Iron adsorption on SiO2/Si(111)

The adsorption of ferric and ferrous iron onto the native oxide of the SiO₂/Si(111) surface has been evaluated using X‐ray photoelectron spectroscopy (XPS). Through a series of immersion experiments, performed at room temperature and pH 1, it has been shown that the ferric species is strongly adsorbed onto the hydrophilic surface, while ferrous iron remains in solution. Dehydroxylation of the silica surface by etching with hydrofluoric acid reduces the concentration of receptive Si‐OH groups, thereby limiting iron adsorption. The experiments were reproduced in a combined ultrahigh vacuum‐electrochemical system (UHV‐EC), which allowed a carbon‐free surface to be prepared before contacting the iron solutions, and confirmed the strong affinity of ferric iron towards the SiO₂/Si(111) surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Direct synthesis, characterization of Cu-SBA-15 and its high catalytic activity in hydroxylation of phenol by H2O2

Transition metal copper substituted mesoporous silica (Cu-SBA-15) was synthesized using triblock copolymers surfactant as template agent under acidic condition. The result Cu-SBA-15 was characterized with XRD, ICP-AES, FT-IR and N₂ adsorption–desorption measurements, which prove that Cu(II) was mainly incorporated into the framework of Cu-SBA-15. Its catalytic activity was studied for phenol hydroxylation using H₂O₂ (30%). The substituting element (Cu²⁺) is incorporated into the framework position forming a new type of active site which raises the phenol conversion to 62.4% and the diphenol (the mixture of catechol (CAT) and hydroquinone (HQ)) selectivity to 97%. The Cu-SBA-15 has very high selectivity for catechol (about 71% selectivity), which is completely different from that of the microporous titanium silicalite zeolites (47.1% phenol conversion and about 50% selectivity to CAT under same reaction conditions). The results obtained indicate that the selective oxidation of phenol with H₂O₂ by a radical substitution mechanism.     

Adsorption of silanes bearing nitrogenated Lewis bases on SiO2/Si (100) model surfaces

The present paper describes the one-pot procedure for the formation of self-assembled thin films of two silanes on the model oxidized silicon wafer, SiO2/Si. SiO2/Si is a model system for other surfaces, such as glass, quartz, aerosol, and silica gel. MALDI-TOF MS with and without a matrix, XPS, and AFM have confirmed the formation of self-assembled thin films of both 3-imidazolylpropyltrimethoxysilane (3-IPTS) and 4-(N-propyltriethoxysilane-imino)pyridine (4-PTSIP) on the SiO2/Si surface after 30 min. Longer adsorption times lead to the deposition of nonreacted 3-IPTS precursors and the formation of agglomerates on the 3-IPTS monolayer. The formation of 4-PTSIP self-assembled layers on SiO2/Si is also demonstrated. The present results for the flat SiO2/Si surface can lead to a better understanding of the formation of a stationary phase for affinity chromatography as well as transition-metal-supported catalysts on silica and their relationship with surface roughness and ordering. The 3-IPTS and 4-PTSIP modified SiO2/Si wafers can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction devices for metal determination or N-heterocycle analytes, such as histidine and histamine, with "on-spot" MALDI-TOF MS detection.     

Synthesis and characterization of SiO2/Gd2O3:Eu core-shell luminescent materials

Europium-doped Gd2O3 with an average size of approximately 15 nm was coated on the surface of preformed silica nanospheres by the wet chemical method. SEM and TEM photographs showed that SiO2/Gd2O3:Eu core-shell submicrospheres are obtained. XRD patterns indicated that the Gd2O3:Eu shell is crystalline after heat treatment. FTIR and XPS spectra showed that the Gd2O3:Eu shell is linked to the silica surface by forming a Si-O-Gd bond. Photoluminescence studies showed that the luminescent properties are still retained after coating on an inert silica core; additionally, we noted that the emitting peaks are broadened, which results from size effects and interface effects of nanocrystal.     

Growth,characterization and interfacial reaction of magnetron sputtered Pt/CeO2 thin films on Si and Si3N4 substrates

Growth of magnetron sputtered Pt/CeO₂ thin films on Si and Si₃N₄ were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS). Interaction of Pt/CeO₂ films with Si on Si and Si₃N₄ substrates was extensively investigated by XPS. XRD studies show that films are oriented preferentially to (200) direction of CeO₂. XPS results show that Pt is mainly present in +2 oxidation state in Pt/CeO₂/Si film, whereas Pt⁴⁺ predominates in Pt/CeO₂/Si₃N₄ film. Concentration of Pt⁴⁺ species is more than four times on Si₃N₄ substrate as compared with that on Si. Ce is present as both +4 and +3 oxidation states in Pt/CeO₂ films deposited on Si and Si₃N₄ substrates, but concentration of Ce³⁺ species is more in Pt/CeO₂/Si film. Interfacial reaction between CeO₂ and Si substrate is controlled in the presence of Pt. Pt/Ce concentration ratio decreases in Pt/CeO₂/Si₃N₄ film upon successive sputtering, whereas this ratio decreases initially and then increases in Pt/CeO₂/Si film. Copyright © 2015 John Wiley & Sons, Ltd.     

Diffusion reaction of oxygen in HfO2/SiO2/Si stacks

We study the oxidation mechanism of silicon in the presence of a thin HfO2 layer. We performed a set of annealing in 18O2 atmosphere on HfO2/SiO2/Si stacks observing the 18O distribution in the SiO2 layer with time-of-flight secondary ion mass spectrometry (ToF-SIMS). The 18O distribution in HfO2/SiO2/Si stacks upon 18O2 annealing suggests that what is responsible for SiO2 growth is the molecular O2, whereas no contribution is found of the atomic oxygen to the oxidation. By studying the dependence of the oxidation velocity from oxygen partial pressure and annealing temperature, we demonstrate that the rate-determining step of the oxidation is the oxygen exchange at the HfO2/SiO2 interface. When moisture is chemisorbed in HfO2 films, the oxidation of the underlying silicon substrate becomes extremely fast and its kinetics can be described as a wet silicon oxidation process. The silicon oxidation during O2 annealing of the atomic layer deposited HfO2/Si is fast in its early stage due to chemisorbed moisture and becomes slow after the first 10 s.     

Deactivation with silazanes in chromatography,mechanism of the reaction and practical consequences in capillary GC and RP-HPLC: A29Si CP-MAS NMR study

The reaction of Cab-O-Sil, a highly dispersed vitreous quartz, with hexamethyldisilazane (HMDS) was studied in the temperature range 380–500°C, using ²⁹Si solid state NMR and other techniques. Such studies are of importance in view of deactivation procedures of fused silica at high temperatures in capillary GC. The commonly accepted reaction equation: predominates only below ca. 400°C. Above ca. 400°C the intermediate cleavage product Me₃SiNH₂ reacts with surface silanol groups to form ?SioSiMe₂NH₂ + CH₄. At higher temperatures these groups may ultimately form (?SiO)₃SiNH₂ groups (analogously to the formation of bi-and tridentate linkages starting from ?SiOSiMe₃ groups), but (?SiO)₃SiNH₂ groups are also directly formed at lower temperatures, simultaneously with the ?SiOSiMe₃ groups, probably by reaction with siloxane bridges: . The reactions of the trimethylsilylamine part of HMDS with Cab-O-Sil were confirmed by an independent series of silylations using N,N-dimethyltrimethylsilylamine instead of HDMS. The presence of amino groups as ?SiNH₂ was confirmed by FT-IR. This may be one of the reasons why very high temperature silylation with disilazanes does not provide a satisfactory deactivation of fused silica GC columns: the active ?SiOH groups are “replaced” by active ?SiNH₂ groups. However, such a material may be of interest in LC. Silylation with silazanes at ca. 350°C in humid atmosphere and/or after extensive hydroxylation (leaching) of the surface should yield sufficiently deactivated surfaces with a rather well defined surface structure.     

Scanning photoemission spectromicroscopic study of 4-nm ultrathin SiO(3.4) protrusions probe-induced on the native SiO(2) layer

Atomic force microscopy probe-induced large-area ultrathin SiO(x) (x ≡ O/Si content ratio and x > 2) protrusions only a few nanometers high on a SiO(2) layer were characterized by scanning photoemission microscopy (SPEM) and X-ray photoemission spectroscopy (XPS). SPEM images of the large-area ultrathin SiO(x) protrusions directly showed the surface chemical distribution and chemical state specifications. The peak intensity ratios of the XPS spectra of the large-area ultrathin SiO(x) protrusions provided the elemental quantification of the Si 2p core levels and Si oxidation states (such as the Si(4+), Si(3+), Si(2+), and Si(1+) species). The O/Si content ratio (x) was evidently determined by the height of the large-area ultrathin SiO(x) protrusions.     

VOx/SiO2-Al2O3催化剂催化苯羟基化制苯酚

以硅溶胶为硅源、偏铝酸钠为铝源及环己胺合成SiO2-Al2O3复合氧化物,并采用水热合成法合成了VOx/SiO2-Al2O3催化剂。采用XRD、SEM、TEM、XPS、NH3-TPD、N2物理吸/脱附等手段对此催化剂和复合氧化物微观结构进行表征分析。由表征结果可知钒活性中心能够高分散于此复合氧化物表面,VOx/SiO2-Al2O3催化剂呈现层片积雪状;当钒的含量为4%时,催化剂中V4+含量最大且总酸量契合于此反应所需要的催化酸环境。探究了4%VOx/SiO2-Al2O3催化剂对苯羟基化制苯酚反应的催化性能,结果表明：基于高分散活性中心、V4+含量最大及载体酸性环境等优点而表现出良好的催化性能,苯转化率为48.1%,苯酚选择性为99.6%。     

Photoluminescence from (Si/SiO2)n superlattices and their use as emitters in [SiO2/Si]n SiO2 [Si/SiO2]m microcavities

Si/SiO2 superlattices are recently under investigation to add optical functionality to silicon based microelectronics. In such superlattices quantum-confinement should drive Si to become a good light emitter. Emission properties can be further improved and controlled by placing the emitter in optical microcavities. In this paper emission properties of (Si/SiO2), superlattices grown by Low Pressure Chemical Vapour Deposition will be compared with the ones obtained by other growth techniques and the origin of the emission will be discussed. Emission properties can be further improved and controlled by placing the emitter in optical microcavities. Optical properties of microcavities produced with standard complementary metal-oxide-semiconductor techniques containing Si/SiO2 superlattices as light emitter will be reviewed and a comparison between properties estimated from calculations and experiments will be given.     

不同催化剂对苯酚H2O2羟基化反应的比较

用苯酚、双氧水经羟基化反应合成邻、对苯二酚,在Fe2O3为催化剂的反应系统中,反应诱导期长,且反应剧烈;当以杂多酸盐或Fe/ZrO2为催化剂时,诱导期消失,且羟基化反应平稳。 反应的诱导期可能是由铁的氧化物转化为活性物种Fe3+和Fe2+的过程引起的;在杂多酸盐或Fe/ZrO2催化剂的反应体系中,羟基化反应可能发生在催化剂表面而使反应变得缓慢平稳,反应诱导期消失。     

{Sn(9)[Si(SiMe(3))(3)](2)}(2-): A Metalloid Tin Cluster Compound With a Sn(9) Core of Oxidation State Zero

The disproportionation reaction of the subvalent metastable halide SnCl proved to be a powerful synthetic method for the synthesis of metalloid cluster compounds of tin. Now we present the synthesis and structural characterization of the anionic metalloid cluster compound [Sn(9)[Si(SiMe(3))(3)](2)](2-)3 where the oxidation state of the tin atoms is zero. Quantum chemical calculations as well as M?ssbauer spectroscopic investigations show that three different kinds of tin atoms are present within the cluster core. Compound 3 is highly reactive as shown by NMR investigations, thus being a good starting material for further ongoing research on the reactivity of such partly shielded metalloid cluster compounds.     

Fe3+-TiO2/SiO2薄膜催化剂的结构对其光催化性能影响

以硅胶为载体,采用溶胶-凝胶法制备了掺杂不同量Fe3+的TiO2光催化剂(Fe3+-TiO2/SiO2),以氙灯为光源,罗丹明B为目标降解物,对其光催化活性进行了研究.结果表明,Fe3+-TiO2/SiO2比TiO2纳米粉有更好的催化活性,Fe3+的最佳掺入量为0.03％.罗丹明B在粉体和膜催化剂的作用下遵循不同的光催化反应机理.根据XRD,SEM,Raman,XPS和FTIR的表征结果可认为,TiO2在SIO2表面薄膜化和Ti-O-Si键的形成是催化活性提高和降解机理不同的主要原因.     

Electrooxidation of nitrite on a silica-cerium mixed oxide carbon paste electrode

A silica-cerium mixed oxide (SiCe) was prepared by the sol-gel process, using tetraethylorthosilicate and cerium nitrate as precursors and obtained as an amorphous solid possessing a specific surface area of 459 m(2) g(-1). Infrared spectroscopy of the SiCe material showed the formation of the Si-O-Ce linkage in the mixed oxide. Scanning electron microscopy/energy dispersive spectroscopy indicated that the cerium oxide particles were homogenously dispersed on the matrix surface. X-ray diffraction and (29)Si solid-state nuclear magnetic resonance implied non-crystalline silica matrices with chemical environments that are typical for silica-based mixed oxides. X-ray photoelectron spectroscopy showed that Ce was present in approximately equal amounts of both the 3+ and 4+ oxidation states. Cyclic voltammetry data of electrode prepared from the silica-cerium mixed oxide showed a peak for oxidation of Ce(3+)/Ce(4+) at 0.76 V and electrochemical impedance spectroscopy equivalent circuit indicated a porous structure with low charge transfer resistance. In the presence of nitrite, the SiCe electrode shows an anodic oxidation peak at 0.76 V with a linear response as the concentration of the analyte increases from 3×10(-5) at 3.9×10(-3) mol L(-1).     

In situ surface oxidation study of a planar Co/SiO2/Si(100) model catalyst with nanosized cobalt crystallites under model Fischer-Tropsch synthesis conditions

The oxidation of nanosized metallic cobalt to cobalt oxide during Fischer-Tropsch synthesis (FTS) has long been postulated as a major deactivation mechanism. In this study a planar Co/SiO(2)/Si(100) model catalyst with well-defined cobalt crystallites, close to the threshold value reported for oxidation in the literature (4-10 nm), was prepared by the spin coating method. The planar Co/SiO(2)/Si(100) model catalyst was characterized with atomic force microscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering. The surface oxidation behavior of the nanosized metallic cobalt crystallites of 4-5 nm was studied using in situ near-edge X-ray absorption fine structure under model FTS conditions, i.e., H(2)/H(2)O = 1, P(Total) = 0.4 mbar, and 150-450 degrees C. No surface oxidation of metallic cobalt was observed under these model FTS conditions over a wide temperature range, i.e., 150-400 degrees C.     

29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations

The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1-6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2-4 with relatively small Mn2+ contents. Because the relaxation curves for 1-6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (相似文献   

Synthesis and catalytic properties of porous α-Fe2O3/SiO2 catalyst

The synthesis of α-Fe₂O₃ supported on high specific surface area SiO₂ has been studied. The hydroxylation of phenol to hydroquinone/catechol mixture is described with the help of BET and XRD. The result indicates that the dispersity and specific surface area of support have an important influence on the catalytic activity.     

X-ray-induced production of gold nanoparticles on a SiO(2)/Si system and in a poly(methyl methacrylate) matrix

Prolonged exposure to X-rays of HAuCl(4) deposited from an aqueous solution onto a SiO(2)/Si substrate or into a poly(methyl methacrylate) (PMMA) matrix induces reduction of the Au(3+) ions to Au(0) and subsequent nucleation to gold nanoclusters as recorded by X-ray photoelectron spectroscopy. The corresponding major oxidation product is determined as chlorine {HAuCl(4)(ads) + X-rays --> Au(ads) + (3/2)Cl(2)(ads) + HCl(ads)}, which is initially adsorbed onto the surface but eventually diffuses out of the system into the vacuum. The reduced gold atoms aggregate (three-dimensionally) into gold nanoclusters as evidenced by the variation in the binding energy during X-ray exposure, which starts as 1.3 eV but approaches a value that is 0.5 eV higher than that of the bulk gold. The disappearance of the oxidation product (Cl2p signal) and the growth of the nanoclusters (related to the measured binding energy difference between the Si2p of the oxide and Au4f of the reduced gold) exhibit first-order kinetics which is approximately 3 times slower than the reduction of Au(3+), indicating that both of the former processes are diffusion controlled. Similarly, gold ions incorporated into PMMA can also be reduced and aggregated to gold nanoclusters using 254 nm deep UV irradiation in air evidenced by UV-vis-NIR absorption spectrocopy.     

Anisotropic polymerization of a long-chain diacetylene derivative Langmuir-Blodgett film on a step-bunched SiO2/Si surface

Alternating facet/terrace nanostructures were fabricated on a SiO2 surface by step-bunching and thermal oxidation of a vicinal Si(111) substrate, and their influence upon the polymerization direction of a long-chain diacetylene derivative monolayer film was investigated by angle-dependent polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that the peak intensity of the C 1s-pi transition was stronger when the electric vector plane of the incident X-ray was parallel to the direction of the periodic facet/terrace structures rather than perpendicular to them. On the contrary, a polymer film fabricated on a flat SiO2 surface showed no in-plane anisotropy of the peak intensity. These results indicate that the diacetylene groups in the diacetylene derivative monolayer are preferentially photopolymerized in the direction not across but along the periodic one-dimensional structures on the step-bunched and thermally oxidized SiO2/Si(111) surface.     

甲基三乙氧基硅烷修饰的Ti3+/SiO2复合薄膜的发光性能

采用溶胶-凝胶(Sol-Gel)法, 以正硅酸乙酯(TEOS)和甲基三乙氧基硅烷(MTES)为先驱物, 盐酸为催化剂, 用二步水解法制备了Ti3+/SiO2薄膜和甲基三乙氧基硅烷修饰的Ti3+/SiO2复合薄膜. 采用红外光谱仪、X射线衍射仪、椭偏仪、荧光光谱仪等对膜层性质进行了分析. 结果表明, 掺杂Ti3+的SiO2薄膜分别在250 nm附近有一弱的激发峰, 294 nm附近有一强的激发峰, 在393 nm附近出现一强的发射峰. IR光谱发现, MTES修饰的Ti3+/SiO2复合薄膜的Si—OH的吸收峰强度比Ti3+/SiO2薄膜的略减小, Si—O—Si的吸收峰明显增强, 表明复合薄膜硅氧网络结构更规则, 有利于Ti3+的均匀分散. Ti3+/SiO2薄膜与复合薄膜的孔隙率分别为13.64%和6.66%, 表明MTES的加入使薄膜更致密. 在空气中陈放30 d后, Ti3+/SiO2薄膜已经检测不到荧光发射峰, 而MTES修饰的Ti3+/SiO2复合薄膜荧光强度只下降了18%. 在氮气中陈放30 d后, 普通薄膜与复合薄膜的荧光强度均仅下降了10%. 表明Ti3+的荧光猝灭的主要原因是由于Ti3+被氧化造成的. 溶胶中加入MTES后, 薄膜表面结构得到改善, 有效地防止了Ti3+的氧化, 荧光强度更稳定.