Synthesis of size-tunable mesoporous anatase titania spheres by a template-free method

A facile route was presented to fabricate mesoporous anatase titania spheres at low temperature; the titania precursor sphere was prepared through a template-free process and then treated by the boiling water. X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were adopted to characterize the morphology and crystal structure of the products. The adsorption properties and photocatalytic activities were also investigated. The results indicated that the porous structure and anatase nanocrystals were gradually formed from the surface to the interior of the titania precursor spheres with increasing treatment time. Moreover, there was little change in the size of the spheres during boiling water treatment, thus the size of the mesoporous anatase titania spheres could be easily tailored by controlling the diameter of precursor spheres. The as-prepared product showed excellent adsorption capacity and photocatalytic activity than the commercial P25 due to its high specific surface area.     

Microstructure, optical and optoelectrical properties of mesoporous nc-TiO2 films by hydrolysis-limited sol-gel process with different inhibitors

Mesoporous nanocrystalline titania (nc-TiO₂) films were synthesized by sol-gel route using poly (alkylene oxide) block copolymer as template and tetrabutyl orthotitanate as titanium source. Influence of acetylacetone (AcAc), glacial acetic acid, HCl and AcAc-HCl as inhibitors on hydrolysis/condensation reaction was investigated. The mesopore structure, crystalline phase and optical characteristics were analyzed by N₂ adsorption, X-ray diffraction, transmission electron microscopy and UV-VIS-NIR spectrum. Photoaction measurements were performed on dye-sensitized solar cells (DSSCs) using the mesoporous nc-TiO₂ as photoanodes. The results show that the formed films are anatase phase and mesoporous structure. Different restraining mechanisms of these inhibitors to hydrolysis/condensation process lead to different mesoporous structure whose specific surface area (S_BET) varies from 34 to 176 m²/g, and crystal size is from 5.6 to 38.2 nm. The mesoporous photoanode with high S_BET and large crystalline grains may be responsible for increasing conversion efficiency of the DSSCs.     

Aerosol-assisted synthesis of nanoporous silica/titania nanoparticles composites and investigation of their photocatalytic properties

Nanoporous silica/titania nanoparticles composites with relatively large TiO2 content are successfully synthesized by aerosol-assisted co-assembly. By the hybridization of titania with nanoporous silica having high surface area, both the adsorption capability and the reaction rates for the photocatalytic decomposition of methylene blue (MB) are dramatically improved in comparison with unmodified titania nanoparticles without nanoporous silica. Through the quantitative evaluation of the amount of adsorbed and photo-decomposed organic molecule throughout the reaction process, the role of nanoporous silica layers on titania surface is clarified. Rational design of future hybrid photocatalyst with precisely controlled nanostructure will be possible by optimization of our synthetic procedure and careful study of the adsorption and photocatalytic properties.     

氮掺杂二氧化钛纳米粉体的制备及光催化性能的研究

以钛酸正四丁酯为钛源、盐酸胍为氮源,用溶胶-凝胶法制备出了氮掺杂的TiO2纳米粉体,采用XRD、TEM、BET和UV-Vis对所制备的粉体进行了物相、形貌和结构表征,并分别在紫外光和可见光下进行了样品对甲基橙的光催化降解实验。结果表明,用该方法制备的N掺杂二氧化钛纳米粉体具有较单一的晶粒尺寸分布,分散性好,团聚少;掺杂样品在紫外光下对甲基橙的降解率比不掺杂样品有大幅度提高,并且在可见光下也具有较高的活性。     

Enhanced efficiency and improved photocatalytic activity of 1 : 1 composite mixture of TiO<Subscript>2</Subscript> nanoparticles and nanotubes in dye-sensitized solar cell

TiO₂-based nanotubes (NTs), nanoparticles (NPs) and composite structural film (50% NP + 50% NT film) were synthesized by sol-gel hydrothermal process. Synthetic indigo dye was used as a sensitizer with the unique combination of electrolyte (EMII + BMII + PMII) and with cobalt sulphide as counter electrode. The structure and morphology of the three films, namely, NP, NT and NPNT is studied through X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The absorption spectra and incident photon-to-current conversion efficiency (IPCE) of the three films were compared and found to be higher for NPNT film. The efficiency and photocatalytic activity of three films were evaluated. The composite structure showed improved efficiency (1.72%) than NP (1%) and NT films (0.78%). The photocatalytic activity of the three films were measured using organic dye, methylene blue under UV light radiation. The composite structure showed higher dye absorption and higher rate of reaction with time. This paper certainly proves that there are many rooms to focus on the photoanode configuration, which plays a key role to improve the efficiency of dye-sensitized solar cell (DSSC).     

TiO2负载硅铝陶瓷介孔球对甲基橙吸附和光催化 降解的研究

：以自制硅铝陶瓷介孔球为基体,经溶胶凝胶法制备TiO2溶胶并将其负载于硅铝陶瓷介孔球表面,用于甲基橙溶液的吸附和光催化降解,再利用扫描电子显微镜、X射线衍射仪、傅里叶变换红外光谱仪和可见分光光度计对样品的表观形貌、晶体结构、吸附和光催化性能等进行表征和测定。研究结果表明：TiO2是以粗糙度较高的多层膜包覆于硅铝陶瓷介孔球表面且TiO2为锐钛矿晶型;在黑暗条件下,硅铝陶瓷介孔球和TiO2负载硅铝陶瓷介孔球对甲基橙仅起到吸附作用,且两者的吸附性能较接近;但在紫外光照条件下,TiO2负载硅铝陶瓷介孔球对甲基橙除有吸附作用外还表现出较好的光催化降解活性。     

Preparation and characterization of nanostructured MWCNT-TiO2 composite materials for photocatalytic water treatment applications

Nanoscale composite materials containing multi-walled carbon nanotubes (MWCNT) and titania were prepared by using a modified sol-gel method. The composites were comprehensively characterized by thermogravimetric analysis, nitrogen adsorption-desorption isotherm, powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy. The analysis revealed the presence of titania crystallites of about 7.5 nm aggregated together with MWCNT in particles of 15-20 nm of diameter. The photoactivity of the prepared materials, under UV or visible irradiation, was tested using the conversion of phenol from model aqueous solutions as probe reaction. A synergy effect on the photocatalytic activities observed for the composite catalysts was discussed in terms of a strong interphase interaction between carbon and TiO₂ phases by comparing the different roles of MWCNT in the composite materials.     

Structural and chemical investigation of CdSe crystals deposited in a nanoporous sol-gel: Effect of chemistry and defects on photovoltaic properties

Nanoporous cadmium selenide films were prepared by electro crystallization inside a nanoporous SiO₂ network, prepared by a sol-gel process on an electrically conducting indium tin oxide (ITO) substrate. Subsequent removal of the SiO₂ template should, according to literature reports, give a nanoporous network of CdSe in electronic contact with the substrate. The structure/morphology of the film was explored during the preparative steps by grazing incidence small/wide angle X-ray scattering, scanning electron microscopy and atomic force microscopy. The chemistry was studied by time of flight secondary ion mass spectrometry methodologies, such as imaging and depth profiling that maps the in-plane and in-depth distribution of chemistry, i.e. full 3-dimensional chemical imaging of the nanoporous CdSe layer. Finally, the nanoporous CdSe films were tested as electron conductors in hybrid organic/inorganic solar cells employing CdSe as the electron conductor and poly-3-hexylthiophene as the hole conductor. ITO and gold served as the electrodes. It was found that removal of the SiO₂ from the micellar SiO₂-CdSe nanostructure led to a collapse of the resulting CdSe structure with a poor structural conservation. Furthermore, a high pinhole density in the sol-gel resulted in a high degree of shunting paths that led to poor photovoltaic properties.     

模板法制备介孔TiO2及其光催化性能研究

以十六烷基三甲基溴化铵(CTAB)作为模板剂,钛酸正四丁酯(TBOT)为钛源,异丙醇为溶剂,通过溶胶-凝胶过程合成出介孔TiO2前驱体凝胶后,经老化、焙烧得到了TiO2介孔材料.利用XRD、HR-TEM、TGA、N2的吸附-脱附、BET等方法对材料的结构、形貌、比表面积、孔径分布进行表征.以亚甲基蓝的降解为模型反应,对其催化性能进行评价并与商品DegussaP-25进行比较.实验结果表明,比表面积为137.5m2/g、孔径为8.62nm的锐钛型介孔TiO2具有很高的催化活性.     

高活性氮掺杂介孔二氧化钛的合成及性能研究

采用水热法, 以聚乙二醇(PEG)为模板, N,N-二甲基甲酰胺为氮源, 制备了氮掺杂的介孔二氧化钛。并用X射线粉末衍射(XRD)、傅立叶红外光谱(FTIR)、BET、透射电子显微镜(TEM)、紫外一可见漫反射谱(DRS)和X射线光电子能谱(XPS)等技术手段对制备样品进行了表征。结果表明: 所合成的样品具有锐钛矿结构,直径约20 nm, 并且具有一定的可见光活性。以甲基橙(MO)为光降解模型, 样品在可见光区表现出了较好的催化活性, 这取决于烷氧基和氮掺杂的协同效应。     

Preparation and application of nanoglued binary titania-silica aerogel

Nanoglued binary titania (TiO2)-silica (SiO2) aerogel, as a novel type of photocatalyst, has been synthesized on glass substrates. Using an about-to-gel SiO2 sol as nanoglue, anatase TiO2 aerogel was immobilized into a three-dimensional mesoporous network of the SiO2. Factorial designs were employed to optimize both TiO2 aerogel and binary TiO2-SiO2 aerogel synthesis. Characterization of the as-prepared TiO2 and binary samples by surface area, porosity, and surface chemical composition showed that the photocatalysts were high-surface-area nanoporous materials, with a Ti4+ valency. The binary aerogel exhibited high photocatalytic activity for the degradation of methylene blue (MB) under simulated solar light; the reaction followed the pseudo first-order Langmuir-Hinshelwood (L-H) kinetic model. Fluorescence spectroscopy revealed that the hydroxyl (*OH) radical was formed during the illumination of the binary TiO2-SiO2 aerogel in a solution of probe molecules, which corroborates the probable mechanism of hydroxyl radical oxidation of contaminants in photocatalytic reactions.     

Photocatalytic activity of vanadium-doped titania-activated carbon composite film under visible light

A V-doped titania-activated carbon composite film was prepared by a modified sol-gel method under mild condition. X-ray diffraction analysis revealed that the titania was a pure anatase phase. From scanning electron microscopy and N₂ adsorption-desorption measurements, we found that the composite film was porous since it formed a micro-nano structure. The photocatalytic activity of such film was evaluated through degradation of azo-dye Reactive Brilliant Red under visible light, and was compared to commercially available TiO₂, pure titania and vanadium-doped titania films. Results showed that the photocatalytic activity was enhanced a lot. It was due to expansion of the absorption edge by vanadium doping, and the synergistic effect of activated carbon with titania. Furthermore, the hydrophilic property of the as-prepared composite film was superior to other samples.     

Nanoporous titania-coated alumina membranes: sol-gel synthesis and characterisation

In this work, nanoporous titania top layers were deposited by dip-coating process on microporous alpha-alumina substrates using the sol-gel process. The alumina substrates were synthesized by slip casting method using Taguchi optimising approach. The microporous substrate was then used to coat nanoporous titania layers by the sol-gel method. The thickness, pore size, structure and permeability of the membranes were characterised using SEM, XRD, STA and Hg-Porosimetry. The process conditions to achieve defect-free nanoporous titania layers with the average pore size of about 4 nm coated on the microporous alumina substrates with the average pore size of about 270 nm were determined.     

V掺杂TiO2纳米管阵列的制备及光催化研究

以钒钛合金为原料,应用阳极氧化法制备出高度致密、有序的V掺杂TiO2纳米管阵列。应用扫描电镜(SEM)和粉末X光衍射仪(XRD)表征分析纳米管阵列的形貌和结构,结果表明在浓度不同的HF电解液下制备出径向不同的纳米管阵列,电解液浓度(0.5%～1.5%(质量分数)),管径变化(39.7～72.7nm)。在室温、可见光照射条件下,以10mg/L的亚甲基蓝溶液为模拟污染物进行光催化降解试验,研究了其光催化性能。结果显示V掺杂TiO2纳米管阵列光催化性能优于纯TiO2纳米管,且在HF电解液浓度为1.0%(质量分数)时制备出来的TiO2纳米管光催化降解有机毒物性能最佳。     

An investigation of nanostructured rutile and anatase plates for improving the photosplitting of water

Developing new semiconductor materials for improving photocatalytic reactivity is important for solving the challenging environmental and energy problems we are facing today. This work focuses on increasing the quantum efficiency in titania photocatalysts for photocatalytic (oxidation of acetaldehyde) and photosynthetic (photosplitting of water) reactions by synthesizing pure phase rutile and anatase nanostructures with well defined morphologies and investigating their photocatalytic performance compared to a commercial titania photocatalyst (Degussa P25). Nanostructured anatase is dominated by {100} surfaces with a small amount of {101} surfaces, whereas the rutile nanoplates consist of nanorods dominated by {110} and {111} crystal surfaces. In accordance with the signals from electron spin resonance (ESR) spectra, both nanostructured anatase and rutile phases have high photocatalytic activity for photosplitting of water compared to P25 titania. The anatase phase shows a high activity for photocatalytic oxidation (PCO) of acetaldehyde whereas the rutile phase shows a lower activity. The results of these experiments basically agree with previously published works that reported that the oxidation and reduction sites on rutile particles are on the {011} and {110} faces respectively, and on {001} and {011} faces respectively for anatase particles. The results have important implications for enhancing the photocatalytic activity of titania for environmental remediation, increasing the quantum efficiency in photo-voltaic (PV) solar cells and other photo-assisted processes.     

Template- and surfactant-free synthesis of mesoporous TiO2 spheres with hollow core-shell structure for dye-sensitized solar cells

We have demonstrated a simple and effective hydrothermal route to synthesize titania mesoporous spheres with hollow core-shell structure. The synthesis is free of any surfactants or templates. The formation mechanism is investigated on the basis of the results of time-dependent experiments. The as-obtained mesoporous titania spheres with a specific surface area of 21.5?m²?g^?1 and diameters of 1.2–2.3?μm are composed of anatase titania nanocrystals. The excellent light scattering property of mesoporous titania spheres with hollow core-shell structure is proved. A higher cell efficiency of 8.27% is achieved with mesoporous titania spheres with hollow core-shell structure as a light scattering layer, compared with a cell efficiency of 6.63% for the P25 film electrode with the similar thickness. The higher cell efficiency is attributed to the hollow core-shell structure scattering layer, resulting in excellent pore fitting for electrolyte diffusion, enhanced light scattering ability, and reduced charge recombination.     

Optimizing sol-gel infiltration for the fabrication of high-quality titania inverse opal and its photocatalytic activity

This article reports an optimized sol-gel opal infiltration technique for the fabrication of high-quality titania inverse opal. Different from previous reports, the presently proposed method is facile, efficient and suitable for other inorganic oxide. We have compared two different infiltration strategies and their influences on the structure, photonic properties and photocatalytic activity. The obtained titania inverse opal displays excellent photonic properties with photonic band gap at 320 nm and better photocatalytic effect, which is attributed to its high-quality inverse opal nanostructure. Reproducibility tests prove that the photocatalytic activity of the resultant titania inverse opal remains intact even after five repeated photocatalytic reactions under the same procedure and experimental conditions.     

Degradation of nitrobenzene using titania photocatalyst co-doped with nitrogen and cerium under visible light illumination

A type of nitrogen and cerium co-doped titania photocatalyst, which could degrade nitrobenzene under visible light irradiation, was prepared by the sol-gel route. Titanium isopropoxide, ammonium nitrate, and cerium nitrate were used as the sources of titanium, nitrogen, and cerium, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffusive reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and N(2) adsorption-desorption isotherm were employed to characterize the as-prepared photocatalyst. The degradation of nitrobenzene under visible light illumination was taken as probe reaction to evaluate the photoactivity of the co-doped photocatalyst. The commercial TiO(2) photocatalyst (Degussa P25), which was thought as a high active photocatalyst, was chosen as standard photocatalyst to contrast the photoactivity of the nitrogen and cerium co-doped titania photocatalyst. The results showed that the photocatalytic performance of the nitrogen and cerium co-doped titania was related with the calcination temperature and the component. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. The doping cerium atoms existed in the forms of Ce(2)O(3) and dispersed on the surface of TiO(2). The improvement of the photocatalytic activity was ascribed to the synergistic effects of the nitrogen and cerium co-doping.     

Ultrasonic-assisted synthesis and solar photoactivity investigation of Ce,B co-modified TiO2 nanoparticles

In this study, Ce and B co-modified TiO₂ nanoparticles were prepared using an ultrasonic-assisted sol–gel method. The prepared sample was characterized by X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy and BET analysis. In order to detect the effect of dopants on the titania, the photocatalytic activity of these as-prepared titania nanoparticles was determined by following the degradation of the reactive dye methylene blue under solar light irradiation. The activity was compared to that of pure titania. It was revealed that the photocatalytic activity of the Ce and B co-modified titania nanoparticles produced a significant enhancement compared to pure titania. The apparent rate constant of the as-prepared co-modified titania was 3 times higher than that of pure titania.     

Synthesis of Ag-AgBr/Al-MCM-41 nanocomposite and its application in photocatalytic oxidative desulfurization of dibenzothiophene

A series of Ag-AgBr/Al-MCM-41 nanocomposites were synthesized by dispersion of Ag-AgBr on mesoporous silica Al-MCM-41 obtained from natural bentonite. The synthesized Ag-AgBr/Al-MCM-41 composites with Ag nanoparticles growing on the surface of Al-MCM-41 were used for photocatalytic oxidative desulfurization of dibenzothiophene. The physical properties of Ag-AgBr/Al-MCM-41 were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ultraviolet–visible diffuse reflection spectroscopy (UV–Vis DRS), photoluminescence (PL) emission spectra, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity results showed that in the presence of 40% Ag-AgBr/Al-MCM-41 photocatalyst the oxidative desulfurization of dibenzothiophene reached the maximum efficiency at 99.22% and the photocatalytic activity still keeps high level after four cycles.