Enhanced Solar-Radiation Induced Photocatalytic Activity of Surface-Modified Nanocrystalline Anatase-Titania

Sol-gel derived pure nanocrystalline (~20–30 nm) anatase-titania has been surface-modified by depositing silver(I) oxide and silver (predominantly the former) via UV-reduction process. The pure and surface-modified nanocrystalline anatase-titania have been characterized using different analytical techniques for determining the average nanocrystallite size, phase-contents, surface-chemistry, as well as the absorption and photoluminescence characteristics. It is demonstrated that, the latter exhibits an enhanced solar-radiation induced photocatalytic activity as compared to that of the former as a result of the absorption in the visible-region and enhanced photo-induced e^?/h⁺ life-time, both caused by the surface-deposition of silver(I) oxide and silver.     

Evaluations of physico-chemical properties of TiO2/clinoptilolite synthesized via three methods on photocatalytic degradation of crystal violet

Different preparation routes for Ti O_2-supported natural and synthetic clinoptilolite(Ti O_2/CP) composites were thoroughly investigated on the basis of sol–gel, hydrothermal, and in-situ hydrothermal methods.The micro-structural features and physicochemical properties of resultant Ti O_2/CPs were characterized via X-ray diffraction patterns, scanning(transmission) electron microscope images, Fourier transform infrared spectra, inductively coupled plasma-optical emission spectrometry methods, BET-isotherms,UV–visible spectra, and surface charge potential distributions. The results showed that in-situ hydrothermal method led to well dispersions of loaded-Ti O_2 particles on the surface of leaf-like CP, while obviously aggregated Ti O_2 on a relatively distorted structure of CP was obtained using sol–gel and hydrothermal methods. Their adsorptive and photocatalytic efficiencies for removal of crystal violet(CV) dye in aqueous solution were also explored under UV-irradiations. The results demonstrated that Ti O_2/CPs synthesized via sol–gel and in-situ hydrothermal methods presented the excellent performances with 98%removal efficiencies as compare to the bare commercial Ti O_2 which achieved 53% removal of CV dye.While, the in-situ hydrothermally synthesized Ti O_2/CPs were the best due to their moderate energy cost,highest adsorption capacities and removal efficiencies. Particularly, the synthetic CPs as supports exhibited synergetic photocatalytic activities for the degradation of CV dye, which is attributed to their high surface areas, better adsorption capability, and fine dispersion of Ti O_2 particles. Adsorption and degradation kinetics of CV dye were found to follow the pseudo-second and pseudo-first order models,respectively.     

The adsorption of malachite green (MG) as a cationic dye onto functionalized multi walled carbon nanotubes

Synthetic dyes are widely used by several industries to color their products. The discharge of colored wastewater into the hydrosphere causes serious environmental problems. We used functionalized multi wall carbon nanotubes as an adsorbent for the adsorption of cationic dye, malachite green, from aqueous solution. Based on information provided by the Iranian Research Institute of Petroleum Industry, carbon nanotubes are produced using a chemical vapor deposition (CVD) technique. These as-received MWCNTs were functionalized by acid treatment. The remaining dye concentration was read by UV-visible absorption spectroscopy at maximum adsorption wavelength. The effect of different operational parameters such as contact time, pH of solution, adsorbent dose and initial dye concentration were studied. The results showed that by increasing of contact time, pH and adsorbent dose the removal of dye increased, but by increasing initial dye concentration, the removal efficiency decreased. Adsorption isotherms and kinetics behavior of f-MWCNTs for removal of malachite green was analyzed, and fitted to various existing models. The experimental data were well correlated with the Langmuir isotherm with a maximum adsorption capacity (q _m ) and regression coefficient (R²) of 142.85 mg/g and 0.997, respectively. The results of this study indicate that functionalized multi wall carbon nanotubes can be used as an effective adsorbent for the removal of dyes.     

铌酸钾纳米管的制备及其光催化还原水制氢研究

以铌酸钾颗粒为前驱体,经酸化和剥落处理,在简单、温和的条件下制得铌酸钾纳米管。透射电镜结果表明,产物具有管状形貌,且管形完整、管径分布窄、长径比大。研究了铌酸钾纳米管在紫外光照射下的光催化还原水制氢性能,铌酸钾纳米管的活性明显高于铌酸钾颗粒,负载Pt的铌酸钾纳米管的制氢活性明显提高,在pH=3的10%(体积分数)甲醇水溶液中负载1.5%铂的铌酸钾纳米管的产氢活性(18.8 mmol/g.h)最高,是铌酸钾纳米管负载前(0.385 mmol/(g.h))的48.8倍。     

Nanocomposite zirconium phosphoborate ion-exchanger incorporating carbon nanotubes with photocatalytic activity

A new form of nanocomposite zirconium phosphoborate (ZrPB) ion exchanger incorporating multi-walled carbon nanotubes (CNTs) has been fabricated and studied. Commercial purity CNTs were used as dopant in ZrPB matrix. The topography and morphology of the composite has been explored with the help of scanning electron microscopy and transmission electron microscopy. The microscopy results confirm the spherical nature and 2–5 nm size of ZrPB particles. CNTs are well reinforced evenly in ZrPB matrix. Multifunctionality of the nanocomposite ion exchange material has been studied for electrochemical characteristics as well as for photocatalytic degradation of methylene blue dye.     

A polyacrylamide gel route to photocatalytically active BiVO4 particles with monoclinic scheelite structure

Sphere-like BiVO₄ particles with average size ranging from 390 to 270 nm were prepared via a polyacrylamide gel route, where the particle size was tailored by using different chelating agents. The bandgap energy of the samples is measured to be 2.49–2.51 eV by ultraviolet–visible diffuse reflectance spectroscopy. The photocatalytic activity of the samples was evaluated by the degradation of methylene blue under irradiation of simulated sunlight, revealing that they exhibit a good photocatalytic activity. Hydroxyl radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and are found to be produced over the irradiated BiVO₄ particles. This indicates that hydroxyl radicals are likely to be the primary active species responsible for the dye degradation.     

Effect of ignition temperature and fuel amount on photocatalytic activity of solution combustion synthesized ZnO

Nanocrystalline zinc oxide (ZnO) photocatalyst has been synthesized by a simple solution combustion method using zinc nitrate as the oxidizer and urea as the fuel. Effect of fuel to oxidizer ratio and ignition temperature on the mechanism of combustion synthesis, crystallinity, morphology, surface area, and optical properties were investigated by thermal analysis, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Diffuse reflectance UV–Visible spectra and Photoluminescence analyses. Photocatalytic activity of the synthesized materials was evaluated by degrading an azo dye at ambient temperature and solution pH. The prepared photocatalysts at the fuel-rich condition possess small crystallite size and more surface area; consequently, a higher photocatalytic dye degradation capability.The powder samples synthesized at the fuel-oxidant ratio of 1.8 and the ignition temperature at 400 °C have shown the maximum percentage (99%) of dye degradation in 180 min. The pseudo-first order photocatalytic dye degradation rate constant of a catalyst sample synthesized at the fuel-oxidant ratio of 1.8 was 0.0253 min⁻¹and it is 3.14 and 2.88 times higher than that of samples synthesized at fuel-oxidant ratios of 0.6 and 1.The outcomes of the present article help to design more pronounced experiments for the synthesis of photocatalysts by varying ignition temperatures and fuel amounts.     

Porous TiO<Subscript>2</Subscript> nanostructures synthesized from peroxotitanic acid-derived anatase

Abstract  

Titania/titanate nanotubes and nanoplates were prepared by an alkali hydrothermal method using the powder and the sol of peroxotitanic acid-derived anatase, respectively, as precursors. XRD patterns and Raman spectra showed that both nanotubes and nanoplates are of titanate structure with the latter involving a slight part of anatase phase. These nanotubes and nanoplates are highly mesoporous based on nitrogen adsorption measurement. After calcination at 823 K, nanotubes were transformed into nanorods, and nanoplates into spherical particles, both of which are pure anatase-type titania. The nanorod material exhibits an enhanced photocatalytic activity in comparison with the spherical particles.     

The pH influence on photocatalytic decomposition of organic dyes over A11 and P25 titanium dioxide

The photocatalytic removal (decomposition+adsorption) of four azodyes (Reactive Red 198, Acid Black 1, Acid Blue 7 and Direct Green 99) in water was investigated using Tytanpol A11 (“Police” Chemical Factory, Poland) and Degussa P25 (“Degussa”, Germany) as photocatalysts. The effect of pH of the reaction solution has been examined. The degree of the dye removal in the solution was measured by UV-Vis spectroscopy. Photodecomposition of dye on photocatalyst surface was monitored by FTIR spectroscopy. A11 photocatalyst has lower activity in the reaction of photocatalytic decomposition of organic dyes than Degussa P25. The photocatalytic decomposition of the dyes takes place on the photocatalyst surface at pH=2 while at pH=12 photocatalytic reaction proceeds via photogenerated hydroxyl radicals for both A11 and P25.     

Effect of Zr doping and aging on optical and photocatalytic properties of ZnS nanopowder

A facile single step chemical method is reported for the synthesis of Zr doped ZnS nanopowder and its photocatalytic performance has been studied. The average crystallite size of the synthesized powder estimated from X-ray diffraction (XRD) is nearly 1.1 nm. Transmission electron microscopy (TEM) study shows that nanoparticles are agglomerated having a particle size of nearly 10 nm. The optical band gap of ZnS and Zr-doped ZnS, estimated with the help of UV–visible spectroscopy, is 3.7 and 2.9 eV, respectively. Photoluminescence (PL) spectroscopy indicated the role of lattice defects (vacancy, interstitial defects) on optical emission characteristics of doped ZnS samples. The photocatalytic activity of synthesized samples has also been investigated by degrading methylene blue (MB) dye under UV–visible illumination. The degradation quenching has been observed beyond 0.4 mol% doping of Zr in ZnS with maximum efficiency i.e. 80% in 4 h. Thereafter, the effect of aging is monitored for 1.5 months in which the modified emission properties of defect sites modulated the photocatalytic performance of Zr-doped ZnS sample. Further, with the help of various spectroscopic techniques (absorbance, PL and XPS), a mechanism for the photodegradation of MB dye by using Zr-doped ZnS nanopowder has been proposed.     

溶剂热制备ZnO微椭圆球及光催化性能

通过简便实用的溶剂热法制备出尺寸和形貌均一、单分散的纳米ZnO微椭圆球.用X-射线衍射仪、扫描电镜、氮气吸附和脱附仪和荧光光谱表征所合成的样品.通过控制实验条件来研究ZnO微椭圆球的形貌形成过程.除此之外我们还研究了ZnO微椭圆球光致发光和光催化性能.     

Dual role of activated carbon as fuel and template for solution combustion synthesis of porous zinc oxide powders

In this work, nanosized zinc oxide (ZnO) powders were fabricated by urea–nitrate solution combustion synthesis using activated carbon as a structure-directing template and secondary fuel at different fuel–oxidant ratios. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption measurements, UV–Vis diffuse reflectance spectroscopy, and photoluminescence. The effect of fuel amount on photocatalytic activity of ZnO powders was evaluated by the degradation of an azo dye Orange G. It was observed that combustion synthesis with activated carbon as a secondary fuel had a profound effect on reducing crystallite size and enhancement of specific surface area. The crystallite size of the as-synthesized powders varied from 46 to 26 nm. The ZnO powder prepared at a fuel–oxidant ratio of 1.8 possessed the small crystallite size and high specific surface area of 69 m²/g. It correspondingly resulted in the highest dye removal percentage of 99% with a rate constant of 0.027 min⁻¹. The improvement in dye degradation can be due to the synergistic interaction and interplay of enhanced surface area and catalytic ability of the photocatalyst. This study provides a simple single-step synthesis methodology to produce metal oxide nanopowders with tunable surface properties for high potential applications in catalysis, optoelectronics, and gas sensors.     

TiO2-Al2O3复合粉体的制备及光催化性能

Al₂O₃陶瓷膜在过滤染料废水过程中容易被染料大分子堵塞,导致Al₂O₃陶瓷膜水通量下降。以钛酸丁酯、异丙醇铝为前驱体,采用溶胶-凝胶法制备Ti(OH)₄-AlOOH复合溶胶,经450 ℃烧成获得TiO₂-Al₂O₃复合粉体。以SEM、纳米粒度/电位仪作为主要表征手段,研究了不同Ti(OH)₄和AlOOH摩尔比对复合溶胶粒径分布的影响,进而探究TiO₂-Al₂O₃复合粉体的光催化性能。结果表明,Ti(OH)₄和AlOOH摩尔比为0~0.4时,随着Ti(OH)₄和AlOOH摩尔比的增大,胶粒的平均粒径从67.5 nm减小到34.0 nm,Ti(OH)₄-AlOOH复合溶胶的电位从43 mV升高至53 mV。当Ti(OH)₄和AlOOH摩尔比为0.4时,复合粉体对结晶紫的去除率高达79.3%,反应速率常数增大到了0.018 min^-1。TiO₂-Al₂O₃复合粉体制备的陶瓷膜能有效降解表面沉积的大分子,解决了陶瓷膜堵塞的问题。     

化学气相沉积工艺制备绳状纳米碳管的研究

用硝酸铁作催化剂,乙炔作碳源气体,高纯氮气作稀释气体,在750℃下化学气相沉积生长了绳状纳米碳管,用高分辨扫描电镜观察了所得绳状纳米碳管的形貌.纳米碳管的直径为100～200nm,长度为10～20 μm.文中还提出了绳状纳米碳管的生长机理.     

Synthesis of TiO2 nanoparticles by a combined sol-gel ball milling method and investigation of nanoparticle size effect on their photocatalytic activities

TiO₂ nanoparticles were synthesized by a sol-gel method and the effect of ball milling of dried gel on the particle size has been investigated. The results show that the ball milling has a crucial role in preparation of nanosized TiO₂ powder. Also thermal treatment at different temperatures can control the size of prepared nanoparticles. The photocatalytic activities of TiO₂ nanoparticles with different sizes were studied by photocatalytic degradation of Congo red dye using a homemade photoreactor. The photo degradation of Congo red dye was monitored by UV-Vis absorption measurements. It was found that the nanopowders which were synthesized at 550 °C with average particle size of 55 nm show the maximum photocatalytic activities. These nanopowders which were a mixture of anatase and rutile phases did not show the same photocatalytic effect on Eriochrome black, Bromocresol green, Methyl orange and Rose Bengal dyes.     

Synthesizing and Comparing the Photocatalytic Properties of High Surface Area Rutile and Anatase Titania Nanoparticles

Rutile titania nanocrystalline particles with high specific surface areas were directly prepared by thermal hydrolysis of titanium tetrachloride aqueous solution. The as-prepared rutile titania powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller surface area analysis, and Fourier transform Raman and IR spectroscopies. Neither anatase nor amorphous titania could be detected in this titania powder by XRD, Raman spectroscopy, and high-resolution TEM. In the phenol degradation reaction, the rutile titania powder with an initial crystalline size of 7 nm was found to have higher photocatalytic activity than that of anatase titania with the same specific surface area. The rutile titania powders calcined at 300° and 450°C also showed a relatively high photocatalytic property. The high activity of the as-prepared rutile titania was attributed to the abundance of hydroxy groups in the powder, as was proven by thermogravimetric analysis data, which provided more active sites for the degradation reaction.     

Performance Characteristics of a Suspended‐Catalyst Oscillatory Membrane Photocatalytic Reactor

The performance characteristics of an oscillatory membrane photocatalytic reactor were investigated using dye degradation over a suspended ZnO catalyst as a model reaction. Both flat‐surface membranes and ones with transverse turbulence promoters (TP) were used. Application of oscillatory motion can be effective in enhancing the performance of suspended‐catalyst membrane photocatalytic reactors. The eddy formation and vortex shedding when using membranes with TP gave rise to several synergistic effects by providing effective removal of catalyst deposits from the membrane surface, which enhanced the flux and increased the suspended‐catalyst fraction in solution, which consequently enhanced the reaction rate. The effective mixing in the reaction channel minimized particles sedimentation and agglomeration which further enhanced the catalyst suspension and increased its effective reaction area. The specific energy consumption favorably compared to a membrane cross‐flow filtration system.     

Enhanced UV-light driven photocatalytic performances and recycling properties of TiO2/AlON composite photocatalyst

AlON has been reported to have photocatalytic capability under ultraviolet-light (UV-light), which can be improved by fabricating large-sized powder (~20?µm) having porous skeleton microstructure. To further enhance photocatalytic property of AlON, highly photocatalytic-efficient nanocrystalline TiO₂ was loaded onto both the outer and inner surface of porous AlON particles by hydrothermal method. In order to ensure easy recovery without secondary pollution, the obtained composite powder was filtered in deionized water three times to remove both small-sized AlON and free TiO₂ particles to produce a composite photocatalyst with particle size >10?µm. The proposed TiO₂/AlON showed excellent photocatalytic performance on Methylene blue (MB) and Methyl orange (MO) for 97.9% and 99.1% of pollutants (in 30?mg/L, 40?mL solution) being degraded by 50?mg as-synthesized composite photocatalyst in 120?min. Further test showed that the hydrothermal process can significantly improve the photocatalytic performance of TiO₂/AlON composite photocatalyst and its enhancement mechanism were discussed. In addition, the large-sized composite photocatalyst is easy to recover and stable to reuse with no regeneration needed.     

Synthesis of highly active nanocrystalline WO3 and its application in laser-induced photocatalytic removal of a dye from water

Tungsten oxide nanoparticles were synthesized using the sol–gel process and applied for heterogeneous photocatalytic removal of a dye using a 355 nm laser radiation generated from Nd:YAG for the first time. Effect of various parameters, such as calcination temperature, calcination time, catalyst concentration and laser energy on the photocatalytic removal of dye has been investigated. The study showed that almost complete degradation of dye can be achieved within very short time of reaction (within few minutes) in presence of nanocrystalline WO₃ under laser irradiation. The removal process obeys first-order kinetics with an appreciable rate constant 0.146 min⁻¹. The main reason of high efficiency is the nanostructure nature of WO₃ and the laser as an excitation source as compared with the conventional setups using lamps and conventional microstructure catalysts.     

Spherical particles for automotive powder coatings

Clear powder coatings that consist of spherical particles with a narrow particle size distribution were produced via a suspension method that involves the agglomeration and unification of smaller particles. These powder coatings have the advantages of excellent powder flowability and high transfer efficiency. This behavior is attributable to the spherical particle shape and absence of finer particles. This production method has been developed for thinner film build clear coats with improved surface smoothness as compared to powder coatings produced by conventional methods.