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.     

晶相组成可调的高活性可见光应答型二氧化钛纳米复合光催化材料的制备

采用新的化学溶液法,通过不同体积的钛酸四异丙酯的2-乙二醇单乙醚溶液与一定浓度的H₂O₂水溶液直接反应并对生成的钛过氧化配合物进行焙烧,制备了一系列TiO₂光催化剂. 表征发现,所得TiO₂样品为金红石和锐钛矿的纳米复合晶体,改变2-乙二醇单乙醚的体积可实现金红石相比例在0~96%广范围的调变.与商业二氧化钛P-25相比,所得的TiO₂紫外-可见光吸收谱出现明显红移,间隙能降低, 在可见光照射下,该样品对亚甲基蓝有良好的降解活性. 当2-乙二醇单乙醚的添加量为5 ml时,所得样品体相中金红石相比例接近50%,其光催化活性和吸附性能最好,可分别是P-25的3倍和5倍. 拉曼光谱结合X射线衍射等表征结果表明,该样品的表面仅含少量的金红石相. TiO₂纳米复合晶表面晶相的组成和分布对其光催化降解亚甲基蓝的活性及其吸附能力有直接的影响. 另外,TiO₂纳米复合晶的缺陷浓度也是增强其光吸收能力,提高其可见光光催化活性的原因之一.     

不同形貌Bi4Ti3O12粒子的可控合成及光催化性能

研究了用一步水热法制备的不同形貌的钛酸铋(Bi₄Ti₃O₁₂, BIT)粒子的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. XRD结果表明, 所制备的BIT 样品为层状钙钛矿结构. FESEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粒子. 紫外-可见漫反射光谱(UV-Vis DRS)表明BIT 样品的带隙能约为2.88-2.93 eV. 利用可见光(λ>420 nm)照射下的甲基橙(MO)降解实验评价了BIT 样品的光催化性能. 结果表明, BIT 的光催化活性比掺氮TiO₂ (N-TiO₂)高得多. 研究了形貌对BIT 光催化性能的影响. 所制备的BIT纳米带光催化效率最高, 经可见光照射360 min, 甲基橙溶液的降解率可达到95.0%.     

三维树枝状C/PbWO4催化剂的制备及其对不同染料的光催化降解性能

采用水热法合成了一种高结晶度的3D树枝状C/PbWO₄复合光催化剂（其中碳的质量分数分别为0.13%、0.26%、0.52%、0.78%）。应用X射线衍射、N₂物理吸附、扫描电子显微镜、透射电子显微镜、能量色散X射线光谱、紫外可见漫反射光谱、光致发光光谱和光电流响应等手段对合成样品进行了表征。研究结果表明,当C的复合量为0.52%时,催化剂在降解偶氮染料酸性橙Ⅱ、甲基橙和罗丹明B呈现出最高的光催化活性,在光照100 min内对20 mg·L^-1酸性橙Ⅱ的降解率达到97%,为纯PbWO₄的2.48倍。C/PbWO₄复合光催化剂活性提高的主要原因是掺杂在催化剂表面的C成为了电子俘获中心,有效俘获光生电子,促进光生电子和空穴分离的显著效果,从而产生更多活性物种（·OH、h⁺）参与染料分子的降解,提升光催化活性。     

Ln掺杂BiVO4(Ln=Eu、Gd、Er)光催化剂的制备和活性研究

采用水热合成法, 制备出Eu、Gd和Er掺杂的BiVO₄复合光催化剂,并采用X射线衍射、X射线光电子谱、扫描电子显微镜和紫外-可见漫反射光谱技术对其进行分析表征。通过可见光下降解水溶液中甲基橙分子来考察其光催化性能,结果显示掺杂的复合光催化剂活性都强于纯的BiVO₄,对掺杂复合光催化剂的催化活性增强机理进行了讨论和描述。     

层状、花形和棒状钛酸铋纳米结构的可控合成及光催化性能

通过可控水热法,制备出层状、花形和棒状钛酸铋(Bi₄Ti₃O₁₂,BIT)纳米结构。通过X射线衍射(XRD)和场发射扫描电子显微镜(FESEM)观测其结构和形貌特征。XRD图显示,所制备的样品为层状钙钛矿结构。FESEM结果表明,通过控制水热过程的反应参数可以得到不同形貌的纳米粉体。紫外-可见漫反射光谱(UV-VisDRS)表明BIT样品的带隙能约为2.63~2.95eV。利用可见光(λ>420nm)照射下的甲基橙降解实验评价了BIT样品的光催化性能。结果表明,BIT的光催化活性比掺氮TiO₂(N-TiO₂)高得多。所制备的层状BIT纳米结构光催化效率最高,经可见光照射360min,甲基橙溶液的降解率可达95.0%。同时还研究了结构和形貌对不同条件下制备的BIT样品光催化活性的影响。     

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.     

Bi3.25La0.75Ti3O12纳米线的可见光催化性能

研究了用一步水热法制备的掺镧钛酸铋(Bi_3.25La_0.75Ti₃O₁₂, BLT)纳米线的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. 结果表明, 制备的纳米线为纯相的Bi_3.25La_0.75Ti₃O₁₂, 平均直径约为25 nm. 室温光致发光谱(PL)显示BLT纳米线在433和565 nm附近有较强的发射峰, 分别对应激子发射和表面缺陷发光. 紫外-可见漫反射光谱(UV-Vis DRS)表明BLT样品的带隙能约为2.07 eV. 利用可见光(λ>420 nm)照射下的甲基橙降解实验评价了BLT样品的光催化性能. 结果表明, BLT的光催化活性比商用TiO₂催化剂P25、掺氮TiO₂和纯相钛酸铋(Bi₄Ti₃O₁₂, BIT)高得多. BLT光催化剂具有更高催化活性的原因是La³⁺离子掺杂拓展了BIT对可见光的吸收范围, 同时抑制了BIT的光生电子-空穴的复合.     

铋掺杂二氧化钛纳米颗粒的制备及其可见光催化性能

采用水热法,以纳米管钛酸为前驱物制备了Bi掺杂的TiO₂,并利用X射线衍射、透射电子显微镜、X射线光电子能谱、紫外-可见漫反射光谱等手段对样品进行了表征. 以甲基橙的光催化降解为模型反应评价了样品的可见光催化性能. 结果表明,Bi离子并没有进入TiO₂的晶格中,而是以BiOCl的形式存在. 所制得的BiOCl/TiO₂复合物对甲基橙降解表现出较优越的可见光催化活性;当Bi/Ti摩尔比为1%,水热温度为130℃时,所制催化剂的光催化性能最佳,并对光催化活性提高的机理进行了讨论. 同时,该催化剂对4-氯苯酚降解也表现出较高的光催化性能.     

含Ce水滑石基复合氧化物对混合染料的光催化性能

将具有光催化活性的CeO₂和锌锡水滑石进行复合,经焙烧得到光催化性能较高的CeO₂/ZnO/SnO₂复合氧化物。通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和紫外-可见漫反射图谱(UV-Vis DRS)技术对样品的晶体结构、表面形貌和光学性能进行表征,并利用密度泛函理论(DFT)计算样品的态密度,分析其电子能态结构。以甲基橙(MO)和亚甲基蓝(MB)的混合溶液(C_MO:C_MB=1:1)模拟染料废水,研究CeO₂含量和焙烧温度对复合氧化物光催化降解混合染料的影响。结果表明:随着CeO₂含量和焙烧温度的增加,复合氧化物的结晶度及对MO和MB的光催化活性得到增强;同时,复合氧化物对混合染料中MO的降解率优于MB。其中CeO₂含量为20%,焙烧温度为700℃时的复合氧化物表现出最佳的光催化性能,对混合染料中MO和MB的降解率分别达到96.7%和95.0%。结合实验结果和理论计算,推测了混合染料中MO和MB的降解路径。     

Synthesis of Mixed-Phase TiO<Subscript>2</Subscript> Nanopowders Using Atmospheric Pressure Plasma Jet Driven by Dual-Frequency Power Sources

Mixed-phase TiO₂ nanopowders with different ratios of anatase and rutile have been successfully synthesized using atmospheric pressure plasma jet driven by dual-frequency power sources. The crystal structures of the TiO₂ nanopowders were characterized by X-ray diffraction, SAED, HRTEM, and Raman shift spectroscopy. These results indicated that samples possessed anatase and rutile structure, in addition, the crystallinity of the TiO₂ nanopowders increased and the chlorine contamination decreased with discharge RF power increasing. The photocatalytic activity of the TiO₂ nanopowders was evaluated by decomposition methylene blue solution. The TiO₂ nanopowders which were produced at the discharge RF power of 110 W had the highest photocatalytic activity. Optical emission spectroscopy (OES) was used to detect various excited species in the plasma jet. The results indicate that the various RF power significantly changes the intensities of emission lines (Ar, Ar⁺, Ti, Ti⁺, Ti²⁺, Ti³⁺ and O), which results in the TiO₂ nanopowders a mixture of anatase and rutile phases. The nonequilibrium chemical composition could be formed in one step without anneal. It may have potential applications for synthesizing nanosized particles of high crystallinity by reactive nonthermal plasma processing.     

Enhanced photocatalytic activity for titanium dioxide by co-modification with copper and iron

A copper(II) and iron(III) co-modified titanium dioxide nano material was prepared by a simple sol–gel process using titanium(IV) isopropoxide plus copper(II) and iron(III) nitrates as raw materials. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence spectra. The XRD results showed that the undoped TiO₂ nanoparticles mainly include anatase phase while the Cu, Fe-codoped TiO₂ nanoparticles showed a mixture of anatase phase with a small fraction of rutile phase displaying higher activity than the pure anatase phase. Optical characterization showed that the codoping with copper(II) and iron(III) resulted in a red shift of adsorption and lower recombination probability between electrons and holes, which were associated with high photocatalytic activity of the Cu, Fe-codoped TiO₂ nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of the samples was tested by aqueous methyl orange degradation. The capability of the codoped catalyst was much higher than that of the pure TiO₂ catalyst under visible irradiation. A mechanism is proposed in order to account for the enhanced catalytic activity.     

Selective dissolution of TiO2 crystalline phases: Physicochemical characterization and photocatalytic activity

In this study, different commercially available TiO₂ powders (Degussa P25, pure anatase, and rutile) were submitted to selective dissolution treatments, with H₂O₂/NH₄OH and 10% HF, known to remove rutile and anatase from physical mixtures. The aim was to check whether a particular separation method designed to remove a specific crystalline phase influences the properties of the other phase from the mixture or not. More precisely, we have studied how the HF dissolution method designed to selectively remove the anatase affected the physicochemical and photocatalytic properties of rutile. In a similar way, the changes in the anatase properties were studied, after the H₂O₂/NH₄OH treatment, initially used to remove rutile from the mixture. All the samples were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, diffuse reflectance (DR) ultraviolet–visible, and Raman spectroscopy. The photocatalytic activity of these powders was tested in the oxidation of p-chlorophenol from water. The selective treatment methods not only dissolved the target phase but also changed some physicochemical and the photocatalytic performances of the other TiO₂ crystalline phase in a considerable manner. These aspects should be taken into account in the studies regarding the synergistic effects of anatase and rutile, especially in reconstructed TiO₂ photocatalysts.     

Preparation and characterization of titania/tetratitanate nanocomposites

Nanocomposite titania/tetratitanate particles were prepared by utilizing the electrostatic interaction of the colloidal tetratitanate nanosheets and TiO₂ powders through dispersing TiO₂ into tetratitanate solution at pH4. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, chemical analysis, and photocatalytic activity measurement. The crystallites of Ti₄O₉^2? in the form of tetratitanate nanosheets have lateral size around 100 nm. The visible light responsive photocatalytic activity of rutile nanoparticles could be improved by forming nanocomposite with layered tetratitanate. The high specific surface area of this kind of composite and a certain amount of mesopores in nanocomposite powder could be responsible for better performance in the NO elimination.     

生物质C-N-P自掺杂TiO_2的合成及其对亚甲基兰的光催化降解活性

采用溶胶-超声辐照技术同步合成了生物质C-N-P自掺杂TiO_2复合催化剂,通过X射线光电子能谱(XPS)、X射线衍射(XRD)、扫描电子显微镜(FESEM)、紫外-可见漫反射光谱(UV-Vis-DRS)及光致发光光谱(PL)对样品进行了表征.以亚甲基兰(MB)为目标污染物,研究了C-N-P共掺杂TiO_2的可见光光催化性能.实验结果表明,在可见光照射下,光催化反应时间为2 h时,C-N-P共掺杂TiO_2复合催化剂对亚甲基兰的降解效率最高可达9 8.5%;相比纯TiO_2,C-N-P共掺杂TiO_2复合催化剂的比表面积增大,吸收边带红移,禁带宽度减小,相变温度升高,光生载流子复合率降低.     

Vanadium-containing polyphosphomolybdate immobilized on TiO<Subscript>2</Subscript> nanoparticles: A recoverable and efficient catalyst for Photochemical,Sonochemical and photosonochemical degradation of dyes under irradiation of UV light

A new photocatalyst, nanoporous anatase TiO₂ crystalline particles coupled by Na₅PV₂Mo₁₀O₄₀ Keggin units, TiO₂-PVMo, was prepared by combination of the methods of sol-gel and hydrothermal treatment. The catalyst was characterized by X-ray diffraction (XRD), UV diffuse reflectance spectroscopy (UV-DRS), FT-IR spectroscopy, Scanning Electron Microscopy (SEM) and cyclovoltametery (CV). This photocatalyst exhibited a good photocatalytic (UV region) and sonocatalytic activity in the decomposition of different dyes in aqueous systems. The TiO₂-PVMo composite showed higher photocatalytic and sonocatalytic activity than pure polyoxometalate or pure TiO₂.     

The influence of titanium dioxide phase composition on dyes photocatalysis

A comparative study of TiO₂ powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes. The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification, for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples. It was found that the only TiO₂ anatase phase of the synthesized TiO₂ develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic properties. Different TiO₂ doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO₂ Aldrich with TiO₂ Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene blue using TiO₂ thin film were investigated.     

Preparation of nanocrystalline TiO<Subscript>2</Subscript> powders for photocatalytic oxidation of phenol

Nanocrystalline TiO₂ powders in the anatase, rutile, and mixed phases prepared by hydrolysis of TiCl₄ solution were of ultrafine size (<7.2 nm) with high specific surface areas in the range 167 to 388 m²/g. In the photocatalytic degradation of phenol as model reaction, the photocatalytic properties of TiO₂ nanoparticles were evaluated by use of UV–vis absorption spectroscopy and total organic carbon (TOC) content. The synthetic mixed-phase TiO₂ powder calcined at 400 °C had higher activity than pure anatase or rutile; it degraded more than 90% phenol to CO₂ (evaluated by TOC) after irradiation with near UV light for 90 min at a catalyst loading of 0.4 g/L. The TOC results indicated that rutile TiO₂ crystallites of particle size 7.2 nm resulted in much better photocatalytic performance than particles of larger size. This result suggested that some intermediates, not determined by UV–vis absorption spectroscopy, existed in the solution after the photocatalytic process over the rutile TiO₂ photocatalysts of larger crystallite size.