Electrochemical behavior of two and one electron redox systems adsorbed on to micro- and mesoporous silicate materials: Influence of the channels and the cationic environment of the host materials

Electrochemical behavior of two electron redox system, phenosafranine (PS⁺) adsorbed on to micro- and mesoporous materials is investigated by cyclic voltammetry and differential pulse voltammetry using modified micro- and mesoporous host electrodes. Two redox peaks were observed when phenosafranine is adsorbed on the surface of microporous materials zeolite-Y and ZSM-5. However, only a single redox peak was observed in the modified electrode with phenosafranine encapsulated into the mesoporous material MCM-41 and when adsorbed on the external surface of silica. The observed redox peaks for the modified electrodes with zeolite-Y and ZSM-5 host are suggested to be primarily due to consecutive two electron processes. The peak separation ΔE and peak potential of phenosafranine adsorbed on zeolite-Y and ZSM-5 were found to be influenced by the pH of the electrolyte solution. The variation of the peak current in the cyclic voltammogram and differential pulse voltammetry with scan rate shows that electrodic processes are controlled by the nature of the surface of the host material. The heterogeneous electron transfer rate constants for phenosafranine adsorbed on to micro- and mesoporous materials were calculated using the Laviron model. Higher rate constant observed for the dye encapsulated into the MCM-41 indicates that the one-dimensional channel of the mesoporous material provides a more facile micro-environment for phenosafranine for the electron transfer reaction as compared to the microporous silicate materials. The stability of the modified electrode surface was investigated by multisweep cyclic voltammetry.     

Synthesis of MCM-41 nanoparticles from stem of common reed ash silica and their application as substrate in electrooxidation of methanol

In this work, stem of common reed ash (SCRA) is introduced as a new source of silica in the preparation of mesoporous materials. Mesoporous silicate MCM-41 nanoparticles were synthesized hydrothermally using sodium silicate prepared from SCRA as a silica source. The characterization of MCM-41was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N\(_{2}\) adsorption/desorption (BET) and transmission electron microscopy (TEM). SEM shows that MCM-41 nanoparticles are sphere-like with size in the range of 30–50 nm with some degree of agglomeration. TEM image of the synthesized sample shows the open framework structure of MCM-41. A type IV isotherm can be observed from adsorption/desorption curves, which is the characteristic of mesoporous materials. The prepared MCM-41 nanoparticles were used as substrate to facilitate the oxidation of methanol through the modification with an electroactive species. The modification was achieved by impregnation of MCM-41 pores with \(\hbox {Ni}^{2+}\) ions (Ni-doped MCM-41). A modified carbon paste electrode (CPE) was prepared by mixing Ni-doped MCM-41 with carbon paste (NiMCM-41CPE). Cyclic voltammetry of NiMCM-41CPE shows an increment in current density of methanol oxidation in comparison with CPE in alkaline solution. Moreover, a decrease in the overpotential of methanol oxidation occurred on the surface of modified electrode. The effects of some parameters such as scan rate and methanol concentration are also investigated on the behaviour of NiMCM-41CPE. Also, the heterogeneous electron transfer rate for the catalytic reaction (k) of methanol is calculated.     

Electrochemical sensor for detecting ultratrace nitroaromatic compounds using mesoporous SiO2-modified electrode

An electrochemical sensor for ultratrace nitroaromatic compounds (NACs) using mesoporous SiO2 of MCM-41 as sensitive materials is reported. MCM-41 was synthesized and characterized by scanning electron microscope, transmission electron microscopy, and small-angle X-ray diffraction. Glassy carbon electrodes modified with MCM-41 show high sensitivity for cathodic voltammetric detection of NACs (including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrotoluene, and 1,3-dinitrobenzene) down to the nanomolar level. The high sensitivity is attributed to the strong adsorption of NACs by MCM-41 and large surface area of the working electrode resulting from MCM-41 modification. The voltammetric response is fast, and the detection of NACs can be finished within 14 s. SiO2 nanospheres were similarly used to modify glassy carbon electrodes for electrochemical detection of TNT and TNB. The detection limit of SiO2 nanosphere-modified electrodes is lower than that of MCM-41-modified electrodes, possibly due to the smaller surface area of SiO2 nanospheres than mesoporous MCM-41. The results show mesoporous SiO2-modified glassy carbon electrodes, particularly MCM-41-modified electrodes, open new opportunities for fast, simple, and sensitive field analysis of NACs.     

Influence of functional silanes on hydrophobicity of MCM-41 synthesized from rice husk

Mesoporous molecular sieve MCM-41 was synthesized from rice husk and rice husk ash, called RH-MCM-41 and RHA-MCM-41. The sol–gel mixtures were prepared with molar composition of 1.0 SiO₂: 1.1 NaOH: 0.13 CTAB: 0.12 H₂O. After calcination, the polarity of MCM-41 still remained on its surface due to the existence of some silanol groups. In this study, both RH-MCM-41 and RHA-MCM-41 were silylated with two different functional silanes trimethylchlorosilane (TMCS) and phenyldimethylchlorosilane (PDMS) in order to reduce the surface polarity. The efficiency of silylation was determined based on the amount of moisture adsorbed using thermogravimetric analysis (TGA). The structure of silylating agents and silica templates were found to be important parameters affecting the hydrophobic property of the MCM-41 surface. The post-grafting silylation with aliphatic silane can decrease the surface polarity better than that with aromatic silane, probably due to less sterric hindrance effect. Thus, the surface hydrophobicity of MCM-41 can be improved by the silylation of small molecular silane on RH-MCM-41.     

Peroxidase catalytic cycle of MCM-41-entrapped microperoxidase-11 as a mechanism for phenol oxidation

The encapsulation of microperoxidases (MPs) into molecular sieves with controlled pore size, such as the mesoporous silica MCM-41, represents a nanotechnology strategy to control the catalytic properties of MPs and mimic the enzymatic activity of hemoproteins. In this work, the ferric microperoxidase-11 (MP-11), obtained from trypsin-catalyzed hydrolysis of horse-heart cytochrome c, was entrapped in MCM-41, thus resulting in a catalyst (Fe(III)MP11MCM41) with catalase and monooxygenase properties. The entrapment of MP-11 inside MCM-41 was confirmed by elemental analysis and UV-visible spectrum, with a red shift in the Soret band indicating that the heme group was in a hydrophobic microenvironment. Similarly to catalase, the catalyst Fe(III)MP11MCM41 exhibited specificity for hydrogen peroxide to be converted to a high-valence oxidized intermediate, Compound II. Also mimicking catalase, the cleavage of hydrogen peroxide by MP11MCM41 resulted in O2 production detected by a Clark electrode. Phenol was able to act as reducing agent of MP11MCM41 Compound II leading to the completion of a peroxidase cycle, as confirmed by UV-visible spectrometry and EPR measurements. The analysis of the reaction products by high performance liquid chromatogram coupled to tandem mass spectrometry (HPLC/MS) revealed 2,4-dihydroxyphenol as the product of phenol oxidation by MP11MCM41. Therefore, in addition to catalase activity, the catalyst MP11MCM41 also displayed monooxygenase properties, which was possible because the MP-11 heme iron promotes homolytic cleavage of the hydrogen peroxide generating hydroxyl radicals. With such characteristics, MCM-41-entrapped MP-11 is a promising catalyst for nanobiotechnological devices.     

Synthesis and characterization of mesoporous Si-MCM-41 materials and their application as solid acid catalysts in some esterification reactions

Mesoporous MCM-41 has been synthesized by sol–gel method at room temperature possessing good thermal stability, high surface area as well as retention of surface area at high temperature. The MCM-41 neutral framework has been modified and put to practical use by incorporating Al³⁺ in the siliceous MCM-41 framework and supporting 12-TPA (12-tungstophosphoric acid) onto MCM-41 by process of anchoring and calcination to induce Brønsted acidity in MCM-41 to yield Al-MCM-41 and 12TPA-MCM-41, respectively. The synthesized materials have been characterized for elemental analysis by ICP-AES, XRD, SEM, TEM, EDX, FT–IR and TGA. Surface area has been determined by BET method and pore size and pore size distribution determined by BJH method. Surface acidity has been evaluated by NH₃-TPD method. The potential use of Al-MCM-41 and 12TPA-MCM-41 as solid acid catalysts has been explored and compared by studying esterification as a model reaction wherein monoesters such as ethyl acetate (EA), propyl acetate (PA), butyl acetate (BA) and benzyl acetate (BzA) have been synthesized, optimizing several parameters such as catalyst amount, reaction time, reaction temperature and mole ratio of reagents.     

Molecular simulation of fluid adsorption in buckytubes and MCM-41

We report grand canonical Monte Carlo (GCMC) molecular-simulation studies of argon and nitrogen in models of two novel adsorbents, buckytubes and MCM-41. Buckytubes are monodisperse carbon tubes with internal diameters of 1–5 nm and a regular pore structure. MCM-41 is one member of a new family of highly uniform mesoporous aluminosilicates produced by Mobil. The pore size of MCM-41 can be accurately controlled within the range 1.5-I.0 nm. The adsorption of argon in a buckytube and the adsorption of nitrogen in two different MCM-41 pores are studied at 77 K. Both fluids are modeled as Lennard-Jones spheres. and an averaged fluid-wall potential, dependent only on the distance of the adsorbed molecule from the center of the tube or pore is used. Isotherms and isosteric heats are calculated. Layering transitions and a hysteresis loop are observed for the buckytube and good agreement is found between simulated and experimental isotherms for the MCM-41 systems.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

磁性MCM-41分离回收RT培司废水中四甲基氢氧化铵的研究

硝基苯法合成RT培司(4-氨基二苯胺)的废水色度高、组分复杂、催化剂四甲基氢氧化铵(TMAOH)难以分离回收。提出采用磁性MCM-41对RT培司废水中有机副产物进行选择性吸附分离。制备的磁性MCM-41样品采用X射线衍射仪(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、N₂吸附-脱附和振动样品磁场计(VSM) 等手段进行表征。结果表明, 磁性MCM-41颗粒的粒径范围为200~300 nm, BET比表面积约为655.2 m²/g, 孔径分布为0.5~4 nm, 内核铁酸镍的存在使磁性MCM-41具有超顺磁性。吸附研究表明磁性MCM-41对RT培司废水中吩嗪、偶氮苯和苯胺等有机物具有良好吸附作用, 经5次吸附磁分离后, RT培司废水中四甲基氢氧化铵能够达到回用要求, 吸附后的磁性MCM-41在外加磁场下极易分离。     

Preparation and use of chemically modified MCM-41 and silica gel as selective adsorbents for Hg(II) ions

Adsorbents for Hg(II) ion extraction were prepared using amorphous silica gel and ordered MCM-41. Grafting with 2-(3-(2-aminoethylthio)propylthio)ethanamine was used to functionalize the silica. The functionalized adsorbents were characterized by nitrogen adsorption, X-ray diffraction, 13C MAS NMR spectroscopy and thermogravimetric analysis. The adsorption properties of the modified silica gel and MCM-41 were compared using batch method. The effect of pH, stirring time, ionic strength and foreign ions were studied. The extraction of Hg(II) ions occurred rapidly with the modified MCM-41 and the optimal pH range for the extraction by the modified materials was pH 4-7. Foreign ions, especially Cl- had some effect on the extraction efficiency of the modified silica gel and the modified MCM-41. The adsorption behavior of both adsorbents could be described by a Langmuir model at 298 K, and the maximum adsorption capacity of the modified silica gel and MCM-41 at pH 3 was 0.79 and 0.70 mmol g(-1), respectively. The modified MCM-41 showed a larger Langmuir constant than that of the modified silica gel, indicating a better ability for Hg(II) ion adsorption. The results indicate that the structure of the materials affects the adsorption behavior. These materials show a potential for the application as effective and selective adsorbents for Hg(II) removal from water.     

用稻壳灰为硅源合成有序介孔二氧化硅材料的研究

用稻壳灰为硅源,用十六烷基三甲基溴化铵作为模板剂,在酸性或碱性条件下均成功地合成了有序介孔SiO2材料MCM-41.利用XRD、N2吸附曲线、SEM、TEM等测试方法分别对稻壳灰及介孔SiO2样品进行了表征.结果表明,稻壳灰为非晶体,呈粒状的多孔结构,其比表面积为250m2/g;在酸性条件下合成的MCM-41具有周期性规则排列的介孔结构,最可几孔径为2.4nm,比表面积为1100m2/g.     

Chemical fluid deposition of monometallic and bimetallic nanoparticles on ordered mesoporous silica as hydrogenation catalysts

A simple and green method of depositing monometallic (Ru, Rh, Pd) and bimetallic nanoparticles (Ru-Rh, Ru-Pd and Rh-Pd) on an ordered mesoporous silica support (MCM-41) in supercritical carbon dioxide (scCO2) is described. Metal acetylacetonates were used in the experiments as CO2-soluble metal precursors. Suitable temperature and pressure conditions for synthesizing each kind of nanoparticles were applied in this study. The characterizations of these nanocomposites were performed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The nanoparticles had average sizes varying from 2 nm to 8 nm. The Ru nanoparticles were clearly shown to be inside the mesopores of MCM-41 from the TEM image. These nanocomposites used as catalysts for hydrogenation was demonstrated. The efficiency of the scCO2 prepared Ru/MCM-41 catalyst was nearly 8 times than that of a Ru/MCM-41 catalyst prepared by conventional impregnation method.     

The investigation of MCM-48-type and MCM-41-type mesoporous silica as oral solid dispersion carriers for water insoluble cilostazol

Objective: To explore the suitable application of MCM-41 (Mobil Composition of Matter number forty-one)-type and MCM-48-type mesoporous silica in the oral water insoluble drug delivery system.

Methods: Cilostazol (CLT) as a model drug was loaded into synthesized MCM-48 (Mobil Composition of Matter number forty-eight) and commercial MCM-41 by three common methods. The obtained MCM-41, MCM-48 and CLT-loaded samples were characterized by means of nitrogen adsorption, thermogravimetric analysis, ultraviolet-visible spectrophotometry, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry and powder X-ray diffractometer.

Results: It was found that solvent evaporation method was preferred according to the drug loading efficiency and the maximum percent cumulative drug dissolution. MCM-48 with 3D cubic pore structure and MCM-41 with 2D long tubular structure are nearly spherical particles in 300–500?nm. Nevertheless, the silica carriers with similar large specific surface areas and concentrating pore size distributions (978.66?m²/g, 3.8?nm for MCM-41 and 1108.04?m²/g, 3.6?nm for MCM-48) exhibited different adsorption behaviors for CLT. The maximum percent cumulative drug release of the two CLT/silica solid dispersion (CLT-MCM-48 and CLT-MCM-41) was 63.41% and 85.78% within 60?min, respectively; while in the subsequent 12?h release experiment, almost 100% cumulative drug release were both obtained. In the pharmacokinetics aspect, the maximum plasma concentrations of CLT-MCM-48 reached 3.63?mg/L by 0.92?h. The AUC_0–∞ values of the CLT-MCM-41 and CLT-MCM-48 were 1.14-fold and 1.73-fold, respectively, compared with the commercial preparation.

Conclusion: Our findings suggest that MCM-41-type and MCM-48-type mesoporous silica have great promise as solid dispersion carriers for sustained and immediate release separately.     

配合物[Fe(bipy)2]3+修饰的MCM-41的合成与表征

以γ－氨丙基修饰介孔分子筛ＭＣＭ－４１内孔壁,将引入的γ－氨丙基与金属配位离子［Ｆｅ（ｂｉｐｙ）_２］^３＋通过配位键首次合成了金属配位化合物修饰的ＭＣＭ－４１（ＭＣＭ－ａｐ－Ｆｅ（ｂｉｐｙ）_２）．通过ＸＲＤ,７７Ｋ氮气吸附－脱附曲线,固体ＵＶ－ｖｉｓ漫反射光谱和循环伏安曲线表征了复合物ＭＣＭ－ａｐ－Ｆｅ（ｂｉｐｙ）_２。由于［Ｆｅ（ｂｉｐｙ）_２］^３＋的引入,使 ＭＣＭ－ａｐ－Ｆｅ（ｂｉｐｙ）_２的结晶度降低, ＢＥＴ比表面积、孔容和最可几孔径急剧下降．γ－氨丙基与Ｆｅ^３＋的配位而使其ＵＶ－ｖｉｓ漫反射吸收光谱与ＭＣＭ－Ｆｅ（ｂｉｐｙ）_２不同;循环伏安特性曲线表明ＭＣＭ－ａｐ－Ｆｅ（ｂｉｐｙ）_２在电化学上比浸渍法制备的ＭＣＭ－Ｆｅ（ｂｉｐｙ）_２稳定．     

Dielectric spectroscopy of nano BaTiO3 confined in MCM-41 mesoporous molecular sieve materials.

Dielectric properties of barium titanate (BaTiO3) particles, synthesized directly in the pores of MCM-41 materials, have been investigated in the frequency range from 20 Hz to 1 MHz for temperature intervals from 100 K to 500 K. The dielectric spectra of BaTiO3 confined in these molecular sieves were compared with the results obtained from the investigation of pure MCM-41 materials. Obtained results confirmed successful incorporation of BaTiO3 into porous matrix, but no phase transition from paraelectric to ferroelectric phase was observed due to the particle size being smaller than the critical size. Also, the overall dielectric response of investigated materials is strongly influenced by adsorbed water molecules.     

Ni and Cu incorporated mesoporous nanocomposite catalytic materials

Nickel and copper incorporated MCM-41-like mesoporous nanocomposite materials prepared by the direct hydrothermal synthesis and the impregnation procedures showed highly attractive pore structure and surface area results for catalytic applications. The XRD patterns showed that characteristic MCM-41 structure was preserved for the materials synthesized following an impregnation procedure before the calcination step. The surface area of the Cu impregnated material with a quite high Cu/Si atomic ratio (0.19) was 631 m2/g. Very narrow pore size distributions with an average pore diameter of about 2.7 nm were obtained as a result of plugging of some of the smaller pores by Cu nanoballs. For lower metal to Si ratios (for instance for Ni/Si = 0.06) much higher surface area values (1130 m2/g) were obtained. In the case of nanocomposite materials synthesized by the direct hydrothermal route, MCM-41 structure was not destroyed for samples containing metal to Si atomic ratios as high as 0.12. In the case of materials containing Cu/Si and Ni/Si ratios over 0.2 wider pore size distributions and some decrease of surface area were observed.     

Preparation and characterization of epoxy composites filled with functionalized nano-sized MCM-41 particles

Mono-dispersed nano-sized MCM-41 (M (with template)) particles were synthesized by sol–gel reaction. The effect of interface modification on the properties of epoxy composites was investigated. Modifications were carried out either by substituting silanol groups on the surface or in the mesopore channels into amine (M-NH₂), calcinating mixture template in the mesopore channels (M(without template)), or recalcinating them at higher temperature to remove silanol groups (–OH) in the mesopore channels or on the surface (CM). Transmission electron micrograph results showed that the dispersing of MCM-41 nanoparticles was not influenced by the modification, while –NH₂ group indeed modified the mesopore channels or the surface of MCM-41 particle by using IR, XRD, and N₂ adsorption–desorption. In addition, tensile tests suggested that M-NH₂ nanoparticles could simultaneously provide epoxy matrix with strengthening and toughening effects. However, due to the different interfacial structures between the fillers and the matrix, the mechanical properties of the composites filled by M-NH₂ were much better than those of composites filled by MCM-41 (without template), MCM-41 (with mixture template), and CM.     

Blending effect of sucrose and surfactant templating agents on silica mesostructure

We report the blending effect of surfactant and sucrose as a nonsurfactant templating agent on the silica mesostructure. The CTAB/sucrose-templated mesoporous silica (SCS) was compared with CTAB-templated MCM-41. The MCM-41 showed spherical morphology with a particle diameter of 1.1–1.5 μm, and gave a bimodal size distribution, centered at 2.1 nm and 8.9 nm, which is assigned to hexagonally-arrayed cylindrical pores and interparticle-pores between small MCM-41 clusters, respectively. SCS gave unique and extraordinary morphology in which two different mesostructures have grown with both of them facing each other. The ordered MCM-41 pore structure clung to silica nanosphere-framed wormlike mesostructure, resulting in a bimodal pore size distribution centered at 2.1 nm and 7.0 nm. It was revealed that both of CTAB and sucrose act independently as a surfactant and a nonsurfactant template.     

Dielectric spectroscopy of Nano BaTiO/sub 3/ confined in MCM-41 mesoporous molecular sieve materials

Dielectric properties of barium titanate (BaTiO₃) particles, synthesized directly in the pores of MCM-41 materials, have been investigated in the frequency range from 20 Hz to 1 MHz for temperature intervals from 100 K to 500 K. The dielectric spectra of BaTiO₃ confined in these molecular sieves were compared with the results obtained from the investigation of pure MCM-41 materials. Obtained results confirmed successful incorporation of BaTiO₃ into porous matrix, but no phase transition from paraelectric to ferroelectric phase was observed due to the particle size being smaller than the critical size. Also, the overall dielectric response of investigated materials is strongly influenced by adsorbed water molecules     

Immobilization of lysozyme on the layered silicate RUB-15

Adsorption of lysozyme over layered silicate, denoted as RUB-15, and the modified compound RUB-15-nano have been studied. The amount of enzyme adsorbed onto RUB-15 or RUB-15-nano was smaller than that recently reported as being adsorbed onto mesoporous silicas such as MCM-41 or SBA-15. However, lysozyme adsorbed onto RUB-15-nano exhibits enzymatic activity. Lysozyme was found to be immobilized on RUB-15-nano, which was modified from the layered silicate RUB-15. RUB-15-nano may therefore be useful as an inorganic substrate to immobilize enzymes.