SiO2 Molar Ratio Research Articles

Synthesis and pervaporation performance of highly reproducible zeolite T membranes from clear solutions

Zeolite T membranes with very good permeation performance were successfully synthesized on porous mullite supports by the secondary growth method with homemade microsized seeds from clear solutions. The influence of synthesis parameters such as the molar ratios of SiO 2 /Al 2 O 3 and H 2 O/SiO 2 , alkalinity, synthesis temperature, and crystallization time on membrane growth and permeation performance was investigated systematically. It is found that these parameters strongly affect the zeolite T growth and pervaporation performance of the membranes. Under the optimized synthesis conditions of 1SiO 2 :0.015Al 2 O 3 :0.41 (Na 2 O+K 2 O):30H 2 O, the crystallization time was shortened to 6 h at 423 K and a continuous and dense T-type zeolite layer as thin as 5 μm formed on the surface of the support. It significantly improved the membrane density and permselective properties. A permeation flux and separation factor of 4.20 kg/(m 2 ·h) and 7800, respectively, were obtained with the as-synthesized membrane for 10 wt% water-90 wt% i -propanol mixtures at 348 K. It also exhibited a very good pervaporation performance for water/ethanol mixtures separation. This high quality zeolite T membrane could be reproducibly prepared. 以自制微米级分子筛为晶种, 在清液体系中成功合成出高性能的 T 型分子筛膜, 考察了硅铝比、水硅比、碱度及合成温度与时间等条件对膜的生长和渗透汽化性能的影响. 结果表明, 在摩尔组成为 1SiO 2 :0.015Al 2 O 3 :0.41 (Na 2 O+K 2 O):30H 2 O 的清液体系中, 于 423 K 晶化 6 h 的条件下可较快地形成一层厚度为 5 μm 的连续致密纯相 T 型分子筛膜, 较大缩短了膜合成时间且提高了膜致密性. 在优化条件下所合成的膜具有优良的分离性能和高重复性. 348 K 时, 在 10 wt% 水-90 wt% 异丙醇混合物体系中膜的渗透通量和分离因子分别高达 4.20 kg/(m 2 ·h) 和 7800. Highly reproducible zeolite T membranes were hydrothermally synthesized from clear solutions. Synthesis parameters, especially alkalinity, strongly affect the membrane growth and pervaporation performance.

Thermal plasma synthesis of SiC

Synthesis of silicon carbide has been carried out using thermal plasma processing technique using SiO2 as the solid feed and CH4 as the gaseous reducing agent. Thermochemical calculations have been performed varying the molar ratio of silicon dioxide and methane to determine the feasibility of the reaction. Experiments using a molar ratio of SiO2:CH4 equal to 1:2 produced maximum yield of SiC of about 65 mol % at a solid feed rate of 5 g/min. Mostly spherical morphology with some nanorods has been observed. The presence of Si had been observed and was quantified using XRD, HRTEM, Raman spectroscopy and X-ray photoelectron microscopy (XPS). Si acts as a nucleating agent for SiC nanorods to grow.

Chromium oxide loaded silica aerogels: Novel visible light photocatalytic materials for environmental remediation

Abstract Various photocatalytic systems have been reported for degradation of harmful air pollutants. Most of the reported catalysts are based on well-known semiconducting material, titanium dioxide (TiO 2 ), while some are based on other materials such as silicon dioxide (SiO 2 ), various zeolites. However, titania based systems are very popular in this regard and the most of the photocatalytic processes that involve titania are considered non-localized. Thus, to study the photocatalytic ability of a localized system, novel aerogel based samples were studied using silica and chromium and tested for photocatalytic activities. The new photocatalytic systems were prepared to obtain aerogel silica as the matrix material by co-hydrolyzing silica precursor with chromium(III) ions to obtain chromium loaded silica materials. Later, these prepared samples were compared to chromium loaded titania and mixed TiO 2 –SiO 2 systems. All the prepared systems have high surface areas compared to the systems that have been reported in literature. Samples were characterized by X-ray diffraction, diffusive reflectance UV spectroscopy, and BET surface analysis methods. The kinetics of photocatalytic degradation of a model pollutant, acetaldehyde, was performed using a Shimadzu GCMS-QP 5000 instrument and a glass reactor with a quartz window. Change in photocatalytic activity was found with various molar ratios of SiO 2 to TiO 2 . From all the systems, chromium loaded pure SiO 2 showed the highest activity towards acetaldehyde degradation compared to mixed TiO 2 –SiO 2 systems and TiO 2 based systems. The interesting photocatalytic activity of silica based materials occurs due to the efficient insertion of chromium ions into silica matrix to generate reactive sites. The photo excitation is believed to occur at molecular orbital level at localized chromium sites.

Synthesis and reaction mechanism of Ti3SiC2 ternary compound by carbothermal reduction of TiO2 and SiO2 powder mixtures

The present study aims to investigate synthesis of Ti3SiC2 from TiO2 and SiO2 powder mixtures by carbothermal reduction method. Equilibrium TiO2–SiO2–C ternary phase diagram was used to predict the conditions for the formation of Ti3SiC2 at 1800K under Ar atmosphere. A reactant mixture with a TiO2:SiO2 molar ratio of 1.5 and a C content of 68.75mol% (26.86wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti3SiC2 at 1800K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti3SiC2 phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti3SiC2 contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO2:SiO2 molar ratio of 1.5 was determined to be 30.05wt% under the experimental conditions studied. Ti3SiC2 content of the products obtained from this reactant was observed to increase with reaction time to 31wt% at 75min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti3SiC2 nanolaminates. Equilibrium thermodynamic analysis of the TiO2–SiO2–C system suggested that the reaction of solid Ti2O3 with SiO and CO gases may play a dominant role in the formation of Ti3SiC2.

Optimization of preparation conditions of ZnO–SiO2 xerogel by sol–gel technique for photodegradation of methylene blue dye

The ZnO–SiO2 xerogel photocatalyst was prepared via the sol–gel technique and applied for photodegradation of methylene blue (MB) dye. The optimum conditions for preparation of ZnO–SiO2 gel is 30:70 ZnO:SiO2 molar ratio and TEOS:C2H5OH:H2O:HNO3 is 1:16:12:0.04 molar ratios at 30°C for 30 min, at these conditions the photoactivity of ZnO–SiO2 xerogel was 99% at a surface area of 500 m2/g after 60 min. The optimum loading of ZnO–SiO2 photocatalyst was 0.050 wt% that gives 99% MB dye removal efficiency after 40 min. The overall kinetics of photodegradation of MB dye using ZnO–SiO2 photocatalyst was found to be of the first order.

Optimization of hydrothermal synthesis of pure phase zeolite Na-P1 from South African coal fly ashes

This study was aimed at optimizing the synthesis conditions for pure phase zeolite Na-P1 from three coal fly ashes obtained from power stations in the Mpumalanga province of South Africa. Synthesis variables evaluated were: hydrothermal treatment time (12–48 hours), temperature (100–160°C) and varying molar quantities of water during the hydrothermal treatment step (H2O:SiO2 molar ratio ranged between 0–0.49). The optimum synthesis conditions for preparing pure phase zeolite Na-P1 were achieved when the molar regime was 1 SiO2: 0.36 Al2O3: 0.59 NaOH: 0.49 H2O and ageing was done at 47°C for 48 hours. The optimum hydrothermal treatment time and temperature was 48 hours and 140°C, respectively. Fly ashes sourced from two coal-fired power plants (A, B) were found to produce nearly same high purity zeolite Na-P1 under identical conditions whereas the third fly ash (C) lead to a low quality zeolite Na-P1 under these conditions. The cation exchange capacity for the high pure phase was found to be 4.11 meq/g. These results highlight the fact that adjustment of reactant composition and presynthesis or synthesis parameters, improved quality of zeolite Na-P1 can be achieved and hence an improved potential for application of zeolites prepared from coal fly ash.

Synthesis and Characterization of Mesoporous Aluminosilicates for Copper Removal from Aqueous Medium

In this study the characterization of an aluminosilicate synthesized from commercial Al2(SO4)3 and colloidal SiO2 is presented, as well as its capacity for the removal of copper from aqueous solution. Characterization of the synthesized material was performed using X-ray diffraction, BET nitrogen adsorption-desorption, mass titration and the Boehm method. In order to obtain stable agglomeration and enhance its surface area (165 - 243 m2/g) and solid adsorbing capabilities, the molar ratio SiO2:Al2O3 (1:3, 1:1 and 3:1) was studied, the solubility of the preparation material, synthesis-procedure time and solution pH function were also examined. The maximum capacity to remove copper ions from an aqueous solution by synthesized aluminosilicate was 16 mg/g at pH 4 and 25℃. The Langmuir model fitted better to the copper adsorption experimental data.

Synthesis of zeolites from coal fly ash: application of a statistical experimental design

With the intention of decreasing the experimental test runs during the optimization of synthesis of zeolites from fly ash, a 24 full-factorial experimental design was applied in this study. The preparation parameters that had showed significant influence on the synthesis of pure phase zeolite Na-P1 using one-step-at-a-time experimental approach were included, but extended also to those parameters of importance identified in the literature. At the same time, it was important that the levels of variation of parameters not be restricted to the conditions where a pure phase of zeolite Na-P1 was formed. The four synthesis variables investigated were; NaOH concentration (NaOH:SiO2 molar ratio ranged between 0.35 and 0.71), ageing temperature (35–55°C), hydrothermal treatment time (36–60 h) and temperature (130–150°C). The results obtained were assessed by the improvement in the cation exchange capacity (CEC) of the obtained zeolite, which showed that the phase purity is strictly controlled by the synthesis conditions. In the end, this approach provided sufficient understanding of the relationship between product properties and the four synthesis parameters, which took into account the individual effects as well as linear and nonlinear interacting phenomena. From the analysis, it was found that the main effects were ageing temperature and hydrothermal treatment time and temperature, which showed some interactions among each other.

Geopolymers based on a coarse low-purity kaolin mineral: Mechanical strength as a function of the chemical composition and temperature

Abstract A coarse mineral with 70% kaolinite and 30% quartz was calcined and chemically activated by alkaline solutions of Na 2 SiO 3 and NaOH. The compressive strength evolution was investigated as a function of the curing temperature at 20 and 80 °C, and the molar ratios of SiO 2 /Al 2 O 3 (2.64–4.04) and Na 2 O/Al 2 O 3 (0.62–1.54). For curing at 20 °C, the best composition was SiO 2 /Al 2 O 3 = 2.96 and NaO/Al 2 O 3 = 0.62, reaching 85 MPa at 28 days. Curing at 80 °C had a positive effect on the strength development only in the first 3 days. X-ray diffraction of the geopolymeric formulations showed the formation of amorphous silicoaluminates of similar nature. The microstructure consisted of unreacted quartz and metakaolinite particles in a matrix of silicoaluminate polymer and condensed silica gel from the unreacted sodium silicate.

Thermal and hydrothermal stability of ZrMCM-41 mesoporous molecular sieves obtained by microwave irradiation

ZrMCM-41 mesoporous molecular sieves were synthesized by using the zirconium sulfate as zirconium source and using cetyltrimethyl ammonium bromide as a template under microwave irradiation condition. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma (ICP) technique, Fourier transform infrared spectroscopy (FT-IR) and N2 physical adsorption, respectively. The effect of the different initial ZrO2: SiO2 molar ratio, the different thermal treatment temperature and hydrothermal treatment time on textural property was investigated. The results show that the obtained products possess a typical mesoporous structure of MCM-41 and have specific surface areas in the range of 598·1∼971·4 m2/g and average pore sizes in the range of ca. 2·46∼3·43 nm. On the other hand, the BET specific surface area and pore volume of the synthesized ZrMCM-41 mesoporous molecular sieve decrease with the increased amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering deteriorates. The mesoporous structure of the ZrMCM-41 mesoporous molecular sieve still retains after calcination at 750°C for 3 h or hydrothermal treatment at 100°C for 6 days, however, the mesoporous ordering is poor.

Vapor phase alkylation of toluene using various alcohols over H3PO4/MCM-41 catalyst: Influence of reaction parameters on Vapor phase alkylation of toluene using various alcohols over H_3PO_4/MCM-41 catalyst: influence of reaction parameters on selectivity and conversion

A mesoporous MCM-41 molecular sieve material with a molar ratio of SiO_2/Al_2O_3 = 70 and loaded with H_3PO_4 was used as a catalyst for the alkylation of toluene, using various alcohols, namely methanol, iso-propanol, and tert-butanol, as alkylating agents. Para-alkylated toluene was the predominant product, formation of which was enhanced by moderate temperature, low amounts of the alkylating agents in the feed, and high carrier gas flow rate. Time on stream was found to exert a profound effect on the selectivity and conversion to the different products.

Aluminosilicates with varying alumina–silica ratios: synthesis via a hybrid sol–gel route and structural characterisation

Aluminosilicates with varying Al2O3:SiO2 molar ratios (3:1, 3:2, 3:3 and 3:4) have been synthesized using a hybrid sol-gel route using boehmite sol as the precursor for alumina and tetraethyl orthosilicate (TEOS) as the precursor for silica. The synthesis of boehmite sol from aluminium nitrate, and its use as the alumina precursor, is cost effective compared to alkoxide precursors. Structural aspects, including bonding and coordination, are studied in detail for samples calcined in the temperature range 400-1400 °C using both NMR and FTIR spectroscopy: the results are correlated with phase formation data (spinel and high temperature phases) obtained from XRD and thermal analysis. FTIR results show a broadening of peaks at 800 °C indicating a disordered distribution of octahedral sites caused by crosslinking between AlO6 octahedral and SiO4 tetrahedral units prior to the formation of mullite. (27)Al MAS NMR spectra are consistent with a progressive decrease in the number of AlO6 polyhedra with increasing temperature corresponding to Al in these units being forced to adopt a tetrahedral coordination due to the increasing presence of similarly coordinated Si species. XRD results confirm the formation of pure mullite at 1250 °C for a 3Al2O3:2SiO2 system. At 1400 °C, phase pure mullite is observed for all compositions except 3Al2O3:SiO2 where α-Al2O3 is the major phase with traces of mullite. The synthesis of aluminosilicates through a hybrid sol-gel route and the detailed insight into structural features gained from spectroscopic and diffraction techniques contributes further to the development of these materials in applications ranging from nanocatalysts to high-temperature ceramics.

Compressive strength and microstructural characteristics of class C fly ash geopolymer

Abstract Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO 2 /Na 2 O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na 2 O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm −1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm −1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.

Mineral and geochemical characterization of a leptic aluandic soil and a thapto aluandic-ferralsol developed on trachytes in Mount Bambouto (Cameroon volcanic line)

Mineral and geochemical investigations were carried out on soil samples and fresh rock (trachytes) from two selected soil profiles (TM profile on leptic aluandic soils and TL profile on thapto aluandic-ferralsols) from Mount Bambouto to better understand geochemical processes and mineral paragenesis involved in the development of soils in this environment. In TM profile, the hydrated halloysites and goethite occur in the weathered saprolite boulders of BC horizon while dehydrated halloysite, gibbsite and goethite dominate the soils matrices of BC and A horizons. In TL profile, the dehydrated halloysites and goethite are the most abundant secondary minerals in the weathered saprolites of C and BC horizons while gibbsite, hematite and kaolinite occur in the soil matrices of BC, B and A horizons. The highest gibbsite content is in the platy nodules of B horizon. In both soil profiles, organo-metal complexes (most likely of Al and Fe) are present in the surface A horizon. Geochemically, between the fresh rock and the weathered saprolites in both soils, SiO 2, K 2O, CaO, Na 2O and MgO contents decrease strongly while Fe 2O 3 and Al 2O 3 tend to accumulate. The molar ratio of SiO 2/Al 2O 3 (Ki) and the sum of Ca, Mg, K and Na ions (TRB) also decreases abruptly between fresh rocks and the weathered saprolites, but increases significantly at the soil surface. The TM profile shows intense Al enrichment whereas the TL profile highlights enrichment in both Al and Fe as the weathering progresses upwards. Both soil profiles are enriched in Ni, Cu, Ba and Co and depleted in U, Th, Ta, Hf, Y, Sr, Pb, Zr and Zn relative to fresh rock. They also show a relatively low fractionation of the rare earth elements (REE: La, Nd, Sm, Eu, Tb, Yb and Lu), except for Ce which tends to be enriched in soils compared to CI chondrite. All these results give evidence of intense hydrolysis at soil deep in Mount Bambouto resulting in the formation of halloysite which progressively transforms into gibbsite and/or dehydrated halloysite. At the soil surface, the prominent pedogenetic process refers to andosolization with formation of organo-metal complexes. In TL profile, the presence of kaolinite in soil matrices BC and B horizons is consistent with ferralitization at soil deep. In conclusion, soil forming processes in Mount Bambouto are strongly influenced by local climate: (i) in the upper mountain (> 2000 m), the fresh, misty and humid climate favors andosolization; whereas (ii) in the middle lands (1700–2000 m) with a relatively dry climate, both andosolization at the soil surface and ferralitization at soil deep act together.

Study on the Synthesis of Clay-Based Titanium Silicalite-1 Catalytic Composite

A clay-based titanium silicalite-1 (TS-1) catalytic composite was synthesized using hydrothermal treatment to crystallize TS-1 (300−400 nm) on a bentonite support. The presence of bentonite is favorable to supported growth attributed to the adsorption properties of the substrate which enhanced the interaction with the dissolved crystallizing species. The rapid crystallization on the bentonite support caused formation of silicalite-1 prior to Ti incorporation. An FT-IR spectroscopic study revealed that the Si defective sites were the exact location at which Ti was bonded. The Ti has been confirmed to exist in the form of a Si−O−Ti bridge instead of a Ti═O group in the clay-based TS-1. The influence of the synthesis temperature, duration, H2O to SiO2 molar ratio, and Ti and TPAOH concentrations in the starting gel on the characteristics of the clay-based TS-1 composite were also studied. In addition to the high and stable catalytic activity, the excellent settling efficiency of the clay-based TS-1 composite...

Preparation and characterization of core–shell structured Co/SiO 2 nanosphere

The Co/SiO 2 nanospheres have been prepared by the improved sol–gel method combined with hydrogen reduction. The size, the phase and the shape of the particles varied with the molar ratio of SiO 2, reduction temperature and drying temperature. The initial temperature of the phase transformation from hcp-Co to fcc-Co in core–shell structured Co/SiO 2 nanospheres is lower than that in the bulk case due to the lower surface energy of nanoscale particles. Result of the thermogravimetric analysis (TGA) indicates that the thermal stability of Co/SiO 2 nanoparticles is much better than that of pure Co particles. The value of saturation magnetization decreases with the increase of SiO 2 content due to the presence of the nonmagnetic silica coating.

Fabrication of silicalite-1 crystals with tunable aspect ratios by microwave-assisted solvothermal synthesis

A new method was developed to finely tune the aspect ratios of silicalite-1 (Si-MFI) crystals. This method involved the utilization of co-solvent of diols and the microwave heating of a reaction system of TEOS–TPAOH–H 2O–Diol with the molar ratio of SiO 2:TPAOH:EtOH:Diol:H 2O = 1.0:0.357:4.0: x: y, where x = 6–9, y = 21.55–45.55. The diols included the ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (tEG). Under microwave radiation the Si-MFI crystals with tunable sizes, shapes, and aspect ratios were crystallized. An excellent linear correlation between the aspect ratio of the Si-MFI crystals and the “concentration” of the C/OH, denoted as C C/OH, where C/OH is the ratio of the number of carbon and hydroxyl of the diols of the co-solvent, was observed. On the basis of this linear relationship, the aspect ratios of the well defined Si-MFI crystals could be effectively tuned. The possible mechanism on how the co-solvent of diols affects the growth kinetics of the Si-MFI crystals is discussed. The resulting products were further characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Vapor phase transport synthesis of SAPO-34 films on cordierite honeycombs

SAPO-34 films coated on cordierite honeycombs were synthesized by a vapor phase transport (VPT) technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and differential scanning calorimeter (DSC) were used to characterize the films. It was found that SAPO-34 films could be prepared on the cordierite honeycombs only when triethylamine (TEA) was presented in both the liquid phase and the SAPO-34 synthesis sol. The loading of SAPO-34 could be adjusted by changing the reaction conditions, such as the impregnation time and the molar ratio of SiO 2/Al 2O 3 in the synthesis sol. Continuous SAPO-34 films, with a thickness of ca. 20–60 μm, were composed of microsized crystals and the adhesion between SAPO-34 films and cordierites was strong.

Impact of supercritical drying and heat treatment on physical properties of titania/silica aerogel monolithic and its applications

Abstract TiO2–SiO2 monolithic aerogels were homogeneously prepared using sol–gel method. Critical point of drying of TiO2–SiO2 gels with ethanol was studied for 30, 60, 90 and 120 min. Subsequently, the gels were dried with supercritical ethanol, resulting in amorphous aerogels that crystallized following heat treatment at 550 °C from 1 to 5 h. The TiO2–SiO2 aerogels were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area measurements. The molar ratio of SiO2:TiO2 was 6 and the synthetic strategy revealed that TiO2–SiO2 aerogel, had a surface area ∼868 m2/g, particle size ∼40 nm, density ∼0.17 g/cm3 and 80% porosity. The finding indicated that from economic point of view, TiO2–SiO2 gel should be supercritical dried for 30 min and heat-treated for 5 h. The TiO2–SiO2 aerogel monoliths photocatalyst synthesized using sol–gel method provided insight into the characteristics that make a photocatalyst material well-suited for photodegradation of phenol and cyanide in an industrial waste stream containing Cl−, S2− and NH4+. Interestingly, after multiple reuse cycles (i.e. ≥7), photodegradation systems with regenerated photocatalyst showed a slightly decreasing of photoactivity ∼2–4%. The overall kinetics of photodegradation of either phenol or cyanide using TiO2–SiO2 aerogel photocatalyst was found to be of first order.

Characterization of CoMCM-41 mesoporous molecular sieves obtained by the microwave irradiation method

CoMCM-41 mesoporous molecular sieves with different amounts of cobalt were synthesized via the microwave irradiation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and N 2 adsorption–desorption technique, and thermal and hydrothermal stabilities of synthesized CoMCM-41 samples were also investigated. Results show that these synthesized materials have typical mesoporous structure of MCM-41. Also, specific surface area and pore volume of synthesized CoMCM-41 decrease with increasing amount of cobalt added, and mesoporous ordering also decreases. When the molar ratio of SiO 2:CoO in the starting material is 1.0:0.05, mesoporous ordering of synthesized CoMCM-41 is the best among the four doping contents. On the other hand, results of thermal and hydrothermal tests show that CoMCM-41 after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 5 days still retains mesostructure. However, mesoporous framework is entirely damaged after calcination at 850 °C for 3 h.