金纳米颗粒在等离子体共振光催化剂中的作用机理研究

金纳米颗粒在等离子体共振光催化剂中具有多种不同的作用机理。本文采用溶胶-凝胶法合成了氮/碳共掺杂超薄二氧化钛(D-TiO₂)包覆的SiO₂/Au/D-TiO₂三明治型及SiO₂/D-TiO₂核壳纳米结构材料,对金纳米颗粒在含有可见光响应型半导体的等离子体共振光催化剂光催化分解水制氢反应中的作用机理进行了探索。研究结果表明,在该等离子体共振光催化剂的光催化反应过程中,金纳米颗粒同时体现出肖特基效应和等离子体共振效应作用机理,且作用机理与光生载流子的多少以及金纳米颗粒的负载量有关。负载量较低时,金纳米颗粒的作用机理与光生载流子的多少有关。而在高负载量条件下,金纳米颗粒在可见光照射下主要表现出肖特基效应对光催化活性的影响。     

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.     

铂修饰的{001}面暴露的二氧化钛纳米片阵列的制备和光催化性能

采用有机溶剂热法在FTO衬底上制备{001}面暴露的单晶锐钛矿相TiO2纳米片阵列,通过FESEM和XRD研究样品的形貌和晶体结构. 与水热法制备的纳米片阵列相比,有机溶剂热法制备的样品取向性更好. 采用光沉积方法在纳米片阵列上沉积Pt,所得到的Pt纳米颗粒粒径更为均匀,并且更容易沉积在{001}面上. 所负载的Pt 纳米颗粒增强了TiO2纳米片的光吸收性能,同时大大减弱了光致发光强度. 在光催化性能测试中,具有最优负载量的样品催化性能提高了一倍. 与传统的Pt负载相比,{001}面的最优负载量显得相当小,这可能源于高活性{001}面的原子结构.     

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.     

Effect of Cl− anions on photocatalytic decomposition of gaseous ozone over Au @ Ag/TiO2 catalyst

Au core Ag shell composite structure nanoparticles were prepared using a sol method. The Au core Ag shell composite nanoparticles were loaded on TiO₂ nanoparticles as support using a modified powder–sol method, enabling the generation of Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone. The sols were characterized by means of ultraviolet–visible light (UV–Vis) reflection spectrometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The activity of the Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone was evaluated and the effect of Cl^? anions on the photocatalytic activity of the catalysts was highlighted. Results showed that Au @ Ag/TiO₂ prepared via the modified powder–sol route in the presence of an appropriate amount of NaCl solid as demulsifier had better activity in the photocatalytic decomposition and elimination of ozone. At the same time, Au @ Ag/TiO₂ catalysts had better ability to resist poisonous Cl^? anions than conventional Au/TiO₂ catalyst. The reasons could be, first, that NaCl was capable of reducing the concentration of free Ag⁺ by adsorption on the surface of Ag particles forming AgCl and enhancing the formation of Au core Ag shell particles, leading to a better resistance to Cl^? anions of the catalysts, and, second, AgCl took part in the photocatalytic decomposition of ozone together with Au @ Ag/TiO₂ catalysts and had a synergistic effect on the latter, resulting in better photocatalytic activity of Au @ Ag/TiO₂ catalysts.     

可见光驱动Au/SrTiO3纳米等离子体光催化剂分解水制氢

采用水热法和光沉积法制备了Au/SrTiO_3纳米等离子体光催化剂。通过XRD、XPS、SEM、TEM、EDS和DRS等技术对光催化剂的结构、组成、形貌、粒子大小和光吸收性质等进行了表征,考察了Au/SrTiO_3纳米光催化剂在可见光照下的制氢性能。结果表明,采用水热法成功合成了SrTiO_3纳米粒子,通过负载Au纳米粒子后,由于表面等离子体共振效应,增强了其对可见光的吸收。此外,测试了不同Au负载量对SrTiO_3光催化剂在可见光照下制氢活性的影响,其中,5%Au/SrTiO_3光催化剂在可见光照下制氢活性最高,并对其光催化反应机理进行了进一步的探讨。     

Cu/Ni助催化剂对TiO2光催化制取苯酚性能的影响

以TiO₂纳米粒子为主催化剂,采用"浸渍-还原法"构筑了铜、镍共负载的二氧化钛基光催化系统。以苯为起始原料,H₂O₂为氧化剂,研究了Cu/Ni助催化剂对TiO₂可见光催化制取苯酚性能的影响并对Cu/Ni助催化剂的作用机制进行了探讨。结果表明,在可见光照射下,纯TiO₂纳米粒子对苯氧化制取苯酚反应没有催化活性。铜、镍的引入可以明显地增强Ti₀₂可见光催化制取苯酚的活性。当使用负载有铜、镍的TiO₂作为催化剂时,苯酚的产率可达到18%。结果还表明Cu、Ni之间存在着很强的协同作用。在该协同作用下,Cu、Ni共负载的TiO₂纳米粒子表现出了较单一金属负载的TiO₂纳米粒子高得多的光催化活性。     

Cu/Ni助催化剂对TiO2光催化制取苯酚性能的影响

以TiO₂纳米粒子为主催化剂, 采用“浸渍-还原法”构筑了铜、镍共负载的二氧化钛基光催化系统。以苯为起始原料, H₂O₂为氧化剂, 研究了Cu/Ni助催化剂对TiO₂可见光催化制取苯酚性能的影响并对Cu/Ni助催化剂的作用机制进行了探讨。结果表明, 在可见光照射下, 纯TiO₂纳米粒子对苯氧化制取苯酚反应没有催化活性。铜、镍的引入可以明显地增强TiO₂可见光催化制取苯酚的活性。当使用负载有铜、镍的TiO₂作为催化剂时, 苯酚的产率可达到18%。结果还表明Cu、Ni之间存在着很强的协同作用。在该协同作用下, Cu、Ni共负载的TiO₂纳米粒子表现出了较单一金属负载的TiO₂纳米粒子高得多的光催化活性。     

Influence of Excitation Wavelength (UV or Visible Light) on the Photocatalytic Activity of Titania Containing Gold Nanoparticles for the Generation of Hydrogen or Oxygen from Water

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.     

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.     

基于等离激元热电子调控的全谱光催化产氢增强（英文）

等离激元效应在光催化体系中的集成为实现广谱光吸收提供了一个新的途径,然而等离激元热电子的较低迁移率和不确定扩散方向使得其光催化效率仍较低.等离激元金属与n型半导体接触后,其界面间会形成肖特基结.在特定波长太阳光照射下,等离激元金属将其表面等离子体能量聚集在表面自由电子上,进而产生热电子.当这些热电子具有的能量高于肖特基势垒时,热电子便可注入到半导体导带上.与此同时,半导体上的电子可以通过肖特基接触发生回流,与金属上的空穴复合,进而降低半导体-等离激元金属复合材料的光催化性能.因此,为了提高光催化效率,如何调控等离激元热电子迁移和充分利用等离激元效应是一个重要挑战.本文尝试将"表面异质结"与肖特基结相结合的复合结构,得以有效地调控等离激元热电子的迁移.在该复合结构中,金纳米颗粒和铂纳米颗粒分别作为等离激元吸光单元和助催化剂,集成在TiO_2纳米片表面.其中"表面异质结"是由TiO_2纳米片的两种不同表面晶面所构成,我们选择由{001}和{101}两组晶面组成的TiO_2纳米片作为半导体衬底.该结构中的{001}晶面导带能级高于{101}导带能级,因而电子由高能级的{001}流向低能级的{101}晶面,可以用来引导等离激元热电子从可见光响应的金纳米颗粒向TiO_2进行高效转移.通过巯基丙酸的桥联作用,将等离激元Au纳米颗粒锚定在TiO_2纳米片的{001}晶面上,获得Au-TiO_2{001}样品.另一方面,利用TiO_2纳米片自身光生电荷导向性光沉积,得到与{101}晶面结合形成的Au-TiO_2{101}样品.我们对两组样品进行光电流和光催化产氢实验对比,确认在"表面异质结"诱导下Au-TiO_2{001}样品中Au产生的光生热电子可以更好地注入到TiO_2纳米片导带上.我们进一步通过光沉积Pt纳米颗粒来判定光生电子所能到达的区域,验证了以上结论.与此同时,肖特基结由铂纳米颗粒与TiO_2纳米片所形成,可以促使电子由TiO_2向铂纳米颗粒进行转移,而避免发生向金纳米颗粒的反向迁移,从而在Au-TiO_2体系中实现高效的单向载流子转移.基于该设计,等离激元光催化剂实现了明显改善的全谱光催化产氢性能.本文为全谱光催化的复合结构理性设计提供了一个新的思路.     

Preparation and enhanced visible-light photocatalytic H2-production activity of CdS-sensitized Pt/TiO2 nanosheets with exposed (001) facets

CdS-sensitized Pt/TiO(2) nanosheets with exposed (001) facets were prepared by hydrothermal treatment of a Ti(OC(4)H(9))(4)-HF-H(2)O mixed solution followed by photochemical reduction deposition of Pt nanoparticles (NPs) on TiO(2) nanosheets (TiO(2) NSs) and chemical bath deposition of CdS NPs on Pt/TiO(2) NSs, successively. The UV and visible-light driven photocatalytic activity of the as-prepared samples was evaluated by photocatalytic H(2) production from lactic acid aqueous solution under UV and visible-light (λ ≥ 420 nm) irradiation. It was shown that no photocatalytic H(2)-production activity was observed on the pure TiO(2) NSs under UV and/or visible-light irradiation. Deposition of CdS NPs on Pt/TiO(2) NSs caused significant enhancement of the UV and visible-light photocatalytic H(2)-production rates. The morphology of TiO(2) particles had also significant influence on the visible-light H(2)-production activity. Among TiO(2) NSs, P25 and the NPs studied, the CdS-sensitized Pt/TiO(2) NSs show the highest photocatalytic activity (13.9% apparent quantum efficiency obtained at 420 nm), exceeding that of CdS-sensitized Pt/P25 by 10.3% and that of Pt/NPs by 1.21%, which can be attributed to the combined effect of several factors including the presence of exposed (001) facets, surface fluorination and high specific surface area. After many replication experiments of the photocatalytic hydrogen production in the presence of lactic acid, the CdS-sensitized Pt/TiO(2) NSs did not show great loss in the photocatalytic activity, confirming that the CdS/Pt/TiO(2) NSs system is stable and not photocorroded.     

Effects of crystallinity, {001}/{101} ratio,and Au decoration on the photocatalytic activity of anatase TiO2 crystals

Anatase TiO₂ nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF₂ precursors. The as-prepared TiO₂ samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N₂ adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800 °C. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO₂ samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF₂ at 700 and 800 °C.     

Photocatalytic Degradation of 2-Propanol and Phenol Using Au Loaded MnWO4 Nanorod Under Visible Light Irradiation

Single crystalline MnWO₄ nanorod has been prepared by low temperature hydrothermal reaction at 180 °C. The prepared MnWO₄ possesses band gap of 2.63 eV. Photochemical decomposition method has been followed to disperse Au nanoparticles onto MnWO₄ nanorod. The prepared Au loaded MnWO₄ nanorod demonstrated greatly enhanced photocatalytic activity in decomposing 2-propanol and evolving CO₂ in gas phase and phenol in aqueous phase compared to bare MnWO₄ and commercial TiO₂ nanoparticles (Degussa P25) under visible light (λ ≥ 420 nm) irradiation. The Au loading was optimized to 3.79 wt% for the highest efficiency. The enhanced photocatalytic activity originates from the absorption of visible light by MnWO₄ as well as the introduction of nanoparticulate Au on the surface of MnWO₄ as cocatalyst to impede the recombination of photogenerated charge-carriers.     

Gold photocatalysis in sustainable hydrogen peroxide generation

Hydrogen peroxide (H₂O₂) is a mild and green oxidant widely employed in organic syntheses, medical sector, disinfection, pulp bleaching, environmental remediation and biological processes. However, its production via the expensive, multistep and energy intensive anthraquinone process renders it less sustainable. Photocatalysis is a viable, sustainable and promising strategy to produce H₂O₂ from green sources: water and molecular O₂. This article presents key developments of photocatalytic H₂O₂ generation using gold (Au) nanoparticles supported on semiconductor photocatalysts. Several photocatalytic systems containing Au nanoparticles and the roles of Au nanoparticles in enhancing photocatalytic H₂O₂ generation including increasing the visible light absorption, facilitating the charge carrier separation and transfer, and as catalytic active sites are discussed. Factors defining the photocatalytic activity such as the effects of Au particle size and loading, localised surface plasmon resonance, mixed-gold component, and the design of photocatalysts are reviewed. Finally, the challenges and prospects for further developments of Au photocatalysis in sustainable H₂O₂ synthesis as well as other related applications are highlighted.     

金/氧化亚铜异质球的制备及其可见光催化性能

使用L-半胱氨酸作为连接剂, 利用硼氢化钠原位还原预先吸附在介孔氧化亚铜表面的氯金酸根离子,得到了Au/Cu₂O异质结构. 应用X射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)、紫外-可见(UV-Vis)光谱和N₂物理吸附等手段对催化剂进行表征, 并以λ>400 nm的可见光作为光源, 评价了该催化剂光催化降解亚甲基蓝(MB)的活性. 实验结果表明, 直径为4 nm的金颗粒完好地负载在介孔氧化亚铜的表面, 并且介孔氧化亚铜的细微结构与孔径均未发生变化. 研究表明, 以乙醇作为反应溶剂有效抑制了AuCl₄^-与Cu₂O之间的氧化还原反应, 从而有利于氧化亚铜介孔结构的保持及金颗粒的原位还原. 光催化降解亚甲基蓝的结果表明, Au/Cu₂O异质结构的光催化活性比纯氧化亚铜光催化活性有明显提高. 推测其光催化性能提高的主要原因如下: 一方面, 金颗粒良好的导电性有利于氧化亚铜表面电子的快速转移, 实现电子-空穴分离; 另一方面, 金颗粒可能存在的表面等离子共振现象加速了光生电子的产生.     

A simple preparation of nitrogen doped titanium dioxide nanocrystals with exposed (001) facets with high visible light activity

Nanoscaled nitrogen doped anatase TiO(2) with dominant (001) facets, which exhibited high photocatalytic activity and excellent photoelectrochemical properties under visible light irradiation, was successfully synthesized by solvothermal treatment of TiN in acidic NaBF(4) solution for the first time.     

Efficient visible-light photocatalytic water splitting by minute amounts of gold supported on nanoparticulate CeO2 obtained by a biopolymer templating method

When irradiated with visible light (λ > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 μmol·h(-1)) more efficiently than the standard WO(3) (1.7 μmol·h(-1)) even under UV irradiation (9.5 μmol·h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce(4+) to alginate gel, subsequent supercritical CO(2) drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.     

氮自掺杂暴露（001）晶面TiO2微米片的可见光光催化CO2还原性能增强

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, TiO2仍是广泛研究的明星材料。在实际使用中, TiO2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TiO2的结构与形貌特征极大地影响其光催化效率。尤其, TiO2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TiO2(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TiO2(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TiO2(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TiO2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TiO2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TiO2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TiO2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, TiO2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TiO2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TiO2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TiO2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TiO2的可见光利用效率和光生电子-空穴分离效率,优化TiO2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。     

锐钛矿(001)与(101)晶面在光催化反应中的作用

采用水热法制备了(001)和(101)晶面暴露的单晶锐钛矿TiO₂颗粒. 利用光还原沉积贵金属(Au, Ag, Pt)和光氧化沉积金属氧化物(PbO₂, MnO_x)的方法研究了暴露的锐钛矿(001)和(101)晶面在光催化中的作用. 通过透射电子显微镜(TEM)、扫描电子显微镜(STM)、能量色散X射线光谱仪(EDX)和X射线光电子能谱(XPS)的表征, 发现发生光还原反应生成的贵金属粒子主要沉积在暴露的锐钛矿(101)晶面上, 而发生光氧化反应产生的金属氧化物颗粒主要沉积在暴露的锐钛矿(001)晶面上. 此结果表明光激发产生的电子与空穴主要并分别分布在单晶锐钛矿TiO₂的(101)与(001)晶面上, 并在其上参与光催化还原反应和氧化反应. 同时也表明暴露的不同晶面对光生电荷具有分离效应. 基于本研究可以认为同时暴露分别进行氧化和还原反应的晶面可以有效促进光催化反应.