La2O3助剂对Au/TiO2催化氧化CO性能的影响

采用溶胶-凝胶法制备了TiO2以及La2O3-TiO2载体, 再用沉积沉淀法制备Au/TiO2和Au/La2O3-TiO2催化剂, 并对催化剂的CO氧化反应活性进行测试. 结果表明, La2O3助剂可以显著提高催化剂催化氧化CO的活性. X射线衍射(XRD)、程序升温脱附(TPD)、N2吸附-脱附(BET)表征结果表明, La2O3助剂不仅提高了催化剂比表面积, 抑制了TiO2晶粒尺寸的长大, 并且增强了TiO2的晶格应变, 在O2气氛吸附过程中主要在TiO2表面形成O-物种. 原位傅立叶变换红外(FT-IR)结果进一步表明, La的掺杂不仅提高了吸附在Au活性位CO的氧化速率, 还使TiO2表面形成第二种活性位, 从而显著提高了催化活性.     

Au掺杂方式对锐钛矿TiO2光催化性能的影响

结合超临界乙醇干燥技术, 采用沉积-沉淀(DP)和共沉淀(CP)法分别制备了具有单一锐钛矿晶相的Au/TiO2和Au(0.2%, 原子分数)-TiO2光催化剂, 通过XRD、BET、TEM、XPS和Raman手段表征样品中Au的掺杂形态, 以光催化降解甲基橙为模型反应考察了样品的光催化活性. 结果表明, DP法制备的Au/TiO2在110 ℃干燥处理后, 表面存在的Au3+能有效地促进锐钛矿TiO2光催化性能, 其一级反应速率常数比纯锐钛矿TiO2提高了3.2倍, 比商用光催化剂Degussa-P25提高了4.1倍, 而当Au3+被还原为Au0后光催化活性下降. 用CP法制备的Au-TiO2并没有较大地提高锐钛矿TiO2光催化性能, 在焙烧温度达到800 ℃时, Au向表面迁移聚集, 造成锐钛矿TiO2晶格氧空位和缺陷位增加, 使光催化活性下降.     

Au/TiO2的制备及其光催化氧化丙烯的研究

采用浸渍法制备了Au/TiO2光催化剂,使用X射线能谱(XPS)和透射电子显微镜(TEM)对样品进行了表征.结果表明,Au颗粒的尺度约为4—6nm;Au4f7/2的结合能为83.3eV,与Au0的标准峰位(84.0eV)相比,向低结合能方向移动了0.7eV,使其表现出俘获电子的特性.以丙烯的光催化氧化为指标反应,对制备的Au/TiO2的活性进行了评价,结果显示,Au/TiO2的光催化活性明显高于单一TiO2的,且当Au的担载量在0.1—5.0%范围内变化时,催化活性随着担载量的增加而显著增加.     

TiO2晶型对Au/TiO2上光催化分解臭氧的影响

以不同晶型TiO2为载体,采用沉积-沉淀法制备了Au/TiO2光催化剂,并用紫外-可见漫反射光谱、X射线光电子能谱(XPS)和表面光电压谱(SPS)等手段进行了催化剂表征,详细考察了Ti O2晶型对Au/TiO2光催化分解臭氧活性的影响.结果表明,光催化分解臭氧的活性顺序为Au/P25>Au/Anatase>Au/Rutile,这与不同的单一Ti O2对光催化臭氧分解的活性顺序是一致的.但在TiO2上沉积金后,其对光催化臭氧的分解活性有了显著的提高.由催化剂的Au4fXPS分析发现,不同晶型Ti O2上的电荷向金簇迁移的能力有明显差异,加之载体本身对光催化臭氧分解活性不同,两者协同作用导致负载金催化剂光催化分解臭氧活性的不同.SPS信号强度与催化剂光催化活性有很好的对应关系,SPS信号越强,光生电子和空穴分离效率越高,光催化活性越好.     

La2O3助剂对Au/TiO2催化氧化CO性能的影响

采用溶胶-凝胶法制备了TiO2以及La2O3-TiO2载体,再用沉积沉淀法制备Au/TiO2和Au/La2O3-TiO2催化剂,并对催化剂的CO氧化反应活性进行测试.结果表明,La2O3助剂可以显著提高催化剂催化氧化CO的活性.X射线衍射(XRD)、程序升温脱附(TPD)、N2吸附-脱附(BET)表征结果表明,La2O3助剂不仅提高了催化剂比表面积,抑制了TiO2晶粒尺寸的长大,并且增强了TiO2的晶格应变,在O2气氛吸附过程中主要在TiO2表面形成O-物种.原位傅立叶变换红外(FT-IR)结果进一步表明,La的掺杂不仅提高了吸附在Au活性位CO的氧化速率,还使TiO2表面形成第二种活性位,从而显著提高了催化活性.     

Au/TiO2光催化分解臭氧

 采用沉积-沉淀法制备了Au/TiO2催化剂,用透射电子显微镜、紫外-可见漫反射光谱和X射线光电子能谱进行了表征,结果表明,样品在空气中于200 ℃处理后,金以金属态Au0的形式沉积在TiO2表面. 与TiO2相比,担载金的TiO2具有明显的光催化分解O3的活性. 黑光灯光照20 h后, 1%Au/TiO2催化剂对O3的分解率仍达98%以上. TiO2上的Au簇作为电子的捕获中心,能够促使电子与空穴的有效分离. 而Au簇和载体TiO2的周界处作为O3新的吸附活性中心,促进了O3的分解.     

金属载体强相互作用增强Au/TiO2催化剂在3-硝基苯乙烯选择性加氢反应的活性

自Haruta与Hutchings于上世纪八十年代末发现金纳米催化剂优异的反应活性以来,科研人员对金催化的应用领域进行了广泛而深入地研究.对金催化科学和应用领域的研究一直在进行.大量的研究表明,金催化剂在各种选择性氧化反应中具有优异的催化性能(高活性和高选择性).然而,在催化加氢反应中,尽管金催化剂相比于铂族金属显示出优越的选择性,但是由于金催化剂选择性加氢反应的活性较差,使其在选择性催化加氢反应中的应用受到了极大的限制.研究表明,金催化剂较弱的活化氢气能力是其催化加氢反应活性低的主要原因.研究发现,氢气活化的活性中心可能是界面、负价金、低配位的金原子等.金催化剂具有明显的载体效应,金属-载体之间的相互作用能够显著地改变金催化剂的催化性能.Tauster等研究发现,铂族金属与还原性载体之间存在强相互作用,能够引发载体包覆金属表面,并且使得电子从载体向金属迁移,导致金属带负电.受金属-载体强相互作用(SMSI)效应的启发,本文探究了Au/TiO2催化剂中SMSI对金催化剂加氢性能的影响.在H2或O2气氛下高温焙烧Au/TiO2,获得一系列金催化剂(Au/TiO2-TA,T为焙烧温度(oC):300、400、500和600;A为气氛:H2或O2).对比在3-硝基苯乙烯(3-NS)选择性加氢反应中的活性发现,Au/TiO2-500H的TOF值是Au/TiO2-500O的3.3倍;动力学测试表明,Au/TiO2-500H和Au/TiO2-500O的反应表观活化能分别为79.5和105.1 kJ/mol.这表明两类催化剂催化活性中心的结构存在差异.X射线光电子能谱测试结果表明,Au/TiO2-H样品中Au带部分负电,而Au/TiO2-O中Au显示为金属态.HAADF-STEM和EELS显示,Au/TiO2-H中Au NPs的表面有TiOx物种,增加了Au-TiO2的界面.EPR结果表明,Au/TiO2-H中存在表面Ti3+物种,而Au/TiO2-O样品中则没有.为确认加氢反应的活性中心到底是界面还是负价金物种,本文探究了不同温度下氢气处理的Au/TiO2的结构与性能的关系,发现Au/TiO2-300H/400H/500H催化剂都显示出较好的催化3-NS加氢活性,而Au/TiO2-600H虽然具有更多的负价金物种,但是3-NS选择性加氢反应的活性反而降低,因此,负价金不是活性中心.这是因为不同温度处理的Au/TiO2-H样品中,SMSI的强弱不同,在300、400、500 oC下,SMSI能够增加Au-TiO2的界面长度,从而增强了3-NS加氢反应的活性;而温度达到600 oC,SMSI效应太强,Au NPs被包覆更密实,导致Au/TiO2-600H的3-NS选择性加氢反应的活性下降.密度泛函理论计算表明,Au/TiO2-H样品具有更低的H2解离活化能以及氢转移活化能.氢氘交换反应也进一步验证了SMSI有利于H2的活化.     

纳米Au/TiO2光催化剂的XPS和SPS研究

 以溶胶-凝胶法制备的TiO2纳米粒子为载体,通过浸渍法制备了Au/TiO2样品,并利用XPS和SPS等技术对样品进行表征,考察了热处理温度和Au含量对TiO2纳米粒子光催化氧化苯酚活性的影响. 结果表明,Au是以金属纳米微晶的形式均匀地分散在TiO2纳米粒子表面. 用适量Au进行表面修饰不仅拓宽了TiO2对光的响应范围,而且改善了TiO2光生电子和空穴的分离效率,提高了样品对氧物种的吸附,并促进了光生电子向吸附氧的传输. 在光催化氧化苯酚反应中,500 ℃处理的Au/TiO2纳米粒子具有较高的光催化活性,这与XPS和SPS表征结果是一致的. 从电子能级匹配的角度揭示了Au对TiO2样品表面光电性质和光催化性能的影响机制.     

室温水汽对Au/TiO2上光催化分解臭氧的影响

 采用沉积-沉淀法制备了Au/TiO2光催化剂,并用紫外-可见漫反射光谱和X射线光电子能谱对其进行了表征,详细考察了室温水汽的引入对Au/TiO2光催化分解臭氧活性的影响. 结果表明,同干燥状态时相比,室温引入水汽后催化剂活性较低,并且较快地达到了稳定值. 催化剂的O 1s和Au 4f的XPS分析结果表明,水汽的存在导致TiO2的表面结构发生变化,进而使金-载体之间的相互作用力减弱. 这是导致催化剂活性下降的主要原因.     

高分散的炭载Au纳米催化剂的制备、表征和催化活性

采用柠檬酸钠还原-胶体负载法, 制备了高分散的炭载Au纳米催化剂, 并以液相催化氧化葡萄糖为葡萄糖酸钠的反应评价了Au/C催化剂的活性. 研究结果表明, 金溶胶制备过程中柠檬酸钠的用量对粒子尺寸以及所获催化剂的催化活性有重要影响; 催化剂在多次使用之后活性的降低可能是由于在活性炭表面金粒子活性位点上形成的Au^δ＋-O^δ－化合态减少的缘故. 同时比较了制备的Au/C和商业Pd/C催化剂对葡萄糖的液相催化氧化反应, 证明Au/C催化剂明显优于Pd/C催化剂.     

Role of micro-structure and interfacial properties in the higher photocatalytic activity of TiO2-supported nanogold for methanol-assisted visible-light-induced splitting of water

This paper deals with the textural, microstructural and interfacial properties of Au/TiO(2) nanocomposites, in relation to their photocatalytic activity for splitting of water. TiO(2) samples of two different morphologies were employed for dispersing different cocatalysts, such as: Au, Pt, Ag or Cu, for the sake of comparison. The samples were characterized using powder XRD, XPS, UV-visible, thermoluminescence, SEM, HRTEM and SAED techniques. Compared to other metal/TiO(2) photocatalysts, Au/TiO(2) with an optimum gold loading of 1 wt% was found to exhibit considerably higher activity for visible light induced production of H(2) from splitting water in the presence of methanol. Further, the sol-gel prepared TiO(2) (s.TiO(2)), having spherical grains of 10-15 nm size, displayed better photoactivity than a Degussa P25 catalyst. The electron microscopy investigations on s.TiO(2) revealed significant heterogeneity in grain morphology of individual TiO(2) particles, exposure of the lattice planes, metal dispersion, and the interfacial metal/TiO(2) contacts. The gold particles were found to be in a better dispersed state. O(2) TPD experiments revealed that the gold nanoparticles and Au/TiO(2) interfaces may serve as distinct binding sites for adsorbate molecules. At the same time, our thermoluminescence measurements provide an insight into Au-induced new defect states that may facilitate the semiconductor-to-metal charge transfer transition. In conclusion, the superior photocatalytic activity of Au/TiO(2) may relate to the grain morphology of TiO(2), dispersion of gold particles, and the peculiar architecture of metal/oxide heterojunctions; giving rise in turn to augmented adsorption of reactant molecules and their interaction with the photo-generated e(-)/h(+) pair. The role played by methanol as a sacrificial reagent in photocatalytic splitting of water is discussed.     

铽负载介孔二氧化钛的制备、表征和协同效应

以嵌段共聚物P123为模板剂,采用蒸发诱导自组装法制备了铽负载介孔TiO2光催化剂,并利用XRD、N2吸附解吸和UV-Vis吸收光谱等技术手段对样品进行了表征。 制备的样品为锐钛矿和金红石混合晶相,以罗丹明B为模拟有机降解物,样品显示了良好的可见光催化活性。 研究发现0.7%的铽负载和380 ℃的煅烧温度是较佳的制备条件。 介孔结构所具有的高的比表面积、小的晶粒尺寸、铽负载诱导的电荷分离和可见光吸收增强协同提高了光催化活性。 同时,提出了铽负载二氧化钛诱导增强光催化作用的机理。     

Titania supported gold nanoparticles as photocatalyst

This Perspective is focused on the photocatalytic activity of gold nanoparticles supported on titania (Au/TiO(2)). Titania is the most widely used photocatalyst, but its limited activity under visible light irradiation has motivated the quest for modified titania materials absorbing visible light. The review starts by justifying how doping with metallic elements is a related strategy, but different, to that leading to the use of Au/TiO(2) in photocatalysis. Data supporting and confirming the photoactivity of gold nanoparticles in colloidal solutions are briefly presented to justify the possibility of gold photosensitization of titania by electron injection into the conduction band. After describing the most common procedures used to prepare Au/TiO(2), the central part of this article is focused on the photocatalytic activity reported for Au/TiO(2) for hydrogen generation, dye decoloration, phenol decomposition and carboxylic acid degradation, among other processes. Emphasis is given to the role that parameters like Au loading, particle size, surface area, spatial structuring and others play on the photocatalytic activity. One important issue has been to distinguish those reports using visible light from those other in which direct titania excitation by UV light has been used. These Au/TiO(2) photocatalysts can find real applications in the near future for environmental remediation and for hydrogen generation.     

Gold-Titanium(IV) Oxide Plasmonic Photocatalysts Prepared by a Colloid-Photodeposition Method: Correlation Between Physical Properties and Photocatalytic Activities

Colloidal gold (Au) nanoparticles were prepared and successfully loaded on titanium(IV) oxide (TiO(2)) without change in the original particle size using a method of colloid photodeposition operated in the presence of a hole scavenger (CPH). The prepared Au nanoparticles supported on TiO(2) showed strong photoabsorption at around 550 nm due to surface plasmon resonance (SPR) of Au and exhibited a photocatalytic activity in mineralization of formic acid in aqueous suspensions under irradiation of visible light (>ca. 520 nm). A linear correlation between photocatalytic activity and the amount of Au loaded, that is, the number of Au nanoparticles, was observed, indicating that the activity of Au/TiO(2) plasmonic photocatalysts can be controlled simply by the amount of Au loading using the CPH method and that the external surface area of Au nanoparticles is a decisive factor in mineralization of formic acid under visible light irradiation. Very high reaction rates were obtained in samples with 5 wt % Au or more, although the rate tended to be saturated. The CPH method can be widely applied for loading of Au nanoparticles on various TiO(2) supports without change in the original size independent of the TiO(2) phase. The rate of CO(2) formation also increased linearly with increase in the external surface area of Au. Interestingly, the TiO(2) supports showed different slopes of the plots. The slope is important for selection of TiO(2) as a material supporting colloidal Au nanoparticles.     

TiO2/YFeO3复合光催化剂的制备、表征及其对气相苯的降解

利用共沉淀法和柠檬酸法制备YFeO3并以其为载体,将TiO2溶胶负载在其表面,制备了复合光催化剂TiO2/YFeO3.在紫外灯的照射下,考察对气相苯的降解效果并利用N2吸附、X射线衍射(XRD)、拉曼光谱、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、UV-Vis漫反射光谱等手段对催化剂进行了表征.结果表明,以共沉淀法制备的YFeO2为载体的复合催化剂,180 min内苯的降解率达到44.7%,表现出更好的光催化活性.两种方法制备的YFeO3均为斜方晶相,TiO2分散在载体的表面,并与YFeO3存在一定的相互作用;两种复合催化剂均具有较窄的带隙能.     

TiO2/YFeO3复合光催化剂的制备、表征及其对气相苯的降解

利用共沉淀法和柠檬酸法制备YFeO3, 并以其为载体, 将TiO2溶胶负载在其表面, 制备了复合光催化剂TiO2/YFeO3. 在紫外灯的照射下, 考察对气相苯的降解效果并利用N2吸附、X射线衍射(XRD)、拉曼光谱、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、UV-Vis漫反射光谱等手段对催化剂进行了表征. 结果表明, 以共沉淀法制备的YFeO3为载体的复合催化剂, 180 min内苯的降解率达到44.7%, 表现出更好的光催化活性. 两种方法制备的YFeO3均为斜方晶相, TiO2分散在载体的表面, 并与YFeO3存在一定的相互作用; 两种复合催化剂均具有较窄的带隙能.     

Mesoporous Fe2O3-doped TiO2 nanostructured fibers with higher photocatalytic activity

Mesoporous Fe(2)O(3)-doped TiO(2) nanostructured fibers were fabricated through electrospinning the relevant gel precursor. The prepared fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface analysis, respectively. The photocatalytic activity of these mesoporous composite fibers was evaluated by photocatalytic degradation of methylene blue (MB) in water under UV irradiation. Compared with different types of photocatalysts, the 1% Fe(2)O(3)-doped TiO(2) fibers exhibited super photocatalytic activity.     

超临界流体干燥法制备TiO2／C纳米粒子及光催化性能

以TiCl4为原料,采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级TiO2/C复合光催化剂.以苯酚的光催化降解对所得催化剂的催化活性进行了评价.结果表明,纳米TiO2/C复合粒子与单组分TiO2比较,复合粒子光催化活性高于单组分的TiO2,h苯酚降解率高达975 ％,COD为957%.并用XRD、TEM、 UV-Vis和XPS等手段进行了表征,iO2以锐钛矿型形式存在.比较了不同制备方法制得的TiO2/C复合催化剂,得出超临界干燥法制备的光催化剂具有粒径小,比表面积大,分散性好,光催化活性高等特点.     

负载金的掺氮二氧化钛的制备及其可见光催化性能

以纳米管钛酸为前驱体,采用水热法先制备得到新型N掺杂二氧化钛,然后用沉积沉淀法在N掺杂二氧化钛表面负载微量贵金属Au,制备得到负载Au的掺N二氧化钛.利用TEM、XRD、XPS、ESR和DRS等手段研究了样品的形貌、晶体结构、元素化学态和光谱吸收性质.样品光催化活性通过可见光催化降解丙烯进行评价,结果表明,样品N-TiO₂和Au/N-TiO₂具有明显的可见光(λ≥420 nm)催化活性.ESR结果表明,掺氮过程中生成的束缚单电子的氧空位是样品具有可见光响应的原因.