TiO2 films loaded with silver nanoparticles: control of multicolor photochromic behavior

Ag-TiO(2) films exhibiting multicolor photochromism were prepared by photoelectrochemical reduction of Ag(+) to Ag nanoparticles in nanoporous TiO(2) films under UV light. Color of the Ag-TiO(2) film, initially brownish-gray, changes under a colored visible light to the color of the light and reverts to brownish-gray under UV light. Their chromogenic properties were improved by simultaneous irradiation for Ag deposition with UV and blue lights to suppress the formation of anisotropic Ag particles. Nonvolatilization of a color image was also achieved by removing Ag(+) that was generated during the irradiation with a colored light. Once nonvolatilized, the image can be reproduced by UV light, even after the image is discolored under white light. This new effect evidenced that nanopores in the TiO(2) film determine the resonance wavelengths of the Ag particles, as their molds. In addition, solvatochromic behavior of the Ag-TiO(2) film proved that nanospaces left around the Ag nanoparticles affect the resonance wavelengths of the Ag particles.     

Mechanisms and applications of plasmon-induced charge separation at TiO2 films loaded with gold nanoparticles

Plasmon-induced photoelectrochemistry in the visible region was studied at gold nanoparticle-nanoporous TiO(2) composites (Au-TiO(2)) prepared by photocatalytic deposition of gold in a porous TiO(2) film. Photoaction spectra for both the open-circuit potential and short-circuit current were in good agreement with the absorption spectrum of the gold nanoparticles in the TiO(2) film. The gold nanoparticles are photoexcited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO(2) conduction band and the simultaneous transfer of compensative electrons from a donor in the solution to the gold particle. Besides its low-cost and facile preparation, a photovoltaic cell with the optimized electron mediator (Fe(2+/3+)) exhibits an optimum incident photon to current conversion efficiency (IPCE) of 26%. The Au-TiO(2) can photocatalytically oxidize ethanol and methanol at the expense of oxygen reduction under visible light; it is potentially applicable to a new class of photocatalysts and photovoltaic fuel cells.     

Spatial electron distribution and its origin in the nanoporous TiO2 network of a dye solar cell

Dye solar cells have been investigated by charge carrier extraction under short and open circuit conditions and an illumination intensity equivalent to 1 sun (AM 1.5). Under short circuit conditions, a surprisingly high amount of charge carriers stored in the nanoporous TiO2 network has been observed. A theoretical model was developed to describe the charge transport in the nanoporous TiO2 network of a dye solar cell, and the spatial distribution of the electron concentration was calculated. These results were compared with the experimental data of charge carriers stored in the TiO2 network under short and open circuit conditions. We were able to conclude that under short circuit conditions, the electrochemical potential of the electrons in the region far from the electrode is up to 550-570 meV higher than that of the electrons at the front electrode. This internal voltage is the driving force across the nanoporous TiO2 film under short circuit conditions.     

Kinetic and DFT studies on the Ag/TiO2-photocatalyzed selective reduction of nitrobenzene to aniline.

TiO2 particles loaded with silver nanoparticles with a mean diameter of 1.5 nm exhibit a high photocatalytic activity (84 % conversion after 1 h irradiation) for the reduction of nitrobenzene to aniline with 100 % selectivity in the presence of CH3OH (concentration=100 mM). High-resolution transmission electron microscopic studies of Pt-photodeposited Ag/TiO2 demonstrate that the Ag nanoparticles act as reduction sites in the photocatalytic reaction. Both spectroscopic measurements and density functional theory (DFT) calculations reveal that nitrobenzene is selectively adsorbed onto the Ag surfaces of Ag/TiO2 via partial electron transfer from Ag to nitrobenzene, whereas the interaction between aniline and Ag/TiO2 is weak. The kinetic analysis indicates that the recombination between the electrons flowing into the Ag nanoparticle and the holes left in the TiO2 valence band is significantly suppressed, particularly in the presence of CH3OH. The high activity and selectivity in the present Ag/TiO2-photocatalyzed reduction are rationalized in terms of the charge separation efficiency, the selective adsorption of the reactants on the catalyst surfaces, and the restriction of the product readsorption.     

Effects of adsorbed water on plasmon-based dissolution, redeposition and resulting spectral changes of Ag nanoparticles on single-crystalline TiO2

Ag nanoparticles photocatalytically deposited on single-crystalline TiO(2)(111) and (100) surfaces exhibit visible light-induced topographic and spectral changes corresponding to the light wavelength. A certain amount of adsorbed water on the surface is essential for the changes. The photoinduced behaviors strongly depend on the amount of the adsorbed water and on interparticle spacing, indicating that ionic conductivity on the TiO(2) surface is a key factor. The results obtained here are rationally explained in terms of a photoelectrochemical mechanism in which photoanodic dissolution of Ag nanoparticles to Ag(+) and cathodic re-deposition of Ag play essential roles.     

TiO_2/CdS/Ru(bpy)_2(NCS)_2作为太阳电池光阳极的探讨

将 Cd S纳米粒子复合在 Ti O2 纳米多孔膜上 ,用染料 Ru( bpy) 2 ( NCS) 2 对此复合半导体纳米膜电极进行敏化 ,测量了不同 Cd S复合量的 ITO/Ti O2 /Cd S/Ru( bpy) 2 ( NCS) 2 光阳极组成光电池的能量转换效率 .实验证明 ,ITO/Ti O2 /Cd S/Ru( bpy) 2 ( NCS) 2 作为太阳电池光阳极的能量转换效率与 Ti O2 /Cd S复合半导体中 Cd S的含量有关 .当 Cd S复合时间为 5 min的电池的短路电流为 5 .2 3A/m2 ,开路电压为 0 .71 6 V,能量转换效率为 0 .77% .     

Photoinduced electron storage and surface plasmon modulation in Ag@TiO2 clusters

The reversible charging and discharging effects associated with photoexcitation of a TiO2 shell in a Ag@TiO2 composite are described. The photoinduced charge separation in the TiO2 shell is followed by electron injection into the silver core. Interestingly, the charging of the silver core is associated with the shift in the surface plasmon band from 460 to 430 nm. The stored electrons are discharged upon exposure of the charged Ag@/TiO2 composite to an electron acceptor. As the electrons from the silver core are discharged, the original surface plasmon absorption of the Ag core is restored.     

TiO2纳米晶多孔膜的电荷传输特性

用光电流作用谱、瞬态光电流、循环伏安及线性电位扫描法研究了TiO2纳米晶／纳米多孔膜电荷传输特性．结果表明TiO2纳米多孔膜的电荷传输与块体半导体不同．TiO2纳米晶电极的能带不弯曲，电子在导带中可向两个方向流动，电子既可以流向电极内部经由外电路输出．也可以流向电解质溶液被溶液中的受主捕获．在TiO2纳米多孔膜电极中，不仅在负电位区能带边随电位变化，而且在正电位区能带边随电位变化而移动，即带边不钉扎。加入合适的施主可提高光电转换效率．加入受主则在电极溶液界面引起电子的严重损失，降低光电转换效率．     

染料敏化TiO2/WO3薄膜电池的光电变色

The light-to-electricity conversion process of the TiO2 nanostructured electrode sensitized by a dye was investigated using the photoelectrochemical method in this paper. At the same time, the WO3 thin film was electrodeposited on conducting glass. The results showed that the dye-sensitized nanoporous TiO2 film has the properties of energy conversion, along with good electrochromic properties of electrodeposited MoO3 thin film. A self-powered smart window was achieved by combining a dye-sensitized nanoporous TiO2 film as the photovoltaic layer and an electrodeposited WO3 film as the electrochromic layer. This window changed from being almost transparent to blue spontaneously under illumination, and thus could modulate light transmittance.     

Preparation of highly uniform Ag/TiO2 and Au/TiO2 supported nanoparticle catalysts by photodeposition

Photodeposition of Ag nanoparticles on commercial TiO2 particles and nanoparticles was performed in order to provide direct visualization of the spatial distribution of photoactive sites on sub-micrometer-scale and nanoscale TiO2 particle surfaces and to create materials for potential catalytic applications. HRTEM (high-resolution transmission electron microscopy) and HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) were used to characterize these materials. The size and spatial distributions of the Ag nanoparticles on the commercial TiO2 were not uniform; the concentration of Ag was higher on grain boundaries and at the edges of these submicrometer particles. In the case of TiO2 nanoparticles, the size distribution of the Ag nanoparticles deposited was relatively uniform and independent of irradiation time and photon energy. The amount of Ag deposited on TiO2 nanoparticles was at least 6 times higher than that on the commercial samples for comparable irradiation conditions. Compared to the case of Ag photodeposition, the difference in the amount of Au photodeposited on TiO2 particles and nanoparticles was even greater, especially at low precursor concentrations. Photodeposition on TiO2 nanoparticles is suggested as a potential method for the preparation of Au/TiO2 catalysts, as loadings in excess of 10 wt % of uniform 1 nm metal particles were achieved in this work.     

Charge separation and catalytic activity of Ag@TiO2 core-shell composite clusters under UV-irradiation

Photocatalytic properties of Ag@TiO2 composite clusters have been investigated using steady state and laser pulse excitations. Photoexcitation of TiO2 shell results in accumulation of the electrons in the Ag core as evidenced from the shift in the surface plasmon band from 460 to 420 nm. The stored electrons are discharged when an electron acceptor such as O2, thionine, or C60 is introduced into the system. Charge equilibration with redox couple such as C60/C60*- shows the ability of these core shell structures to carry out photocatalytic reduction reactions. The charge separation, charge storage, and interfacial charge-transfer steps that follow excitation of the TiO2 shell are discussed.     

银纳米粒子沉积含有氧空位的钒酸铋能够提高其近红外光催化性能（英文）

钒酸铋因其独有的廉价、低毒性、热稳定性和高氧化性能等特性而备受瞩目,是利用太阳能降解污染物、水分解等应用方面最优选择的半导体纳米材料之一.选择表面粗糙多孔尺寸均匀的橄榄状钒酸铋有助于吸附更多的电子受体参与到半导体表面的氧化还原反应当中,从而提高其光催化活性.另外,太阳能谱中紫外光占不到5%,可见光占45%,与传统的半导体TiO_2材料相比,钒酸铋禁带宽度在2.4 eV左右,能较好地吸收太阳光能实现光能转化.但是太阳光中近一半的光能属于近红外,不能被传统的纯相钒酸铋所利用.为了更好地利用太阳能,可将氧空位缺陷引入到钒酸铋晶体中,以实现近红外光能的转化利用.氧空位缺陷在半导体材料中不仅能够吸收近红外光,在低于导带的位置形成电子传输的桥梁,而且能够吸附更多的氧分子转化成活性物种.另一方面,氧空位缺陷态的引入使半导体钒酸铋材料暴露更多的活性位点,参与到溶液的氧化还原反应中.由于钒酸铋光激发的载流子浓度有限,并且光生电子-空穴容易复合,本文采用银纳米粒子负载在钒酸铋表面,利用其等离子共振效应产生的热电子与氧空位缺陷的协同作用,能够提高其载流子传输速率,抑制光生电子-空穴复合,达到更优的光能到化学能转化的目的.基于此,本文采用电子自旋共振光谱(ESR),X射线光电子能谱(XPS)和紫外可见光谱(UV-Vis)等手段研究了氧空位缺陷引入到钒酸铋以及Ag纳米粒子担载于橄榄状半导体材料上对光催化降解罗丹明B染料中太阳能驱动活性的影响.ESR结果证明,在测试过程中橄榄状钒酸铋材料吸收了更多的电子,表明存在很多氧空位缺陷.XPS结果表明出现高浓度的吸收氧峰意味着钒酸铋材料上存在大量氧空位缺陷;银纳米粒子成功负载在具有氧空位缺陷的钒酸铋材料上.UV-Vis结果表明该材料光吸收范围扩展到近红外光范围,其禁带宽度比传统纯相钒酸铋减小,Ag-BiVO_4-OV样品的导价带位置发生明显变化.因此,由于氧空位和银纳米粒子存在于橄榄状钒酸铋主体中,其光催化降解罗丹明B的效率远远高于纯相钒酸铋样品.由此可见氧空位缺陷和银纳米粒子的引入使得半导体光催化材料光学性能正效应增加.Supporting Information for Ag nanoparticles deposited on oxygen-vacancy-containing BiV O4 for enhanced near-infrared photocatalytic activity Chunjing Shi,Xiaoli Dong*,Xiuying Wang,Hongchao Ma,Xiufang Zhang School of Light Industry and Chemical Engineering,Dalian Polytechnic University,Dalian 116034,Liaoning,China*Corresponding author.E-mail:dongxl@dlpu.edu.cn On the other hand,the nitrogen sorption isotherm of the reactions,but also can provide more surface active sites for as-prepared samples possesses an obvious condensation step oxygen activation and reduction,and thereby positively around P/P0=0.5-0.9,which is typical hysteresis loops of facilitating the reaction process and endowing the catalyst with mesoporous materials(Fig.S1).It is indicated that the robust redox kinetics.as-prepared Ag-BiV O4-OV possesses the mesoporous structure To further prove remarkable photocatalytic activities of the(Fig.S2).In addition,the Ag-BiV O4-OV exhibits ultra-large as-prepared samples,the photocatalytic activities of the typical surface area(34.8 m3/g),which is more than 2 times larger samples based on previous report was listed(Table S1).This than that of pure BiV O4(Fig.S1).The novel mesoporous statistics indicated that the as-prepared Ag-BiV O4-OV reveals structure and larger surface area not only can promote the more excellent photocatalytic performance.diffusion of active species and accelerate subsequent surface50Ag-Bi VO-OV41)-g3m40(c d Bi VO4be30ords a20me u olV1000.0 0.2 0.4 0.6 0.8 1.0Relative pressure(P/P)0Fig.S1.N2-sorption isotherm of pure BiV O4 and Ag-BiV O4-OV.Ag-Bi VO4-OV Bi VO41)-mn1-g3m(c D d V/d0 10 20 30 40 50 60 70 80Pore size(nm)Fig.S2.Pore size distributions of pure BiV O4 and Ag-BiV O4-OV.Table S1Summary for the photocatalytic activities of the typical samples.Sample Amount Amount of dye Light source Time Degradation rate Reference Ag-BiV O4-OV 20 mg 50 mL RhB(10 mg/L)simulated sunlight 100 min 99%this work mono-dispersed m-BiV O4 0.1 g 50 mL RhB(15μmol/L)visible light 10 h 99%[1]BiV O4–Ag/Co3O4 100 mg 50 mL RhB(10 mg/L)simulated sunlight 120 min 97%[2]the BiV O-4 80 mg 80 mL RhB(1×105 mol/L)visible light 6 h 97%[3]Dy-BiV O4 50 mg 50 mL(10 mg/L)visible light 10 h 66.9%[4]m-BiV O4 0.2 g 100 mL of RhB(0.01 mmol/L)visible light 150 min 98%[5]BiV O4/CeO 2 50 mg 50 mL RhB(2×10-5 mol/L)visible light 210 min 90%[6]     

TiO2 surface modification and characterization with nanosized PbS in dye-sensitized solar cells

The nanoporous TiO2 films utilized in dye-sensitized solar cells (DSSCs) possess a large surface-to-volume ratio, which facilitates the adsorption of sensitizing dye and the recombination due to the high density of surface traps. In this paper, nanosized PbS was fabricated on the TiO2 films. The components of the modified TiO2 film were studied by X-ray diffraction (XRD) and electron probe microanalysis (EPMA), while the structure of the film was characterized with BET physisorption and high-resolution scanning electron microscopy (HRSEM). The results showed that the PbS particles were 2-3 nm and discrete on the surface of TiO2. Diffusion photovoltage (PV) spectroscopy was employed to study the charge separation and diffusion processes inside modified and unmodified TiO2 films. The diffusion PV signals revealed that the traps on the surface of TiO2 were extremely reduced due to the presence of PbS. The results of transient photovoltage and back I-V characteristics showed that the back reaction, that is, the recombination due to the reaction between an electron on TiO2 and the hole-transporting media, was retarded significantly.     

染料敏化TiO2/MoO3薄膜电池的光电变色

在导电玻璃上电沉积得到MoO3薄膜,该薄膜具有良好的电致变色特性,用它和顺二硫氰根 双(2,2′ 联吡啶 4,4′ 二羧酸)合钌(II)[cis bis(thiocyanato) bis(2,2′ bipyridyl 4,4′ dicarboxylate)ruthenium(II),简写为[RuL2(SCN)2]染料敏化的TiO2纳米结构多孔膜组成电池,在白光照射下可产生显著的颜色变化,有望用于自供电源的电色灵巧窗(self powered smart window).     

高活性Ag修饰TiO2空心八面体光催化剂的简易模板诱导合成

贵金属修饰的TiO2空心纳米光催化材料由于具有大的比表面积、低的质量密度、良好的表面渗透性、强的光吸收能力以及界面电荷的快速转移,因而表现出优异的光催化性能.为了制备结构可控且精良的贵金属修饰TiO2空心纳米光催化材料,人们先后采用湿化学法、高温固相法、声化学法及光化学沉积法等.由于在制备过程中涉及多种异相材料的合成和结构控制,因此上述合成方法通常需要复杂且多步过程(有些过程甚至很容易导致结构破坏),从而限制了其在光催化领域的实际应用.本文开发了一种简单的模板诱导法,成功制备了Ag纳米粒子修饰的TiO2空心八面体光催化剂.合成过程包括模板指导沉积和原位模板溶解.以Ag2O八面体为模板, TiF4水溶液为前驱体,首先通过TiF4水解形成TiO2纳米粒子沉积在Ag2O模板表面,而TiF4水解产生的酸性HF水溶液可原位溶解碱性的Ag2O模板,从而一步制得TiO2空心八面体.同时,利用Ag2O以及Ag+离子的光敏特性,在光照条件下使Ag2O和Ag+离子生成Ag纳米颗粒,直接沉积在TiO2空心八面体的内外表面,得到Ag/TiO2光催化剂.由此可见,该合成方法具有明显的步骤少的优点.扫描电镜、透射电镜、能量散射和紫外-可见光谱等表征结果表明成功制得内外Ag纳米粒子修饰的TiO2空心八面体光催化剂,其中TiO2空心八面体的壁厚约为25 nm,边长约为1μm,而修饰在其表面的Ag纳米粒子尺寸仅为5–10 nm.此外,通过控制TiF4前驱体浓度,还可制备核壳结构的Ag2O@TiO2八面体以及不同壁厚Ag修饰的TiO2空心八面体,表明该方法在Ag/TiO2形貌合成上的多样性和可控性.为了获得良好的光催化活性,对制备的Ag纳米粒子修饰的TiO2空心八面体光催化剂进行了不同温度的热处理. X射线衍射结果表明,即使在600 oC高温下,制备的Ag/TiO2空心八面体光催化剂依然能够保持原有的特殊形貌和锐钛矿TiO2晶型.该温度明显高于TiO2从锐钛矿向金红石转变的温度.这说明合成的Ag/TiO2能在保持高活性锐钛矿相的同时获得更好的结晶性.这可能是由于分散在TiO2原始晶粒周围的Ag纳米粒子能阻止其进一步长大,从而抑制了其晶型转变.不同样品光催化降解甲基橙的结果表明,经600oC高温热处理的样品表现出最高的光催化活性,相应的反应速率常数为0.11 min？1.这应得益于该光催化剂具有以下三个特点：(1) TiO2空心八面体的薄壁结构能够缩短光照条件下光生电子和空穴从内部扩散到表面的距离;(2)由于贵金属Ag纳米粒子沉积在TiO2薄壁的内外两个表面以及TiO2和Ag形成肖脱基势垒,因此在它们接触的界面上能够发生更快的界面电荷转移;(3)高温处理导致TiO2良好的晶化以及高活性锐钛矿TiO2晶型的保持.     

Protein adsorption on nanoporous TiO2 films: a novel approach to studying photoinduced protein/electrode transfer reactions

We have investigated the use of nanoporous TiO2 films as substrates for protein immobilisation. Such films are of interest due to their high surface area, optical transparency, electrochemical activity and ease of fabrication. These films moreover allow detailed spectroscopic study of protein/electrode electron transfer processes. We find that protein immobilisation on such films may be readily achieved from aqueous solutions at 4 degrees C with a high binding stability and no detectable protein denaturation. The nanoporous structure of the film greatly enhances the active surface area available for protein binding (by a factor of up to 850 for an 8 microns thick film). We demonstrate that the redox state of proteins such as immobilised cytochrome-c (Cyt-c) and haemoglobin (Hb) may be modulated by the application of an electrical bias potential to the TiO2 film, without the addition of electron transfer mediators. The binding of Cyt-c on the TiO2 films is investigated as a function of film thickness, protein concentration, protein surface charge and ionic strength. We demonstrate the potential use of immobilised Hb on such TiO2 films for the detection of dissolved CO in aqueous solutions. We further show that protein/electrode electron transfer may be initiated by UV bandgap excitation of the TiO2 electrode. Both photooxidation and photoreduction of the immobilised proteins can be achieved. By employing pulsed UV laser excitation, the interfacial electron transfer kinetics can be monitored by transient optical spectroscopy, providing a novel probe of protein/electrode electron transfer kinetics. We conclude that nanoporous TiO2 films may be useful both for basic studies of protein/electrode interactions and for the development of novel bioanalytical devices such as biosensors.     

Interface dominated high photocatalytic properties of electrostatic self-assembled Ag(2)O/TiO(2) heterostructure

Electrostatic self-assembled Ag(2)O/TiO(2) nanobelts heterostructure was synthesized via simple physical mixing of Ag(2)O nanoparticles and TiO(2) nanobelts. The morphologies and microstructures of Ag(2)O/TiO(2) nanobelt heterostructure were characterized by high resolution transmission electron microscopy. The interface dominated high UV photocatalytic activity and degraded photoluminescence strength of composite catalyst confirmed the heterostructure effect between Ag(2)O nanoparticles and TiO(2) nanobelts. X-ray photoelectron spectroscope provided direct evidence of charge transfer on the heterostructures between them.     

不对称菁染料敏化纳米TiO2的光生电流过程

用光电化学方法研究了不对称菁类染料敏化TiO2纳米结构电极的光电转换过程.结果表明,该染料的电子激发态能级位置与TiO2纳米粒子导带边位置匹配较好,光激发染料后,其激发态电子可以注入到TiO2纳米多孔膜的导带,从而使TiO2纳米结构电极的吸收光谱和光电流谱红移至可见光区,其 IPCE(Incident photon-to-electron conversion efficiency)值最高可达84.3%.并进一步结合现场紫外-可见吸收光谱研究了外加电势对激发态染料往TiO2纳米多孔膜注入电子过程的影响.     

Capacitance and field-driven electron transport in electrochemically self-assembled nanoporous ZnO/dye hybrid films

Electrodeposited nanoporous ZnO/eosin Y hybrid films have been investigated in view of their potential applications in dye-sensitized solar cells and supercapacitors. Intensity-modulated photocurrent spectra were measured at different electrode potentials at films of different thicknesses. It was found that the results represent either the RC constant of the cell and surface recombination of photogenerated holes with electrons or the diffusion of photogenerated electrons and are dependent on the electron concentration in the ZnO, which is influenced by the film thickness, the electrode potential, and the light intensity. The results suggest that the porosity of the electrodeposited ZnO increases with the film thickness and the films therefore consist of two parts, a less porous part deposited in the first few minutes that exhibits field-driven electron transport and a more porous outer part where electron transport is by diffusion. The results are supported by frequency-dependent capacitance measurements, which also show that the material is suitable for supercapacitors.     

Catalysis with TiO2/gold nanocomposites. Effect of metal particle size on the Fermi level equilibration

Photoexcited semiconductor nanoparticles undergo charge equilibration when they are in contact with metal nanoparticles. Such a charge distribution has direct influence in dictating the energetics of the composite by shifting the Fermi level to more negative potentials. The transfer of electrons to Au nanoparticles has now been probed by exciting TiO(2) nanoparticles under steady-state and laser pulse excitation. Equilibration with the C(60)/C(60)(-) redox couple provides a means to determine the apparent Fermi level of the TiO(2)-Au composite system. The size-dependent shift in the apparent Fermi level of the TiO(2)-Au composite (20 mV for 8-nm diameter and 40 mV for 5-nm and 60 mV for 3-nm gold nanoparticles) shows the ability of Au nanoparticles to influence the energetics by improving the photoinduced charge separation. Isolation of individual charge-transfer steps from UV-excited TiO(2) --> Au --> C(60) has provided mechanistic and kinetic information on the role of metal in semiconductor-assisted photocatalysis and size-dependent catalytic activity of metal-semiconductor nanocomposites.