One-pot synthesis of highly crystalline mesoporous TiO2 nanoparticle assemblies with enhanced photocatalytic activity

We report an unprecedented formation of mesoporous titania via a surfactant-assisted aggregating assembly of TiO(2) nanoparticles. These mesostructures possess a highly crystalline anatase phase, large and accessible pore surface area, and exhibit superior photocatalytic performance.     

Efficient silver modification of TiO2 nanotubes with enhanced photocatalytic activity

In this paper, Ag(CH₃NH₂)₂⁺, Ag(NH₃)₂⁺ and Ag⁺ with different radii have been used as silver sources to find out the distribution of Ag ions on the H-TNT surface, which is critical to the final performance. The influence of this distribution on visible photocatalytic activity is further studied. The results indicate that, when Ag⁺ used as silver source with low concentration, these small sized silver ions mainly distribute on interlayer spacing of H-TNT. After heat-treatment and photo-reduction, the generated silver nanoparticles uniformly embed in the anatase TiO₂ nanotube walls, and bring large interfacial area between Ag particles and TiO₂ nanotubes. The separation effect of photogenerated electron-hole pair in TiO₂ is enhanced by Ag particles, and achieves the best at 0.15 g/L, much higher than P25, TiO₂/0, Ag-N@TiO₂ and Ag-C-N@TiO₂. This paper provides new ideas for the modification of TiO₂ nanotubes.     

A facile synthesis of hierarchical flower-like TiO2 with enhanced photocatalytic activity

The hierarchical flower-like TiO₂ has been achieved by using a simple solvothermal process without any surfactants or colloidal crystals as a template. The structures of the products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption analysis. The relationship between hierarchical structure and photocatalytic performance has been presented based on detailed characterizations. It was found that the hierarchical flower-like structure was a benefit for light absorption and significantly enhanced the photocatalytic activity.     

Facile synthesis of spiny mesoporous titania tubes with enhanced photocatalytic activity

We demonstrate here for the first time an original and facile approach to synthesizing a novel TiO(2) tube with a spiny mesoporous wall. The photocatalytic activity of the spiny mesoporous tube was greatly enhanced owing to the superior light reflecting ability of the tubular structure as well as the crosslinked spiny nanosheets.     

Defect induced nickel,nitrogen-codoped mesoporous TiO2 microspheres with enhanced visible light photocatalytic activity

Nickel, nitrogen-codoped mesoporous TiO₂ microspheres (Ni–N–TiO₂) with high surface area, and an effective direct band gap energy of ∼2.58 eV. Nickel sulfate used as the Ni source and ammonia gas as the N source here. The efficiency of the as-prepared samples was investigated by monitoring the degradation of Rhodamine B under visible light irradiation. The experimental results indicate that Ni-doped mesoporous TiO₂ microspheres show higher photocatalytic activity than mesoporous TiO₂ microspheres under visible light irradiation. It mainly due to that the electron trap level (Ni²⁺/Ni⁺) promoting the separation of charge carriers and the oxygen vacancies inducing the visible light absorption. In addition, Ni–N–TiO₂ shows enhanced activity compared with Ni–TiO₂. Codopants and dopants are found to be uniformly distributed in TiO₂ matrix. Among the all samples the 0.5% molar quantity of Ni dopant and 500 °C 2 h nitriding condition gives the highest photocatalytic activity. The treatment of ammonia gas on Ni–TiO₂ sample induced oxygen vancancies, substitutional and interstitial N. A suitable treatment by ammonia gas also promote separation of charge carriers and the absorption of visible light. The active species generated in the photocatalytic system were also investigated. The strategy presented here gives a promising route towards the development of a metal and non-metal codoped semiconductor materials for applied photocatalysis and related applications.     

介孔AgBr/TiO_2-SiO_2光催化剂的制备及其可见光催化活性

通过沉积法将光活性AgBr半导体负载到介孔TiO_2-SiO_2载体上合成了新型的AgBr/TiO_2-SiO_2复合光催化剂.采用X射线衍射仪、高分辨透射电镜、紫外-可见吸收光谱仪等分析了AgBr/TiO_2-SiO_2复合光催化剂的结构和光谱性质;并采用BET法测定了样品的比表面积和孔分布.结果表明,介孔TiO_2-SiO_2载体的比表面积为135.5m2/g,平均孔径约为3.8nm,AgBr的负载可以有效地将AgBr/TiO_2-SiO_2复合光催化剂的吸收光谱从紫外光区扩展到可见光区,且AgBr和TiO_2形成了异质结结构,强化了AgBr与介孔TiO_2-SiO_2载体的协同作用.以罗丹明B作为探针分子,评价了AgBr负载量对复合光催化剂可见光催化活性的影响.结果发现,当AgBr∶TiO_2=0.1,0.2,0.3和0.4(物质的量之比,下同)时,复合光催化剂的光催化反应速率常数分别为0.008 5、0.028 6、0.024 6和0.019 3min-1,活性先增加后减小,当AgBr∶TiO_2=0.2时,复合光催化剂表现出最高的光催化活性,并且在5次循环测试中均表现出较高的光催化活性.     

二氧化钛纳米管的制备与光催化活性

用阳极氧化法,室温条件下在含NH4F和H2O的电解液(丙三醇+NH4F+H2O;乙二醇+NH4F+H2O)中制备了TiO2纳米管阵列。用环境扫描电子显微镜(SEM)、X射线衍射仪(XRD)表征二氧化钛纳米管阵列的微观形貌和物相结构。在丙三醇电解液中,电压为60 V,65 V,70 V,75 V制备的纳米管直径依次为160、170、190、220 nm。对甲基橙(10 mg/L)降解测试TiO2纳米管阵列的光催化性能。研究结果表明:在100 V阳极电压制备经过500℃退火处理后的TiO2纳米管阵列的光催化效果最好,其光催化降解率在光照时间120 min时达到89.2%。     

Enhanced photocatalytic activity of mesoporous TiO2 aggregates by embedding carbon nanotubes as electron-transfer channel

Mesoporous multiwalled carbon nanotubes/titanium dioxide (CNTs/TiO(2)) nanocomposites with low loading amounts (0-0.5 wt%) of CNTs embedded inside mesoporous TiO(2) aggregates has been prepared by a simple one-pot hydrothermal method using titanium sulfate as titanium source. The as-prepared CNTs/TiO(2) samples are carefully characterized, analyzed and discussed. In contrast to previous reports with high CNT loading, our results indicate that a low CNT loading slightly influences the textural properties (including crystallite size, degree of crystallinity, specific surface areas, and pore volume etc.) and UV-light absorption of the mesoporous TiO(2) aggregates. The SEM and TEM results demonstrate that the CNTs are mostly embedded in the mesoporous TiO(2) aggregates. Moreover, chemical bonds are formed at the interface between CNTs and TiO(2), which is confirmed by the Raman, IR and XPS analyses. Significantly, we point out that PL analysis in terms of intensity of PL signals seems to not be a reliable way to monitor the recombination rate in the CNTs/TiO(2) composite, due to the quenching effect of CNTs. Instead, the analysis of transient photocurrent responses is introduced, which definitely reflects CNTs as fast electron transfer channels in chemically-bonded CNTs/TiO(2) composites with low CNT loading. Notably, the positive synergy effects of CNTs and TiO(2) depend on both the CNT loading amount and the state of interfacial contacts. In our study, only these chemically bonded CNTs/TiO(2) nanocomposites with appropriate loading amounts (<0.1 wt%) favor the separation of photogenerated electron-hole pairs and decrease their recombination rate and thus display significantly enhanced photocatalytic activity for degrading acetone in air under UV irradiation, as compared with pristine TiO(2) counterparts and commercial P25 photocatalyst. In contrast, a high CNT loading (>0.1 wt%) results in a decrease in photocatalytic activity; a simple mechanical mixing of CNTs and TiO(2) without forming chemical bonds at the interface also results in inferior photocatalytic performance.     

具有高光催化活性的介孔单晶TiO2薄膜的制备

光催化技术在常温下能够直接利用太阳能来驱动反应, 已成为一种理想的环境污染治理和洁净能源生产技术. 但是比较多的限制条件阻碍了光催化发展和实际应用, 如何有效解决这些限制因素成为光催化技术走向工业化应用必须解决的问题. 目前光催化材料研究存在的问题主要包括: (1)研究工作主要集中的粉体催化剂存在分离困难、难以重复利用的缺点, 开发与基底结合牢固的薄膜材料是十分必要的; (2)光催化材料本身的光响应范围影响光催化材料的应用, 拓宽催化剂材料的光吸收范围是亟待解决的; (3)光生电子和空穴的复合问题是影响光催化剂催化活性的主要因素之一, 很多方法被用来阻止电子-空穴对的复合, 如: 金属和非金属的掺杂、贵金属修饰、异质结、新型催化剂结构的设计等, 如何设计促进催化剂光生电子和空穴的分离成为光催化技术应用的重要问题.介孔单晶TiO2通过自组装的方法被制备, 成为TiO2的一种新结构材料. 介孔单晶TiO2结合了介孔材料的大比表面积、单晶材料的电荷传输快等优点, 对于光催化性能有了很大的提高. 目前介孔单晶TiO2主要是以粉体的形式存在, 但是粉体TiO2的应用受到多方面的影响, 如: 难回收不易重复利用, 与电催化结合难, 不能借助电催化提高电荷分离效率等. TiO2薄膜能够解决粉体的不足, 近年来, TiO2光催化薄膜得到广泛的研究, TiO2薄膜的制备方法很多, 主要有液相制备方法、物理气相沉积法、化学气相沉积法、电化学方法、溅射法等. TiO2薄膜主要是以纳米颗粒的形式沉积在基底上, 并且多为多晶和无定形. 而对于介孔单晶TiO2薄膜的制备和研究还没有报道. 我们通过直接焙烧一步法制备了介孔单晶TiO2薄膜, 并对TiO2薄膜的生长情况、表面结构、TiO2晶相和晶体完整程度的变化对性能的影响进行了研究. 通过调变Ti与F的比例和煅烧温度, 研究不同的制备条件对其性能的影响, 从而制备高活性TiO2薄膜. 为了进一步提高介孔单晶TiO2薄膜的活性和拓展其吸收光谱范围, 使用高温热解自组装技术一步法制备了贵金属Au负载的介孔单价TiO2薄膜, Au纳米颗粒跟TiO2有较好的结合度. 在可见光照射下, Au/TiO2异质结构中Au表面由等离子体共振效应产生的活泼电子会注入TiO2导带, 使光生电子和空穴得到分离; 同时Au具有特殊的可见光等离子体共振效应能显著改善TiO2类宽带隙半导体的可见光响应性能.实验用还原Cr(Ⅵ)作为探针反应, 考察不同Au含量对光催化性能的影响.     

Nitrogen-doped carbon enhanced mesoporous TiO2 in photocatalytic remediation of organic pollutants

Research on Chemical Intermediates - Controllable synthesis of mesoporous photocatalysts is of great interest for the photocatalytic remediation of organic pollutants from wastewater by sunlight....     

Novel one step hydrothermal synthesis of TiO2/WO3 nanocomposites with enhanced photocatalytic activity

A novel and simple one step hydrothermal process is used to prepare TiO(2)/WO(3) nanocomposites, in which WO(3) and TiO(2) are present in hexagonal and anatase crystalline forms, respectively, and have enhanced photocatalytic activity towards trichloroethylene degradation in the gas phase.     

Flame synthesis of TiO2 nanoparticles with high photocatalytic activity

Growth behaviour of TiO₂ particles, which has significant influence on their crystallinity and surface area, has been controlled by varying the process parameters of the flame aerosol synthesis. An existing method to determine the crystallinity of the powder has been modified which facilitates comparison of the degree of crystallinity of the nanoparticles synthesized by various methods. Resultant TiO₂ nanoparticles were characterized by XRD and nitrogen physisorption to determine the degree of crystallinity quantitatively and surface area, respectively, and the decomposition rate of an industrial dye, methylene blue, has been taken as the measure of the photocatalytic activity (PCA). TiO₂ nanoparticles showed improved photocatalytic activity compared to the commercial photocatalyst, Degussa P25. This is attributed to the increased degree of crystallinity and surface area of the TiO₂ nanoparticles compared to Degussa P25. The results of this study elucidate the importance of the gas-phase processes and strategy to synthesize highly active TiO₂ photocatalysts in a single step. Moreover, difference in the PCA of the nanoparticles synthesized by the similar gas-phase routes has been shown and the particles are tailor-made for improved PCA in the present study.     

Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO₂ materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C₁₆TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S⁺ and the negatively charged inorganic framework I^? (S⁺I^? type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO₂ materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO₂ possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m² g^?1. This ordered mesoporous anatase TiO₂ also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.     

Fluorine ions-mediated morphology control of anatase TiO2 with enhanced photocatalytic activity

This review briefly summarizes recent advances in fluorine ions-mediated morphology control of anatase TiO(2) in the forms of nanotube arrays, nanosheets with high-energy facets, and hollow spheres. The correlations between the enhanced photocatalytic activity and structural and morphological modifications of anatase TiO(2) by fluorine ions are addressed.     

Hydrothermal synthesis and enhanced photocatalytic activity of mixed-phase TiO2 powders with controllable anatase/rutile ratio

In this study, mixed-phase TiO₂ powders were novelly synthesized via a facile and mild hydrothermal method without any post-heat treatment. TiOSO₄ and peroxide titanic acid (PTA) were used as inorganic titanium sources, while no special solvent or additive were introduced. The XRD and TEM results showed the mixed-phase TiO₂ powders were composed of anatase and rutile phases, and the PTA sol played an important role on forming the rutile nucleus. The proportion of rutile in the mixed-phase TiO₂ could be easily controlled in the range of 0%–70.5% by changing the amount of PTA sol used in the synthesis process. The UV-Visible absorption spectra indicated the prepared mixed-phase TiO₂ showed enhanced visible light absorption with the increase of rutile ratio. The photodegradation experiments revealed the mixed-phase TiO₂ exhibited the best photocatalytic activity at the rutile ratio of 41.5%, while a higher or lower rutile ratio both resulted in the decrease of photocatalytic activity.     

Solgel-hydrothermal synthesis of Tb/Tourmaline/TiO2 nano tubes and enhanced photocatalytic activity

In this study, we synthesized Tb/Tourmaline/TiO₂ nano tubes (NTs) through a solgel-hydrothermal method. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectromicroscope, scanning electron microscopy, transmission electron microscopy and UV-vis diffuse reflectance spectroscopy. The resulting Tb/Tourmaline/TiO₂ NTs exhibited higher photocatalytic activity than pure TiO₂ and TiO₂ nano particles (NPs) in the degradation of menthyl orange under UV-light. Results revealed that doping rare earth element Tb could narrow the wide band gap of TiO₂ and tourmaline could trap the photogenerated electron of TiO₂ to inhibit the recombination of photogenerated electron-hole pairs.     

Fabrication and photocatalytic activity of TiO2/SiO2 composite nanotubes

TiO₂/SiO₂ composite nanotube photocatalysts supported on Al substrates were prepared by the anodic aluminum oxide (AAO) liquid-phase deposition method for degradation of 100 mg/L methyl blue (MB). AAO templates were prepared in H₃PO₄ acidic electrolytes through the two-step anodic oxidation method. The photocatalysts were characterized by field-emission scanning electron microscopy, thermal analysis (TG-DTA), and Fourier-transform infrared, x-ray photoelectron, and UV?CVis diffuse spectroscopies. The results showed that the presence of SiO₂ in TiO₂ inhibited the crystal phase transformation temperature effectively, with a greater wall thickness of 80?C100 nm. It was found that Ti?CO?CSi bonds were formed on the surface and the surface hydroxyl concentration was increased, resulting in enhanced photocatalytic activity, being about 20% higher than for pure TiO₂ films. The calculated band structure for TiO₂/SiO₂ was investigated using first-principle calculations. The TiO₂/SiO₂ composite exhibited a wider conduction band which would effectively prohibit recombination of photogenerated electrons and holes.     

S掺杂的还原态TiO2-x的制备及其可见光催化性能

作为一种稳定、价廉的光催化剂,TiO2被广泛应用于各种污染物的降解;但是,较大的宽禁带(~3.2 eV)和较低的电子迁移率不仅使TiO2很难吸收可见光,而且光生电子和空穴的复合几率高,从而导致TiO2的总体光电效率不高.因此,设计能够被可见光激发、并具有快速光生电子传输的TiO2一直是研究热点.研究表明,Ti3+自掺杂的TiO2(还原态TiO2-x)不仅能够被可见光激发,而且使TiO2具有良好的电子导电性,从而有利于提高TiO2的光电转换效率.另外,非金属元素的掺杂能够减小TiO2的禁带宽度,使TiO2能够响应可见光并具有良好的可见光催化性能,其中S元素的掺杂被广泛研究.目前,S掺杂纳米TiO2的制备通常采用TiS2,单质S,硫脲、二甲亚砜等为S源,但这类原料通常价格昂贵或者具有一定的毒性,因而实际应用受到限制.而制备Ti3+自掺杂TiO2的方法大都是基于"还原法",在真空或强还原性气氛如H2,CO中加热TiO2,或采用高能粒子(电子、氩离子)轰击.在实际应用中,这些方法存在步骤多、条件苛刻、反应时间长和设备昂贵等不足.而且,还原法反应通常发生在颗粒的表面,形成的Ti3+很容易被空气和水中的溶解O2氧化,降低材料的稳定性.虽然在温和的液相中还原Ti4+可用于制备Ti3+掺杂的TiO2,但是由于反应过程中有副产物生成,需要进行后续处理才能得到纯的Ti3+自掺杂TiO2.因此,设计一种简单的制备S掺杂还原态TiO2-x光催化剂仍具有十分重要的意义.前期我们采用H2O2氧化TiH2得到不同状态的前驱体凝胶,然后进行不同方式的后处理得到Ti3+自掺杂的纳米TiO2.本文以TiH2和H2O2反应得到的黄色前驱体凝胶为Ti源,以价格低廉、无毒、稳定的二氧化硫脲为S源和还原剂,采用不同的方法制备了S掺杂的还原态TiO2-x光催化剂.本文初步研究了在凝胶中加入二氧化硫脲后进行水热处理,以及将干燥的凝胶粉末与二氧化硫脲混合热处理对所得产物的影响.并与纯的TiO2、还原态TiO2-x和S掺杂TiO2的光吸收、电化学、光催化性能进行对比研究.采用X射线衍射、透射电子显微镜、高分辨透射电子显微镜、X-射线光电子能谱、紫外-可见漫反射光谱、比表面分析和电化学工作站等技术对产物的结构、形貌和光电性能进行了表征.以罗丹明B(RhB)溶液为模拟废水,考察样品的可见光催化性能.结果表明,不同的后续处理方式不仅影响S掺杂TiO2-x的结晶性和形貌,而且影响产物的光吸收性能和电子传输性能,从而使不同条件下所得产物的可见光催化性能不同.其中,采用热处理方式得到的S掺杂TiO2-x样品在可见光下降解RhB的速率分别是纯的TiO2,TiO2-x和S掺杂TiO2的31,2.5和3.6倍,而且样品具有良好的循环稳定性.