具有丰富(001)面的锐钛矿TiO2晶体的无氟合成

采用一种全新的方法实现了无氟、在阳离子聚合物参与下合成具有丰富(001)面的锐钛矿TiO₂晶体(TiO₂-P), 并通过X射线衍射、扫描电镜、透射电镜、紫外-可见光谱等手段对样品进行了表征. 光催化测试显示, 该样品对甲基橙的降解具有比常规锐钛矿TiO₂和商业P25更好的活性, 这可归因于TiO₂-P具有大量的暴露(001)晶面.     

纳米TiO2催化剂微晶结构对光催化反应的影响

采用正交试验方法, 调控Ti(SO₄)₂原料浓度、沉淀剂NH₄HCO₃浓度、沉淀pH值、焙烧温度和焙烧时间等制备条件制备得到了25个锐钛矿相TiO₂光催化剂. 对TiO₂光催化降解十二烷基苯磺酸钠(SDBS)的催化活性与TiO₂锐钛矿相10个晶面的法向粒子尺寸、晶格畸变应力、X射线衍射强度之间的关系进行了分析. 发现TiO₂光催化SDBS的降解遵循一级反应动力学; 其主要影响因素为(101)晶面结晶情况, 而与其余晶面的相关性不大; 光催化反应需要晶格畸变较少的结晶较完整的(101)晶面; 晶粒尺寸减小, 比表面积增大有利于提高反应速率; 光催化反应过程主要在结晶的锐钛矿相(101)晶面表面上发生, 而无定形TiO₂催化活性较低.     

TiO2纳米薄片的合成及其光催化降解苯酚性能

以钛酸纳米管为前驱体,通过添加NaF高温水热合成了(001)面暴露的TiO₂纳米薄片,并对其催化苯酚光降解行为进行了研究。结果表明经水热反应后,钛酸型TiO₂纳米管(NT)转晶成锐钛矿型TiO₂纳米薄片(NS),且具有高(001)暴露面。和NT相比,NS对苯酚的光催化降解活性显著提高,其活性随水热温度升高而增加。NS光催化去除苯酚符合一级动力学,其中200 ℃合成的NS反应速率常数k最高,为0.083 min^-1。同时,苯酚的光催化反应初活性与其初浓度的关系符合Langmuir-Hinshelwood模型,表明苯酚的光催化降解受吸附控制。     

氟掺杂TiO2纳米管的可见光催化活性及第一性原理计算

作为光催化技术的核心, 提高TiO₂的光催化活性和对可见光的利用率是当前光催化研究中最重要的研究课题. 为了提高TiO₂纳米管的可见光催化活性, 采用化学气相沉积法对TiO₂纳米管进行了氟掺杂. 扫描电子显微镜(SEM)结果表明退火温度对于TiO₂纳米管的形貌完整性有较大影响, 当样品在550和700 °C下退火, 氟掺杂TiO₂纳米管结构受损; X射线衍射(XRD)分析表明氟掺杂对TiO₂由锐钛矿相转化为金红石相有阻碍作用; X射线光电子能谱(XPS)测试表明化学气相沉积能有效地对TiO₂纳米管进行非金属掺杂, 且该方法安全、操作简单. 氟掺杂TiO₂纳米管对甲基橙有较高的可见光催化降解活性. 第一性原理计算结果表明氟掺杂对TiO₂带隙无显著影响, 费米能级附近的F 2p轨道电子位于价带底部, 与O 2p交联作用较小, 因此对TiO₂光吸收带边影响不大. 氟掺杂能促进表面氧空穴的产生, 增加表面酸度与Ti³⁺, 有利于减少电子-空穴复合率, 从而提高其光催化活性.     

非水溶剂热法制备(001)面暴露的F/TiO2纳米晶及其光催化活性

采用非水体系溶剂热法制备了(001)面暴露的锐钛矿相F/TiO2纳米光催化剂.结果表明,F的掺杂对TiO2纳米单晶的形成影响很大.一方面,F离子作为晶面导向剂稳定(001)晶面,形成(001)面暴露的锐钛矿相TiO2;另一方面,F离子也起到稳定剂作用,抑制纳米粒子的快速生长.以光催化降解甲基橙为模型反应比较了不同F/T...     

氮自掺杂暴露(001)晶面TiO_2微米片的可见光光催化CO_2还原性能增强（英文）

化石能源的使用可产生大量CO2,带来严重的温室效应.光催化CO2还原生产太阳燃料技术既有望缓解温室效应,又可以将低能量密度的太阳能转化为高能量密度的化学能储存起来方便使用.高效光催化材料的开发是发展光催化技术的关键.迄今,在已开发的所有半导体光催化材料中,Ti O2仍是广泛研究的明星材料.在实际使用中,Ti O2的光催化效率仍受限于其极弱的可见光利用率和较高的电子-空穴复合几率.近年来,越来越多的研究表明Ti O2的结构与形貌特征极大地影响其光催化效率.尤其,Ti O2的外露晶面设计与晶面效应研究引起了广泛关注.由于具有较高表面能和较多表面不饱和键,起初大多数理论和实验研究认为锐钛矿Ti O2(001)晶面是光催化活性晶面.后来,越来越多研究表明并非锐钛矿Ti O2(001)晶面的暴露比例越高其光催化活性就越高.最近,我们发现锐钛矿Ti O2(001)晶面与(101)晶面在调控光催化CO2还原性能上具有良好的协同效应.密度泛函理论计算表明,锐钛矿Ti O2的(001)晶面与(101)晶面的能带结构有差异,(001)晶面的导带位置相对于(101)晶面而言较高,而(101)晶面的价带位置相对于(001)晶面而言较低.基于此我们提出,具有合适比例的锐钛矿Ti O2的(001)晶面与(101)晶面的交界处可以形成最佳的表面异质结或晶面异质结.表面异质结的形成导致光生电子倾向于向(101)扩散,光生空穴倾向于向(001)扩散,从而促进光生电子-空穴分离,降低光生电子-空穴复合几率.在此工作基础上,我们直接以氮化钛为原料,氢氟酸为添加剂,通过简单的水热反应一步合成了氮自掺杂的Ti O2微米片.利用X射线粉末衍射、扫描电镜、X射线光电子能谱、紫外-可见漫反射光谱、氮气吸附-脱附以及电化学阻抗谱等方法手段对所制备的光催化剂进行了基本结构与理化性质表征分析,并研究了其可见光光催化CO2还原性能.电镜照片结果表明,我们所制备的氮自掺杂锐钛矿Ti O2微米片的(001)晶面与(101)晶面比例分别为65%和35%.基于我们前期研究结果,Ti O2微米片的(001)晶面与(101)晶面可以形成表面异质结,具有良好的电荷分离效率,这也得到了电化学阻抗谱研究结果的证明.同时,由于N的原位掺杂,所制备的Ti O2微米片具有优异的可见光捕获能力.由于可见光利用效率增强与光生电子-空穴分离效率提高这两方面的综合作用,所制备的氮自掺杂Ti O2微米片具有非常好的可见光光催化CO2还原制甲醇性能,比商用P25及氮掺杂Ti O2纳米粒子等参考样品的可见光光催化性能更优异.研究表明,通过原位自掺杂方法与晶面设计方法相结合,可以同时改善Ti O2的可见光利用效率和光生电子-空穴分离效率,优化Ti O2的可见光光催化性能,这也为后续开发新型高效光催化材料提供了新思路.     

部分还原氧化石墨烯/二氧化钛复合材料的水热合成及其光催化活性

采用水热法以Hummers氧化法制备的氧化石墨和钛酸四丁酯为原料制备了部分还原的氧化石墨烯/二氧化钛(RGO/TiO₂)复合光催化剂, 并研究了该复合材料在可见光以及紫外光下对亚甲基蓝的光催化降解活性.结果表明, 通过改变反应温度和氧化石墨加入量可以调控TiO₂的晶相组成及其在复合材料中的分散性; 在水热反应过程中氧化石墨烯发生了部分还原; 所制备的RGO/TiO₂复合材料的可见光和紫外光催化活性均高于纯TiO₂; 部分还原的氧化石墨烯在复合材料中担当载体和电子受体, 同时可以使TiO₂的初始吸收边向可见光区域红移, 增强了TiO₂在可见光区域的吸收, 能有效提高对目标污染物的吸附性和光催化降解活性.     

原位红外光谱法研究La/TiO2对有机污染物的光催化降解

本工作采用改进的溶胶-凝胶法和浸渍法制备了TiO₂掺杂稀土离子La³⁺的La/TiO₂光催化剂，运用XRD、N₂吸附脱附、紫外可见漫反射光谱(DRS)、表面光电压谱(SPS)等手段进行表征，同时利用原位红外技术考察了La/TiO₂样品光催化降解乙烯、丙酮、苯的气-固相光催化氧化反应，对其光催化降解有机污染物的过程进行了研究。结果表明，TiO₂经适量La³⁺掺杂后，锐钛矿晶型的含量增加，晶粒度减小，比表面积增大，禁带宽度增加，表面光电压信号增强，光生电子-空穴对有效分离；La/TiO₂样品对乙烯、丙酮、苯的光催化性能与纯TiO₂相比均有不同程度的改善，乙烯可以被光催化氧化完全矿化生成CO₂，而丙酮被光催化氧化可能生成中间产物丙酸，苯被光催化氧化可能生成中间产物苯酚和苯醌。     

水热法制备具有高光催化活性的镧掺杂二氧化钛纳米晶

采用水热法合成钛酸钾(K₂Ti₈O₁₇)纳米棒,并将它作为前驱体水热转晶合成TiO₂纳米晶,同时通过在水热体系中引入稀土元素La³⁺实现对TiO₂的La掺杂.考察了不同条件下钛酸盐向TiO₂的转晶过程,发现水热溶液的pH值、温度以及预处理步骤对转晶过程有很大的影响.利用X射线衍射以及透射电子显微镜对样品的晶相和形貌进行了表征.利用电感耦合等离子体原子发射光谱测量了所合成的La掺杂TiO₂样品中的La含量.通过在紫外光下降解甲基橙(MO,10mg/L)测试了La掺杂TiO₂样品的光催化性能.结果表明La掺杂后TiO₂的光催化活性大大提高.在0.15mol/LLa³⁺浓度下180oC水热合成的La掺杂TiO₂样品显示了最佳的光催化活性.其对MO的光催化降解反应常数高达0.11min^-1,大约是空白TiO₂样品的9.20倍,P25TiO₂的3.69倍.     

溶胶-凝胶-水热晶化法制备锐钛矿TiO2纳米膜的耐蚀性能

以钛酸正丁酯为前驱体, 采用溶胶-凝胶-水热晶化法在不锈钢(SS)表面制备TiO₂纳米膜. 利用X射线衍射(XRD)、Raman光谱、场发射扫描电子显微镜(SEM)、原子力显微镜(AFM)和俄歇电子能谱(AES)表征了TiO₂纳米膜的晶型、表面形貌和表面化学组成. 通过极化曲线和电化学阻抗谱(EIS)研究了TiO₂纳米膜的耐蚀性能. 170 °C下水热晶化制备的锐钛矿TiO₂与450 °C焙烧制备的锐钛矿TiO₂的结晶度类似, 但两种TiO₂薄膜的表面结构存在明显差异, 水热晶化法制备的TiO₂纳米膜在3.5% (w) NaCl溶液中的耐蚀性能优于焙烧法制备的.     

Synthesis of {100} Facet Dominant Anatase TiO2 Nanobelts and the Origin of Facet‐Dependent Photoreactivity

Sword‐like anatase TiO₂ nanobelts exposed with 78 % clean {100} facets were synthesized and the facet‐dependent photoreactivity of anatase TiO₂ was investigated. By quantitative comparison with the reference {001} facets, the {100} facets possessed about ten‐times higher active sites density than that on {001} facets, resulting in higher photoreaction efficiency. After the active sites density normalization, the {100} and {001} facets exhibited distinct wavelength‐dependent photocatalytic performance, attributed to the anisotropic electronic structures in TiO₂ crystals.     

Facet-Control versus Co-Catalyst-Control in Photocatalytic H2 Evolution from Anatase TiO2 Nanocrystals

Titanium dioxide (TiO₂) and, in particular, its anatase polymorph, is widely studied for photocatalytic H₂ production. In the present work, we examine the importance of reactive facets of anatase crystallites on the photocatalytic H₂ evolution from aqueous methanol solutions. For this, we synthesized anatase TiO₂ nanocrystals with a large amount of either {001} facets, that is, nanosheets, or {101} facets, that is, octahedral nanocubes, and examined their photocatalytic H₂ evolution and then repeated this procedure with samples where Pt co-catalyst is present on all facets. Octahedral nanocubes with abundant {101} facets produce >4 times more H₂ than nanosheets enriched in {001} facets if the reaction is carried out under co-catalyst-free conditions. For samples that carry Pt co-catalyst on both {001} and {101} facets, faceting loses entirely its significance. This demonstrates that the beneficial role of faceting, namely the introduction of {101} facets that act as electron transfer mediator is relevant only for co-catalyst-free TiO₂ surfaces.     

Graphite-like carbon deposited anatase TiO<Subscript>2</Subscript> single crystals as efficient visible-light photocatalysts

Graphite-like carbon deposited single-crystal anatase TiO₂ with exposed {001} facets was fabricated through a two-step solvothermal process by using glucose as carbon source. The physicochemical properties of the as-prepared samples were investigated by X-ray diffraction, Brunauer-Emmett-Teller, transmission electron microscopy, Raman, UV–vis diffuse reflectance spectra, electrochemical impedance spectroscopy and surface photovoltage spectroscopy. These results demonstrated that graphite-like carbon layers were deposited on the surface of TiO₂ single-crystal nanosheets with exposed highly reactive {001} facets via the dehydration of glucose during the process of hydrothermal treatment. The loading of the graphite-like carbon layers could effectively extend the light absorption edge of the single-crystal anatase TiO₂ nanosheets to visible light region and accelerate the separation of photo-generated electrons and holes, contributing an excellent visible-light driven photocatalytic performance to the graphite-like carbon deposited single-crystal anatase TiO₂ nanosheets for the degradation of methyl orange.     

Unifying the Nitrogen Reduction Activity of Anatase and Rutile TiO2 Surfaces

TiO₂ is a model transition metal oxide that has been applied frequently in both photocatalytic and electrocatalytic nitrogen reduction reactions (NRR). However, the phase which is more NRR active still remains a puzzle. This work presents a theoretical study on the NRR activity of the (001), (100), (101), and (110) surfaces of both anatase and rutile TiO₂. We found that perfect surfaces are not active for NRR, while the oxygen vacancy can promote the reaction by providing excess electrons and low-coordinated Ti atoms that enhance the binding of the key intermediate (HNN*). The NRR activity of the eight facets can be unified into a single scaling line. The anatase TiO₂(101) and rutile TiO₂(101) surfaces were found to be the most and the second most active surfaces with a limiting potential of −0.91 V and −0.95 V respectively, suggesting that the TiO₂ NRR activity is not very phase-sensitive. For photocatalytic NRR, the results suggest that the anatase TiO₂(101) surface is still the most active facet. We further found that the binding strength of key intermediates scale well with the formation energy of oxygen vacancy, which is determined by the oxygen coordination number and the degree of relaxation of the surface after the creation of oxygen vacancy. This work provides a comprehensive understanding of the activity of TiO₂ surfaces. The results should be helpful for the design of more efficient TiO₂-based NRR catalysts.     

Enhancing the Photocatalytic Activity of Anatase TiO2 by Improving the Specific Facet‐Induced Spontaneous Separation of Photogenerated Electrons and Holes

Recently, it has been proven that directional flow of photogenerated charge carriers occurs on specific facets of TiO₂ nanocrystals. Herein, we demonstrate that the photocatalytic activity of anatase TiO₂ nanocrystals in both photoreduction and photooxidation processes can be enhanced by selectively depositing Pt nanoparticles on the {101} facets, which strengthens spontaneously surface‐induced separation between photogenerated electrons and holes in the photocatalysis process. An optimal ratio of the oxidative {001} facets to the reductive {101} facets exists with regard to the photocatalysis of the faceted TiO₂ nanocrystals, and this is crucial for balancing the recombination and redox reaction rates of photogenerated electrons and holes. The present work might help us gain deeper insight into the relation between the specific surface of semiconductor photocatalysts and their photocatalytic activities and provides us with a new route to design photocatalysts with high photocatalytic activity.     

Experimental Insights into the Growth of Single Truncated Anatase Bipyramids

Fluorine has been recognized to selectively stabilize anatase titanium dioxide (TiO₂) crystal facets; however, resolving its physical location at the nanometer scale remains empirically elusive. Here, we provide direct experimental evidence to reveal the spatial distribution of fluorine on single truncated anatase bipyramids (TABs) using nanoscale secondary ion mass spectrometry (NanoSIMS). Fluorine was found to preferentially adsorb on the (001) facet compared to the (101) facet of TABs. Moreover, NanoSIMS depth profiling exhibited a significantly different fluorine distribution between these two facets in the near-surface region, illustrating the essential role of lattice-doped fluorine in the anisotropic crystal growth of TABs.     

Prolonging charge-separation states by doping lanthanide-ions into {001}/{101} facets-coexposed TiO2 nanosheets for enhancing photocatalytic H2 evolution

Ultrathin TiO₂ nanosheets with coexposed {001}/{101} facets have attracted considerable attention because of their high photocatalytic activity. However, the charge-separated states in the TiO₂ nanosheets must be extended to further enhance their photocatalytic activity for H₂ evolution. Herein, we present a successful attempt to selectively dope lanthanide ions into the {101} facets of ultrathin TiO₂ nanosheets with coexposed {001}/{101} facets through a facile one-step solvothermal method. The lanthanide doping slightly extended the light-harvesting region and markedly improved the charge-separated states of the TiO₂ nanosheets as evidenced by UV-vis absorption and steady-state/transient photoluminescence spectra. Upon simulated sunlight irradiation, we observed a 4.2-fold enhancement in the photocatalytic H₂ evolution activity of optimal Yb³⁺-doped TiO₂ nanosheets compared to that of their undoped counterparts. Furthermore, when Pt nanoparticles were used as cocatalysts to reduce the H₂ overpotential in this system, the photocatalytic activity enhancement factor increased to 8.5. By combining these results with those of control experiments, we confirmed that the extended charge-separated states play the main role in the enhancement of the photocatalytic H₂ evolution activity of lanthanide-doped TiO₂ nanosheets with coexposed {001}/{101} facets.     

Active Sites for Adsorption and Reaction of Molecules on Rutile TiO2(110) and Anatase TiO2(001) Surfaces (cited: 1)

The reactivity of specific sites on rutile TiO₂(110)-(1×1) surface and anatase TiO₂(001)-(1×4) surface has been comparably studied by means of high resolution scanning tunneling microscopy. At the rutile TiO₂(110)-(1×1) surface, we find the defects of oxygen vacancy provide distinct reactivity for O₂ and CO₂ adsorption, while the terminal fivefold-coordinated Ti sites dominate the photocatalytic reactivity for H₂O and CH₃OH dissociation. At the anatase TiO₂(001)-(1×4) surface, the sixfold-coordinated terminal Ti sites at the oxidized surface seem to be inert in both O₂ and H₂O reactions, but the Ti-rich defects which introduce the Ti³⁺ state into the reduced surface are found to provide high reactivity for the reactions of O₂ and H₂O. By comparing the reactions on both rutile and anatase surfaces under similar experimental conditions, we find the reactivity of anatase TiO₂(001) is actually lower than rutile TiO₂(110), which challenges the conventional knowledge that the anatase (001) is the most reactive TiO₂ surface. Our findings could provide atomic level insights into the mechanisms of TiO₂ based catalytic and photocatalytic chemical reactions.     

Methanol Conversion into Dimethyl Ether on the Anatase TiO2(001) Surface

Exploring reactions of methanol on TiO₂ surfaces is of great importance in both C1 chemistry and photocatalysis. Reported herein is a combined experimental and theoretical calculation study of methanol adsorption and reaction on a mineral anatase TiO₂(001)‐(1×4) surface. The methanol‐to‐dimethyl ether (DME) reaction was unambiguously identified to occur by the dehydration coupling of methoxy species at the fourfold‐coordinated Ti⁴⁺ sites (Ti_4c), and for the first time confirms the predicted higher reactivity of this facet compared to other reported TiO₂ facets. Surface chemistry of methanol on the anatase TiO₂(001)‐(1×4) surface is seldom affected by co‐chemisorbed water. These results not only greatly deepen the fundamental understanding of elementary surface reactions of methanol on TiO₂ surfaces but also show that TiO₂ with a high density of Ti_4c sites is a potentially active and selective catalyst for the important methanol‐to‐DME reaction.