Loss of phosphorous in silica-phosphate sol-gel films

Phosphosilicate films with 90%SiO₂-10%P₂O₅ molar composition, derived from tetraethoxysilane as SiO₂ precursor and triethylphosphate, triethylphosphite or phosphoric acid as P₂O₅ precursors were prepared using the sol-gel method. The films were deposited on glass and ITO coated glass supports. The influence of the type of P₂O₅ precursor, type of substrate and of the thermal treatment (200, 300 and 500°C) on their structure and properties was studied. By spectroellipsometric and XPS measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when alkoxide were used, underlying that the mentioned precursors are not recommended for thin phosphosilicate films preparation. The phosphoric acid that forms chemical bond with silica network during the sol-gel process lead to better incorporation of P in the silica network as compared to the P-alkoxides.     

Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Ni/SiO₂ materials with identical composition (SiO₂/Ni = 1.0) have been synthesized by precipitation of Ni(NO₃)₂ · 6H₂O solution with Na₂CO₃ solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO₂ precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H₂-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni²⁺-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni²⁺-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of high activity in the vegetable oil hydrogenation.     

Microporous Silica Hollow Nanospheres Templated by Anionic Polypeptide

Anionic polypeptide, the poly(sodium L-glutamate), was applied to fabricate microporous silica hollow nanospheres templated by the secondary structures of the polypeptide as porogens. In the synthesis, 3-aminopropyltrimethoxysilane (APMS) and tetraethyl orthosilicate (TEOS) were used as the silica sources, and the coassembly followed the mechanism of the anionic surfactant-templated mesoporous silica (AMS) through a S_-N₊-I_- pathway, where S indicates the anionic polypeptide, I indicates inorganic precursors (TEOS), and N indicates costructure-directing agent (APMS), which interacted with the negatively charged anionic polypeptide secondary structures electrostatically and cocondensed with silica source to form the silica framework. The product was subjected to characterizations of X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric (TG) analysis, scanning electron microscopy (SEM), transmitted electron microscopy (TEM), and nitrogen adsorption-desorption measurement. It was found that the pH value of the synthesis solution was an important factor to the morphological control of the silica products. Besides the microporous hollow nanospheres, microporous submicron silica solid and hollow spheres were also obtained facilely by changing the synthesis parameters. Our study further implied that anionic polypeptides, which were able to control mineralization of calcium carbonate and calcium phosphate, could also induce silica condensation in the presence of proper silica precursors. It was also expected that functional calcium carbonate (phosphate)/silica-nanocomposite materials would be fabricated under the control of the anionic polypeptide.     

Solution chemistry and secondary ion emission from amine-glycerol solutions

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Secondary ion mass spectra were obtained from a series of C₄-C₁₀ n-alkylamines introduced via the gas phase onto glycerol. It was found that the amine-characteristic secondary ion intensity varied linearly with amine partial pressure. Henry's law constants and surface activity constants for each of the amines in glycerol solution were measured. A linear correlation was found between amine-characteristic secondary ion intensity and Henry's law concentrations. The concentrations calculated from Henry's law were too low to yield the intensities observed, indicating that secondary ion precursors were not free-base amine molecules but ions in solution. Explicit kinetic equations describing glycerol and amine protonation and deprotonation as a result of primary ion damage to the solutions are derived to rationalize the observed spectra.     

Subtle interactions in silica-alumina mixtures

Object of the study in this paper was the mechanical mixtures of amorphous silica and α-Al₂O₃ with different precursors (gibbsite, boehmite, and γ-Al₂O₃). The results obtained revealed that measurable interactions exist in different binary systems without previous thermal treatment. These interactions could be explained by the existence of attractive and repulsive forces which appear between the OH⁻ groups present on the surfaces of alumina and silica constituents. In thermally treated samples, the interactions are not driven by intermolecular forces but rather by polymorphic transformations of alumina and silica, which are followed by sintering.     

Escaping the Tyranny of Carbothermal Reduction: Fumed Silica from Sustainable,Green Sources without First Having to Make SiCl4

Fumed silica is produced in 1000 tons per year quantities by combusting SiCl₄ in H₂/O₂ flames. Given that both SiCl₄ and combustion byproduct HCl are corrosive, toxic and polluting, this route to fumed silica requires extensive safeguards that may be obviated if an alternate route were found. Silica, including rice hull ash (RHA) can be directly depolymerized using hindered diols to generate distillable spirocyclic alkoxysilanes or Si(OEt)₄. We report here the use of liquid‐feed flame spray pyrolysis (LF‐FSP) to combust the aforementioned precursors to produce fumed silica very similar to SiCl₄‐derived products. The resulting powders are amorphous, necked, <50 nm average particle sizes, with specific surface areas (SSAs) of 140–230 m² g^?1. The LF‐FSP approach does not require the containment constraints of the SiCl₄ process and given that the RHA silica source is produced in million ton per year quantities worldwide, the reported approach represents a sustainable, green and potentially lower‐cost alternative.     

The state of nickel in the silver modified NiMg/SiO<Subscript>2</Subscript> vegetable oil hydrogenation catalysts

Two series of silver modified Ni-Mg materials were synthesized by precipitation-deposition on SiO₂ support derived from two silica sources: diatomite activated at 800°C (Series a; Mg/Ni = 0.1 and SiO₂/Ni = 1.07) and synthetic water glass (Series b; Mg/Ni = 0.1 and SiO₂/Ni = 1.15). The modification with silver was made at three molar Ag/Ni ratios, namely 0.0025, 0.025, and 0.1. The effects of the source of the silica support and the silver presence and content on the nickel state in the silver modified reduced-passivated NiMg/SiO₂ precursors of the vegetable oil hydrogenation catalyst were established by X-ray diffraction and X-ray photoelectron spectroscopy techniques. The passivation procedure was applied in order to protect the metallic nickel particles from further oxidation. The crystallization of the formed nickel hydrosilicate phases depends on the source of the silica support, more expressed in the diatomite supported samples. It was shown that the silver modification of the NiMg/SiO₂ precursors enhances the reduction of the nickel hydrosilicates accompanied by formation of relatively smaller metallic nickel particles, more pronounced in the water glass supported precursors. The increase of the silver content in the water glass deposited samples is responsible for the metallic nickel dispersion increase. The higher content of the Ni⁰ particles on the surface of the diatomite deposited samples is in accordance with the higher stability of the larger metallic nickel crystallites to oxidation during the passivation step. On contrary, higher dispersed Ni⁰ particles on the surface of the water glass supported samples are more susceptible to the oxida The article is published in the original.     

新型球形纳米空心SiO2的模板合成方法研究

以纳米碳酸钙颗粒为新颖的无机模板剂, 硅酸钠为无机硅源, 通过溶胶-凝胶法形成CaCO₃/SiO₂的核壳结构; 随后通过高温煅烧、酸溶和干燥处理, 合成出了具有高比表面积的球形纳米空心二氧化硅粒子. 然后, 分别采用TEM, SEM, EDS, XRD, FTIR和TG等测试手段对样品进行了分析和表征, 并考察了不同合成条件, 如反应温度、反应pH值、煅烧温度和包覆反应时SiO₂/CaCO₃的配比对纳米空心二氧化硅粒子的比表面积变化. 实验结果表明: 较高的反应温度如60～80 ℃, pH值9左右、SiO₂包覆量为碳酸钙质量的10%, 以及煅烧温度为700 ℃, 有利于形成空心形貌较好、比表面较大的球形纳米空心二氧化硅.     

Synthesis of nanoporous silica aerogel by ambient pressure drying

A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.     

Influence of the Structure of Precursors on the Crystallization of PbTiO3 Thin Films

PbTiO₃ (PT) thin films and their respective sols derived from three lead sources have been studied in order to elucidate the role of the starting materials in the crystallization of the products. EXAFS analysis of sols revealed similar oligomeric Ti-units in PT precursors derived from lead oxide or lead 2-methoxyethoxide acetate and a significantly different local Ti neighborhood in those derived from lead acetate. Structural details of the perovskite phase in the thin films follow the same pattern of similarity.     

Electro-assisted generation of functionalized silica films on gold

Electrochemical tuning of pH at electrode/solution interfaces is exploited for preparing thiol-functionalized silica films on gold surfaces by the sol–gel process. Film formation is carried out from a sol solution containing various ratios of prehydrolyzed mercaptopropyltrimethoxysilane and tetraethoxysilane precursors. This mixture is allowed to gelify only on the electrode surface by maintaining a negative potential value (to reduce protons and water and to generate hydroxyl species) to increase the local pH, which is known to catalyze polycondensation of the precursors. High mechanical stability of the resulting films is ensured by the strong interactions between thiol functions and the gold surface. Film porosity is very dependent on the amount of mercaptopropyl groups in the composite layer as pointed out by cyclic voltammetry of a redox probe (Fe(CN)₆³⁻). The organic group content is also a key factor influencing the sensitivity of Hg^(II) detection by anodic stripping voltammetry after accumulation at open-circuit. The preparation method can be extended to the deposition of other silica-based films on gold electrodes.     

Spectrometry: Speciation of Parts PER Billion of Metal Ions Using Silica and C18-Bonded Silica Columns and Graphite Furnace Atomic Absorption Spectrometry

Abstract

It is demonstrated that silica gel columns will quantitatively adsorb free Cu²⁺ and Pb²⁺ ions at pH > 8. These are eluted with 0.1 M HNO₃ but not with methanol. Negatively charged EDTA chelates are not adsorbed. Neutral APDC chelates are partially adsorbed on silica columns, but are quantitatively adsorbed on C18-bonded columns, and are eluted with methanol. The metal ions are partially adsorbed on C18-bonded columns, due to residual silanol groups. A microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer, using either methanol or 0.1 M HNO₃ in methanol eluant, allowing speciation and measurement of parts per billion of metals. These studies demonstrate that by using a mixed column or sequential columns of silica gel and C18-bonded silica, cationic and neutral metal species could be adsorbed, followed by sequential elution and measurement using methanol and then 0.1 M HNO. Negatively charged species could be measured directly in the sample eluant or obtained by difference from a total metal measurement.     

Effect of pH on the formation and combustion process of sol-gel auto-combustion derived NiZn ferrite/SiO2 composites

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid, and silica powder by sol-gel process, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/5wt% SiO₂ nanocomposites by auto-combustion. The effect of pH on the formation of NiZn ferrite/SiO₂ and thermal properties of gel precursors was studied by XRD, IR, EPR, TGA and DTA techniques. The results revealed that the ratio of the citrate ion to the nitrate ion is directly related to the pH of the solution. The pH in the starting solution affects the combustion process, and then determines the particle size of the as-synthesized powder. The EPR parameters (peak-to-peak linewidth, g factor, and spin number) increased with increasing pH, whereas the spin-spin relaxation time (T₂) decreased. The thermal stability and enthalpy of the decomposition process in air decreased with increasing pH, whereas the enthalpy in nitrogen increased. Moreover, the activation energy (E_a) of thermo-oxidative degradation of the gel precursor at pH 3 was much lower than the gel precursor at pH 5 and 7, and that increased with increasing pH.     

Adsorption of di-2-pyridyl ketone salicyloylhydrazone on silica gel: characteristics and isotherms

The adsorption of DPKSH onto silica gel was investigated, at 25±1 °C and pH 1, 4.7 and 12. For the same DPKSH concentration interval, the minimum required time of contact for adsorption maximum at pH 4.7 was smaller than at pH 1 and the maximum amount of DPKSH adsorbed per gram of silica at pH 1 is smaller than at pH 4.7. At pH 12 the DPKSH adsorption onto silica gel was not significant. The adsorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum amount of solute adsorbed (m_ads^max) and the adsorption constant, K_L, were derived from Langmuir isotherm. The Freundlich constants 1/n and K_F related, respectively, to the energetic heterogeneity of adsorption sites and an empirical constant were evaluated. The mean sorption free energy (E) of DPKSH adsorption onto silica gel was calculated from D-R isotherm indicating a physical adsorption mode. Finally, conductimetric titrations showed the silica particle basicity and acidity as 0.002 and 0.3 mmol g⁻¹, respectively.     

Synthesis of ZrO2 nanotubes in inorganic and organic electrolytes by anodic oxidation of zirconium

Present work reports on the results of the electrochemical growth of self-ordered zirconia nanotubes formed in aqueous Na₂SO₄?+?HF and nonaqueous electrolytes with glycerol addition. Anodization process was carried out in this inorganic water-based mixture with constant pH?=?2.5 and in the voltage range from 5 to 60 V. Similar experiments were repeated in an organic glycerol-based electrolyte with the voltage equal to 20 V and with variable glycerol concentration. All experiments were conducted at constant room temperature. The tube diameter dependence on the voltage of anodization process in an inorganic electrolyte was derived. It was found that when glycerol addition to water electrolyte was used, it takes more time to produce long zirconia nanotubes. However, they do not collapse as the similar structure of the same length formed in aqueous electrolyte.     

A New Synthetic Route to Microporous Silica with Well‐Defined Pores by Replication of a Metal–Organic Framework

Microporous amorphous hydrophobic silica materials with well‐defined pores were synthesized by replication of the metal–organic framework (MOF) [Cu₃(1,3,5‐benzenetricarboxylate)₂] (HKUST‐1). The silica replicas were obtained by using tetramethoxysilane or tetraethoxysilane as silica precursors and have a micro–meso binary pore system. The BET surface area, the micropore volume, and the mesopore volume of the silica replica, obtained by means of hydrothermal treatment at 423 K with tetraethoxysilane, are 620 m²g^?1, 0.18 mL g^?1, and 0.55 mL g^?1, respectively. Interestingly, the silica has micropores with a pore size of 0.55 nm that corresponds to the pore‐wall thickness of the template MOF. The silica replica is hydrophobic, as confirmed by adsorption analyses, although the replica has a certain amount of silanol groups. This hydrophobicity is due to the unique condensation environment of the silica precursors in the template MOF.     

Secondary ion emission from glycerol under continuous and pulsed primary ion current

Secondary ion intensity from glycerol is measured as a function of 5 keV primary ion current density and is found to be linear over the range 0.1–1 μA cm^?2. The possibility that protonated glycerol, or some other condensed-phase precursor to secondary protonated glycerol, exists in solution and enhances secondary ion emission from glycerol is investigated. Kinetics for formation of such precursors by the primary ion beam are described and evaluated by pulsed primary ion beam experiments. Depletion rates are calculated assuming diffusion from the surface as the major loss mechanism Results of this analysis indicate that the mechanism for secondary emission of protonated glycerol does not involve formation of precursors, e.g. solution-phase protonated glycerol, directly or indirectly by the primary ion beam.     

Silica from rice husks employed as drug delivery for folic acid

Silica was obtained from rice husk, this type of silica is also known as SiO₂-rice, was investigated as drug delivery for the folic acid. The SiO₂-rice was obtained from calcinations at 600 °C and its textural properties were compared with mesoporous silica (MS). The maximum folic acid adsorption on SiO₂-rice was at the 18 % weight, while MS adsorbs 19 % weight. An important pH effect on the drug released was observed; both silicas released around 35 % of acid folic at pH 7, while at pH 3 only 3 % of the drug was released. Differential Thermal Analyzer analysis suggests that the folic acid was not crystallized into the porous of the silica; therefore, it is possible that the drug was trapped within the complex network of pores preventing their full release. However, the drug released for 400 μg of folic acid, a commercial dose, indicated that until 93 % of drug could be released for the silicas at pH of 5.5; a minor desorption was observed by commercial tablet.     

New synthetic routes to nano-composites with ceramic particles, using lanthanide compounds

Gas-phase as well as sol–gel techniques can be used to access to materials which contain two sorts of solid phases, of which one is mostly acting as the matrix. The choice of the molecular precursor in both processing techniques is crucial to obtain the desired composite product. Single source precursors have advantages over multi source precursors, as they allow a simplified technique and often also lead to purer materials. Moreover, the same precursor may behave similarly in the gas phase or wet process or may behave very differently. In this review composite compounds are discussed with Al₂O₃ mostly acting as a matrix and with Ln₂O₃ (Ln = lanthanide element) acting as a second phase. Two processes for Nd:YAG materials are described in more detail as well as some new alcoholates of lanthanides derived from carbinol substituted by thiophenes.