Oxidation of acetaldehyde to glyoxal by nitric acid

The liquid phase oxidation of acetaldehyde or paraldehyde by aqueous nitric acid to glyoxal was investigated in a stainless steel autoclave maintained under autogenous pressure. The presence of nitrous acid was necessary for the reaction. Acetic acid and glyoxalic acid were the major by-products. The effects of concentration of nitric acid, nitrous acid and acetaldehyde as well as temperature and period of reaction on the conversion and yield of glyoxal were studied with a view to obtaining the most suitable conditions for the production of glyoxal.     

Novel nitrogen-doped anatase TiO2 mesoporous bead photocatalysts for enhanced visible light response

This work reports the synthesis and characterization of a novel, high surface area N-doped anatase TiO₂ mesoporous bead as a photocatalyst for visible light photodegradation. The beads were prepared using a two-cycle microwave-assisted hydrothermal method using three different types of nitrogen dopants: diaminohexane, triethylamine, and urea. In the first cycle, TiO₂mesoporous beads with controlled structures were synthesized at 200 °C without further calcination. The obtained beads were then subjected to a second cycle of microwave -assisted hydrothermal process for nitrogen doping. The photocatalytic activity of the N-doped mesoporous TiO₂ beads was determined by measuring the decomposition of a methyl blue aqueous solution under UV and visible light. It was found that different precursors lead to different degrees of doping which enhances the light absorption primarily in the visible light region. We demonstrate that the photocatalytic activity or photodegradation is enhanced in the visible light region.     

Synthesis and characterization of mesoporous anatase TiO2 nanostructures via organic acid precursor process for dye-sensitized solar cells applications

Titania (TiO₂) nanoparticles have been synthesized using organic precursor technique. The titania nanoparticles were characterized. The results indicated that the prepared titanium oxalate and citrate precursors were transformed to anatase TiO₂ phase at temperature 400 °C for 2 h. Dye-sensitized solar cells were assembled using the prepared nanocrystalline TiO₂ with large surface area. The specific surface area S_BET was 80.9 and 78.6 m²/g using oxalic and citric acids, respectively. The power efficiency was 3.5 and 2.4%. A brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells was reported.     

Effects of templating surfactant concentrations on the mesostructure of ordered mesoporous anatase TiO2 by an evaporation-induced self-assembly method

We prepared ordered hexagonal mesoporous TiO₂ by an evaporation-induced self-assembly (EISA) method using Pluronic P123 and tetrabutyl orthotitanate (Ti(OBuⁿ)₄, TBOT) as the templating agent and the titanium source, respectively. The main purpose of this study was to elucidate the effects of surfactant concentrations on the pore arrangement, pore size, specific surface area and structure of mesoporous TiO₂ by the EISA method. The mesostructures of mesoporous TiO₂ were characterized with X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, and transmission electron microscopy (TEM). By varying the concentration of the block copolymer, mesoporous TiO₂ of various pore sizes and pore ordering were prepared. Because the mesostructure is governed by the concentration of P123 surfactant at gelation of the solution, a higher P123/TBOT mole ratio favored the formation of highly ordered mesoporous TiO₂ with a maximum pore volume of 0.26 cm³/g, a high specific surface area of 244 m²/g, and a BJH average pore size of 4.7 nm.     

Oxidation of multiwalled carbon nanotubes by nitric acid

The oxidation of MWCNTs in nitric acid was monitored using sample weight, Raman spectrum, solubility, morphology and alignment. The influence of the acid concentration, temperature and oxidation duration on the monitored parameters was assessed. A new method, based on optical microscopy is proposed for the determination of MWCNT solubility in concentrated aqueous-suspensions. The investigations revealed that the solubility is determined not only by the functional groups on the MWCNT, but also by the functionalized amorphous carbon generated during the digestion of the nanotubes. High solubility (20–40 mg/ml) is obtained only after prolonged exposure (24–48 h) in concentrated acid (60%). But in these conditions 60–90% of the MWCNTs are lost. Furthermore the MWCNTs are strongly fragmented and covered by amorphous carbon after 48 h of oxidation. It was found that the solubility correlates well with the area ratio of the G and D bands from the Raman spectrum. SEM examination of the MWCNT films showed extended alignment after 24 h of oxidation.     

Nano-to-macroporous TiO2 (anatase) by cold sintering process

Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO₂ anatase with nano-to-macro porosity. Nanoporous TiO₂ based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO₂ nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m²/g), using water as transient aqueous environment. Although TiO₂ is insoluble in water, a density of 68% and s.s.a. = 117 m²/g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m²/g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO₂ nanopowder during CSP, followed by a debonding at 500 °C.     

Enhanced photocatalysis by coupling of anatase TiO2 film to triangular Ag nanoparticle island

ABSTRACT: In order to overcome the low utilization ratio of solar light and high electron-hole pair recombination rate of TiO2, the triangular Ag nanoparticle island is covered on the surface of the TiO2 thin film. Enhancement of the photocatalytic activity of the Ag/TiO2 nanocomposite system is observed. The increase of electron-hole pair generation is caused by the enhanced near-field amplitudes of localized surface plasmon of the Ag nanoparticles. The efficiently suppressed recombination of electron-hole pair caused by the metal-semiconductor contact can also enhance the photocatalytic activity of the TiO2 film.     

锐钛型介孔偏钛酸催化剂的制备及其催化酯化性能

以工业偏钛浆为原料,通过水洗、碱洗、酸洗处理制备了锐钛型介孔偏钛酸催化剂,将催化剂用于α-蒎烯酯化反应中考察其催化性能,采用FT-IR、XRD、SEM、BET手段对催化剂的晶相结构、形貌、表面积、孔径等结构进行了表征。结果表明,最佳制备条件为：温度30 ℃,碱洗pH=8.5,酸洗pH=4.0;处理后的偏钛酸催化剂基本没有SO42?,且晶型没有发生明显变化,均为锐钛矿相,最佳条件下制备的偏钛酸催化剂孔径分布均匀,晶粒团聚较少,比表面积为334.82 m2/g,平均孔径为3.96 nm,催化α-蒎烯酯化生成草酸龙脑酯含量可达48.59 %,皂化后水蒸气蒸馏收集龙脑,m1（正龙脑）∶m2（异龙脑）=59.27∶37.07。     

阳极氧化法制备具有可见光光催化活性的二氧化钛

以钛片为底板通过阳极氧化法在3种不同电解质溶液[1 mol·L-1硝酸铵乙二醇溶液（1-M ANEG）、0.1mol·L-1硝酸铵乙二醇溶液（0.1-M ANEG）、0.1 mol·L-1硝酸铵水溶液（0.1-M ANA）]中制备二氧化钛,并对其光催化性能进行了比较.结果表明,在0.1 mol·L-1硝酸铵乙二醇溶液中制得的二氧化钛在可见光下具有较好的光催化活性且表面光滑平整.     

Ag nanoparticles-polypyrrole-carbon black/mesoporous TiO2 novel nanocomposite as ultrafast visible-light-driven photocatalyst

Effective design and fabrication of novel visible light-oriented photocatalysts is an existing challenging task that requires further dedicated efforts, and it has been always a main concern among the scientific community. This study deals with the design and fabrication of an extremely active and ultrafast ternary photocatalyst based on Ag nanoparticles, polypyrrole doped carbon black (PPy-C) and mesoporous TiO₂ (m-TiO₂). Sol-gel methodology along with sonication and photodeposition routes have been employed for the successful creation of the ternary framework. Ternary photocatalyst composed of uniform spherical titania nanoparticles (10–15 nm in size) perfectly intermingled with the polymeric linkage of PPy-C. Fruitful creation of unique trio photocatalyst between AgNPs, PPy-C and m-TiO₂ was confirmed by XPS and XRD. FTIR analysis further supports the development of nanocomposite photocatalyst. TEM analysis showed uniform spherical m-TiO₂ nanoparticles (10–15 nm in size) covered by PPy-C with compact nodes like appearance interlocked very well among each other. The newly developed Ag@PPy-C/m-TiO₂ ternary photocatalyst exhibited band gap energy in desired visible range of spectra. The photocatalytic efficiency for all created photocatalysts has been evaluated taking Imidacloprid (insecticide derivative) and methylene blue (MB) dye as target pollutants. The novel Ag@PPy-C/m-TiO₂ photocatalyst produced astonishing results with ultrafast removal of both Imidacloprid as well MB dye under visible light irradiation. The newly created ultrafast Ag@PPy-C/m-TiO₂ photocatalyst has removed 96.0% of the insecticide Imidacloprid in only 25 min with almost ? 2.65 times more efficient than bare m-TiO₂ towards the removal of insecticide derivative. The present report offers a highly encouraging and vastly talented Ag@PPy-C/m-TiO₂ ternary photocatalyst, enabling the ideal management of extremely lethal and notorious chemicals.     

直接氧化法制备TiO2-Al2TiO5复相陶瓷

以Ti—Al—C和TiC—Ti—Al体系为反应体系,采用直接氧化法制备Al2TiO3-TiO2复相陶瓷。研究了氧化温度对体系合成产物组成的影响。结果表明,两种体系的合成产物都由Al2TiO3和TiO2相组成,没有杂质相存在。碳高温氧化成CO2向外扩散,在坯体内形成疏松通道,利于O2的渗入,提高了氧化反应程度。     

锐钛型TiO2对尿素热解过程的影响

通过实验的方法收集了不同温度下纯尿素和尿素/TiO₂混合物热解后的固体残留物，使用红外光谱（IR）及气相色谱质谱联机（GC-MS）方法对这些热解残留物进行成分分析；使用热重-红外联机（TG-FTIR）技术研究尿素及三聚氰酸在有无催化剂TiO₂的情况下的热解特性及气体产物的生成规律；根据Coats-Renfern方法对尿素热解第一阶段的非等温热失重率曲线的数据进行动力学研究，建立动力学方程。结果表明，100~250℃的尿素热解残留物中主要为尿素和缩二脲，300~400℃的尿素热解残留物中主要为三聚氰酸等含氮杂环有机化合物；锐钛型TiO₂能促进尿素和三聚氰酸的热解反应，缩短其反应进程，HNCO与水蒸气在TiO₂表面易发生反应；尿素第一阶段热解的反应级数为2，单独热解时活化能为113.25kJ/mol，指前因子A为2.01×10¹¹min^-1，在催化剂TiO₂的作用下，活化能E为77.42kJ/mol，指前因子A为4.82×10⁷min^-1。     

A novel approach for preparation of highly crystalline anatase TiO2 nanopowder from the agglomerates

A new approach for synthesis of dry and well-shaped anatase titania nanocrystals by different methods of synthesis, like sol-gel and precipitation, is reported. The significance of this new method is the dehydration of titania agglomerates by simple azeotropic distillation to afford uniform and reproducible anatase nanocrystals with particle size < 20 nm and average surface area as high as 106.44 m² g^− 1.     

Tunable TiO2 (anatase and rutile) materials manufactured by mechanical means

Anatase and rutile are two naturally found titanium dioxide phases with attractive dielectric, catalytic, and photo-catalytic characteristics. Anatase and rutile are photo-catalytically active in the UV region, since their band gaps are 3.2 eV and 3.75 eV, respectively. In this work is proposed a cost-effective, easy to launch methodology for modification of the TiO₂ bandgap. Such modifications will make the oxides photo-catalytically active in a wider optical range from the visible wavelengths to an extended UV spectrum. The proposed methodology is based on mechanical means such as mixing and milling. Various ratios of anatase:rutile were investigated and milled from 0 (mixing only) to 50 h using high energy mills. The results on mixing and milling show that it is possible to modify the bandgap of the TiO₂ from 2.53 eV to 4.04 eV. The characterization was conducted by means of X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, and optical spectroscopy.     

低温下水热法合成锐钛矿型二氧化钛微米球

以硫酸钛的水溶液为原料,加尿素作添加剂(尿素与Ti4+摩尔比1:5),较低温度下用水热法在玻璃基板上制备了TiO2微米球,结果显示生成的TiO2晶体为锐钛矿型.并讨论了形成微米球的机理.     

Photocatalytic degradation of azo dyes by organic-capped anatase TiO2 nanocrystals immobilized onto substrates

The UV-induced photocatalytic degradation of two azo dyes, Methyl Red and Methyl Orange, has been carried out in aqueous media in the presence of oleic acid (OLEA)- and tri-n-octylphosphine oxide (TOPO)-capped anatase TiO₂ nanocrystal powders (mean particle size: 6 nm) deposited onto a quartz substrate. The progress of photodegradation was followed by combining UV–vis absorption measurements with HPLC–MS analysis. The abatement efficiency for the two organic compounds was compared with that obtained with commercial TiO₂ P25 Degussa by evaluating a few significant variables, such as the dye chemical structure, pH of the solution, and catalyst surface status. Identification of several by-products by HPLC–MS analysis has allowed to propose a reasonable degradation pathway for both target molecules. Significantly, although all titania catalysts were effective in removing both parent dyes and their related derivatives, the degradation rate by the OLEA-capped TiO₂ nanocrystals was double as that obtained with both its TOPO-capped analogous and TiO₂ P25 Degussa. It is suggested that efficient catalysis strictly depends on microscopic mechanisms that occur at the catalyst surface, basically involving specific dye adsorption and local density of terminal OH moieties.     

二氧化钛介孔材料的制备

基于溶胶-凝胶过程,以十六烷基溴化铵为模板剂,合成了TiO2以及V/Ce/F-TiO2 介孔材料。利用XRD、Ｎ２吸附、TEM、TG-DTA和UV-Vis DRS等手段表征了材料的晶相组成、晶粒尺寸、介孔结构、热稳定性及吸光性能。通过系统研究表明,延长凝胶时间和优化陈化工艺可以得到TiO2介孔材料。TiO2和V/Ce/F/TiO2的平均孔径为3.1～5.1 nm,最大比表面积可达189 m2/g。焙烧温度大于450 ℃脱除模板剂时可引起孔道的塌陷,而掺杂V/Ce/F后可稳定材料的介孔结构。相对于纯TiO2光催化剂,掺杂V/F的TiO2吸光带边红移至可见光区。     

The synthesis of cadmium doped mesoporous TiO2

Cd doped mesoporous titanium oxide was prepared using non-ionic surfactants and easily handled titanium precursors. The Cd doping was found to be able to significantly inhibit the growth of anatase crystal size, stabilize the mesoporous structure, and retard the densification of nanoporous TiO₂ at elevated temperatures.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Synthesis of recrystallized anatase TiO2 mesocrystals with Wulff shape assisted by oriented attachment

In this work, we describe a kinetically controlled crystallization process assisted by an oriented attachment (OA) mechanism based on a nonaqueous sol-gel synthetic method (specifically, the reaction of titanium(IV) chloride (TiCl(4)) with n-octanol) to prepare re-crystallized anatase TiO(2) mesocrystals (single crystal). The kinetics study revealed a multi-step and hierarchical process controlled by OA, and a high resolution transmission electron microscopy (HRTEM) analysis clearly shows that the synthesized mesocrystal presents a truncated bipyramidal Wulff shape, indicating that its surface is dominated by {101} facets. This shape is developed during the recrystallization step. The material developed here displayed superior photocatalytic activity under visible light irradiation compared to TiO(2)-P25 as a benchmarking.