Stability and textural properties of cobalt incorporated MCM-48 mesoporous molecular sieve

Transition metal cobalt incorporated MCM-48 mesoporous molecular sieves (CoMCM-48) with different Co contents were synthesized hydrothermally at 120 °C for 24 h by directly adding fluoride ions to the initial gel. The resulting materials were characterized by means of XRD, TEM, FT-IR, UV-vis, TPR and N₂ physical adsorption, respectively. The effect of various factors, such as the Si/Co molar ratio, calcination temperature and hydrothermal treatment time, on the crystalline structure and textural properties of CoMCM-48 was investigated in detail. The results show that the CoMCM-48 mesoporous materials with high specific surface area were successfully synthesized. A small amount substitution of Co for Si in MCM-48 did not significantly change the textural properties while the higher cobalt incorporated leads to decrease of the surface area and deterioration of structural regularity. Furthermore, the resulting CoMCM-48 still retained the cubic mesoporous framework even after calcination at 800 °C for 4 h or hydrothermal treatment at 100 °C for 24 h.     

Effect of the Si/Ce molar ratio on the textural properties of rare earth element cerium incorporated mesoporous molecular sieves obtained room temperature

Rare earth Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized via a direct and nonhydrothermal method at room temperature from sodium silicate and ammonium cerium (IV) nitrate as raw materials. Cetyltrimethyl ammonium bromide (CTAB) was used as a template. The resultant samples were characterized by means of powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis) and N₂ physical adsorption, respectively. The effect of the Si/Ce molar ratio on the crystalline structure and textural properties of CeMCM-41 was also investigated. The experimental results show that ordered CeMCM-41 mesoporous molecular sieves were successfully synthesized at room temperature and the resultant mesoporous materials have specific surface areas in the range of 594–1369 m²/g and average pore sizes in the range of ca. 2.5–2.8 nm. It has been found that the structural properties are strongly related to the amounts of cerium incorporation. When the cerium content increased in the samples, the intensity of the peak (1 0 0) was gradually reduced, and the surface area and structural regularity were diminished.     

Comparative studies of Zr-based MCM-41 and MCM-48 mesoporous molecular sieves: Synthesis and physicochemical properties

Two surfactant-templated synthetic routes are developed for the preparation of new types of mesoporous molecular sieves, Zr-MCM-41 and Zr-MCM-48, using different Si sources but keeping the same zirconium precursor (zirconium-n-propoxide). When fumed silica was used as Si precursor, a Zr-MCM-48 material of cubic structure was formed with a surface area of 654.8 m²/g and an unimodal pore diameter distribution. It shows low stability: after calcination at 600 °C, the ordered structure was transformed into a relatively disordered worm-like mesostructure with many defects and silanol groups. The use of tetraethyl orthosilicate as Si source led to the formation of a Zr-MCM-41 mesoporous solid, which had good thermal stability and a highly ordered hexagonal arrangement, with a surface area 677.9 m²/g and an uniform pore diameter distribution. Fourier transform infrared (FT-IR) characterization and ²⁹Si NMR analysis confirm that zirconium ions indeed incorporated into the framework of the solid. The in situ FT-IR spectroscopy of pyridine adsorption reveals that both, Lewis and Brönsted acid sites, were formed on the surface of these mesoporous materials. The strength and number of the Brönsted acid sites of the Zr-MCM-48 solid were greater than those of the Zr-MCM-41, due to a lower degree of condensation reaction during the synthesis that led to more structural defects in the framework and more silanol groups stretching from the solid surface.     

Synthesis and characterization of Co (Ni or Cu)-MCM-41 mesoporous molecular sieves with different amount of metal obtained by using microwave irradiation method

Co (Ni or Cu)-MCM-41 mesoporous molecular sieves with different amount of metal were synthesized by using cetyltrimethyl ammonium bromide as a template and by a novel microwave irradiation method. These samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and N₂ physical adsorption. The experimental results show that Co (Ni or Cu)-MCM-41 mesoporous molecular sieves were successfully synthesized. When the as-synthesized samples were calcined at 550 °C for 10 h, the template was effectively removed. Under microwave irradiation condition, Co-MCM-41 mesoporous molecular sieves have specific surface areas in a range of 745.7-1188.8 m²/g and average pore sizes in a range of 2.46-2.75 nm; Ni-MCM-41 mesoporous molecular sieves have specific surface areas in a range of 625.8-1161.3 m²/g and average pore sizes of ca. 2.7 nm; Cu-MCM-41 mesoporous molecular sieves have specific surface areas in a range of 601.6-1142.9 m²/g and average pore sizes in a range of 2.46-2.76 nm. On the other hand, with increasing the introduced metal amount, the specific surface area and pore volume of the synthesized Co (Ni or Cu)-MCM-41 mesoporous molecular sieves became small, and the mesoporous ordering of the samples became poor. Under the comparable synthesis conditions, the synthesized Co-MCM-41 mesoporous molecular sieve has a bigger specific surface area and a more uniform pore distribution as compared with the synthesized Ni-MCM-41and Cu-MCM-41 mesoporous molecular sieves.     

Synthesis and characterization of a hexagonal mesoporous silica with enhanced thermal and hydrothermal stabilities

A synthetic route was developed for a novel hexagonal mesoporous silica that has remarkably wide channel diameters and thick walls. The procedure involved the acid-catalyzed hydrolysis of tetraethylorthosilicate in a water/ethanol/isopropoanol solvent mixture while employing 1-hexadecylamine as a templating agent and mesitylene as an auxiliary agent. After removal of the template by either extraction with ethanolic hydrochloric acid or by calcination at 550 °C, the resulting mesoporous materials had surface areas of 1283 and 1211 m²/g. The channel diameters were found to be 47.2-51.1 Å, while the wall thicknesses were 20.9-21.1 Å. X-ray powder diffraction demonstrated that the novel mesoporous silica belonged to the MCM-41 structural family. Notably, they displayed higher thermal and hydrothermal stabilities, and have higher surface areas than conventionally prepared MCM-41 silica. The thickest channel walls (21.1 Å) can withstand calcination to nearly 850 °C with minimal structural damage. The calcined sample was more resistant to hydrothermal treatment in boiling water than was the solvent-extracted product but both materials showed minimal change after 25 h of hydrothermal treatment.     

Stability and characterization of mesoporous molecular sieve using natural clay as a raw material obtained by microwave irradiation

Mesoporous molecular sieve was synthesized via microwave irradiation method, and using natural clay, sodium silicate and aluminum chloride as raw materials and cetyl trimethyl ammonium bromide (CTAB) as a template agent under alkaline condition. The samples were characterized by various analytic and spectroscopic tools such as XRD, FT-IR, TEM, TG-DSC and N₂ physical adsorption, respectively. The results show that the synthesized sample has typical mesoporous structure and exhibits good mesoporous ordering. On the other hand, the as synthesized sample after calcination at 550 °C for 10 h has a surface area of 576.0 m²/g and an average pore size of 4.83 nm. Furthermore, the synthesized mesoporous molecular sieve still exhibits good mesoporous ordering after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 10 days.     

Immobilization of naringinase on mesoporous molecular sieve MCM-41 and its application to debittering of white grapefruit

Naringinase was bound to mesoporous silica MCM-41 via adsorption with glutaraldehyde and used to debitter white grapefruit. K_m value of the immobilized naringinase was lower than that of free naringinase. The immobilized catalysts showed excellent thermal stability and storage stability and could be recycled 6 times retained about 44.57% activities. The unaltered structural order of the prepared catalyst was characterized with reference to bulky and surface properties by infrared spectroscopy (FT-IR), elemental analysis and nitrogen adsorption-desorption isotherms analysis.     

多酸-介孔分子筛复合材料的制备、表征及光催化活性

采用浸渍法将具有光催化活性的多金属氧酸盐(polyoxometalate,POM)磷钨酸和硅钨酸负载到介孔分子筛MCM-41,制备了H3PW12O40/MCM-41和H4SiW12O40/MCM-41两种复合材料,以红外光谱(FT-IR)、X射线衍射(XRD)、N2吸附、高分辨透射电镜(HRTEM)等分析手段对所合成的多酸-分子筛复合材料进行了表征,并以农药百草枯的光催化降解考察了复合材料的光催化活性。所合成的复合材料同时保留了母体多酸的Keggin特征结构和载体MCM-41分子筛均匀的六方孔道结构,比表面积超过200m2.g-1。用于农药百草枯的光催化降解实验表明,两种复合材料均具有较高的光催化活性。在365nm紫外光辐照下,以H3PW12O40/MCM-41和H4SiW12O40/MCM-41为催化剂催化反应14h后,百草枯(10mg.L-1)的降解转化率分别达到92.0%和87.6%,反应符合一级化学动力学模型,半衰期分别为3.7和4.6h。     

Synthesis of multi-wall carbon nanotubes by the pyrolysis of ethanol on Fe/MCM-41 mesoporous molecular sieves

Ordered hexagonal arrangement MCM-41 mesoporous molecular sieves were synthesized by the traditional hydrothermal method, and Fe-loaded MCM-41 mesoporous molecular sieves (Fe/MCM-41) were prepared by the wet impregnation method. Their mesoporous structures were testified by X-ray diffraction (XRD) and the N₂ physical adsorption technique. Carbon nanotubes (CNTs) were synthesized by the chemical vapor deposition (CVD) method via the pyrolysis of ethanol at atmospheric pressure using Fe/MCM-41 as a catalytic template. The effect of different reaction temperatures ranging from 600 to 800 ^°C on the formation of CNTs was investigated. The resulting carbon materials were characterized by various physicochemical techniques such as transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The results show that multi-wall carbon nanotubes (MWCNTs) with an internal diameter of ca. 7.7 nm and an external diameter of ca. 16.9 nm were successfully obtained by the pyrolysis of ethanol at 800 ^°C utilizing Fe/MCM-41 as a catalytic template.     

Synthesis and characterization of manganese ferrite nanoparticles by thermal treatment method

Cubic structured manganese ferrite nanoparticles were synthesized by a thermal treatment method followed by calcination at various temperatures from 723 to 873 K. In this investigation, we used polyvinyl pyrrolidon (PVP) as a capping agent to control the agglomeration of the nanoparticles. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle sizes of manganese ferrite nanoparticles were determined by TEM, which increased with the calcination temperature from 12 to 22 nm and they had good agreement with XRD results. Fourier transform infrared spectroscopy confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K. Magnetic properties were demonstrated by a vibrating sample magnetometer, which showed a super-paramagnetic behavior for all samples and also saturation magnetization (M_s) increases from 3.06 to 15.78 emu/g by increasing the calcination temperature. The magnetic properties were also confirmed by the use of electron paramagnetic resonance spectroscopy, which revealed the existence of unpaired electrons and also measured peak-to-peak line width, resonant magnetic field and the g-factor.     

Effect of reaction parameters on the growth of MWCNTs using mesoporous Sb/MCM-41 by chemical vapour deposition

Mesoporous Si-MCM-41 molecular sieve was synthesized hydrothermally and different wt.% of Sb (1.0, 2.0, 3.0, 5.0, 10.0, 15.0 and 20.0) was loaded on it by wet impregnation method. The Sb/MCM-41 materials were characterized by various physico-chemical techniques such as XRD, TGA and TEM. The TEM image showed a honeycomb structure of the host material. They were used as catalytic templates for the growth of MWCNTs by CVD method with different temperatures at 700, 800, 900 and 1000 °C using acetylene as a carbon precursor. The reaction temperature was optimized for the better formation of MWCNTs and they were purified and then characterized by XRD, SEM, HR-TEM and Raman spectroscopy techniques. The formation of MWCNTs with diameter in the range of 4−6 nm was observed from HR-TEM. The good thermal stability and high productivity of catalyst observed in this study revealed that the 2 wt.% Sb loaded MCM-41 could be a promising support for the catalytic synthesis of MWCNTs at 800 °C by CVD method.     

Effects of surface treatments and annealing on carbon-based molecular sieve membranes for gas separation

A new method in preparing carbon-based molecular sieve (CMS) membranes for gas separation has been proposed. Carbon-based films are deposited on porous Al₂O₃ disks using hexamethyldisiloxane (HMDSO) by remote inductively coupled plasma (ICP) chemical vapor deposition (CVD). After treating the film with ion bombardment and subsequent pyrolysis at a high temperature, carbon-based molecule sieve membranes can be obtained, exhibiting a very high H₂/N₂ selectivity around 100 and an extremely high permeance of H₂ around 1.5 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 298 K. The O₂/N₂ selectivity could reach 5.4 with the O₂ permeance of 2 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 423 K.

During surface treatments, HMDSO ions were found to be more effective than CH₄, Ar, O₂ and N₂ ions to improve the selectivity and permeance. Short and optimized surface treatment periods were required for high efficiency. Without pyrolysis, surface treatments alone greatly reduced the H₂ and N₂ permeances and had no effect on the selectivity. Besides, without any surface treatment, pyrolysis alone greatly increased the H₂ and N₂ permeances, but had no improvement on the selectivity, owing to the creation of large pores by desorption of carbon. A combination of surface treatment and pyrolysis is necessary for simultaneously enhancing the permeance and the selectivity of CMS membranes, very different from the conventional pore-plugging mechanism in typical CVD.     

纳米级介孔分子筛及其超分子发光功能材料的制备与表征

本文在超声波条件下以三甲基十六烷基溴化铵为模板剂,正硅酸乙酯为硅源合成了纳米级（10－40nm)的介孔分子筛（MCM－41）,其筛孔直径在2．7nm左右,选择Eu(Phen)4为客体,纳米级介孔分子筛为主体,在无水乙醇中进行分子组装,制备具有强发光性能的超分子纳米材料MCM－41－Eu(Phen),采用HRTEM,TEM,XRD,TG,IR和荧光光谱检测手段对产物进行了表征。     

真空紫外辐照对MQ增强硅橡胶热性能及光学性能的影响

 采用空间综合辐照模拟设备研究了真空紫外辐照对MQ增强加成型硅橡胶的表面形貌、质量损失、热性能及光学性能的影响。试验结果表明：真空紫外辐照后,硅橡胶表面出现损伤裂纹,随辐照剂量的增加,裂纹的数量增多;真空紫外辐照后,硅橡胶的质量有所损失,其质损率随辐照剂量的增加而增加;真空紫外辐照后硅橡胶的耐热性随辐照剂量的增加先增加而后下降;真空紫外辐照对硅橡胶材料的体膨胀/收缩变形影响不大,但对材料的光学性能有较大影响,随着辐照剂量的增加,材料的光学透过率下降。     

Effect of ultrasound on the structural and textural properties of copper-impregnated cerium-modified zirconium-pillared bentonite

In this study, the synthesis of zirconium-pillared bentonite modified with cerium was performed via two different methods by the application of conventional and ultrasonic treatments during the intercalation stage. To synthesise copper-impregnated pillared clays by wet impregnation, cerium-modified zirconium-pillared clays were used as supportive materials after being calcined at 300 °C. Ultrasonic treatment significantly decreased the required processing time compared with the conventional treatment of the synthesised pillared bentonites. Chemical analysis confirmed the incorporation of Zr⁴⁺, Ce⁴⁺ and Cu²⁺ species into the pillared bentonites. X-ray diffraction (XRD) patterns of zirconium- and cerium/zirconium-pillared bentonites prepared by conventional treatment show that one large d-spacing above 3.5 nm corresponds to the mesoporous delaminated part, and another small d-spacing above 1.7 nm is indicative of the microporous pillared part. Zirconium- and cerium/zirconium-pillared bentonites prepared via ultrasonic treatment exhibited similar results, with the same high d-spacing but with a second low-intensity d-spacing above 1.9 nm. The delaminated structures of the pillared bentonites synthesised by both methods were conserved after copper impregnation. Nitrogen-adsorption isotherm analysis showed that the textural characteristics of products synthesised by ultrasonic treatment were comparable to those of products synthesised by conventional treatment. Fourier-transform infrared spectroscopy (FTIR) analyses showed the presence of Brønsted- and Lewis-acid sites, and zirconium-pillared clays synthesised by conventional treatment exhibited increased numbers of Brønsted- and Lewis-acid sites after cerium addition and copper impregnation. However, the products synthesised by ultrasonic treatment exhibited an increased number of Brønsted- and Lewis-acid sites after cerium addition, but a decreased number of acid sites after copper impregnation.     

Fabrication of hydroxyapatite and TiO2 nanorods on microarc-oxidized titanium surface using hydrothermal treatment

AC-type microarc oxidation (MAO) and hydrothermal treatment techniques were used to enhance the bioactivity of commercially pure titanium (CP-Ti). The porous TiO₂ layer fabricated by the MAO treatment had a dominant anatase structure and contained Ca and P ions. The MAO-treated specimens were treated hydrothermally to form HAp crystallites on the titanium oxide layer in an alkaline aqueous solution (OH-solution) or phosphorous-containing alkaline solution (POH-solution). A small number of micro-sized hydroxyapatite (HAp) crystallites and a thin layer composed of nano-sized HAps were formed on the Ti-MAO-OH group treated hydrothermally in an OH-solution, whereas a large number of micro-sized HAp crystallites and dense anatase TiO₂ nanorods were formed on the Ti-MAO-POH group treated hydrothermally in a POH-solution. The layer of bone-like apatite that formed on the surface of the POH-treated sample after soaking in a modified simulated body fluid was thicker than that on the OH-treated samples.     

质子辐照对MQ硅树脂增强的加成型硅橡胶质损及热性能的影响

 采用空间综合辐照模拟设备研究了100 keV和150 keV能量的质子辐照对MQ硅树脂增强的加成型硅橡胶的损伤及其对硅橡胶热性能的影响。试验结果表明：质子辐照后,硅橡胶表面出现损伤裂纹,随辐照能量和剂量的增加,裂纹的数量增多,裂纹增大;质子辐照后,硅橡胶的质量有所损失,其质损率随辐照能量和剂量的增加而增加;质子辐照后硅橡胶的耐热性随辐照剂量的增加先略有增加而后下降,经辐照后的硅橡胶在玻璃态和玻璃转变区的温度区间内收缩率降低,而在高弹态的温度区间内膨胀率增加。     

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K.     

Effect of hydrothermal treatment on the acidity distribution of γ-Al2O3 support

The influence of hydrothermal treatment on the total acidity and the acidity distribution of γ-Al₂O₃ were studied in this paper. The experimental results indicated that the hydrothermal treatment of γ-Al₂O₃ at moderate condition (140 °C, 1.0-24.0 h) led to the formation of the plate-like γ-AlOOH crystallites with different morphologies, which resulted in the change of the surface acidity of the corresponding γ-Al₂O₃ supports. The increase of the reaction time in the period of 1.0-2.0 h led to the increase of the specific surface area, the surface OH, the total acidity and the ratio of the weak acidity in the acidity distribution of γ-Al₂O₃. The further prolongation of reaction time caused the overgrowth of γ-AlOOH crystallites, leading to the decrease of the specific surface area, the surface OH and the total acidity of the corresponding γ-Al₂O₃.     

Structural, elastic and thermal properties of the compound LaNi4.5Sn0.5

The equilibrium lattice constants, cell volumes, densities of states and electron density distributions of LaNi_4.5Sn_0.5 crystal are evaluated by the density functional theory using the plane wave pseudopotential (PW-PP) method. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained from the PW-PP method, is applied to the study of thermal and vibrational effects. We have analyzed the bulk modulus of LaNi_4.5Sn_0.5 as a function of temperature up to 1000 K. The thermodynamic properties such as thermal expansion coefficients and heat capacities are also predicted using the quasi-harmonic Debye model. Significant differences in properties are observed at high temperatures and pressures. Moreover, the Debye temperatures are determined from the non-equilibrium Gibbs functions. The calculated results are in excellent agreement with the available experimental data, and compared favorably with other theoretical results.