(2) films deposited by RBE at Ts < 473 K showed higher refractive indices, were more compact, and had lower absorption coefficients than the film deposited by TE at Ts = 473 K.     

Photocatalytic properties of nano-structured TiO2-carbon films obtained by means of electrophoretic deposition

Recent studies have shown that the light-absorption and photocatalytic efficiencies of TiO2 can be improved by coupling TiO2 nano-particles with nonmetallic dopants, such as carbon. In this paper, we describe the electrophoretic preparation of a novel TiO2-carbon nano-composite photocatalyst on a glass indium thin oxide (ITO) substrate. The objective is to take better advantage of the (e-/h+) pair generated by photoexcitation of semiconducting TiO2 particles. The transfer of electrons (e-) into adjacent carbon nano-particles promotes reduction of oxygen to produce hydrogen peroxide (H2O2) which, in the presence of iron ions, can subsequently form hydroxyl radicals (*OH) via the Fenton reaction. At the same time, *OH is formed from water by the (h+) holes in the TiO2. Thus, the *OH oxidant is produced by two routes. The efficiency of this photolytic-Fenton process was tested with a model organic compound, Orange-II (OG-II) azo dye, which is employed in the textile industry.     

Improved photocatalytic activity of polymer-modified TiO2 films obtained by a wet chemical route

Porous TiO₂ films, exhibiting improved photocatalytic activity compared with commercial materials, have been deposited on glass. The films were dipcoated from a polymer-modified TiO₂ precursor solution, containing about 90 vol% water as solvent. The addition of water-soluble polymers such as polyethyleneglycol and polyvinylalcohol has produced TiO₂ films with different morphologies, exhibiting RMS roughnesses of up to 60 nm and increased porosity. We studied the effect of the polymers on the morphology and surface topography of a series of polymer-modified TiO₂ films and evaluated how their presence in the precursor influences the crystallinity, optical transmittance and most importantly, the photocatalytic activity of the films. X-ray diffraction analysis shows that all films exhibit the anatase crystal structure after calcining for 2 h at 500 °C. We find that the presence of polyethyleneglycol inhibits the crystallization of the TiO₂ films. Transmittance spectra show that most of the polymer-modified TiO₂ films obtained in this work are transparent although high polymer content can lead to opaque films because of increased porosity and surface roughness. The surface morphology of the films was studied by scanning electron microscopy and atomic force microscopy. Their photocatalytic efficiency was studied by following the decomposition of methylene blue under UV irradiation. The activity of the reference TiO₂ film obtained from a precursor without polymers is comparable to that of Saint-Gobain (SG) self-cleaning Bioclean glass, while some of the polymer-modified films show efficiencies that can be up to seven times higher.     

Synthesis of TiO2 nanotube films via pulsed laser deposition followed by a hydrothermal treatment

Titanium dioxide nanotube (TNT) films were prepared by pulsed laser deposition (PLD) of P25 and P90 TiO₂ nanoparticles onto stainless steel foils followed by a hydrothermal treatment (HT). Heating the PLD films in a TNT precursor solution at 150°C resulted in a well-adhered dense mat of TNTs that were ～10?nm in diameter with a pore size of ～4?nm. The TiO₂ nanotube films were characterised by SEM, TEM, XRD and Raman spectroscopy.     

In situ synthesis of transparent TiO2 nanoparticle/polymer hybrid

Transparent TiO₂ nanoparticle/polymer hybrids were synthesized from titanium isopropoxy methacrylate via hydrolysis and polymerization in 2-methoxymethanol. Crystalline TiO₂ nanoparticles were uniformly dispersed in the polymer matrix. A highly transparent free-standing TiO₂ nanoparticle/polymer hybrid film was synthesized. The refractive index (RI) of the hybrid films on Si substrates could be controlled by varying the concentration of TiO₂ nanoparticles: the RI increased with increase in Ti content. A further increase in the RI was achieved upon irradiation with ultraviolet light. A TiO₂ nanoparticle/PMMA hybrid without the silica component exhibited an RI of 1.717 and an Abbe number of 21.6.     

Growth of epitaxial substituted garnet films by hydrothermal synthesis

A new hydrothermal technique is described in which the garnet synthesis is performed directly in the autoclave in low concentration basic solutions (NaOH or KOH). This method avoids a strong attack of the substrate and leads to uniform thickness and composition films. The best experimental conditions are given for the growth of Ga:YIG, Gd:Ga:YIG, Eu:Ga:YIG, Eu:Ga:ErIG and Gd:Ga:ErIG films on GdGaG substrates. Magnetic characterizations are presented and the properties of hydrothermal garnet films are discussed and compared with those of L.P.E. and C.V.D. garnet films.     

Effect of Fe-doped TiO2 nanoparticle derived from modified hydrothermal process on the photocatalytic degradation performance on methylene blue

Anatase Fe-doped TiO2 nanoparticles with 10-15 nm particles sizes were directly prepared with amorphous TiO2 nanoparticles and Fe(NO3)3.9H2O by hydrothermal method. The TiO2 crystallite grain sizes decreased with the increase of Fe contents. When Fe contents increased, the diffuse reflectance spectra of Fe-doped TiO2 nanoparticles displayed a red shift in the band gap transition. And the absorbing band edge moved to visible range when the Fe contents were more than 2 mol%. XPS analysis showed that Fe3+ was not on the surface of TiO2 nanoparticles, but inserting into the matrix interior. As a result, the photoactivity degradation of MB on Fe-doped TiO2 nanoparticles decreased.     

Facile synthesis of SnO2 nanograss array films by hydrothermal method

SnO₂ nanograss array films (SNAFs) were synthesized on indium tin oxide glass substrates by hydrothermal method. The effects of preparing conditions such as precursor concentration, reaction temperature and growth time on the formation of the SNAFs have been investigated in detail by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and photoluminescence spectrum. It is shown that the precursor concentration plays an important role in determining the morphology of the prepared SnO₂. The average diameter, length and growth rate of the SNAFs can be controlled to some extent by varying growth time. The reaction temperature has also influence on the growth rate of SNAFs. Moreover, the growth mechanism of the SNAFs was also discussed. Room-temperature photoluminescence spectra were further carried out to investigate their optical properties.     

Template-free hydrothermal synthesis of macroporous TiO2 microspheres on a large scale

Macroporous TiO₂ microspheres have been synthesized on a large scale by a facile hydrothermal process using titanium tetrachloride (TiCl₄) as the titanium source, ammonium fluoride (NH₄F) and hydrogen peroxide (H₂O₂) as the etchant. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) studies show that the anatase TiO₂ microspheres are well-crystalline with an average diameter of 5.43 μm. N₂ adsorption–desorption and mercury intrusion porosimetry analysis reveal that the as-prepared TiO₂ microspheres are composed of numerous pore networks with an average pore diameter of 274 nm and porosity of 39.8%. In addition, the formation mechanisms of macroporous TiO₂ microspheres were also investigated.     

Ionic liquid-assisted one-step hydrothermal synthesis of TiO2-reduced graphene oxide composites

We have demonstrated a facile and efficient strategy for the fabrication of soluble reduced graphene oxide sheets (RGO) and the preparation of titanium oxide (TiO₂) nanoparticle-RGO composites using a modified one-step hydrothermal method. It was found that graphene oxide could be easily reduced under solvothermal conditions with ascorbic acid as reductant, with concomitant growth of TiO₂ particles on the RGO surface. The TiO₂-RGO composite has been thoroughly characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy, and transmission electron microscopy) have been employed to probe the morphological characteristics as well as to investigate the exfoliation of RGO sheets. The TiO₂-RGO composite exhibited excellent photocatalysis of hydrogen evolution.      

The preparation and characterization of photocatalytically active TiO2 thin films and nanoparticles using Successive-Ionic-Layer-Adsorption-and-Reaction

Photocatalytically active TiO₂ thin-films were deposited on silicon wafers using the Successive-Ionic-Layer-Adsorption-and-Reaction technique and subsequent hydrothermal and/or furnace annealing. Atomic-force-microscopy images and X-ray diffraction measurements of the TiO₂ films obtained under various annealing conditions show how changes of the micro-scale surface structure depend on the post-SILAR treatment. The hydrogen evolution over various TiO₂ films was measured. Hydrothermally treated TiO₂ films show a higher photocatalytic activity and a much better mechanical stability compared to furnace-annealed films. The optical transmittance of TiO₂ thin films on glass substrates was also studied. A red shift was observed with increasing film thickness. TiO₂ nanoparticles (∼10 nm) that were peeled off from the TiO₂ films were investigated using high-resolution-transmission-electron-microscopy.