Synthesis and photo-degradation application of WO3/TiO2 hollow spheres

A WO(3)/TiO(2) composite, hollow-sphere photocatalyst with average diameter of 320 nm and shell thickness of 50 nm was successfully prepared using a template method. UV-vis diffuse reflectance spectra illustrated that the main absorption edges of the WO(3)/TiO(2) hollow spheres were red-shifted compared to the TiO(2) hollow spheres, indicating an extension of light absorption into the visible region of the composite photocatalyst. The WO(3) and TiO(2) phases were confirmed by X-ray diffraction analysis. BET isotherms revealed that the specific surface area and average pore diameter of the hollow spheres were 40.95 m(2)/g and 19 nm, respectively. Photocatalytic experiments indicate that 78% MB was degraded by WO(3)/TiO(2) hollow spheres under visible light within 80 min. Under the same conditions, only 24% MB can be photodegraded by TiO(2). The photocatalytic mineralization of MB, catalyzed by TiO(2) and WO(3)/TiO(2), proceeded at a significantly higher rate under UV irradiation than that under visible light, and more significant was the increase in the apparent rate constant with the WO(3)/TiO(2) composite semiconductor material which was 3.2- and 3.5-fold higher than with the TiO(2) material under both UV and visible light irradiation. The increased photocatalytic activity of the coupled nanocomposites was attributed to photoelectron/hole separation efficiency and the extension of the wavelength range of photoexcitation.     

纳米TiO2/SiO2复合催化剂的制备与表征

以钛酸四丁酯、正硅酸乙酯作为前驱体,冰醋酸作为水解抑制剂,用溶胶-凝胶法制备了纳米TiO2/SiO2复合物.讨论了加水量、稳定剂、催化剂、乙醇用量、反应温度等工艺因素对制备过程的影响.用X射线衍射、红外光谱、比表面积仪等测试手段对纳米TiO2/SiO2复合粒子进行了表征.结果表明,用溶胶-凝胶法制备TiO2/SO2复合光催化粒子,整个反应采用滴加方式;各反应组分用量为n(TEOS+TBOT) :n(EtOH) :n(HCl) :n(H2O)=1 :16 :0.06 :4,n(TBOT) :n(HAc)=1 :0.6;反应温度为室温.制备得到的纳米TiO2/SiO2复合粒子主要以锐钛矿型存在;SiO进入TiO2晶体结构中,两者以化学键相结合;TiO2/SiO2复合粒子的比表面积要比纯TiO2粒子的比表面积大得多,当xTi :xsi=3时,TiO2/SiO2复合粒子比表面积达389.11 m2/g.     

半导体TiO2光催化剂及其有机光敏化研究进展

半导体TiO2光催化研究是当今化学、材料和环境科学等学科研究的一个热点领域。比较评述了通过掺杂改性、结构修饰和有机光敏化拓宽TiO2可见光波长响应范围和提高光催化量子效率等的研究进展、面临的主要问题和发展趋势。     

纳米TiO2薄膜光催化剂的制备及性能研究

以钛酸四丁酯作为前驱体,用溶胶一凝胶法,在玻璃载体上煅烧制备了纳米TiO2薄膜光催化剂,利用扫描电子显微镜（SEM）、X射线衍射（XRD）等表征技术研究了TiO2薄膜的形貌和特性,其光催化性能用4支20W紫外石英杀菌灯照射TiO2薄膜分解亚甲基兰染料溶液表征,结果表明,该催化剂具有锐钛班红石混合晶相和纳米花状结构,纳米TiO2薄膜的光催化能力随着镀膜层数的增加而增加。     

Ab initio study of phase stability in doped TiO2

Ab initio density functional theory calculations of the relative stability of the anatase and rutile polymorphs of TiO₂ were carried out using all-electron atomic orbitals methods with local density approximation. The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F^? doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F?>?Si?>?Fe?>?Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies.     

Degradation of 4-chlorophenol in TiO2, WO3, SnO2, TiO2/WO3 and TiO2/SnO2 systems

The present study was undertaken to evaluate the degradation performance of 4-chlorophenol (4-CP) using TiO2/WO3 and TiO2/SnO2 systems. A BET surface area analyzer, UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were employed to characterize the photocatalyst. The band edge wavelength increased to 475 nm and gap energy decreased to 2.61 eV in the TiO2/WO3 system as compare to the single TiO2. Although the specific surfaces area of TiO2/WO3 decreases due to its larger size as compared to either TiO2 or WO3, the 4-CP degradation efficiency significantly increased as compared to single TiO2 or WO3 system at 435 nm wavelength. The TiO2/WO3 degradation of 4-CP at 369 nm was in fact inhibited. For TiO2/SnO2, the degradation efficiency also suffered at 369 nm, and only slightly increased compared to otherwise hardly 4-CP degraded in single TiO2 or SnO2 system. Since there is a significant accumulation of byproducts, the buildup of these intermediates on the catalyst surface may be responsible for their poor performance.     

Comparative assessment of the efficiency of Fe-doped TiO2 prepared by two doping methods and photocatalytic degradation of phenol in domestic water suspensions

Fe-doped TiO₂ particles responding to visible light were synthesized by impregnation and calcination method using TiO₂ particle and Ti element, respectively. The optical and the chemical properties were characterized by measuring the X-ray diffraction (XRD) and UV–visible spectroscopy. The onset of absorption shifted to longer wavelengths on doping TiO₂ by the calcination process, which showed a better response as compared to the impregnation method. The photocatalytic reactivity was evaluated by the degradation of phenol with impregnated Fe-doped (0.5% w/w in Fe) and calcined Fe-doped (Fe_xTi_{1 x}O₂, x ¼ 0.005 (Fe/Ti molar ratio)) TiO₂ separately in distilled and tap water. The characterization results have confirmed the advanced possibility of correlation between photoactivity and the special property of sulfur-containing calcined Fe-doped TiO₂. In case of the coagulation of the undoped A-I and the Fe-doped B-I, the photoactivity showed a decrease due to the presence of natural electrolytes and due to the high pH of tap water, whereas in the case of the coagulation of calcined Fe-doped TiO₂ prepared from sulfides (Fe_xTiS₂), the photoactivity showed an increase. In this study, highest catalytic activity was found to be strongly dependent both on catalyst structure and on the type of water used.     

纳米二氧化钛粉体水基体系分散稳定性评价研究

以乙二醇为分散剂，设计了正交实验考察纳米二氧化钛粉体在水中的分散性能，采用重力沉降法、分光光度法、粘度法、Zeta电位测定法、粒径分析等方法评价其分散效果。比较不同的表征手段的优劣及其适用的条件，寻求一种科学、准确、简易的表征二氧化钛粉体分散稳定性的方法。实验结果表明，分光光度法操作简便，对实验仪器要求不高，能快速表征体系的分散稳定性：结合Zeta电位测定和粒径分析，可以得到纳米二氧化钛分散稳定性的可靠信息。最后提出了纳米粉体分散研究的一般方法。     

The photoelectrochemistry of transition metal-ion-doped TiO2 nanocrystalline electrodes and higher solar cell conversion efficiency based on Zn2+-doped TiO2 electrode

Metal-ion-doped TiO₂ nanoparticles were prepared with hydrothermal method. The change of photocurrents at different electrode potentials and wavelengths of incident light showed two different characteristics for various transition metal-ion-doped TiO₂ electrodes. In Zn²⁺ and Cd²⁺-doped TiO₂ electrodes, a characteristic of n-type semiconductor was observed and the incident photon to conversion efficiency (IPCE) were larger than that of pure TiO₂ electrode at the thickness of electrode film of 0.5 m when the content of doped metal ion was less than 0.5%. The effect of the thickness of films on IPCE was also investigated. The IPCE of pure TiO₂ electrode was strongly dependent on the thickness of films. The change tendency of the IPCE for Zn²⁺-doped TiO₂ (0.5% Zn²⁺) electrodes with its thickness was different from that of pure TiO₂. In Fe³⁺, Co²⁺, Ni²⁺, Cr³⁺ and V⁵⁺-doped TiO₂ electrodes, a phenomenon of p-n conversion was observed. The difference of photoresponse and the value of photocurrents are dependent on the doping method and concentration of the doped metal ions. The maximum conversion efficiency of RuL₂(SCN)₂-sensitized Zn²⁺-doped TiO₂ solar cell (1.01%) was larger than that of RuL₂(SCN)₂-sensitized pure TiO₂ solar cell (0.82%) at the same conditions when 0.5 mol·l^–1 (CH₃)₄N·I+0.05 mol·l^–1 I₂ in propylene carbonate solution was used as electrolyte.     

Photocatalytic degradation of azo dyes using Au:TiO2, gamma-Fe2O3:TiO2 functional nanosystems

We report photocatalytic degradation studies on Navy Blue HE2R (NB) dye on significant details as a representative from the class of azo dyes using functional nanosystems specifically designed to allow a strong photocatalytic activity. A modified sol-gel route was employed to synthesize Au and gamma-Fe2O3 modified TiO2 nanoparticles (NPs) at low temperature. The attachment strategy is better because it allows clear surface of TiO2 to remain open for photo-catalysis. X-ray diffraction, Raman and UV-VIS spectroscopy studies showed the presence of gold and iron oxide phases along-with the anatase TiO2 phase. TEM studies showed TiO2 nanocomposite particles of size approximately 10-12 nm. A detailed investigation on heterogeneous photocatalytic performance for Navy Blue HE2R dye was done using the as-synthesized catalysts Au:TiO2 and gamma-Fe2O3:TiO2 in aqueous suspension under 8 W low-pressure mercury vapour lamp irradiation. Also, the photocatalytic degradation of Amranth and Orange G azo dyes were studied. The surface modified TiO2 NPs showed significantly improved photocatalytic activity as compared to pure TiO2. Exposure of the dye to the UV light in the presence of pure and gold NPs attached TiO2 catalysts caused dye degradation of about approximately 20% and approximately 80%, respectively, in the first couple of hours. In the presence of gamma-Fe2O3 NPs attached TiO2, a remarkable approximately 95% degradation of the azo dye was observed only in the first 15 min of UV exposure. The process parameters for the optimum catalytic activity are established which lead to a complete decoloration and substantial dye degradation, supported by the values of the Chemical Oxygen Demand (COD) approximately 93% and Total Organic Carbon (TOC) approximately 65% of the treated dye solution after 5 hours on the employment of the UV/Au:TiO2/H2O2 photocatalytic process.     

Influence of TiO2 nanoparticles on the photovoltaic efficiency of the ITO/PEDOT:PSS/fluorine copolymers/polythiophene: TiO2/Al architecture

Results of a study on the application of a copolymer of fluorine as acceptor and 1H-pyrazolo[3,4-b]quinoxaline as a donor in bulk heterojunction solar cells are given. To the best of our knowledge, 1H-pyrazolo[3,4-b]quinoxaline co-polymers were not applied in organic photovoltaic devices yet. Organic photovoltaic devices as well as devices of active layers with TiO₂ nanocrystals of different crystallite size were investigated. The methods of polymer and TiO₂ nanocrystllites synthesis are presented and their physical properties are given. The fabricated photovoltaic structures possess high values of U _oc voltage as as well as relatively high parameters of I _sc currents. The maximally achieved parameters corresponded to open circuit voltage U _oc  = 1.13[V], and short current density I_sc = 33.49[μA] under illumination 1,3 [μW cm^?2], which correspond to energy conversion efficiency equal to about 0.80 %. The TiO₂ nanocrystallites play a crucial role in the photovoltaics parameters.     

Different methods in TiO2 photodegradation mechanism studies: gaseous and TiO2-adsorbed phases

The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution. It is proved that the photo-oxidizing properties of photocatalyst (TiO(2)) activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by TiO(2). This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant's adsorption on the photocatalyst and radical degradation reactions. The main objective of the study is the understanding of the TiO(2)-photocatalysis phenomenon including gaseous and adsorbed phase mechanisms. Results obtained with three different apparatus are compared; gaseous phases are analysed and mechanisms at the gaseous phase/photocatalyst interface are identified. This study leads to improve understanding of various mechanisms during pollutant photodegradation: adsorption of pollutants on TiO(2) first takes place, then desorption and/or photodegradation, and finally, desorption of degradation products on TiO(2). The association of analytical methods and different processes makes the determination of all parameters that affect the photocatalytic process possible. Mastering these parameters is fundamental for the design and construction of industrial size reactors that aim to purify the atmosphere.     

Reaction paths and efficiency of photocatalysis on TiO2 and of H2O2 photolysis in the degradation of 2-chlorophenol

The kinetics of 2-chlorophenol (2-CP) degradation and mineralization in the aqueous phase was investigated under irradiation at 254 nm, employing either photocatalysis in the presence of titanium dioxide, or hydrogen peroxide photolysis, to compare the efficiency of these photoinduced advanced oxidation techniques. Photocatalysis under 315-400 nm wavelength irradiation was also investigated. The concentration versus time profiles of the degradation intermediates catechol, chloro- and hydroxy-hydroquinone allowed the identification of the reaction paths prevailing under the different experimental conditions. Efficient CCl bond cleavage occurred as a consequence of direct light absorption by 2-CP, while hydroxyl radicals, photogenerated at the water-photocatalyst interface or during H(2)O(2) photolysis, were the main oxidation agents, able to attack both 2-CP and its degradation intermediates. Highest degradation and mineralization efficiencies were achieved under H(2)O(2) photolysis at 254 nm.     

TiO_2纳米材料在直接甲醇燃料电池阳极催化剂中应用的研究进展

阳极催化剂是影响直接甲醇燃料电池(DMFC)性能及成本的主要因素,本文综述了TiO_2纳米粉体、TiO_2纳米管和TiO_2纳米纤维及其复合材料在DMFC阳极催化剂中应用的研究进展,并对其作用、对催化剂活性的影响机理等进行简要分析,展望了其应用前景。     

Fundamentals of TiO2 Photocatalysis: Concepts,Mechanisms, and Challenges

Photocatalysis has been widely applied in various areas, such as solar cells, water splitting, and pollutant degradation. Therefore, the photochemical mechanisms and basic principles of photocatalysis, especially TiO₂ photocatalysis, have been extensively investigated by various surface science methods in the last decade, aiming to provide important information for TiO₂ photocatalysis under real environmental conditions. Recent progress that provides fundamental insights into TiO₂ photocatalysis at a molecular level is highlighted. Insights into the structures of TiO₂ and the basic principles of TiO₂ photocatalysis are discussed first, which provides the basic concepts of TiO₂ photocatalysis. Following this, details of the photochemistry of three important molecules (oxygen, water, methanol) on the model TiO₂ surfaces are presented, in an attempt to unravel the relationship between charge/energy transfer and bond breaking/forming in TiO₂ photocatalysis. Lastly, challenges and opportunities of the mechanistic studies of TiO₂ photocatalysis at the molecular level are discussed briefly, as well as possible photocatalysis models.     

废钒-钛系脱硝催化剂回收利用策略与技术进展

我国以煤为主的能源结构以及日趋严格的氮氧化物排放标准催生了选择性催化还原法(SCR)脱硝技术的广泛应用,由于化学失活或物理结构破损等导致大量的废弃脱硝催化剂产生,造成严重的环境污染.然而,SCR催化剂的主要成分钒、钨、钛等有价金属具有重要的经济和战略价值.随着SCR催化剂的广泛使用,脱硝领域将面临严峻的环境污染和资源浪费问题.针对从废SCR催化剂回收TiO2、WO3、V2 O5等金属元素,目前主要有酸法、碱法或氯化法等主要回收技术路线.在此过程中,通过化学反应,催化剂中钒、钨、钛等金属转变为其他形式化合物或进入到液相,再经过氧化、水解、结晶及煅烧等反应过程,实现产物分离以及产品性能提升的目的.回收的TiO2既可以作为催化剂的载体,也可以用作涂料、光催化剂等其他材料;WO3、V2 O5、MoO3等可以直接作为原料用于脱硝催化剂再生或制备中,也可用于生产其他化工产品.从我国特有的煤电局面,以及钒、钨、钛冶金工业为基础,以资源循环利用的未来绿色化工为理念,从废脱硝催化剂的成分及原料性质出发,建议因地制宜、因时制宜及因材制宜地选择技术路线和生产.通过冶金和化工过程回收其有价金属,从强化工艺、高效回收利用、清洁生产三个方面考虑,探索低温反应降低能耗,减少酸碱用量、水耗,缩短工艺流程,提高产量和品质,从而优化整合出一套适合于废SCR脱硝催化剂回收的工艺,实现脱硝催化剂"生产-再生-回收"绿色循环.本文归纳了废钒-钛系脱硝催化剂回收的研究进展,分别对酸法、碱法和氯化法回收钛白,以及钒-钨分离提纯工艺等进行介绍,分析了废脱硝催化剂回收面临的问题并展望其前景,以期为开发出一套高效清洁的废脱硝催化剂回收技术提供参考.     

Dielectric response and energy storage efficiency of low content TiO2-polymer matrix nanocomposites

TiO₂/epoxy nanocomposites were prepared at different filler concentrations varying from 3 to 12 phr (parts per hundred resin per weight). The dispersion of TiO₂ was examined by Scanning Electron Microscopy and proved to be adequate. Differential Scanning Calorimetry was implemented to determine the glass to rubber transition temperature of the polymer matrix. The dielectric analysis was performed via Broadband Dielectric Spectroscopy in a wide frequency and temperature range. Five different mechanisms were observed in the spectra of the examined composites which are identified, in terms of increasing temperature at constant frequency, as γ, β, Intermediate Dipolar Effect (IDE), α and Interfacial Polarization (IP) relaxation modes. The activation energies of all relaxation modes were calculated. Finally, the dielectric response of the TiO₂ nanocomposites compared to that of the TiO₂ microcomposites reveals that the former exhibit significantly higher energy storage efficiency even at lower TiO₂ concentration than the corresponding of the microcomposites.