Supported heteropoly acids offering strong option for efficient and cleaner processing for the synthesis of imidazole derivatives under solvent-free condition

A series of 12-phosphotungstic acid (PWA) supported on various porous carriers, such as silica, alumina, titania, clay, and carbon were prepared, and their catalytic performance evaluated in the synthesis of imidazoles in solvent-free condition. It was found that PWA supported on silica (PWA/SiO₂) showed higher activity compared to other catalysts. The observed behavior has more or less correlated with the acidic characteristic found through the potentiometrically titrated acidic sites and proton availability. The catalyst was characterized by FTIR, XRD, TGA/DSC, BET, and SEM. The presence of the Keggin structure can be followed by the above techniques, eliminating any doubt about the collapse of the supported anion. It can be observed that the process tolerates both electron donating and electron withdrawing substituents on the aldehyde with both benzil and benzoin. The general applicability of the method is demonstrated by using both benzylic and aromatic amines. The yields obtained were excellent without forming any side products such as trisubstituted imidazoles, which are normally produced in the presence of strong acids. The protocol developed using PWA/SiO₂ is superior in terms of process simplicity, reusable catalyst, high yields, short reaction time, and preclusion of toxic solvent.     

Study of silica templates in the rice husk and the carbon–silica nanocomposites produced from rice husk

Carbon–silica nanocomposites obtained by rice husk carbonization in a fluidized-bed reactor using a deep oxidation copper–chromium catalyst were studied. Dispersion characteristics of the silica phase in these systems were determined by small-angle X-ray scattering (SAXS) using the full contrast technique. SiO₂ was found in the initial rice husk as compact nanoparticles having a wide size distribution. This distribution consists of a narrow fraction with particle sizes from 1 to 7 nm and a wider fraction with particle sizes from 8 to 22 nm. Oxidative heat treatment of rice husk in a fluidized bed in the presence of the catalyst decreased the fraction of small SiO₂ particles and increased the fraction of large ones. It was demonstrated that the particle size of silica in the carbon matrix can be determined selectively for deliberate design of porous carbon materials with desired properties.     

Functional Nanostructured Silica Powders Derived from Colloidal Suspensions by Sol Spraying

The preparation of silica powders derived from sols with a variety of primary particle sizes from 4 to 100 nm and the influences of preparation conditions such as drying temperature and initial concentration of precursor on the final powders morphology were investigated for the first time. The prepared silica powders have spherical morphology, and the final diameter (between 0.1 and 2 um) was controlled by changing the concentration of starting colloidal suspension. The preparation of silica based luminescent powders was investigated by adding europium ion as the dopant. The Eu-doped silica powders showed a visible-luminescence with wavelength of 613 nm, a red emission, under excitation of 394 nm light source. The effects of Eu-doping concentration, operation temperature and primary particle size of silica sols on the luminescence were also investigated.     

One-step synthesis of hydrophobic mesoporous silica and its application in nonylphenol adsorption

Highly CH₃-functionalized mesoporous silica with nearly spherical morphology was synthesized under acidic conditions by co-condensation of two different silica precursors polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) in the presence of triblock copolymer P123 as template. XRD, N₂ adsorption–desorption, HRTEM, SEM and ²⁹Si MAS NMR were used to identify its highly-ordered mesopore array structure, nearly spherical particle morphology and CH₃ functionalization of the as-synthesized material. The resulting hydrophobic mesoporous silica possessed regular mesochannel arrays, indicating that the introduction of PMHS had little impact on the formation of an ordered mesostructure. Also, PMHS played an important role in morphology control and organic functionalization, ensuring nearly spherical particle morphology and high CH₃ functionalization degree of the obtained mesoporous silica material. As compared with pristine mesoporous silica SBA-15, the hydrophobic mesoporous silica showed the higher adsorption performance when they were used as adsorbents to remove organic pollutant nonylphenol at a very low concentration from aqueous solution.     

Effect of drying technique on the physicochemical properties of sodium silicate-based mesoporous precipitated silica

The conventional drying (oven drying) method used for the preparation of precipitated mesoporous silica with low surface area (>300 m²/g) and small pore volume is often associated with a high production cost and a time consuming process. Therefore, the main goal of this study was to develop a cost-effective and fast drying process for the production of precipitated mesoporous silica using inexpensive industrial grade sodium silicate and spray drying of the precipitated wet-gel silica slurry. The precipitated wet-gel silica slurry was prepared from an aqueous sodium silicate solution through the drop-wise addition of sulfuric acid. Mesoporous precipitated silica powder was prepared by drying the wet-gel slurry with different drying techniques. The effects of the oven drying (OD), microwave drying (MD), and spray drying (SD) techniques on the physical (oil, water absorption, and tapping density), and textural properties (specific BET surface area, pore volume, pore size, and % porosity) of the precipitated mesoporous silica powder were studied. The dried precipitated mesoporous silica powders were characterized with field-emission scanning electron microscopy; Brunauer, Emmett and Teller and BJH nitrogen gas adsorption/desorption methods; Fourier-transform infrared spectroscopy; thermogravimetric and differential analysis; N₂ physisorption isotherm; pore size distribution and particle size analysis. There was a significant effect of drying technique on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the mesoporous silica powder. Additionally, the effect of the microwave-drying period on the physicochemical properties of the precipitated mesoporous silica powder was investigated and discussed.     

Chemical and electrochemical investigations of high carbon steel corrosion inhibition in 10 % HCl medium by quinoline chalcones

The corrosion inhibitive effect of 3-(3-oxo-3-phenyl-propenyl)-1H-quinolin-2-one (PPQ) and 3-(3-oxo-3-phenyl-propenyl)-1H-benzoquinolin-2-one (PPBQ) on high carbon steel (HCS) in 10 % HCl media was evaluated by chemical (weight loss) and electrochemical (electrochemical impedance spectroscopy and potentiodynamic polarization technique) measurements. The inhibition efficiencies obtained from weight loss and electrochemical measurements were in good agreement. The inhibition efficiency was found to increase with the increase in inhibitor concentration but decreased with rise in temperature. Potentiodynamic polarization studies revealed the mixed mode inhibition of inhibitors. The adsorption behavior of these inhibitors on the HCS surface was found to obey the Langmuir adsorption isotherm. The thermodynamic parameter values of free energy of adsorption (?G _ads) and enthalpy of adsorption (?H _ads) revealed that the inhibitor was adsorbed on the HCS surface via both chemisorption and physisorption mechanisms. The adsorption mechanism of inhibition was supported by spectroscopic techniques (UV–visible, FT-IR, and wide-angle X-ray diffraction), surface analysis (SEM–EDS), and adsorption isotherms.     

Mesoporous Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>/C nanocomposites with enhanced performance synthesized from fumed nano silica

Mesoporous Li₂FeSiO₄/C nanocomposites (LFS-FNS and LFS-NS) were prepared from fumed nano silica (FNS) and nano silica (NS) through facile solid-state reactions, respectively. XRD analysis indicates that the crystalline structures of LFS-FNS and LFS-NS are indexed to monoclinic Li₂FeSiO₄ of P2₁. SEM results prove that the particle size of LFS-FNS and FNS (25~40 nm) is smaller than that of LFS-NS and NS, revealing the particle size of Li₂FeSiO₄/C nanocomposites can be tuned by choosing different silica. TEM further indicates Li₂FeSiO₄ nanoparticles are uniformly dispersed in the amorphous carbon networking of LFS-FNS. Pore structure analysis indicates the external surface areas of LFS-FNS as well as LFS-NS are 51.4 and 36.1 m² g^?1, indicating the pore properties of mesoporous Li₂FeSiO₄/C nanocomposites can be controlled by using different silica as silicon resource. The reduced particle size and high external surface area shorten the lithium-ion diffusion path and make LFS-FNS possess better electrochemical performance over LFS-NS. The discharge capacity of LFS-FNS is as high as 172 mA h g^?1 at 0.1 C.     

1 and 2-Photon Fluorescence Anisotropy Decay to Probe the Kinetic and Structural Evolution of Sol-Gel Glasses: A Summary

We review recent 1- and 2-photon fluorescence studies of the formation dynamics and structure of sol-gel glasses, from nanometre-sized particles to clusters, prepared from both aqueous silicates and tetramethylorthosilicate (TMOS), over a broad pH range. Through the careful choice of a fluorescent probe, anisotropy decay has been shown to provide both silica particle size and viscosity information and offers advantages over traditional techniques for silica particle sizing based on small-angle neutron, Xray, or light scattering. Subsequently, we are now able to observe the self-assembly mechanisms (or recently termed kinetic life history) of silica, produced under both acidic and alkaline conditions from sodium silicate solution (water glass) in the case of hydrogels and from alkoxides in the case of alcogels. The controlled preparation of hydrogels, often deemed a blackart, is also discussed in some detail, as are the potential applications and benefits of fluorescence anisotropy decay to industrial sol-gel systems. The insight into the sol-gel process provided by these new interpretations of fluorescence decay data, promises to have implications for both our fundamental understanding and the production of sol-gel systems in general.     

Synthesis and characterization of polyester bionanocomposite membrane with ultrasonic irradiation process for gas permeation and antibacterial activity

Optically active bionanocomposite membranes composed of polyester (PE) and cellulose/silica bionanocomposite (BNCs) prepared with simple, green and inexpensive ultrasonic irradiation process. It is a novel method to enhance the gas separation performance. The novel optically active diol containing functional trifluoromethyl groups was prepared in four steps reaction and it was fully characterized by different techniques. Commercially available silica nanoparticles were modified with biodegradable nanocellulose through ultrasonic irradiation technique. Transmission electron microscopy (TEM) analyses showed that the cellulose/silica composites were well dispersed in the polymer matrix on a nanometer scale. The mechanical properties nanocomposite films were improved by the addition of cellulose/silica. Thermo gravimetric analysis (TGA) data indicated an increase thermal stability of the PE/BNCs in compared to the pure polymer. The results obtained from gas permeation experiments showed that adding cellulose/silica to the PE membrane structure increased the permeability of the membranes. The increase in the permeability of the gases was as follows: P_CH4 (38%) <P_N2 (58%) <P_CO2 (88%) <P_O2 (98%) Adding silica nanoparticles into the PE matrix, improved the separation performance of carbon dioxide/methane and carbon dioxide/nitrogen gases. Increasing the cellulose/silica mass fraction in the membrane increased the diffusion coefficients of gases considered in the current study. Further, antimicrobial test against pathogenic bacteria was carried out.     

Effects of Preparation Parameters on the Characteristics of NiPxBY Nanomaterials

A series of NiP _x B _y nanomaterials were prepared by a chemical reduction method under various preparation parameters. Experiment results show that the different preparation parameters affected the morphology, particle size, surface area and the composition of the sample. However, they did not influence the electronic state of nickel. The type of solution showed significant influence on the properties of the sample, whereas, the type of nickel salt did not. The particle size of NiPB, NiB, and NiP were 10–30 nm. The NiP sample prepared in the aqueous solution had the largest particle size 50–150 nm. If the solvent was 50% ethanol in water, the surface area of the sample significantly increased nine fold for NiP and four fold for NiPB powders. In contrast, the surface area of NiB did not increase. The NiPB, NiB, and NiP powders had a spherical morphology if they were prepared with aqueous solution. The NiPB prepared in 50% ethanol solution showed floss morphology and had a very high surface area.     

Preparation of silica nanowires using porous silicon as Si source

This very paper is focusing on the preparation of silica nano-wires via annealing porous silicon wafer at 1200 °C in H₂ atmosphere and without the assistant metal catalysts. X-ray diffraction, X-ray energy dispersion spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and selected area diffraction technology have been employed for characterizing the structures, the morphology and the chemical components of the nano-wires prepared, respectively. It is found that the diameter and the length of the nano-wires were about 100 nm and tens micron, respectively. Meanwhile, it is also necessary to be pointed out that silica NWs only formed in the cracks of porous wafers, where the stress induced both by the electro-chemical etching procedure for the porous silicon preparation and nanowires growth procedure is believed to be lower than that at the center of the island. Therefore, a stress-driven mechanism for the NWs growth model is proposed to explain these findings.     

Capacitance properties of ordered porous carbon materials prepared by a templating procedure

The electrochemical performance of carbon materials with a highly ordered nanoporous structure is investigated in two-electrode supercapacitors. The materials were prepared by a templating procedure using a silica matrix (type MCM-48 or SBA-15) with an organized porosity in which carbon was inserted, either by chemical vapor decomposition of propylene or by impregnation with a sucrose solution followed by carbonisation. After the removal of silica, a micro-mesoporous carbon residue is recovered which displays an uniform pore size distribution. Such a well-defined nanostructure is interesting for a fundamental study of the double layer capacitance behavior. The performance of supercapacitors built with electrodes prepared from the templated carbon was tested in acidic, alkaline and organic electrolyte solutions. High values of capacitance in aqueous and organic media were obtained with a rectangular shape of the voltammograms over a wide range of scan rates indicating a quick charge propagation. Especially, the templated carbons prepared by the impregnation of sucrose in MCM-48 display high capacitance values due to the formation of an adequate micro-mesoporous network during their formation. A marked shift of capacitance drop at higher values of frequency is clearly observed for the materials rich in mesopores; the mesopores make easier the diffusion of the ions to the active surface.     

Ultrasound effects on restricted silica gelation during silica extraction from Pyro-Metallurgical copper slag under acidifying conditions

Pyro-metallurgical copper slag (CS) waste was used as the source material for ultrasound (US) silica extraction under acidification processes with 26 kHz with HCl, HNO₃, and H₂SO₄ at different concentrations at 100, 300, and 600 W. During acidifying extraction processes, US irradiation inhibited silica gel formation under acidic conditions, especially at lower acid concentrations of less than 6 M, whereas a lack of US irradiation led to enhanced gelation. When US stopped, gelation occurred to a considerable degree, suggesting that the gel particle size distribution was aggregated in the 3–400 µm size range. However, with US, the size was mainly in the 1–10 µm range. Results of elemental analysis indicated that US treatment decreased the co-precipitation of other metal ions such as Fe, Cu, and Al sourced from CS for lower acidic medium, whereas the higher concentration medium accelerated silica gelation and the co-precipitation of other metals. With acids of HCl and HNO₃, and H₂SO₄, the gelations were less likely to occur at 6 M and 3 M during US irradiation, but acidic extraction without US was efficient for silica gelation and co-precipitation of other metals in the purified silica. The silica extraction yield with H₂SO₄ concentration of 3 M was 80% with 0.04% of Fe, whereas the silica product from HCl 6 M had a 90% extraction yield with only 0.08% of Fe impurity. In contrast, even though the non-US system of HCl 6 M had a higher yield at 96%, the final product had 0.5% Fe impurity, which was much higher than the US system. Consequently, the US extraction process was quite noticeable for silica recovery from CS waste.     

核桃果皮基活性炭的氯化锌活化制备及工艺优化

以核桃果皮为原料,以氯化锌为活化剂,采用正交设计,马弗炉加热法制备了核桃果皮基活性炭,并对所得活性炭进行表征,测定了不同实验条件下制备的核桃果皮基活性炭的得率、比表面积和碘吸附值,对最优条件下制备的活性炭进行了孔径分析、红外光谱分析,Boehm法测定其表面酸性基团含量等。实验结果表明：以氯化锌为活化剂制备核桃果皮基活性炭的最佳工艺参数分别为：活化温度600 ℃,活化时间1 h,氯化锌浓度50%,粒径大小为60目。最优条件下制备的活性炭比表面积达到1 258.05 m2·g-1,中孔率为32.18%,说明核桃果皮可以制备出比表面积高的优质活性炭,不但实现了农业废料的资源化,还解决了农业废料污染的问题,同时提供了廉价的吸附剂,对于开辟活性炭原料的新来源具有重要意义。     

Particle Sampling and Real Time Size Distribution Measurement in H2/O2/TEOS Diffusion Flame

Growth characteristics of silica particles have been studied experimentally using in situ particle sampling technique from H₂/O₂/Tetraethylorthosilicate (TEOS) diffusion flame with carefully devised sampling probe. The particle morphology and the size comparisons are made between the particles sampled by the local thermophoretic method from the inside of the flame and by the electrostatic collector sampling method after the dilution sampling probe. The Transmission Electron Microscope (TEM) image processed data of these two sampling techniques are compared with Scanning Mobility Particle Sizer (SMPS) measurement. TEM image analysis of two sampling methods showed a good agreement with SMPS measurement. The effects of flame conditions and TEOS flow rates on silica particle size distributions are also investigated using the new particle dilution sampling probe. It is found that the particle size distribution characteristics and morphology are mostly governed by the coagulation process and sintering process in the flame. As the flame temperature increases, the effect of coalescence or sintering becomes an important particle growth mechanism which reduces the coagulation process. However, if the flame temperature is not high enough to sinter the aggregated particles then the coagulation process is a dominant particle growth mechanism. In a certain flame condition a secondary particle formation is observed which results in a bimodal particle size distribution.     

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm) for the samples prepared with FeCl₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.This revised version was published online in August 2005 with a corrected issue number.     

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm)=" for=" the=" samples=" prepared=" with=">₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.     

二氧化硅纳米颗粒与碳黑纳米颗粒红外漫反射光谱的测量与分析

用FTIR-FTS3000光谱仪和漫反射附件分别采集了二氧化硅纳米颗粒、炭黑纳米颗粒和二氧化硅纳米颗粒与碳黑纳米颗粒的不同配比的混合样品的红外漫反射光谱。通过对测量结果的分析,发现二氧化硅纳米颗粒的红外漫反射光谱较之体材料有蓝移和宽化现象,此现象可以用纳米粒子的小尺寸效应和量子尺寸效应来进行初步解释。而碳黑纳米颗粒因为其强吸光性的原因,实验中没有得到理想的光谱。混合样品中,碳黑纳米颗粒有一个最大吸收临界浓度,此时二氧化硅纳米颗粒与碳黑纳米颗粒的质量比是100∶20。在这个比例以内,碳黑纳米颗粒的特征峰位的F(R)函数与浓度符合朗伯-比尔定律。当碳黑纳米颗粒在体系中的含量超过这个比值,随着碳黑在体系中比例的增加,吸光度将不再增大。     

Immobilization of silver nanoparticles on silica microspheres

The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction of Ag⁺ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared through sol–gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag⁺ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount of AgNO₃.     

Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds

Immobilized iridium complexes synthesized using [Ir(COD)Cl]₂ by anchoring on hydrous and anhydrous silica gels were studied in terms of generating parahydrogen-induced polarization (PHIP) in the gas-phase hydrogenation of propylene and propyne. Distinguishing differences in the hydrogenations of carbon–carbon double and triple bonds were found. It has been shown that in the double bond hydrogenation both catalysts are very active even at 25 °C. The reaction yield in continuous flow experiments is more than 70 %, whereas the obtained PHIP degrees are very low. In the case of the triple bond hydrogenation, a more or less active hydrogenation reaction was observed at relatively high temperatures (≈70–80 °C) for the catalyst immobilized on anhydrous silica, while the catalyst immobilized on hydrous silica was inactive at these temperatures. Contrary to the double bond hydrogenation, the triple bond hydrogenation provided significant signal enhancements observed in ¹H nuclear magnetic resonance spectra for the signals corresponding to protons of vinyl fragments of product propylene in both PASADENA and ALTADENA experiments. The catalyst, however, is not stable under the triple bond hydrogenation reaction conditions, and deactivates within several minutes. It was also found that at higher temperatures (100–120 °C), this catalyst demonstrates a reactivation most likely associated with the reduction of Ir(I) that results in the formation of Ir(0) surface metal nanoparticles.