Effect of strong coupling on interfacial electron transfer dynamics in dye-sensitized TiO2 semiconductor nanoparticles

Dynamics of interfacial electron transfer (ET) in ruthenium polypyridyl complex [{bis-(2,2′-bpy)-(4-[2-(4′-methyl-[2,2′]bipyridinyl-4-yl)-vinyl]-benzene-1,2-diol)}ruthenium(II) hexafluorophosphate] (Ru-cat) and 5,10,15-tris phenyl-20-(3,4-dihydroxy benzene) porphyrin (TPP-cat)-sensitized TiO₂ nanoparticles have been investigated using femtosecond transient absorption spectroscopic detection in the visible and near-infrared region. We have observed that both Ru-cat and TPP-cat are coupled strongly with the TiO₂ nanoparticles through their pendant catechol moieties. We have observed a single exponential and pulse-width limited (<100 fs) electron injection from nonthermalized-excited states of Ru-complex. Here electron injection competes with the singlet-triplet manifold relaxation due to strong coupling of catecholate binding, which is a unique observation. Optical absorption spectra indicate that the catechol moiety interacts with TiO₂ nanoparticles showing the characteristic pure catechol-TiO₂ charge-transfer (CT) band in the visible region. Transient absorption studies on TPP-cat/TiO₂ system exciting both the Soret band at 400 nm and the Q-band at 800 nm have been carried out to determine excitation wavelength-dependence on ET dynamics. The reaction channel for the electron-injection process has been found to be different for both the excitation wavelengths. Excitation at 800 nm, is found directly populate directly the excited CT state from where diffusion of electrons into the conduction band takes place. On the other hand, excitation at 400 nm light excites both the CT band of cat-TiO₂ and also Soret band of TPP-cat.     

Photosensitization of nanoparticulate TiO2 using a Re(I)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain

We have synthesized a new photoactive rhenium(i)-complex having a pendant catechol functionality [Re(CO)(3)Cl(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO(2) and the photoexcited states of this Re(i)-complex using femtosecond transient absorption spectroscopy. Our steady state absorption studies revealed that complex 1 can bind strongly to TiO(2) surfaces through the catechol functionality with the formation of a charge transfer (CT) complex, which has been confirmed by the appearance of a new red-shifted CT band. The longer wavelength absorption band for 1, bound to TiO(2) through the proposed catecholate functionality, could also be explained based on the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO(2) nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near infrared regions. Electron injection into the conduction band of the nanoparticulate TiO(2) was confirmed by detection of the conduction band electron in TiO(2) ([e(-)](TiO(2)(CB))) and the cation radical of the adsorbed dye (1˙(+)) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (<100 fs) electron injection was observed. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1˙(+) and .     

Observation of pH-dependent back-electron-transfer dynamics in alizarin/TiO2 adsorbates: importance of trap states

The dependence of the interfacial electron transfer in alizarin-sensitized TiO2 nanoparticles on the sample pH has been examined via transient absorbance spectroscopy in the visible spectral region (443-763 nm). Excitation of the alizarin/TiO2 system with visible pump pulses (lambdaexc = 500 nm) leads to a very fast electron injection (tauinj < 100 fs) over a wide pH range. Back electron transfer shows complicated multiphasic kinetics and strongly depends on the acidity of the solution. The strong dependence of back-electron-transfer dynamics on the ambient pH value is explained by a Nernstian-type change in the semiconductor band energy. Indeed, a variation of pH values over 7 units leads to a approximately 0.42 eV change of the conduction band edge position (i.e., the nominal free energy of the electron in the electrode). Assuming a pH-independent redox potential of the dye, this change was sufficient to push the system to a condition where direct photoinitiated electron injection to intraband gap surface states could be investigated. The existence of an electron-transfer pathway via surface trap states is supported by the similarity of the observed back-electron-transfer kinetics of alizarin/TiO2 at pH 9 and alizarin/ZrO2 reported in earlier work (J. Phys. Chem. B 2000, 104, 8995), where the conduction band edge is approximately 1 eV above the excited state of the dye. The influence of surface trap states on interfacial electron transfer has been studied, and a detailed analysis of their population, depopulation, and relaxation kinetics is performed. Therefore, alizarin adsorbed on the surface of TiO2 nanoparticles is an ideally suited system, where pH-dependent investigations allow a detailed study of the electron dynamics in trap states of TiO2 nanoparticles.     

Strongly coupled ruthenium-polypyridyl complexes for efficient electron injection in dye-sensitized semiconductor nanoparticles

Dynamics of interfacial electron transfer (ET) in the ruthenium-polypyridyl complex [{bis(2,2'-bpy)-(4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol)} ruthenium(II) hexafluorophosphate] (Ru-cat)-sensitized TiO(2) nanoparticles has been investigated using femtosecond transient absorption spectroscopy detecting in the visible and near-infrared region. It has been observed that Ru-cat is coupled strongly with the TiO(2) nanoparticles through its pendant catechol moiety. Electron injection has been confirmed by direct detection of electrons in the conduction band, cation radical of the adsorbed dye, and a bleach of the dye in real time as monitored by transient absorption spectroscopy. A single-exponential and pulse width limited (<100 fs) electron injection has been observed, and the origin of it might have been from the nonthermalized excited states of the Ru-cat molecule. The result gave a strong indication that the electron injection competes with the thermalization of the photoexcited states due to large coupling elements for the forward ET reaction. Back-ET dynamics has been determined by monitoring the decay kinetics of the cation radical and injected electron and also from recovery kinetics of the bleach of the adsorbed dye. It has been fit with a multiexponential function, where approximately 30% of the injected electrons are recombined with a time constant of <2 ps, again indicating large coupling elements for the charge recombination reaction. However, our results have shown relatively long-lived charge separation in the Ru-cat/TiO(2) system as compared to other organic dye-sensitized TiO(2) nanoparticles with similar interactions.     

Exciton-coupled charge-transfer dynamics in a porphyrin J-aggregate/TiO(2) complex

Exciton-coupled charge-transfer (CT) dynamics in TiO(2) nanoparticles (NP) sensitized with porphyrin J-aggregates has been studied by femtosecond time-resolved transient absorption spectroscopy. J-aggregates of 5,10,15-triphenyl-20-(3,4-dihydroxyphenyl) porphyrin (TPPcat) form CT complexes on TiO(2) NP surfaces. Catechol-mediated strong CT coupling between J-aggregate and TiO(2) NP facilitates interfacial exciton dissociation for electron injection into the conduction band of the TiO(2) nanoparticle in pulse width limited time (<80 fs). Here, the electron-transfer (<80 fs) process dominates over the intrinsic exciton-relaxation process (J-aggregates: ca. 200 fs) on account of exciton-coupled CT interaction. The parent hole on J-aggregates is delocalized through J-aggregate excitonic coherence. As a result, holes immobilized on J-aggregates are spatially less accessible to electrons injected into TiO(2) , and thus the back electron transfer (BET) process is slower than that of the monomer/TiO(2) system. The J-aggregate/porphyrin system shows exciton spectral and temporal properties for better charge separation in strongly coupled composite systems.     

Lithium ion effect on electron injection from a photoexcited coumarin derivative into a TiO2 nanocrystalline film investigated by visible-to-IR ultrafast spectroscopy

The dynamics of ultrafast electron injection from a coumarin derivative (NKX-2311), which is an efficient photosensitizer for dye-sensitized solar cells, into the conduction band of TiO(2) nanocrystalline films have been investigated by means of femtosecond transient absorption spectroscopy in a wide wavelength range from 600 nm to 10 mum. In the absence of Li(+) ions, electron injection into the TiO(2) conduction band occurred in about 300 fs. In the presence of Li(+) ions, however, electron injection occurred within approximately 100 fs, and the oxidized dye generated was found to interact with nearby Li(+) ions. Possible positions of Li(+) ion attachment to the dye molecule were examined by means of semiempirical molecular orbital calculations. The electron injection efficiency was found to increase by a factor of 1.37 in the presence of Li(+) ions. The effects of Li(+) ions on the energy of the TiO(2) conduction band and the electronic interaction between the dye molecule and Li(+) ions are discussed, and the major cause for the acceleration of electron injection was suggested to be a conduction-band shift of TiO(2).     

Oligothiophene-containing coumarin dyes for efficient dye-sensitized solar cells

We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.     

A strategy to increase the efficiency of the dye-sensitized TiO2 solar cells operated by photoexcitation of dye-to-TiO2 charge-transfer bands

Dye-sensitized nanoporous TiO2 solar cells (DSSCs) can be classified into two types, namely, Type-I and Type-II. Type-I DSSCs are the DSSCs in which electrons are injected from the adsorbed dyes by photoexcitation of the dyes followed by electron injection from the excited dyes to TiO2 (pathway A). Type-II DSSCs are the DSSCs in which electrons are injected not only by pathway A but also by direct one-step electron injection from the dyes to TiO2 by photoexcitation of the dye-to-TiO2 charge-transfer (DTCT) bands (pathway B). The DSSCs employing catechol (Cat) or its derivatives as the sensitizers have been the typical examples of Type-II DSSCs. However, their solar energy-to-electricity conversion efficiencies (eta) have never exceeded 0.7%, and the external quantum efficiencies (EQE) at the absorption maximums of the DTCT bands have never exceeded 10%. We found that the attachment of electron-donating compounds such as (pyridin-4-yl)vinyl and (quinolin-4-yl)vinyl, respectively, to Cat (designated as Cat-v-P and Cat-v-Q, respectively) leads to 2- and 2.7-fold increases, respectively, in eta, driven by large increases in short circuit current (Jsc). The EQE increased from 8.5 to 30% at 400 nm upon changing from Cat to Cat-v-P, at which only the DTCT band absorbs. In the case of the Cat-v-Q-sensitized DSSC, even the eta obtained by exciting only the DTCT band was higher than 1%. Interestingly, the illumination of only the DTCT band resulted in the increase of fill factor from 62.6% to 72.3%. This paper provides for the first time an insight into the strategy to increase the eta values of Type-II DSSCs.     

Electronic transitions of the Soret band of reaction centers from Rhodobacter sphaeroides studied by femtosecond transient absorbance spectroscopy

The Soret band of reaction centers from Rhodobacter sphaeroides has been systematically studied using femtosecond transient absorption spectroscopy. When the excitation wavelength was scanned over the entire Soret band, the approximate absorption spectra of the bacteriochlorophyll dimer, the monomer bacteriochlorophylls, and the bacteriopheophytins within the Soret band were determined by analyzing the ground state bleaching with about 100 fs resolution. The main contribution of H is on the blue end of the spectrum, peaking near 350 nm, P absorbs mostly on the red side of the spectrum, but probably has multiple bands, and the main absorbance of B likely lies between H and P, overlapping with P on the red side (particularly near 390 nm). The energy transfer from B to P in the QY band takes about 300 fs when Soret-band excitation is used and the time constant of overall energy transfer from H to B to P in the QY band when H is specifically excited near 350 nm is about 500 fs. Internal conversion after Soret-band excitation is the rate-limiting step for the energy-transfer process. The time constant of internal conversion for B and P is less than 300 fs, and for H it is about 500 fs.     

Fine tuning of photophysical properties of meso-meso-linked ZnII-diporphyrins by dihedral angle control

A series of meso-meso-linked diporphyrins S(n) strapped with a dioxymethylene group of various length were synthesized by intramolecular Ag(I)-promoted coupling of dioxymethylene-bridged diporphyrins B(n), for n=10, 8, 6, 5, 4, 3, 2, and 1. Shortening of the strap length causes a gradual decrease in the dihedral angle between the porphyrins and increasing distortion of porphyrin ring, as suggested by MM2 calculations and (1)H NMR studies. This trend has been also suggested by X-ray crystallographic studies on the corresponding Cu(II) complexes of nonstrapped diporphyrin 2 Cu, and strapped diporphyrins S(8)Cu, S(4)Cu, and S(2)Cu. The absorption spectrum of relatively unconstrained diporphyrins S(10) strapped with a long chain exhibits split Soret bands at 414 and 447 nm and weak Q(0,0)- and prominent Q(1,0)-bands, both of which are similar to those of nonstrapped diporphyrin 2. Shortening of the strap length causes systematic changes in the absorption spectra, in which the intensities of the split Soret bands decrease, the absorption bands at about 400 nm and > 460 nm increase in intensity, and a prominent one-band feature of a Q-band is changed to a distinct two-band feature with concurrent progressive red-shifts of the lowest Q(0,0)-band. The fluorescence spectra also exhibit systematic changes, roughly reflecting the changes of the absorption spectra. The strapped diporphyrins S(n) are all chiral and have been separated into enantiomers over a chiral column. The CD spectra of the optically active S(n) display two Cotton effects at 430-450 and at about 400 nm with the opposite signs. The latter effect can be explained in terms of oblique arrangement of m( perpendicular 1) and m( perpendicular 2) dipole moments, while the former effect cannot be accounted for within a framework of the excition coupling theory. The resonance Raman (RR) spectra taken for excitation at 457.9 nm are variable among S(n), while the RR spectra taken for excitation at 488.0 nm are constant throughout the S(n) series. These photophysical properties can be explained in terms of INDO/S-SCI calculations, which have revealed charge transfer (CT) transitions accidentally located close in energy to the excitonic Soret transitions. This feature arises from a close proximity of the two porphyrins in meso-meso-linked diporphyrins. In addition to the gradual red-shift of the exciton split Soret band, the calculations predict that the high-energy absorption band at about 400 nm, the lower energy Cotton effect, and the RR spectra taken for excitation at 457.9 nm are due to the CT states which are intensified upon a decrease in the dihedral angle.     

水热法合成多孔Ag_2S敏化二氧化钛催化剂及其可见光催化活性(英文)

Porous Ag2S sensitized TiO2 catalysts were synthesized by the hydrothermal process.The crystallization and porous structure of the Ag2S/TiO2 composite photocatalysts were investigated by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray analysis,UV-Vis diffuse reflectance spectroscopy,and N2 adsorption.The Ag2S/TiO2 composites were mainly composed of anatase TiO2 and acanthite Ag2S.The absorption edge wavelengths of TiO2 and the Ag2S/TiO2 composite prepared with 3 mmol Na2S.5H2O were 400 and 800 nm,respectively,that is,the absorption edge of the composite had a pronounced red shift.The photocatalytic activity under visible light was investigated by the degradation of methylene blue with a UV-Vis spectrophotometer.The photocatalytic activities under visible light of the Ag2S/TiO2 photocatalysts were much higher than that of TiO2.     

Standing wave enhancement of red absorbance and photocurrent in dye-sensitized titanium dioxide photoelectrodes coupled to photonic crystals

The light harvesting efficiency of dye-sensitized photoelectrodes was enhanced by coupling a TiO(2) photonic crystal layer to a conventional film of TiO(2) nanoparticles. In addition to acting as a dielectric mirror, the inverse opal photonic crystal caused a significant change in dye absorbance which depended on the position of the stop band. Absorbance was suppressed at wavelengths shorter than the stop band maximum and was enhanced at longer wavelengths. This effect arises from the slow group velocity of light in the vicinity of the stop band, and the consequent localization of light intensity in the voids (to the blue) or in the dye-sensitized TiO(2) (to the red) portions of the photonic crystal. By coupling a photonic crystal to a film of TiO(2) nanoparticles, the short circuit photocurrent efficiency across the visible spectrum (400-750 nm) could be increased by about 26%, relative to an ordinary dye-sensitized nanocrystalline TiO(2) photoelectrode.     

Ultrafast studies of gold, nickel, and palladium nanorods

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.     

Pd(II)-mediated triad multilayers with zinc tetrapyridylporphyrin and pyridine-functionalized nano-TiO2 as linkers: assembly, characterization, and photocatalytic properties

Triad hybrid multilayers containing the light sensitizers of zinc tetrapyridylporphyrin (ZnTPyP) and pyridine-functionalized TiO(2) (TiO(2)-Py) nanoparticles were constructed on substrate surfaces with the use of Pd(II) ions as the connectors using the layer-by-layer (LBL) method. The assembly process was monitored using ultraviolet-visible (UV-vis) absorption and X-ray photoelectron spectra as well as scanning electron microscopy and atomic force microscopy. The content of the pyridine substituents in the TiO(2)-Py nanocomposites was about 2% (w/w). The Soret absorption band of ZnTPyP was 24 nm red-shifted in the hybrid multilayers due to a strong intermolecular electronic coupling interaction among porphyrin macrocycles or porphyrin macrocycle/TiO(2)-Py nanoparticles. The average surface density of each ZnTPyP layer was about 1.4 × 10(-10) mol/cm(2). Aggregation of the small TiO(2)-Py nanoparticles to larger domains with sizes up to hundreds of nanometers occurred in the hybrid multilayers; however, such an aggregation behavior was weaker than that in the solutions. The quartz substrate modified with the as-prepared Pd/ZnTPyP/Pd/TiO(2)-Py triad hybrid multilayers was used as a heterogeneous photocatalyst for the degradation of methyl orange (MO) under irradiation (λ > 420 nm) at room temperature with a catalytic efficiency of about 1.3 × 10(-3) MO/ZnTPyP·s. Without the use of the filter, the catalytic efficiency increased because both ZnTPyP and TiO(2)-Py nanocomposites acted as the light sensitizers. It is suggested that the present heterogeneous catalyst has the advantages of facile separation, high stability, structural controllability on the molecular and nanoscale level, and good recyclability.     

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.     

TiO2浓度对核-壳结构Ag/TiO2纳米复合粒子结构以及三阶非线性光学性质的影响

采用光还原方法制备了核-壳结构的Ag/TiO2纳米复合粒子, 通过TEM、UV-Vis光谱和XRD表征了不同TiO2浓度下Ag/TiO2纳米复合粒子的结构和光学性质. UV-Vis光谱证明了银颗粒的存在, 且复合粒子中的银粒径随着TiO2含量的增加而增加, 同时随着TiO2浓度的增加, 银的吸收峰出现明显的增强和展宽；从TEM照片 发现, Ag/TiO2纳米复合粒子是一种以Ag为核, 外面包覆一层TiO2的核-壳结构, TiO2浓度和Ag+浓度的增加, 使得复合粒子的银颗粒粒径增大. 用Z-扫描技术, 以锁模Ti:sapphire飞秒激光器发出的脉宽为130 fs激光做光源, 在790 nm波长的光作用下, 研究了0.5%(w)Ag+含量, 不同TiO2浓度的Ag/TiO2纳米复合粒子的非线性光学特性. 结果发现, 在790 nm激光作用下, 0.25%(w)TiO2样品膜有双光子吸收和自聚焦非线性折射现象; 而当TiO2浓度为0.70%(w)时, 样品膜的非线性吸收由反饱和吸收转变为饱和吸收.     

Excited-state processes in the carotenoid zeaxanthin after excess energy excitation

Aiming for better understanding of the large complexity of excited-state processes in carotenoids, we have studied the excitation wavelength dependence of the relaxation dynamics in the carotenoid zeaxanthin. Excitation into the lowest vibrational band of the S2 state at 485 nm, into the 0-3 vibrational band of the S2 state at 400 nm, and into the 2B(u)+ state at 266 nm resulted in different relaxation patterns. While excitation at 485 nm produces the known four-state scheme (S2 --> hot S1 --> S1 --> S0), excess energy excitation led to additional dynamics occurring with a time constant of 2.8 ps (400 nm excitation) and 4.9 ps (266 nm excitation), respectively. This process is ascribed to a conformational relaxation of conformers generated by the excess energy excitation. The zeaxanthin S state was observed regardless of the excitation wavelength, but its population increased after 400 and 266 nm excitation, suggesting that conformers generated by the excess energy excitation are important for directing the population toward the S state. The S2-S1 internal conversion time was shortened from 135 to 70 fs when going from 485 to 400 nm excitation, as a result of competition between the S2-S1 internal conversion from the vibrationally hot S2 state and S2 vibrational relaxation. The S1 lifetime of zeaxanthin was within experimental error the same for all excitation wavelengths, yielding approximately 9 ps. No long-lived species have been observed after excitation by femtosecond pulses regardless of the excitation wavelength, but excitation by nanosecond pulses at 266 nm generated both zeaxanthin triplet state and cation radical.     

Optical absorption of tetraphenylporphyrin thin films in UV-vis-NIR region

The optical absorption of thermally-evaporated tetraphenylporphyrin (TPP), in the UV-vis-NIR region has been studied. The absorption spectra recorded in the UV-vis region for the as-deposited and annealed films showed different absorption bands, namely the Soret, B, at region 360-490 nm, Q-band region consist of four bands in the region 500-720 nm and two other bands labeled N and M in UV region. The Soret band always shows splitting in all the TPP thin films and the effect of annealing on the intensities of these components have been observed. The spectra of the infrared absorption allow characterization of vibrational modes for the powder, as deposited and annealed thin films. Some of the optical absorption parameters, namely molar extinction coefficient (epsilon), half band width (Deltalambda), electronic dipole strength (q2), and oscillator strength (f), of the principal optical transitions have also been evaluated.     

Formation and properties of composites based on microgels of a responsive polymer and TiO2 nanoparticles

Organic-inorganic composites were prepared with titanium dioxide (TiO2) nanoparticles embedded within colloidal particles of a cross-linked, thermally responsive polymer. To promote the incorporation of unaggregated nanoparticles of TiO2, temperature responsive microspherical gels (microgels) of N-isopropylacrylamide (NIPAM) with interpenetrating (IP) linear chains of poly(acrylic acid) (PAAc) were synthesized. Dynamic light scattering (DLS) measurements revealed that these microgels reversibly shrink and swell in diameter from 300-400 nm to 600-800 nm with temperature. Two types of nanoparticles of TiO2 were immobilized within the IP-microgels-fine TiO2 nanoparticles synthesized by the hydrolysis of titanium(IV) isopropoxide and commercially available Degussa P25. Characterization of the composite was conducted using transmission electron microscopy (TEM) and UV-vis absorption spectroscopy from which it was determined that the extent of loading of the TiO2 within the colloidal particles can be easily manipulated from a low value of 10% (weight) to a value as high as 75%. The TiO2 nanoparticles were in a dispersed state within the microgels and the composites showed rapid (approximately minutes) sedimentation, which is useful for gravity separations. By using turbidometry to characterize the settling behavior of the organic-inorganic composites, it was found that the settling time decreases as the content of TiO2 increases within the particles.     

Rup_2P表面敏化TiO_2基复合薄膜光致界面电荷转移

采用离子束溅射技术制备出TiO2/ITO、Zn2+掺杂的TiO2(TiO2-Zn)/ITO和TiO2/ZnO/ITO薄膜,采用表面敏化技术和旋转涂膜法,制备出(1,10-邻菲咯啉)2-2-(2-吡啶基)苯咪唑钌混配配合物(Rup2P)表面敏化的TiO2基复合薄膜Rup2P/TiO2/ITO、Rup2P/TiO2-Zn/ITO和Rup2P/TiO2/ZnO/ITO.表面光电压谱(SPS)结果发现:敏化后的TiO2基薄膜在可见区(400-600nm)产生SPS响应;TiO2基薄膜的能带结构不同,其在400-600nm和350nm处的SPS响应的峰高比不同.利用电场诱导表面光电压谱(EFISPS),测定TiO2基薄膜和表面敏化TiO2基复合薄膜各种物理参数,并确定其能带结构.分析可知,表面敏化TiO2基复合薄膜在400-600nm的SPS响应峰主要源于Rup2P分子的中心离子Ru4d能级到配体1,10-邻菲咯啉π*1和2-(2-吡啶基)苯咪唑π*2能级的跃迁;TiO2中Zn2+掺杂能级有利于Ru4d能级到配体π*1和π*2跃迁的光生电子向TiO2-Zn导带的注入;TiO2/ZnO异质结构有利于光生电子向ITO表面的转移,从而导致可见光(400-600nm)SPS响应增强以及光电转换效率的提高.