Synthesis and characterization of photoswitchable fluorescent SiO2 nanoparticles

Switchable fluorescent silica nanoparticles have been prepared by covalently incorporating a fluorophore and a photochromic compound inside the particle core. The fluorescence can be switched reversibly between an on‐ and off‐state via energy transfer. The particles were synthesized using different amounts of the photoswitchable compound (spiropyran) and the fluorophore (rhodamine B) in a size distribution between 98 and 140 nm and were characterized in terms of size, switching properties, and fluorescence efficiency by TEM, and UV\Vis and fluorescence spectroscopy.     

Structural and Optical Properties of Sol-Gel Deposited Proton Conducting Ta2O5 Films

Proton conducting tantalum oxide films were deposited on ITO (Indium Tin Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prepared using Ta(OC₂H₅)₅ as a precursor. X-ray diffraction studies determined that the sol-gel films, heat treated at temperatures below 400°C, were amorphous. Films heat treated at higher temperatures were crystalline with the hexagonal δ-Ta₂O₅ structure. The solar transmission values (T _s ) of tantala films on glass generally range from 0.8–0.9, depending on thickness. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the UV-VIS-NIR regions. The refractive index values calculated at λ=550 nm increased fromn=1.78 to 1.97 with increasing heat treatment from 150 to 450°C. The films heat treated at different temperatures showed low absorption, with extinction coefficients of smaller thank=1×10⁻³ in the visible range. Impedance spectroscopic investigations performed on Ta₂O₅ films revealed that these films have a protonic conductivity of 3.2×10⁻⁴S/m. The films are suitable for proton conducting layers in electrochromic (EC) devices.     

Synthesis and photoactivity of novel 5‐arylthianthrenium salt cationic photoinitiators

5‐Arylthianthrenium salts are a class of efficient triarylsulfonium salt photoinitiators for cationic polymerization. These compounds were prepared by a simple, straightforward, versatile, and high yield route. The new photoinitiators were characterized by standard analytical and spectroscopic techniques, and their activity as cationic photoinitiators was compared with related triarylsulfonium salts of similar structures using Fourier transform real‐time infrared spectroscopy. Through the use of electron‐transfer photosensitizers, the response of these photoinitiators can be readily spectrally broadened into the long‐wavelength UV–visible regions of the spectrum. The results obtained suggest that 5‐arylthianthrenium salts are potential replacements for now available triarysulfonium salt photoinitiators in many applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3465–3480, 2002     

Na2Ta2O6光催化剂的合成、表征及光催化性能分析

通过结合固相反应与水热法制得一种新型的光催化剂Na2Ta2O6,并对其进行了XRD、SEM表征。由紫外可见漫反射光谱推测其禁带宽度约为4.6 eV,并对其在紫外光区下光催化降解碱性藏花红溶液的行为进行了研究。发现其具有好的结晶性、特殊的棒状结构以及较好的光催化活性。     

Physicochemical Study of Ta2O5 and SiO2-Ta2O5 Film Formation from Film-Forming Solutions

In order to study physicochemical processes of formation of Ta₂O₅ and SiO₂-Ta₂O₅ films from film-forming solutions, the properties of these solutions, and also the thermal-oxidative breakdown and the properties of the obtained films, were studied.     

SiO2@Fe2O3核-壳结构催化剂的制备及表征

采用优化的Stöber法制备了平均粒径为230 nm的单分散球形SiO₂颗粒,并以此为内核,通过水解沉积法制备了不同壳层厚度的核-壳结构SiO₂@Fe₂O₃催化剂。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、N₂物理吸附和X射线衍射分析(XRD)等手段对催化剂进行表征,探讨了不同制备条件对SiO₂@Fe₂O₃催化剂形貌的影响。结果表明,通过水解沉积法制备的SiO₂@Fe₂O₃催化剂具有明显的核-壳结构,并且保持了原始SiO₂核的球形形貌,Fe₂O₃纳米粒子通过-OH的氢键作用连接在SiO₂表面,形成了2~10 nm厚的Fe₂O₃均匀连续包覆层。     

二维金纳米粒子结构的制备及影响因素

用电泳沉积方法制备了金纳米粒子的二维排列结构。研究了电场强度、沉积时间、溶胶浓度、温度和方波脉冲等对沉积结构的影响。提高外加电场强度和旋加方波脉冲可以提高金粒子结构的有序性。粒子浓度减小,温度升高不利于粒子的电泳沉积。     

Silane grafting of TiO2 nanoparticles: dispersibility and photoactivity in aqueous solutions

Titania nano‐sized particles were treated by various amounts of tetraethyl orthosilicate precursor. The extent of grafting was characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐Vis) spectroscopy techniques, thermal gravimetric analysis, X‐ray fluorescence and zeta potential measurements. Sedimentation behaviour of titanium dioxide (TiO₂) nanoparticles in aqueous solutions was evaluated visually and using a separation analyser. Photocatalytic activity of nanoparticles was studied by photo‐activated degradation reaction of Rhodamine B dyestuff in aqueous solutions. The results showed that grafted particles had acquired enhanced dispersion stability and lower photocatalytic activity in aqueous solutions. Untreated TiO₂ dispersions settled rapidly and sedimentation completed within 24 h through the coagulation mechanism, whereas that of the silica‐treated nanoparticles, depending on the silica content, showed different degrees of stability by flocculation mechanism. Photodebleaching of Rhodamine B in the presence of treated nanoparticles is evident by weaker intensity of UV absorption peak of 554 nm due to lowering concentration of Rhodamine B accompanied with the blue shift in UV absorption peaks. However, untreated TiO₂ nanoparticles showed only weaker intensity of UV absorption peak. Copyright © 2011 John Wiley & Sons, Ltd.     

Interfacial properties of thermally oxidized Ta2Si on Si

Many refractory metal silicides have received great attention due to their potential for innovative developments in the silicon‐based microelectronic industry. However, tantalum silicide, Ta₂Si, has remained practically unnoticed since its successful application in silicon carbide technology as a simple route for a high‐k dielectric formation. The thermal oxidation of Ta₂Si produces high‐k dielectric layers, (O? Ta₂Si)‐based on a combination of Ta₂O₅ and SiO₂. In this work, we investigate the interfacial properties of thermally oxidized (850–1050 °C) Ta₂Si on commercial silicon substrates. The implications of diffusion processes in the dielectric properties of an oxidized layer are analyzed. In particular, we observe migration of tantalum pentoxide nanocrystals into the substrate with increasing oxidation temperature. An estimation of the insulator charge and interfacial O? Ta₂Si/Si trap density is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis,Crystal Structures,and Optical Properties of New Quaternary Metal Chalcogenides of Group 5: Cs2AgVS4, K2AgVSe4, Rb2AgVSe4, Rb2AgNbS4, and Cs2AgNbSe4

The new quaternary compounds Cs₂AgVS₄, K₂AgVSe₄, Rb₂AgVSe₄, Rb₂AgNbS₄, and Cs₂AgNbSe₄ were prepared using the reactive flux method. In this structure type infinite chains of edge-sharing AgQ₄- and M^VQ₄-tetrahedra are running parallel to the crystallographic a-axis. The chains are separated by alkali cations. A linear relationship between the size of the alkali cation A⁺ and the Q–Q interchain distances was found. These compounds are isostructural with the analogous quaternary copper chalcogenides. The optical properties were studied by collecting UV/Vis transmission and reflectance spectra which allowed to derive the optical band gaps. The colours of the vanadium compounds range from black to dark violet with optical band gaps between 1.7 and 1.8 eV. In addition, the behaviour of the samples was studied using polarized light. Under these experimental conditions the niobium compound Rb₂AgNbS₄ changes its colour from green to red when the direction of the polarization plane is changed by 90°.     

Unprecedented Electron‐Poor Octahedral Ta6 Clusters in a Solid‐State Compound: Synthesis,Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

The crystal structure of Cs₂BaTa₆Br₁₅O₃ has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta₆ clusters is similar to that of Cs₂LaTa₆Br₁₅O₃ exhibiting 14‐MEs per [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta₆ cluster in the solid state.     

Features of doxorubicin adsorption on Fe3O4 magnetic nanoparticles coated with SiO2 or SiO2/aminopropylsilane

New nanocomposites based on Fe₃O₄ magnetic nanoparticles coated with SiO₂ or SiO₂/aminopropylsilane (APS), including those using N-(phosphonomethyl)iminodiacetic acid (PMIDA), were obtained, and the immobilization of the antitumor agent doxorubicin (Dox) on nanocomposites was examined. It has been shown that the binding of Dox to the negatively charged surface of SiO₂ particles occurs more efficiently than that to the APS-modified surface with positively charged amino groups; the presence of PMIDA molecules on the surface significantly increased the loading content. Based on DFT calculations, a mechanism for Dox binding to the surface of the synthesized nanocomposites was proposed.     

Synthesis of Ordered Porous Graphitic‐C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self‐Assembled Silica Nanospheres as a Primary Template

Uniform‐sized silica nanospheres (SNSs) assembled into close‐packed structures were used as a primary template for ordered porous graphitic carbon nitride (g‐C₃N₄), which was subsequently used as a hard template to generate regularly arranged Ta₃N₅ nanoparticles of well‐controlled size. Inverse opal g‐C₃N₄ structures with the uniform pore size of 20–80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back‐filling of the C₃N₄ pores with tantalum precursors, followed by nitridation in an NH₃ flow gave regularly arranged, crystalline Ta₃N₅ nanoparticles that are connected with each other. The surface areas of the Ta₃N₅ samples were as high as 60 m² g⁻¹, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g‐C₃N₄. Polycrystalline hollow nanoparticles of Ta₃N₅ were also obtained by infiltration of a reduced amount of the tantalum source into the g‐C₃N₄ template. An improved photocatalytic activity for H₂ evolution on the assembly of the Ta₃N₅ nanoparticles under visible‐light irradiation was attained as compared with that on a conventional Ta₃N₅ bulk material with low surface area.     

Synthesis of Mesoporous TiO2/SiO2 Hybrid Films as an Efficient Photocatalyst by Polymeric Micelle Assembly

Thermally stable mesoporous TiO₂/SiO₂ hybrid films with pore size of 50 nm have been synthesized by adopting the polymeric micelle‐assembly method. A triblock copolymer, poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide), which serves as a template for the mesopores, was utilized to form polymeric micelles. The effective interaction of titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) with the polymeric micelles enabled us to fabricate stable mesoporous films. By changing the molar ratio of TEOS and TTIP, several mesoporous TiO₂/SiO₂ hybrid films with different compositions can be synthesized. The presence of amorphous SiO₂ phase effectively retards the growth of anatase TiO₂ crystal in the pore walls and retains the original mesoporous structure, even at higher temperature (650 °C). These TiO₂/SiO₂ hybrid films are of very high quality, without any cracks or voids. The addition of SiO₂ phase to mesoporous TiO₂ films not only adsorbs more organic dyes, but also significantly enhances the photocatalytic activity compared to mesoporous pure TiO₂ film without SiO₂ phase.