Physical state of poorly water soluble therapeutic molecules loaded into SBA-15 ordered mesoporous silica carriers: a case study with itraconazole and ibuprofen

The ordered mesoporous silica material SBA-15 was loaded with the model drugs itraconazole and ibuprofen using three different procedures: (i) adsorption from solution, (ii) incipient wetness impregnation, and (iii) heating of a mixture of drug and SBA-15 powder. The location of the drug molecules in the SBA-15 particles and molecular interactions were investigated using nitrogen adsorption, TGA, DSC, DRS UV-vis, and XPS. The in vitro release of hydrophobic model drugs was evaluated in an aqueous environment simulating gastric fluid. The effectiveness of the loading method was found to be strongly compound dependent. Incipient wetness impregnation using a concentrated itraconazole solution in dichloromethane followed by solvent evaporation was most efficient for dispersing itraconazole in SBA-15. The itraconazole molecules were located on the mesopore walls and inside micropores of the mesopore walls. When SBA-15 was loaded by slurrying it in a diluted itraconazole solution from which the solvent was evaporated, the itraconazole molecules ended up in the mesopores that they plugged locally. At a loading of 30 wt %, itraconazole exhibited intermolecular interactions inside the mesopores revealed by UV spectroscopy and endothermic events traced with DSC. The physical mixing of itraconazole and SBA-15 powder followed by heating above the itraconazole melting temperature resulted in formulations in which glassy itraconazole particles were deposited externally on the SBA-15 particles. Loading with ibuprofen was successful with each of the three loading procedures. Ibuprofen preferably is positioned inside the micropores. In vitro release experiments showed fast release kinetics provided the drug molecules were evenly deposited over the mesoporous surface.     

Controlled synthesis, characterization, and catalytic properties of Mn(2)O(3) and Mn(3)O(4) nanoparticles supported on mesoporous silica SBA-15

A method established in the present study has proven to be effective in the synthesis of Mn(2)O(3) nanocrystals by the thermolysis of manganese(III) acetyl acetonate ([CH(3)COCH=C(O)CH(3)](3)-Mn) and Mn(3)O(4) nanocrystals by the thermolysis of manganese(II) acetyl acetonate ([CH(3)COCH=C(O)-CH(3)](2)Mn) on a mesoporous silica, SBA-15. In particular, Mn(2)O(3) nanocrystals are the first to be reported to be synthesized on SBA-15. The structure, texture, and electronic properties of nanocomposites were studied using various characterization techniques such as N2 physisorption, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results of powder XRD at low angles show that the framework of SBA-15 remains unaffected after generation of the manganese oxide (MnO(x)) nanoparticles, whereas the pore volume and the surface area of SBA-15 dramatically decreased as indicated by N2 adsorption-desorption. TEM images reveal that the pores of SBA-15 are progressively blocked with MnO(x) nanoparticles. The formation of the hausmannite Mn(3)O(4) and bixbyite Mn(2)O(3) structures was clearly confirmed by XRD. The surface structures of MnO(x) were also determined by LRS, XPS, and TPR. The crystalline phases of MnO(x) were identified by LRS with corresponding out-of-plane bending and symmetric stretching vibrations of bridging oxygen species (M-O-M) of both MnO(x) nanoparticles and bulk MnO(x). We also observed the terminal Mn=O bonds corresponding to vibrations at 940 and 974 cm-1 for Mn(3)O(4)/SBA-15 and Mn(2)O(3)/SBA-15, respectively. These results show that the MnO(x) species to be highly dispersed inside the channels of SBA-15. The nanostructure of the particles was further identified by the TPR profiles. Furthermore, the chemical states of the surface manganese (Mn) determined by XPS agreed well with the findings of LRS and XRD. These results suggest that the method developed in the present study resulted in the production of MnO(x) nanoparticles on mesoporous silica SBA-15 by controlling the crystalline phases precisely. The thus-prepared nanocomposites of MnO(x) showed significant catalytic activity toward CO oxidation below 523 K. In particular, the MnO(x) prepared from manganese acetyl acetonate showed a higher catalytic reactivity than that prepared from Mn(NO(3))2.     

Carboxylic groups in mesoporous silica and ethane-bridged organosilica: effect of the surface on the reactivity

Proton-donor ability of carboxylic groups incorporated by co-condensation into SBA-15 and ethane-bridged periodic mesoporous organosilica (PMO) has been studied through IR spectroscopy by dosing ammonia, which forms reversibly COO(-) groups and NH(4)(+) ions. The related equilibrium constants, determined by elaboration of IR data, reveal a lower reactivity of -COOH groups at the surface of PMO than on SBA-15, when the two samples have been outgassed at the same temperature. This finding is interpreted in terms of different dielectric constants and intermolecular interactions engaged with the surface species. Carboxylic groups on ethane-bridged organosilica react with silanols upon thermal treatment at 473 K to form a mixed anhydride species Si-O-C(O)-, at variance with the same groups on SBA-15.     

原位还原法制备SBA-15介孔分子筛负载纳米银颗粒

利用一种温和的还原剂六亚甲基四胺(HMT)通过一步合成的方法制备了介孔Ag/SBA-15分子筛, 采用粉末X射线衍射(XRD)、透射电镜(TEM)和氮气吸附/脱附等手段对样品进行了表征. 样品的比表面积为525 m²/g, 平均孔径为5.4 nm. 用XPS、广角XRD和高分辨TEM等手段证实样品中的银为金属态的纳米颗粒. 研究结果表明, 以六亚甲基四胺为还原剂通过原位还原的方法能使银纳米颗粒较好地分散到介孔材料的孔道中.     

Iron oxide nanoparticles within the pore system of mesoporous SBA-15 in different acidity: the synthesis and characterization

Direct hydrothermal method is employed for incorporating iron into the pore structure of SBA-15. The resultant materials were analyzed by X-ray diffraction (XRD) patterns, N₂ sorption isotherm and X-ray photoelectron spectroscopy (XPS). The characterizations of XRD patterns and XPS revealed that iron nanoparticles were present as highly dispersed nanoclusters in the well-ordered mesoporous channels of SBA-15. The characterizations of t-plot reveal only microporous channels of SBA-15 are confirmed to be filled with iron nanoparticles, leaving the mesopores unaffected. The supported material still maintained its ordered mesoporous structure similar to SBA-15 and possessed high surface area, large pore volume and uniform pore size.     

Preparation,characterization, and luminescence of (SBA-15) immobilized pepsin

SBA-15 mesoporous silica was synthesized by hydrothermal method and its surface was methylated by treatment with methyltrimethoxysilane. Pepsin was immobilized on the obtained materials giving host-guest composite materials (SBA-15)-pepsin and (methylated SBA-15)-pepsin. The optimum conditions for preparation of these materials were established. Methylated SBA-15 (M-SBA-15) has improved immobilization efficiency of enzyme compared to initial SBA-15 silica. It was shown that with the gradual increase of NaCl solution ionic strength the immobilized amount of enzyme was reduced. Powder X-ray diffraction and Fourier transform infrared spectroscopy showed that the host frameworks in the prepared host-guest composite materials are intact and the ordered structure was retained. Scanning electron microscopic studies revealed fibrous morphologic characteristics of the SBA-15 and the immobilized pepsin composite materials. The average particle diameter of (SBA-15)-pepsin composite was 338 ± 10 and 343 ± 10 nm for (M-SBA-15)-pepsin. The low temperature N₂ adsorption-desorption study at 77 K showed that the pore sizes and specific surface areas of the host-guest composite materials were smaller than those before the introduction of the enzyme, suggesting that the immobilized enzyme occupied a definite position in the host material pore channels. The UV-vis solid diffuse reflectance and luminescence studies showed that the enzyme was successfully immobilized on to the host material and that after the immobilization of enzyme on SBA-15 the conformation of pepsin macromolecule has not been changed.     

丙烯腈-衣康酸基纳米纤维纱线的热稳定及碳化研究

碳纳米纤维主要以聚丙烯腈(PAN)作为前驱体,通过纺丝、热稳定、碳化等后处理工艺制备而得.但是,PAN基纳米纤维取向度低、致密性差,热稳定后环化度低,碳化后导电性差等缺点阻碍其在高性能碳纳米纤维领域的发展.因此,在PAN分子链中引入衣康酸(IA),通过溶液聚合法合成了P(AN-co-IA)共聚物并通过静电纺丝法制备了P...     

Highly Porous Amidoximed Carbon Nanofibers Supported Palladium(0) Nanoparticle Catalyzed Heck Reaction

Highly porous amidoximed carbon nanofibers(AOCNFs), which were fabricated via a conventional electrospinning technique followed by chemically modification, impregnation-reduction and carbonization process, had been used for the immobilization of palladium nanoparticles(Pd NPs) catalyst. During the carbonization process, polystyrene(PS) was selectively decomposed from bicomponent fibers, generating porous fibers. Fourier transform infrared spectroscopy(FTIR) result revealed the functional groups on PAN-PS fibers(PAN=polyacrylonitrile), AOPAN-PS fibers and AOCNFs; scanning electron microscopy(SEM) was used to observe the morphology of all stages of nanofibers; transmission electron microscopy(TEM) result gave the structure of through-hole morphology clearly visible and the dispersion of Pd NPs on the surface of nanofibers; and X-ray photoelectron spectra(XPS) confirmed that Pd nanoparticles on the surface of AOCNFs was of the metallic state. Moreover, the as-prepared catalyst exhibited high catalytic activity and efficient recycle for Heck coupling reactions between iodobenzene and acrylates.     

CuO-SBA-15的表面酸性对燃料油吸附脱硫的影响

固相研磨法是将不同量的活性组分掺入到介孔材料上的一种简单有效的方法.采用该法以焙烧脱模前后的SBA-15为载体分别制备了不同负载量的CuO-SBA-15吸附剂.利用X射线衍射(XRD)、N2物理吸附、傅里叶变换红外(FTIR)等方法表征了吸附剂的物理性质.通过原位红外技术考察了改性前后介孔材料表面羟基的变化.借助吡啶-原位傅里叶变换红外(py-FTIR)技术考察了吸附剂表面的酸类型及相对酸量.采用静态吸附实验评价了吸附剂对催化裂化(FCC)燃料油的吸附脱硫性能.结果表明:CuO是与SBA-15表面的Si―OH结合形成[Si-O-Cu-O-Si]交联从而达到分散的目的;以SBA-15介孔材料(APS)为载体能够有效抑制在焙烧过程中介孔材料表面羟基的缩合,且CuO负载量达到3mmo·lg-1时仍能够均匀分散在载体SBA-15上,而采用焙烧脱模的SBA-15(CS)为载体制备的CuO-SBA-15吸附剂却出现了活性组分团聚现象;吸附剂的酸性与脱硫性能均随着CuO的增加出现先增加后降低的趋势,当CuO负载量达到3mmo·lg-1时吸附剂具有最高的Lewis酸(L酸)酸量及最佳的脱硫性能;吸附剂的L酸酸量与其脱硫性能成正相关关系;另外吸附剂的L酸的形成是由于改性后Cu周围的电荷密度降低引起的.     

Carbon-nitrogen place exchange on NO exposed beta-Mo2C

Atomic nitrogen and oxygen were deposited on beta-Mo(2)C through dissociative adsorption of NO. Reflectance absorbance infrared spectroscopy (RAIRS), thermal desorption, and synchrotron X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the interplay between atomic nitrogen, carbon, and oxygen in the 400-1250 K region. The combination of the high resolution and high surface sensitivity offered by the synchrotron XPS technique was used to show that atomic nitrogen displaces interstitial carbon onto the carbide surface. Thermal desorption measurements show that the burnoff of the displaced carbon occurs at approximately 890 K. The incorporation of nitrogen into interstitial sites inhibits oxygen dissolution into the bulk. RAIRS spectroscopy was used to identify surface oxo, terminal oxygen, species formed from O(2) and NO on beta-Mo(2)C.     

The composition and structure of Pd-Au surfaces

Pd, Au, and Pd-Au mixtures were deposited via physical vapor deposition onto a Mo(110) substrate, and the surface concentration and morphology of the Pd-Au mixtures were determined by low-energy ion scattering spectroscopy (LEISS), infrared absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Pd-Au mixtures form a stable alloy between 700 and 1000 K with substantial enrichment in Au compared to the bulk composition. Annealing a 1:1 Pd-Au mixture at 800 K leads to the formation of a surface alloy with a composition Au(0.8)Pd(0.2) where Pd is predominantly surrounded by Au. The surface concentration of this isolated Pd site can be systematically controlled by altering the bulk Pd-Au alloy concentration.     

Effect of the concentration of aluminum on the adsorption,texture, and structure characteristics of a mesoporous mineral mesophase of the SBA-15 type

The effect of Al ion implantation on the properties of mesoporous aluminosilicate mineral phases of the SBA-15 type was studied. The implantation of Al was performed immediately under conditions of the synthesis of SBA-15 in a weakly acidic medium (pH ～ 2.9). It was found that, under these conditions, the amount of Al that can be implanted into the SBA-15 framework is limited (a maximum of 7.2 mol %). According to XPS data, aluminum ions were implanted into the matrix of silica rather than occurring on the surface as an individual phase. The study of nitrogen adsorption at 77 K and the results obtained by X-ray diffractometry and high-resolution electron microscopy suggest that Al-SBA-15 materials exhibited a hexagonal structure of channel pores of the same diameter of 8.3 nm, and the unit cell parameter was 12.3 nm. The degree of crystallinity of the material increased with the concentration of Al.     

不同助剂对CuO-ZnO/SBA-15催化CO_2加氢制甲醇性能影响的研究

以硅质骨架结构介孔分子筛SBA-15为载体,采用浸渍法合成CuO-ZnO/SBA-15(CZ/SBA-15)、CuO-ZnO-MnO_2/SBA-15(CZM/SBA-15)、CuO-ZnO-ZrO_2/SBA-15(CZZ/SBA-15)三组多孔催化剂,在固定床反应器上评价了各组催化剂催化CO_2加氢合成甲醇的性能,同时结合N_2吸附-脱附(BET)、X射线衍射(XRD)、H_2程序升温还原(H_2-TPR)、程序升温脱附(H_2-TPD、CO_2-TPD)、N_2O滴定、X射线光电子能谱(XPS)、透射电子显微镜(TEM)等表征研究了不同助剂对CO_2催化加氢制甲醇的影响。结果表明,催化剂中的金属氧化物改变了SBA-15分子筛载体的孔径大小和比表面积;催化剂CuO-ZnO-MnO_2/SBA-15、CuO-Zn O-ZrO_2/SBA-15中铜的分散度(D_(Cu))和比表面积(A_(Cu))更大,表面CuO粒径更小,更易被还原;相比Mn-O簇,Zr-O簇为增强了碱性位点,提高了甲醇选择性。此外,CuO-ZnO-ZrO_2/SBA-15具有更高的氧空位浓度,催化活性更好,其甲醇选择性为25.02%,与CuO-ZnO/SBA-15、CuO-ZnO-Mn O_2/SBA-15相比分别提高了28%和136.9%,催化效果最好。     

Ni-W Catalysts Supported on Mesoporous SBA-15: Trace W Steering CO2 Methanation

Aseries of Ni-W catalysts supported on mesoporous SBA-15 with different Ni:W ratios(Ni_xW/SBA-15, Ni-5%, x=1,10,50) was prepared and fully characterized by powder X-ray diffraction(PXRD), Brunner-Emmet-Teller(BET), transmission electronic microscopy(TEM), H₂-temperature programmed reduction(H₂-TPR), and X-ray photoelectron spectroscopy(XPS). High-resolution TEM images, XPS measurements, H₂-TPR experiments coupled with PXRD results determined the evolution of Ni and W species. It is found that a trace amount of W from H₂WO₄ can significantly improve Ni dispersion on SBA-15 (Ni₅₀W/SBA-15) with Ni⁰ andnon-stoichiometric WO_x species as small as ca. 3.6 nm. The prepared Ni_xW/SBA-15 was utilized for CO₂ hydrogenation, which showed that a higher W content restrained the CO₂ hydrogenation while a lower W ratio promoted both conversion rate and selectivity for methane compared with Ni/SBA-15. The Ni₅₀W/SBA-15 catalyst showed the best performance with a 93.3% CO₂ conversion rate and 99.7% selectivity for methane at 400 ^oC under 0.1 MPa and maintained ca. 97% initial performance for 24 h. Tracking product evolution experiments by in-situ Fourier transform infrared spectrascopy(FTIR) indicated that a small amount of W can modify the surface of Ni particles by geometric coverage and electronic modification, which facilitates the adsorption of the CO intermedia and results in the formation of CH₄. This work provides a new clue to fabricating efficient CO₂ conversion bimetallic materials.     

Co-Ni2P/SBA-15/Cordierite整体式催化剂的制备及其二苯并噻吩加氢脱硫性能

用共浸渍法制备了Co-Ni2P/SBA-15前躯体,将其调制成活性胶后均匀涂覆到预处理后的堇青石载体上,程序升温还原后制备了一系列Co-Ni2P/SBA-15/堇青石整体式催化剂。采用XRD、N2吸脱附和XPS等对催化剂进行了表征,以1 wt%二苯并噻吩(DBT)/十氢萘溶液为模型化合物,在微型固定床反应器上对催化剂的加氢脱硫(HDS)性能进行了评价。结果表明,不同Co含量的Co-Ni2P/SBA-15/堇青石整体式催化剂中都形成了Ni2P相。Co的加入提高Ni2P/SBA-15/堇青石催化剂的比表面积和孔体积。Co含量为0.55wt%的Co-Ni2P/SBA-15/堇青石整体式催化剂有最好的二苯并噻吩加氢脱硫活性,在380℃,二苯并噻吩转化率能够达到98.8%。Co的加入能够提高二苯并噻吩直接加氢脱硫产物联苯的选择性。     

Synthesis and characterization of mesoporous SBA-15/propranolol hydrochloride for controlled drug release study

Propranolol hydrochloride was incorporated into SBA-15 mesoporous material host by impregnation method to obtain host-guest nanocomposite material (SBA-15)-propranolol hydrochloride. By spectrophotometry, the amount of propranolol hydrochloride assembly was determined to be 382.05?mg/g (drug/SBA-15). Powder X-ray diffraction test results indicated that during the process of incorporation the framework of the molecular sieve was not destroyed and the molecular sieve still remained its structure ordering. Fourier transform infrared spectra showed that the framework of the prepared host-guest material was remained in good condition. Low-temperature nitrogen adsorption-desorption at 77?K results showed that the surface area and the pore volume of (SBA-15)-propranolol hydrochloride host-guest material decreased compared to those of the host molecular sieve, indicating that propranolol hydrochloride guest molecules have partially occupied the channels of the molecular sieve. Transmission electron microscopy and scanning electron microscopy results indicated that two-dimensional hexagonal mesoporous pore channels of the molecular sieve were retained and (SBA-15)-propranolol hydrochloride composite material remained fibrous crystals and the average diameter of sample was 336?nm. It was discovered in drug release principle in the simulated body fluid that the effective release time of the drug reached 30?h and the maximum cumulative released amount of propranolol hydrochloride was 99.3?%. When drug release time arrived at 5?h in the simulated gastric juice, the maximum cumulative released amount was 51.2?%.When drug release time arrived at 9?h in the simulated intestinal fluid, the maximum cumulative released amount was 70.1?%. The drug sustained release results showed that SBA-15 is a well-controlled drug release carrier.     

Structural and sorption properties of carbon replicas obtained by matrix carbonization of organic precursors in SBA-15 and KIT-6

We have carried out a comparative study of matrix carbonization of some organic precursors (sucrose, polydivinylbenzene, polyphenol-formaldehyde, polyacrylonitrile, acetonitrile) in SBA-15 and KIT-6 silica mesoporous molecular sieves. We have shown that carbon mesoporous molecular sieves of the CMK-8 type, obtained in KIT-6 mesopores, have better adsorption characteristics due to the features of the three-dimensional cubic structure, the larger pore volume and thickness of the walls of the framework. The maximum micropore volume is observed in CMK-3 and CMK-8, obtained by carbonization of polyphenol-formaldehyde and polydivinylbenzene, while the greatest specific surface area is observed on carbonization of sucrose, where the maximum hydrogen adsorption capacity is achieved at a level of ∼1.4 wt.% (77 K, 1 atm). We show that the mesopore surface coverage by hydrogen in carbon mesoporous molecular sieves increases as the degree of graphitization increases.     

Functionalized SBA-15 materials as carriers for controlled drug delivery: influence of surface properties on matrix-drug interactions

Mesoporous SBA-15 materials were functionalized with amine groups through postsynthesis and one-pot synthesis, and the resulting functionalized materials were investigated as matrixes for controlled drug delivery. The materials were characterized by FTIR, N(2) adsorption/desorption analysis, zeta potential measurement, XRD, XPS, and TEM. Ibuprofen (IBU) and bovine serum albumin (BSA) were selected as model drugs and loaded onto the unmodified and functionalized SBA-15. It was revealed that the adsorption capacities and release behaviors of these model drugs were highly dependent on the different surface properties of SBA-15 materials. The release rate of IBU from SBA-15 functionalized by postsynthesis is found to be effectively controlled as compared to that from pure SBA-15 and SBA-15 functionalized by one-pot synthesis due to the ionic interaction between carboxyl groups in IBU and amine groups on the surface of SBA-15. However, SBA-15 functionalized by one-pot synthesis is found to be more favorable for the adsorption and release of BSA due to the balance of electrostatic interaction and hydrophilic interaction between BSA and the functionalized SBA-15 matrix.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Characterization and acidic properties of Al-SBA-15 materials prepared by post-synthesis alumination of a low-cost ordered mesoporous silica

A series of Al-containing SBA-15 type materials with different Si/Al ratio, were prepared by post-synthesis modification of a pure highly ordered mesoporous silica SBA-15 obtained by using sodium silicate as silica source, and amphiphilic block copolymer as structure-directing agent. A high level of aluminum incorporation was achieved, reaching an Si/Al ratio of up to 5.5, without any significant loss in the textural properties of SBA-15. These materials were fully characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ²⁷Al NMR spectroscopy, and N₂ adsorption at 77 K. The acid properties of these materials have been evaluated by NH₃-TPD, adsorption of pyridine and deuterated acetonitrile coupled to FTIR spectroscopy. The effective acidity of these materials was evaluated using two catalytic reactions: 2-propanol dehydrogenation and 1-butene isomerization. The adsorption of basic probe molecules and the catalytic behavior revealed an evolution of the acid properties with the Al content. These studies have shown that the Al-SBA-15 materials contain Brønsted and Lewis acid sites with medium acidity which makes them appropriate to be used as acid catalysts in heterogeneous catalysis, catalytic supports, and adsorbents.