Synthesis of TiO2 photocatalysts with abundant surface defects using a TiO2@NaCl precursor

TiO2 nanoparticles have been synthesized by using a TiO2@NaCl core-shell structure as the precursor. The surface defects were well preserved by the NaCl shell, and therefore high oxygen adsorption capacity was observed. After the NaCl shell was removed, the resulting pure TiO2 nanoparticles were of anatase phase and uniform size of around 20?24 nm. The presence of an abundance of surface defects contributes to the high photocatalytic activity of the synthesized materials, and the TiO2 materials obtained from the TiO2@NaCl precursor can be used as efficient photocatalysts for degradation of rhodamine B under UV light irradiation.     

掺杂TiO2介孔材料的合成与表征

基于溶胶-凝胶过程, 以非表面活性剂有机小分子三乙醇胺为模板剂, 合成了TiO2及Fe3+/V5+-TiO2介孔材料. 利用XRD, TEM, BET, UV-Vis DRS等手段表征了材料的结构、形貌、比表面积、孔径分布及吸光性能. 研究结果表明, 用乙醇萃取法脱除模板剂可形成具有蠕虫状孔道结构的TiO2介孔材料, 而利用焙烧法在450 ℃脱除模板剂时可引起孔道的塌陷. 掺杂Fe3+或V5+可稳定材料的介孔结构, 适宜的掺杂摩尔分数为0.5％. 于450 ℃下焙烧后, 掺杂Fe3+/V5+的TiO2的平均孔径分别为10.5和9.6 nm, 比表面积分别达到103.59和90.80 m2/g. 相对于P25光催化剂, 掺杂Fe3+或V5+的TiO2吸光带边红移至可见光区, 说明掺杂离子在此合成过程中可有效地进入TiO2的晶格结构而引起其微观电子结构的改变.     

掺杂纳米金粒子的火焰氧化TiO2膜的光电化学性质的研究

A nano-Au modified TiO2 electrode was prepared via the oxidation of Ti sheet in flame and subsequent modification with gold nanoparticles. The results of SEM and TEM measurements show that the Au nanoparticles are well dispersed on TiO2 surface. A near 2-fold enhancement in photocurrent was achieved upon the modification with Au nanoparticles. From the results of photocurrent and electrochemical impedance experiments it was found that the flatband potential of nano-Au/TiO2 electrode negatively shifted about 100 mV in 0.5 mol/L Na2SO4 solutions compared with that of bare TiO2 electrode. The improvement of photoelectrochemical performance was explained by the inhibition for charge recombination of photo-induced electrons and holes, and the promotion for interracial charge-transfer kinetics at nano-Au/TiO2 composite film. Such nanometal-semiconductor composite films have the potential application in improving the performance of photoelectrochemical solar cells.     

Mesoporous Au/TiO2 Nanocomposite Microspheres for Visible‐Light Photocatalysis

Mesoporous Au/TiO₂ nanocomposite microspheres have been synthesized by using a microemulsion‐based bottom‐up self‐assembly (EBS) process starting from monodisperse gold and titania nanocrystals as building blocks. The microspheres had large surface areas (above 270 m² g^?1) and open mesopores (about 5 nm), which led to the adsorption‐driven concentration of organic molecules in the vicinity of the microspheres. Au nanoparticles, which were stably confined within the microspheres, enhanced the absorption over the broad UV/Vis/NIR spectroscopic range, owing to their strong surface plasmon resonance (SPR); as a result, the Au nanoparticles promoted the visible‐light photo‐induced degradation of organic compounds.     

TiO2/SiO2复合材料的制备与表征

以钛酸四丁酯和正硅酸乙酯为原料,采用溶胶凝胶法和水解法相结合,在室温下制备了两种形态的TiO2/SiO2复合材料.采用透射电镜、傅里叶红外光谱、X射线衍射和紫外-可见光谱等测试方法对所得复合材料进行了表征,并对其光催化降解甲基橙溶液的性能进行了研究.结果表明:对TiO2进行表面处理制备的TiO2/SiO2复合材料比以SiO2为载体制备的TiO2/SiO2复合材料在光催化和抗紫外线性能上更优异.     

TiO2/SiO2/CeO2复合纳米薄膜超亲水性能的研究

采用溶胶凝胶法在载玻片表面制备了均匀透明的TiO2-SiO2-CeO2超亲水性薄膜，并用X射线衍射、傅立叶红外光谱、紫外-可见分光光度计研究了SiO2及稀土铈添加对TiO2薄膜表面特征及超亲水性能的影响。结果表明，Ti02-SiO2-CeO2薄膜亲水性能及亲水持续效应显著提高。实验中掺杂的铈是以三价离子态引入的，由于Ce^3 在高温下很容易氧化，故在薄膜中铈主要以四价态形式存在。Ce^4 在光激发下很容易捕获光生电子生成Ce^3 离子，光生空穴则与表面氧离子反应形成氧空位，而氧空位对亲水性的提高具有关键作用。添加SiO2后，薄膜表面的羟基含量增加，这主要是由于TiO2与SiO2复合在表面形成Lewis酸所致。表面稳定的羟基可使亲水性在暗中保持较长时间，因而亲水持续效应提高。添加SiO2及稀土铈后，薄膜中TiO2晶粒尺寸变小，量子效应增强，这也导致亲水性提高。因此添加稀土铈及SiO2后，薄膜表面的氧空穴增多，薄膜的超亲水性及亲水持续效应提高。     

Azo dyes degradation using TiO2-Pt/graphene oxide and TiO2-Pt/reduced graphene oxide photocatalysts under UV and natural sunlight irradiation

The photocatalytic degradation of azo dyes with different structures (amaranth, sunset yellow and tartrazine) using TiO₂-Pt nanoparticles (TPt), TiO₂-Pt/graphene oxide (TPt-GO) and TiO₂-Pt/reduced graphene oxide (TPt-rGO) composites were investigated in the presence of UV and natural sunlight irradiation. The composites were prepared by a combined chemical-thermal method and characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Infrared (FTIR) and UV–Vis spectroscopy. The modification of TiO₂-Pt with graphene oxide shifted its optical absorption edge towards the visible region and increased its photocatalytic activity under UV and natural sunlight irradiation. The efficiency of catalysts on azo dyes degradation (in similar conditions) reached high values (above 99%) under sunlight conditions, proving the remarkable photocatalytic activities of obtained composites. TPt-GO nanocomposite exhibited higher photoactivity than TPt or TPt-rGO, demonstrating degradation efficiencies of 99.56% for amaranth, 99.15% for sunset yellow and 96.23% for tartrazine. The dye photodegradation process follows a pseudo-first-order kinetic with respect to the Langmuir-Hinshelwood reaction mechanism. A direct dependence between azo dyes degradation rate and chemical structure of dyes has been observed.     

Comment on "Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions"

We comment on the electrorheological (ER) behavior of copper phthalocyanine (CuPC)-doped mesoporous TiO(2) suspensions. Our Cole-Cole plot not only fits the dielectric spectra of the two CuPC-doped mesoporous TiO(2) templated ER fluids with CuPC/cetyltrimethylammonium (CTAB) molar ratios of 0.10 and 0.15, respectively, but also provides a better explanation of their polarizability by differentiating their ER performance.     

锐钛矿型纳米氧化钛及其复合材料的低温制备技术

探索低温合成高催化活性纳米TiO2及其复合材料的有效方法,突破传统的高温煅烧法制备锐钛矿相纳米TiO2光催化剂带来的局限,已成为该领域研究的热点问题。本文综述了近年来低温合成锐钛矿型纳米TiO2光催化剂的研究进展,讨论了目前所报道的各种方法（胶溶－相转移法、衍生溶胶－凝胶法、水热法、超声水解法、微波照射法、微乳液法和低温直接氧化法）的原理、操作步骤、反应进程以及优缺点。针对纳米TiO2晶体用作光催化剂时固有的缺陷,即量子效率低且无法利用可见光,进一步评述了离子掺杂、贵金属沉积以及半导体复合等纳米TiO2复合材料的低温制备技术,展望了该领域今后的发展方向和研究重点。     

Thermal behaviour study of some sol-gel TiO2 based materials

Among the great number of sol-gel materials prepared, TiO₂ holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO₂ nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO₂ matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO₂ crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.     

Reactive uptake of HONO to TiO2 surface: "dark" reaction

The interaction of HONO with TiO(2) solid films was studied under dark conditions using a low pressure flow reactor (1-10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to TiO(2) was studied as a function of HONO concentration ([HONO)(0) = (0.3-3.3) × 10(12) molecules cm(-3)), water concentration (RH = 3 × 10(-4) to 13%), and temperature (T = 275-320 K). TiO(2) surface deactivation upon exposure to HONO was observed. The measured initial uptake coefficient of HONO on TiO(2) surface was independent of the HONO concentration and showed slight negative temperature dependence (activation factor = -1405 ± 110 K). In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ(0) = 1.8 × 10(-5) (RH)(-0.63) (calculated using BET surface area, 40% uncertainty) at T = 300 K. NO(2) and NO were observed as products of the HONO reaction with TiO(2) surface with sum of their yields corresponding to nearly 100% of the nitrogen mass balance. The yields of the NO and NO(2) products were found to be 42 ± 7% and 60 ± 9%, respectively, independent of relative humidity, temperature, and concentration of HONO under experimental conditions used. The contribution of aerosol to the total HONO loss in the boundary layer (calculated with initial uptake data for HONO on TiO(2) surface) showed the unimportance of this process in the atmosphere. In addition, the diffusion coefficient of HONO in He was determined to be D(HONO-He) = 490 ± 50 Torr cm(2) s(-1) at T = 300 K.     

Chromogenic WPA/TiO 2 Hybrid Gels and Films

A novel low-temperature electrochromic and photochromic material in the form of gels and thin solid films composed of H₃PW₁₂O₄₀·nH₂O (WPA) incorporated in titanium oxide gel issued of Ti(OPr ⁱ )₄ with addition of acetic acid were made via the sol-gel route by the dip-coating technique. Gels in bulk and thin film forms have been studied with the help of FT-IR transmission, reflection absorption and Raman spectroscopy. Similarity of the characteristic band frequencies with pure WPA confirmed that entrapped Keggin salt is well preserved inside the gel. Photochromism of WPA/TiO₂ gels which appears after short exposure to UV (λ=366 nm) radiation is related to the excitation effect of branched alcohol leading to formation of carbonyl modes due to the alcohol transformation to aldehyde. Electrochromic properties of WPA/TiO₂ gel films were tested in aqueous 0.001M HClO₄ and 0.1M LiClO₄ electrolytes as well as in the sol-gel electrochromic device (ECD) composed of LiClO₄ doped ormolyte and Sb:Mo:SnO₂ counter electrode film with optically passive response. Slight improvement of the WPA/TiO₂ intercalation/deintercalation kinetics was obtained with the films exhibiting one order of magnitude higher electronic conductivity which were made with addition of in situ polymerized pyrrole with Fe(NO₃)₃.     

Mesoporous electrode material from alumina-stabilized anatase TiO2 for lithium ion batteries

A mesoporous electrode material whose structure is composed of anatase nanocrystals stabilized by alumina is reported. Powder X-ray diffraction shows the anatase phase only, but micro-Raman spectroscopy shows that the materials have a core-shell morphology with grains of bulk anatase covered by a thin rutile layer on the surface. This structure is unique when compared to analogous materials stabilized by zirconia (PNNL-1). Nitrogen adsorption isotherms demonstrate a monotonous increase in surface area and mesopore volume with increasing Al content. Thin film electrodes from these materials were characterized by lithium insertion electrochemistry. Cyclic voltammograms exhibit significant differences in Li accommodation in Al-free and Al-stabilized materials.     

TiO2 nanocrystals/graphene hybrids with enhanced Li-ion storage performance

TiO_2 nanocrystals/graphene hybrids(TiO_2-G) with ultrafine TiO_2 nanocrystals(~7 nm in size) conformally coated on ultrathin graphene nanosheets(~ 2 layers thick) were successfully prepared via a facile one-pot solvothermal route under mediated conditions.With the feature of large surface area,abundant mesopores and high thermal stability,the TiOi-G nanohybrids exhibited large reversible Li-ion storage capacity with excellent cycling stability(629 mAh·g~(-1) after 400 cycles at a current of 60 mA·g~(-1)) and good rate capability(184 mAh·g~(-1) at a current density of 3 A·g~(-1)) due to the synergetic effects and strong interactions between the components,showing great promise in applications for advanced energy storage devices.     

PMMA/SiO2透明块体材料的热性能分析与微观结构表征

以正硅酸乙酯为前驱体,采用无溶剂水解技术,制备出了均一、稳定、透明的二氧化硅溶胶,通过透射电镜分析,粒径在100nm左右;在溶胶中加入甲基丙烯酸甲酯（MMA）和偶氮二异丁腈（AIBN）,采用热固化的方式制备出透明的块体PMMA/SiO2杂化材料,通过差热分析、热重和透射电镜表征杂化材料的热性能和微观结构,实验结果表明：当体系中的SiO2含量超过20%时,杂化材料无明显的玻璃化转变温度;无机相均匀分散在有机相中,两相之间没有明显的相分离现象,制备出均一的杂化材料。     

Synthesis of Mesoporous TiO2/SiO2 Hybrid Films as an Efficient Photocatalyst by Polymeric Micelle Assembly

Thermally stable mesoporous TiO₂/SiO₂ hybrid films with pore size of 50 nm have been synthesized by adopting the polymeric micelle‐assembly method. A triblock copolymer, poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide), which serves as a template for the mesopores, was utilized to form polymeric micelles. The effective interaction of titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) with the polymeric micelles enabled us to fabricate stable mesoporous films. By changing the molar ratio of TEOS and TTIP, several mesoporous TiO₂/SiO₂ hybrid films with different compositions can be synthesized. The presence of amorphous SiO₂ phase effectively retards the growth of anatase TiO₂ crystal in the pore walls and retains the original mesoporous structure, even at higher temperature (650 °C). These TiO₂/SiO₂ hybrid films are of very high quality, without any cracks or voids. The addition of SiO₂ phase to mesoporous TiO₂ films not only adsorbs more organic dyes, but also significantly enhances the photocatalytic activity compared to mesoporous pure TiO₂ film without SiO₂ phase.