TiO_2光催化材料掺杂改性的研究进展

TiO2是当前最有应用潜力的光催化材料,但其量子效率低、降解效果不理想、难以充分利用太阳能。选用合适的掺杂组分、制备方法和载体,制备出具有宽光谱响应范围、光量子效率高、易于回收利用的TiO2/载体光催化材料,对实现TiO2的工业化应用具有重大意义。根据半导体能带理论和异质结构的工作原理,研究各种表面改性技术和研制新的光催化剂,将是今后研究的主要方向。     

TiO2光催化剂的研究进展

TiO2具有光催化效率高、稳定性好、不容易产生二次污染和成本低等特点,已广泛应用于抑菌抗癌、制备氢气、废水处理、太阳能电池、防晒、自清洁等领域.首先,介绍了TiO2光催化作用机理,探讨了晶型、粒径和缺陷对TiO2光催化活性的影响;然后,综述了近年来国内外TiO2光催化剂的研究现状与进展;接着总结了目前TiO2光催化剂的改性方法;最后,阐述了TiO2光催化剂改性过程中所面临的问题,对未来发展提出了建议.     

Minimization of defects in Nb-doped TiO2 photocatalysts by molten salt flux

Transition metal doping is a popular pathway to improve the photocatalytic performance of TiO₂. However, most dopants are aliovalent (e.g., Nb⁵⁺, W⁶⁺, and Fe³⁺), where defects are inevitably introduced (e.g., oxygen or Ti³⁺ defects). To minimize defects and hence ensure better separation of photogenerated charges, this work incorporates an Nb dopant into TiO₂ in a flux of molten salt. The molten salt flux not only induces recrystallization of TiO₂ nanoparticles into nanowires but also allows a + 4 valence dopant in the TiO₂ lattice to inhibit formation of Ti³⁺ or oxygen defects. This minimization of defects enhances the photocatalytic activity in the degradation of gaseous acetaldehyde. This enhancement is mainly attributed to the higher crystallinity of TiO₂ and better separation of charge carriers induced by equivalent Nb-doping.     

纳米TiO2光催化剂固定化技术研究进展

纳米TiO₂光催化剂在废水治理领域有广阔的应用前景,固定化技术是其应用关键。将TiO₂光催化剂在一定基材上进行负载和固定化,解决TiO₂悬浮体系存在的后期分离回收难的问题。介绍了固定化常用的载体和固定化技术方法,指出今后纳米TiO₂光催化剂固定化技术需要解决和研究的问题：寻找合适的载体与固定方法完成对TiO₂的固定化,既能提供较强的牢固性,又能保护甚至提高TiO₂的光催化活性; 研究载体与光催化剂之间的相互作用,探讨固载过程中各个影响因素对光催化效率的影响; 固定化所带来的传质受限问题以及负载所引起比表面积减少的问题还有待进一步研究;由实验室小型反应装置转向大型化高效光催化反应器的设计还缺少工程经验。     

共沉淀法制备Mo/N共掺杂TiO_2可见光光催化剂

采用共沉淀法制备了Mo/N共掺杂TiO2光催化剂(Mo-N-TiO2)。结果表明,所得光催化剂为锐钛矿晶型,Mo/N共掺杂使样品对可见光吸收增强,吸收带边明显红移。在Mo∶N∶Ti摩尔比为0.012 5∶0.02∶1,煅烧温度为500℃的最优制备条件下,样品在白炽灯下照射2 h对亚甲基蓝溶液脱色率达55.7%。Mo以+6价的形式存在,并取代Ti4+进入TiO2晶格中,导致TiO2表面的Lew is酸性增强,有利于其导带中光生电子向表面迁移,促进了光生电子-空穴对的分离,同时与共掺杂引起的带边红移和较完整的锐钛矿相的协同作用有效提高了TiO2的可见光催化活性。     

纳米二氧化钛光催化剂共掺杂的研究进展

综述了近年来纳米二氧化钛光催化剂共掺杂的研究进展。介绍了纳米二氧化钛光催化剂的作用机理,从促进二氧化钛可见光响应、抑制光生电子与空穴的复合、造成晶格缺陷,增加氧空位、提高二氧化钛光催化剂表面羟基含量等方面解释了纳米二氧化钛光催化剂掺杂改性的作用机理。分析比较了非金属与非金属共掺杂、非金属与金属共掺杂、金属与金属共掺杂等不同掺杂方式对二氧化钛光催化剂的催化性能影响,并对今后的研究方向提出了建议。     

TiO2薄膜光催化剂的性能研究

采用溶胶-凝胶法在玻璃管上制备了透明的TiO₂薄膜，并利用XRD、Raman、UV-Vis和XPS技术对薄膜进行了表征。结果表明,在773 K焙烧的TiO₂样品在290～330 nm处的吸收明显强于573 K焙烧的样品。在573 K焙烧的情况下，薄膜基本为非晶态，但却表现出良好的光催化活性，并随着负载层数的增加，薄膜的光催化活性逐渐增加。在573 K以上，随焙烧温度的升高，TiO₂薄膜的光催化活性逐渐降低。     

具有高活性晶面的TiO_2光催化剂研究进展

高能量的锐钛矿相TiO_2由于在光催化作用中具有潜在的高活性而成为研究热点,介绍理论预测的几种高活性晶面锐钛矿相TiO_2的形貌和形成机理,综述近年来合成具有高活性晶面锐钛矿相TiO_2光催化剂的制备方法与研究进展,提出未来的发展方向。     

Degradation of chlorophenol by photocatalysts with various transition metals

In this research, the photocatalytic degradation of 4-chlorophenol (4-CP) in TiO₂ aqueous suspension was studied. TiO₂ photocatalysts were prepared by sol-gel method. The dominant anatase-structure on TiO₂ particles was observed after calcining the TiO₂ gel at 500 °C for 1 hr. Photocatalysts with various transition metals (Fe, Cu, Nd, Pd and Pt) loading were tested to evaluate the effect of transition metal impurities on photodegradation. The photocatalytic degradation in most cases follows first-order kinetics. The maximum photodegradation efficiency was obtained with TiO₂ dosage of 0.4 g/L, retention time of 1 min and air flow rate of 2,500 cc/min. The photodegradation efficiency with Pt-TiO₂ or Pd-TiO₂ is higher than pure TiO₂ powder. The optimal content value of Pt and Pd is 2 wt%. However, the photodegradation efficiency with Fe(1.0 wt%)-TiO₂ and Cu(1.0 wt%)-TiO₂ is lower than pure TiO₂ powder. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

稀土元素La对TiO_2光催化剂的改性作用

采用溶胶-凝胶法制备系列不同掺杂量的稀土元素La改性的TiO2光催化剂,借助X射线衍射、X射线光电子能谱和固体光致发光光谱等对催化剂进行表征,以光催化降解甲基橙染料溶液为反应模型,探讨稀土元素La对TiO2光催化剂的改性作用。结果表明,稀土元素La可明显促进锐钛矿相的形成并显著细化晶粒;La以La2O3化学态形式高度分散在TiO2表面,增加了催化剂表面氧空位,有助于提高光催化活性。当掺杂稀土元素La质量分数为1%时,可使TiO2催化剂催化活性提高约22%。     

负载型光催化剂TiO_2/Al_2O_3的制备与研究

以γ Al2O3小球为载体,以钛酸正丁酯的正丁醇溶液为浸涂液,采用浸渍涂覆法制备了TiO2/Al2O3光催化剂,用XRD对催化剂的物相进行了表征,并通过可溶性偶氮染料酸性媒介红B考察其光催化活性。实验表明,当TiO2的负载量为8.79%时,TiO2/Al2O3对酸性媒介红B的脱色率可达到95%以上;酸性媒介红B的光催化氧化符合一级反应动力学。     

超声在TiO_2基光催化剂制备过程中的应用

综述了超声空化效应在TiO2基光催化剂制备中的应用进展,重点介绍了超声制备纯TiO2、TiO2复合物及离子掺杂改性TiO2的原理、方法及效果。指出利用超声提高TiO2非金属掺杂改性的效果有望成为重要的研究方向。     

碱溶法回收废SCR脱硝催化剂中的二氧化钛

采用碱溶法分离回收燃煤电厂废SCR脱硝催化剂中的载体成分TiO2,通过正交实验考察了NaOH浓度、反应温度、固液比和转速对碱溶法回收TiO2过程中主要杂质W浸出分离、W和Ti浸出率的影响规律及浸出渣物相的变化规律,所得含钛浸出渣经20% H2SO4溶液或20% HCl溶液洗涤、煅烧回收TiO2。结果表明,反应温度对杂质W浸出影响最明显。回收Ti元素的最优条件为反应温度110℃及NaOH浓度40wt%、固液比1/5 g/mL、转速400 r/min,该条件下废SCR脱硝催化剂中W的脱除率达87.5%,Ti的溶出率仅为0.04%,浸出液中W/Ti浓度比为210。经H2SO4处理后生成锐钛型TiO2,经HCl处理生成金红石型TiO2,二者纯度均大于98%,实现了TiO2晶体的可控制备。     

加入碱金属盐合成超微沸石

采用水热合成法,用工业水玻璃作硅源,考察了各种碱金属盐、晶化时间、晶化温度和搅拌速度对合成超微低硅沸石的影响,经X射线衍射、红外光谱、扫描电镜、激光粒度分析和吸附量的测定证实,合成配比取Na2O∶Al2O3∶SiO2∶H2O=3∶1∶2∶185,在晶化温度90℃、晶化时间5 h、搅拌速度3 000 r/min(成胶)和1 500 r/min(成核)的合成条件下,加入0.1 mol NaF,沸石粒度由常规法合成沸石的2μm减小为180 nm;吸附总量由普通沸石的0.25 mg/L增加为0.26~0.272 mg/L;5 min吸附量由0.13 mg/L增加为0.2~0.22 mg/L。     

Fabrication of high-efficiency anatase TiO2 photocatalysts using electrospinning with ultra-violet treatment

In metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low-temperature phase metal oxides that crystallize at low temperatures. TiO₂, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low-temperature phase (anatase structure) than in the high-temperature phase (rutile structure). Studies on the fabrication of TiO₂ anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO₂ nanofiber as a high-efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra-violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO₂ nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO₂ nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO₂ nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV-treated TiO₂ nanofibers was approximately six times higher than of P25 and the heat-treated nanofibers.     

Loss of alkali promoter by desorption from promoted vanadium oxide catalysts

Experiments have been done with molecular beam mass spectrometric methods to characterize the desorption and emission processes of alkali promoter from a commercial vanadium oxide catalyst. It is a potassium and cesium promoted catalyst used for SO₃ production, with a K, Cs/V molar ratio of 2.5. An excited state signal is detected, as in our previous studies of other oxide catalysts. Desorption of both K and Cs is also detected. All signals are observed at temperatures above 910 K, which is just above the process temperature range. The values found for atomic desorption are 2.66±0.16 eV for K and 3.89±0.27 eV for Cs, while the excited state emission has a barrier of 0.89±0.08 eV. The difference in desorption energies between Cs and K is larger than expected. This is probably mainly due to different rate limiting steps in the release and diffusion processes. After an approximate compensation for this, Cs still has a larger activation barrier equal to 3.0±0.3 eV towards desorption than K, which indicates a slower loss for Cs from the catalyst.     

CO2 gasification of carbon catalysed by alkali metals: Reactivity and mechanism

A systematic study of the catalytic activity of alkali metal carbonates on the CO₂ gasification of activated carbon revealed the following order: Li < Na < K < Rb < Cs. Outgassing in an inert gas results in a pronounced activity decrease for Cs, whereas the other alkali metals show a slight increase. The activated carbon itself is unaffected. Apparent activation energies for the CO₂ gasification are also changed by outgassing and decrease from Li to Cs. Upon outgassing of the samples, CO₂ and CO are released in five distinguishable temperature regions, arising from decomposition of surface complexes and carbonate-like species, gasification phenomena and reduction of oxidic species. Outgassing patterns of all alkali metals are quite similar. During alkali-metal-catalysed gasification in CO₂ two types of oxidic species are present: surface bonded -OM species of high stability and oxidic species having less interaction with the carbon surface.     

Effect of the sonication and coating time on the photocatalytic degradation of TiO2, TiO2-Ag,and TiO2-ZnO thin film photocatalysts

Abstract

Today, the ultrasound utilizing for material synthesis has been extensively investigated. The unusual acoustic cavitation phenomenon caused by ultrasonic waves has created a new world for the production of high efficiency photocatalysts with new structures. In this study, TiO₂, TiO₂-Ag, and TiO₂-ZnO thin film photocatalysts were prepared using titanium isopropoxide Ti[OCH(CH₃)₂]₄, zinc acetate dehydrates (CH₃COO)₂Zn·2H₂O, and silver nitrate AgNO₃ by a sol–gel method under the ultrasonic irradiation. The prepared photocatalysts were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy. The SEM images showed that the Ag and ZnO particles were evenly dispersed in the photocatalysts due to the ultrasonic irradiation, and Ag particles were approximately 90?nm, which is relatively small compared to the photocatalysts which is not treated with ultrasonic irradiation. The catalytic activity of the photocatalysts was determined using Acid Red 27 dye. The most excellent catalytic degradation was obtained with TiO₂-ZnO thin film photocatalyst. In comparison to the conventional photocatalyst, the efficiency of photocatalytic activity of the photocatalyst produced under ultrasonication has been increased due to the reduced size of Ag and ZnO and its uniform dispersion.     

Novel nitrogen-doped anatase TiO2 mesoporous bead photocatalysts for enhanced visible light response

This work reports the synthesis and characterization of a novel, high surface area N-doped anatase TiO₂ mesoporous bead as a photocatalyst for visible light photodegradation. The beads were prepared using a two-cycle microwave-assisted hydrothermal method using three different types of nitrogen dopants: diaminohexane, triethylamine, and urea. In the first cycle, TiO₂mesoporous beads with controlled structures were synthesized at 200 °C without further calcination. The obtained beads were then subjected to a second cycle of microwave -assisted hydrothermal process for nitrogen doping. The photocatalytic activity of the N-doped mesoporous TiO₂ beads was determined by measuring the decomposition of a methyl blue aqueous solution under UV and visible light. It was found that different precursors lead to different degrees of doping which enhances the light absorption primarily in the visible light region. We demonstrate that the photocatalytic activity or photodegradation is enhanced in the visible light region.