Preparation of amino-functionalized mesoporous silica thin films with highly ordered large pore structures

Highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer Pluronic P123 surfactant species under acidic conditions by sol-gel dip-coating. The effect of the sol aging on thin films organization is systematically studied, and the optimal sol aging time is obtained. The amino-functionalized mesoporous silica thin films exhibit a long-range ordering of 2D hexagonal (p6mm) mesostructure with a large pore size of 8.3 nm, a large Brunauer–Emmett–Teller (BET) specific surface area of 680 m² g⁻¹ and a large pore volume of 1.06 cm³ g⁻¹ following surfactant extraction as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM), and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for the amino-functionalized mesoporous silica thin films is calculated to be 3.2 amino-groups per nm². Moreover, the functionalized thin films display improved properties for immobilization of cytochrome c in comparison with pure-silica mesoporous thin films.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests

Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests.     

UV-light and visible-light photochromism of inorganic–organic multilayer films based on polyoxometalate and poly(acrylamide)

Novel UV-light and visible-light photochromic inorganic–organic multilayers composed of polyoxometalates (phosphomolybdic acid (PMoA)) and poly(acrylamide) (PAM) were prepared by the layer-by-layer (LbL) self-assembly method. The grown process, composition, surface topography, and photochromic properties and mechanism of the multilayer films were investigated by ultraviolet–visible (UV–vis) spectra, Fourier transform infrared spectra (FT-IR), atomic force microscopy (AFM), electron resonance spectra (ESR), and X-ray photoelectron spectra (XPS). Irradiation with UV-light or visible-light, the transparent films changed from colorless to blue and showed reversible photochromism. PMoA/PAM LbL films had higher photochromic efficiency under UV-light irradiation than visible-light irradiation. The bleaching process occurred when the films were in contact with O₂ in the dark or heated in air. The photochromic process of PMoA/PAM LbL film was in accordance with radical mechanism.     

TiO2介孔薄膜的制备及紫外光电响应性质

采用蒸发诱导自组装法制备了高度有序的TiO2介孔薄膜. 利用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等分析手段对其进行了表征. 结果表明, 所得样品的孔径约为5 nm, 孔道规则, 且骨架为纯锐钛矿结构. 紫外-可见光谱(UV-Vis)的表征结果表明, 制备的TiO2介孔薄膜对波长小于380 nm的紫外线有很强的吸收. 对TiO2介孔薄膜的I-V(电流-电压)特性进行了表征, 发现加光后其I-V曲线由暗态时的肖特基特性转变为欧姆特性, 表明TiO2介孔薄膜对紫外光有很敏感的光电响应.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO_2 composite films

TiO_2 sol-gel composite films with dropping molybdenumphosphoric acid(PMoA) have been prepared by sol-gel method.The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy(FT-IR),atomic force microscopy(AFM),and X-ray diffraction(XRD) patterns,respectively.The photochromic behavior and mechanism of composite thin films were inves-tigated with ultraviolet-visible spectra(UV-vis) and electron spin resonance(ESR).FT-IR results showed that the Keggin geometry...     

Immobilization and electrochemistry of cytochrome c on amino-functionalized mesoporous silica thin films

The immobilization and electrochemistry of cytochrome c (cyt c) on amino-functionalized mesoporous silica thin films are described. The functionalized silica films with an Im3m cubic phase structure were deposited on conducting ITO substrate by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Pluronic F127 under acidic conditions. The high specific surface area, large pore size and functional inner surface of mesoporous silica thin films result in a high cyt c loading, and the cyt c immobilization on this silicate framework is stable. After adsorption of cyt c, the ordered cubic structure of mesoporous silica and the redox activity of immobilized cyt c are retained as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM) and cyclic voltammetry. The redox behavior of the cyt c/silica film-modified ITO electrode is a surface-controlled quasi-reversible process for the experimental conditions used in this work and the electron transfer rate constant is calculated is 1.33 s⁻¹. The ITO electrode modified by cyt c/silica film possesses a high stability; even cyt c retains its redox activity following immobilization for several months. Furthermore, the electrocatalytic activities of the modified ITO electrode to hydrogen peroxide and ascorbic acid have been studied. Since these behaviors are quite pronounced, the modified electrode can be used for detection of hydrogen peroxide and ascorbic acid.     

Photoinduced one-electron reduction of MV2+ in titania nanosheets using porphyrin in mesoporous silica thin films

Composite films of a meso-(tetramethylpyridinium)porphyrin (TMPyP) hybrid incorporated in mesoporous silica (MPS) and cast on a methyl viologen (MV2+)/titania nanosheet hybrid were synthesized and a light-induced charge separation between the two could be observed. These composite thin films were able to initiate a one-electron reduction of the MV2+ ions accompanied by the simultaneous decomposition of the TMPyP organic dye within the mesoporous silica channels.     

Preparation and photochromic properties of pyrazolones/polyvinyl alcohol composite films

Novel photochromic composite films have been successfully fabricated by dispersing pyrazolone derivative:1,3-Diphenyl-4-(3-chlorobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (1a) into hydrosol of polyvinyl alcohol (PVA). The microstructure, photochromic behaviors and thermal bleaching properties were investigated by Raman spectroscopy, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet-visible absorption spectroscopy (UV-vis). The results showed that 1a was not only blended but also well dispersed in the PVA polymer films with a suitable content of chromophore. Upon UV light irradiation, the composite films gradually changed from colorless to yellow and recovered fully to the initial state upon thermal bleaching. The time constants of photochromic reactions were almost the same as those of 1a observed in their crystalline state, indicating that the photochromic phenomenon is barely disturbed by the polymer matrix.     

Manipulation of molecular transport into mesoporous silica thin films by the infiltration of polyelectrolytes

The design of hybrid mesoporous materials incorporating polymeric assemblies as versatile functional units has become a very fertile research area offering major opportunities for controlling molecular transport through interfaces. However, the creation of such functional materials depends critically on our ability to assemble polymeric units in a predictable manner within mesopores with dimensions comparable to the size of the macromolecular blocks themselves. In this work, we describe for the first time the manipulation of the molecular transport properties of mesoporous silica thin films by the direct infiltration of polyelectrolytes into the inner environment of the 3D porous framework. The hybrid architectures were built up through the infiltration-electrostatic assembly of polyallylamine (PAH) on the mesopore silica walls, and the resulting systems were studied by a combination of experimental techniques including ellipso-porosimetry, cyclic voltammetry and X-ray photoelectron spectroscopy, among others. Our results show that the infiltration-assembly of PAH alters the intrinsic cation-permselective properties of mesoporous silica films, rendering them ion-permeable mesochannels and enabling the unrestricted diffusion of cationic and anionic species through the hybrid interfacial architecture. Contrary to what happens during the electrostatic assembly of PAH on planar silica films (quantitative charge reversal), the surface charge of the mesoporous walls is completely neutralized upon assembling the cationic PAH layer (i.e., no charge reversal occurs). We consider this work to have profound implications not only on the molecular design of multifunctional mesoporous thin films but also on understanding the predominant role of nanoconfinement effects in dictating the functional properties of polymer-inorganic hybrid nanomaterials.     

Keggin结构钨磷酸/聚乙烯吡咯烷酮复合膜的制备和光致变色性质研究

近年来,由于无机－有机复合材料具有潜在的应用前景和特殊性能,尤其是光致变色性能,引起研究者们的广泛兴趣^[1-3],以杂多化合物为多核配合物,通过化合键或氢键作用与高分子底物结合,形成电荷转移物质,可以大大提高复合材料的化学和物理性能。目前,这一领域的研究在国外已经成为热点^[4-7]。本文以Keggin结构钨磷酸和聚乙烯吡咯烷酮为原料,报道了该类复合物的合成、表征及光致变色性质。     

Polyoxometalate cured epoxy resins with photochromic properties

Novel photochromic thermosetting materials were facilely prepared by polyoxometalate, Keggin-type H₃PW₁₂O₄₀, cured epoxy networks with ethylene oxide blocks. The dual functions of polyoxometalate as both hardener and photochromophore were studied by differential scanning calorimetry, infrared spectroscopy, ultraviolet–visible spectroscopy (UV–vis), and generalized two-dimensional correlation analysis. Polyoxometalate initiates the cationic polymerization of epoxy resin through dissolving in either polyethylene oxide epoxy or organic solvents. When subjected to UV irradiation, the transparent thermosetting materials with ethylene oxide blocks change from colorless to blue, and could be bleached in air at various temperatures to recover its initial state. From the UV–vis measurements, all the resultant thermosetting materials demonstrated similar photochromic behavior after ultraviolet irradiation showing characteristic d–d transition band and intervalence charge transfer band. The 2D correlation analysis of the photochromic spectra clearly revealed the sequence of electron movements in the framework of PW₁₂ anion.     

Visible-light Photochromism of Phosphomolybdic Acid/ZnO Composite

A novel photochromic hybrid ZnO was synthesized by doping with phosphomolybdic acid(PMoA). It could respond to visible light and fade in color when treated with hydrogen peroxide(H₂O₂). The microstructure and photochromic properties were investigated via X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), transmission electron microscopy(TEM), ultraviolet-visible spectroscopy(UV-Vis) and X-ray photoelectron spectroscopy(XPS). The XRD patterns show that the prepared ZnO is pure and has a hexagonal wurtzite structure. The FTIR results demonstrate the existence of a strong interaction between PMoA and ZnO. Due to PMoA doping, the rough surface morphology of ZnO became smooth, as verified by the SEM images. The TEM images illustrate that pure ZnO exhibits a polycrystalline structure with irregular morphology. PMoA was wrapped on the surface of ZnO. After visible-light irradiation, the composite changed from slight yellow to blue and returned to the original color in the presence of H₂O₂. The composite had good photosensitivity and photochromic reversibility. The photochromic process was in accord with photoinduced electrons transfer mechanism.     

Non‐covalent Immobilization of Iron‐triazole (Fe(Htrz)3) Molecular Mediator in Mesoporous Silica Films for the Electrochemical Detection of Hydrogen Peroxide

Mesoporous silica thin films encapsulating a molecular iron‐triazole complex, Fe(Htrz)₃ (Htrz=1,2,4,‐1H‐triazole), have been generated by electrochemically assisted self‐assembly (EASA) on indium‐tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well‐defined voltammetric signals corresponding to the Fe^II/III centers of the Fe(Htrz)₃ species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.6×10^?4 mol g^?1 Fe(Htrz)₃ in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)₃ species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)₃@SiO₂) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of ?0.4 V versus Ag/AgCl and by flow injection analysis. The organic‐inorganic hybrid film electrode displays good sensitivity for H₂O₂ sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM.     

Photocatalytic activity of (sulfur,nitrogen)-codoped mesoporous TiO<Subscript>2</Subscript> thin films

Nitrogen and sulfur co-doped mesoporous TiO₂ thin films were fabricated using thiourea as a doping resource by the combination of the sol–gel and evaporation-induced self-assembly (EISA) processes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and UV–vis spectra were performed to characterize the as-synthesized mesoporous TiO₂ materials. The XPS result shows that O–Ti–N and O–Ti–S bonds in the (S, N)-codoped mesoporous TiO₂ were formed. The resultant mesoporous (S, N)-codoped TiO₂ exhibited anatase framework with a high porosity and a narrow pore distribution. After being illuminated for 3 h, methyl orange (MO) could be degraded completely by the co-doped sample under the ultraviolet irradiation, whereas mesoporous TiO₂ film without doping could only degrade 60% MO. After being illuminated by visible light, the water contact angles of the mesoporous co-doped TiO₂ samples decreased slightly, but the pure TiO₂ mesoporous film exhibited no change in the hydrophilicity.     

Nanostructured silica thin films self-assembled with electron donors and acceptors to measure electron tunneling

Surfactant-templated, mesostructured thin films are synthesized such that photoelectron donors and electron acceptors are separated spatially in the different regions of the thin film. A photoelectron donor is placed within the silica framework by using a silylated derivative of the well-known tris(bipyridine)ruthenium(II) cation. Selective placement of the electron acceptor is achieved by using a surfactant derivative of methyl viologen. Luminescence decay traces and luminescence spectra are collected for the electron donor in the presence of varying amounts of the electron acceptor. Because of the spatial separation of the donor and acceptor noncontact electron transfer occurs and the electron-transfer rate decreases exponentially with the distance separating the donor and acceptor. Luminescence decay traces are calculated and fit to the experimental data in order to extract a value for the contact quenching rate, k0 (s(-1)), as well as the exponential decay constant beta (A(-1)) which governs how fast the electron-transfer rate decreases as a function of the donor-acceptor distance. The value beta = 2.5 +/- 0.4 A(-1) shows that the mesostructured material is an excellent insulator, better than frozen organic glasses or proteins and approaching that of vacuum. Combining deliberate placement methods, spectroscopy, and calculations has made possible the first measurement of beta for the silica region of mesoporous thin films.     

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12(O)40 Langmuir-Blodgett film

We used the Langmuir-Blodgett (LB) technique to construct a well-defined and structure-controllable photochromic material-a highly ordered multilayer film composed of dioctadecylamine and 12-molybdophosphoric acid (PMo12). We identified well-ordered lamellar structures using X-ray diffraction, polarized IR, and Raman spectra, and we determined a packing model of the two components in the LB film. We found the Keggin structure and fundamental features of the PMo12 ion to be maintained in the hybrid film. This hybrid LB film displayed photochromic properties upon UV light irradiation and we observed the following process from first-order kinetics. The photochromism exhibited the ability to switch between colorless and blue. A fading process occurred when the film was exposed to ambient air or O2 in the dark. During the color change, the packing structure of the film was well maintained. We also examined the electrochemical behavior of the hybrid LB film by cyclic voltammetry in detail and we propose different kinetic mechanisms for the film before and after irradiation.     

Photoelectrodes based on acceptor–donor assemblies in functionalized polypyrrole films

The capability to act as molecular photoelectrodes under visible light irradiation of optically transparent electrodes (ITO) modified by thin films of polypyrrole containing several kind of electron acceptor–donor assemblies has been examined. Photolysis of electrodes coated by thin films of polypyrrole substituted by a reversible electron donor (phenothiazine) in the presence of an irreversible electron acceptor (tropylium cation) in acetonitrile gives weak photocurrents. In contrast, appreciable photocurrents can be obtained using a symmetrical arrangement; viologen as reversible electron acceptor, benzilate anion as irreversible donor. The photoresponses result from the photo-induced charge separation of the charge transfer complexes created in the film. The measured photocurrents are markedly larger (up to five times), with films of polypyrrole substituted by a reversible electron acceptor (viologen) covalently linked with a donor (phenothiazine, triphenylamine or benzidine) than with the unimolecular immobilized system in similar experimental conditions. The greater efficiency of these materials is attributed to the formation of an intramolecular charge transfer complex occurring inside films between the two molecular entities. Markedly weaker photocurrents are obtained with polypyrrole films based on bilayers of the two independent components than those with the unimolecular design, while films based on copolymers arrangements give moderately weaker photoresponses.     

三氧化钼与金纳米粒子复合薄膜光致变色特性的研究

MoO3具有光致变色特性,在大屏幕显示、高密度存储和灵巧窗等研究领域中具有潜在的应用前景^[1-3]。但由于MoO3薄膜中相当一部分光生载流子被复合,其参与变色反应的利用率很低,导致MoO3薄膜的变色效率较低,使其难以实现实用化。半导体表面修饰贵金属后,在半导体／金属界面上可形成Schottky势垒,这将有助于光生载流子的有效分离,从而提高其利用率。据此,本文采用在MoO3薄膜表面修饰金纳米粒子的方法,制备了MnO3和金纳米粒子的复合薄膜（MoO3/Au),变色试验结果表明,MoO3/Au复合薄膜的紫外和可见光变色效率相对MoO3薄膜均有较大的提高。     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.