Catalytic activity of Co/MCM-41 and Co/SBA-15 materials in toluene oxidation

Cobalt-containing MCM-41 and SBA-15 mesoporous materials were prepared by the pH-adjusting of the impregnation solution. The modified materials were investigated by X-ray diffraction, N₂ physisorption, temperature-programmed reduction, DR UV–Vis diffuse reflectance, and FT-IR spectroscopy of adsorbed pyridine. The pH of the impregnation solution influences the surface charge of the mesoporous support and therefore determines the strength of interaction between the cobalt precursor and the mesoporous support. The formation of different cobalt oxide species in different ratios, depending on the pH of the impregnation solution, was established for both materials. The modified Co/MCM-41 and Co/SBA-15 materials were active in toluene oxidation. Their catalytic activity is predetermined by the nature, the reducibility, and the dispersion of the obtained cobalt oxide species.     

Synthesis and characterization of surface-modified and organic-functionalized MCM-41 type ordered mesoporous materials

A new and efficient method for the preparation of MCM-41 type ordered mesoporous phases using phosphate as promoter under reflux conditions is reported. The various mesoporous materials studied were: silica (Si-MCM-41), alumino-silicate (Al-MCM-41), and titanium-silicate (Ti-MCM-41). Our concept of promoter-assisted synthesis of zeolites and related microporous materials was found to be applicable in the synthesis of ordered mesoporous materials as well. The addition of small catalytic quantity of phosphate ions (PO ₄ ³⁻ ), used as promoters, significantly reduced the synthesis time (by a factor of 3–4) of all these mesoporous materials. The synthesis of new MCM-41 type organic-inorganic composite materials with unique properties is also reported.     

ZnO clusters in situ generated inside mesoporous silica

A new aqueous chemical growth method for in situ generation of ZnO clusters inside MCM-41 without modification scheme has been developed. Different from classical methods, the host MCM-41 does not need to be surface modified. Furthermore, ZnO clusters were prepared without calcinations, which could pack in the channels of mesoporous materials to produce quantum size effects. The PL emission peak was blue shifted to 420 nm.     

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.     

Tunable adsorption behavior of silica materials in the removal of dense non-aqueous phase liquids

Mesoporous silica material has dual characteristics including adsorption of organic contaminants and transport through the sediments, making it an ideal material as a platform for zerovalent iron particles in the in situ remediation of dense non-aqueous phase liquids such as trichloroethylene. In this paper, tunable adsorption behavior of silica materials was quantitatively investigated by batches of equilibrium experiments. Significant enhancement in adsorption capacity was observed on mesoporous organo-silica particles as a consequence of the functionalization of particle surface from hydrophilicity to hydrophobicity. The fact that there is a wide difference in adsorption capacities between the non-functionalized mesoporous silica (MCM-41) and the alkyl-functionalized mesoporous silica prompted a study to control adsorption levels by simply adjusting the amount of methyl triethoxysilane (MTES) precursor in a mixture of MTES and tetramethoxysilane. In comparison with the most commonly used adsorbent activated carbon, the higher yield of adsorbent of 83 ± 2.6% was observed for mesoporous methyl silica particles. Particle characterizations were performed by means of X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, Brunauer–Emmett–Teller, thermogravimetric analysis and Fourier transform infrared measurements.     

两步晶化法制备介孔材料及其催化性能研究

采用两步晶化法,由MCM-22沸石前驱体合成了一种介孔材料.通过XRD、N2吸附-脱附、TEM、27A lMAS NMR以及吡啶吸附红外光谱等技术对样品进行了表征.结果显示所合成的样品不是微孔沸石与介孔材料的混合物,而是含强酸性中心、水热稳定性良好的新型介孔分子筛.利用异丙苯的裂解反应、苯和1-十二烯烃的烷基化反应,评价了其对大分子的酸催化活性,并与常规介孔材料MCM-41进行了比较.在350℃时,所合成的介孔材料和常规介孔材料MCM-41对异丙苯的裂解转化率分别为68.98%和48.80%.在210℃苯和1-十二烯烃的烷基化反应时,所合成的介孔材料和MCM-41对1-十二烯烃的转化率分别约为95.20%和86.89%,产物直链烷基苯的选择性分别约为88.11%和90.06%.结果表明所合成的介孔材料对大分子的酸催化性能优越于常规介孔材料MCM-41.     

介孔硅酸锰镁可充镁电池正极材料的制备及其电化学性能研究

采用介孔二氧化硅MCM-41作模板和硅源, 合成了具有介孔结构的可充镁电池正极材料硅酸锰镁. 分别用XRD、SEM、TEM和氮气吸脱附测试研究了合成材料的介孔结构, 并通过循环伏安、恒电流充放电测试比较了介孔与无孔硅酸锰镁材料的电化学性能. 由于介孔材料活性表面较大, 可增加电解液与活性材料的接触, 使材料具有较多的电化学反应位. 因而, 与相应的无孔材料相比, 具有介孔结构的硅酸锰镁材料呈现出较低的充放电极化、较大的放电容量和较高的放电电压平台. 在0.25 mol/L Mg(AlCl₂EtBu)₂/THF 电解液中, 0.2 C(约62.8 mA/g)充放电速率下, 介孔硅酸锰镁材料首次放电容量可达到241.8 mAh/g, 放电平台为1.65 V ( vs Mg/Mg²⁺). 设计具有介孔结构的材料为提高可充镁电池正极的电化学性能提供了一条有效的途径.     

Synthesis and characterization of CuO containing mesoporous silica spheres

A new series of mesoporous silica spheres containing nanodispersed copper oxides were synthesized in H₂O/EtOH/ammonia solution at room temperature. The mesoporous structures were characterised using X-ray powder diffraction and N₂ adsorption-desorption techniques. Scanning electron micrograph and transmission electron micrograph revealed that the MCM-41 particles have spherical morphologies. The DTA curve of pure MCM-41 exhibited a sharp single exothermic peak between 290°C and 340°C, while a broad peak with several shoulders in the temperature range between 180°C and 380°C was observed for Cu-MCM-41, indicating the possible complexation of Cu²⁺ with surfactants adhering to the inner surfaces of the mesopores. Electron paramagnetic resonance spectra of uncalcined samples revealed that Cu²⁺ ions are in an octahedral or distorted octahedral coordination with nitrogen ligands of the surfactant while in the calcined samples they are coordinated with oxygen of the MCM-41 framework. The redox properties of samples were examined by a temperature-programmed reduction and N₂O passivation method. The results indicate that CuO with increasing particle size could be formed in the mesoporous materials with increasing Cu contents, and this decreased the reducibility of the resulting CuO.     

两步晶化法制备MCM-48/ZSM-5复合分子筛

利用两步晶化法制备了高水热稳定性的MCM48/ZSM-5介微孔复合分子筛.通过SEM、TEM、XRD、IR和N₂吸附脱附进行表征,结果显示,该材料的结构不同于简单的机械混合,而是具有微孔孔壁和三维立方介孔孔道的复合材料,其孔道尺寸为2.6nm左右.该复合分子筛在沸水中处理6h后,介孔结构仍保留完好.通过考察晶化时间对复合分子筛的影响,证明了介孔和微孔的组装是一个竞争的过程,复合分子筛中介孔与微孔结构的比例随晶化时间的变化而变化,且具有介孔孔道和微孔孔壁的复合分子筛150℃的最优晶化时间为8h.     

Steam-assisted crystallization of TPA+-exchanged MCM-41 type mesoporous materials with thick pore walls

Hierarchical MCM-41/MFI composites were synthesized through ion-exchange of as-made MCM-41 type mesoporous materials with tetrapropylammonium bromide and subsequent steam-assisted recrystallization. The obtained samples were characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis, FT-IR, ¹H–¹³C CP/MAS and nitrogen adsorption–desorption. The XRD patterns show that the MCM-41/MFI composite possesses both ordered MCM-41 phase and zeolite MFI phase. SEM and TEM images indicate that the recrystallized materials retained the mesoporous characteristics and the morphology of as-made mesoporous materials without the formation of bulky zeolite, quite different from the mechanical mixture of MCM-41 and MFI structured zeolite. Among others, lower recrystallization temperature and the introduction of the titanium to the parent materials are beneficial to preserve the mesoporous structure during the recrystallization process.     

SiC-dopped MCM-41 materials with enhanced thermal and hydrothermal stabilities

SiC-dopped MCM-41 mesoporous materials were synthesized by the in situ hydrothermal synthesis, in which a small amount of SiC was added in the precursor solvent of molecular sieve before the hydrothermal treatment. The materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ physical adsorption and thermogravimetric analysis, respectively. The results show that the thermal and hydrothermal stabilities of MCM-41 materials can be improved obviously by incorporating a small amount of SiC. The structure collapse temperature of SiC-dopped MCM-41 materials is 100 °C higher than that of pure MCM-41 according to the differential scanning calorimetry analysis. Hydrothermal treatment experiments also show that the pure MCM-41 will losses it's ordered mesoporous structure in boiling water for 24 h while the SiC-dopped MCM-41 materials still keep partial porous structure.     

Optical studies of ZSM-5 crystals infiltrated with TiO2

ZSM-5 crystals, of which granule size is about 120 µm along c axis, are employed as a good host material for TiO₂ loading. Optical microscopy photographs, X-ray powder diffraction spectra and surface area calculated from nitrogen adsorption data at − 196 °C have been carried out and show that the titanium dioxide clusters are infiltrating into the pores of ZSM-5. TiO₂/ZSM-5 host-guest material, regardless of whether being prepared by microwave and water bath heating, shows similar features except for the TiO₂ contents. The materials have a photoluminescence emission peak at 2.85 eV, which is ascribed to the band edge emission. A red shift was observed on the photoluminescence emission spectra when NH₃ adsorbed into the pores of TiO₂/ZSM-5 material.     

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.     

Electrochemical Behavior of Heteropoly Acid Anions Adsorbed in Electrodes Modified with Mesoporous Molecular Sieve Silica

Heteropoly acid H4SiW12O48 (denoted as SiW12) was assembled with the mesoporous materials MCM-41 modified with 3-aminopropyltriethoxysilane (APTES) (denote MCM-41((m))). The electrochemical behavior of SiW12/MCM-41((m)) complexes-based electrode indicated SiW12 anion was adsorbed by MCM-41((m)). In MCM-41((m)) electrode, large voltammetric waves, showing that the electrostatic bound ions adsorbed in MCM-41((m)) were electrochemically active. The potential application as amperometric sensors for nitrite is anticipated.     

Novel, benign, solid catalysts for the oxidation of hydrocarbons

The catalytic properties of two classes of solid catalysts for the oxidation of hydrocarbons in the liquid phase are discussed: (i) microporous solids, encapsulating transition metal complexes in their cavities and (ii) titanosilicate molecular sieves. Copper acetate dimers encapsulated in molecular sieves Y, MCM-22 and VPI-5 use dioxygen to regioselectively ortho-hydroxylate L-tyrosine to L-dopa, phenol to catechol and cresols to the corresponding o-dihydroxy and o-quinone compounds. Monomeric copper phthalocyanine and salen complexes entrapped in zeolite-Y oxidize methane to methanol, toluene to cresols, naphthalene to naphthols, xylene to xylenols and phenol to diphenols. Trimeric mu3-oxo-bridged Co/Mn cluster complexes, encapsulated inside Y-zeolite, oxidize para-xylene, almost quantitatively, to terephthalic acid. In almost all cases, the intrinsic catalytic activity (turnover frequency) of the metal complex is enhanced very significantly, upon encapsulation in the porous solids. Spectroscopic and electrochemical studies suggest that the geometric distortions of the complex on encapsulation change the electron density at the metal ion site and its redox behaviour, thereby influencing its catalytic activity and selectivity in oxidation reactions.Titanosilicate molecular sieves can oxidize hydrocarbons using dioxygen when loaded with transition metals like Pd, Au or Ag. The structure of surface Ti ions and the type of oxo-Ti species generated on contact with oxidants depend on several factors including the method of zeolite synthesis, zeolite structure, solvent, temperature and oxidant. Although, similar oxo-Ti species are present on all the titanosilicates, their relative concentrations vary among different structures and determine the product selectivity.     

Nonionic surfactant-templated mesoporous carbon as an electrocatalyst support for methanol oxidation

Two carbons were synthesized for use as platinum electrocatalyst supports for methanol oxidation. For both materials, furfuryl alcohol was used as the carbon precursor; however, one (CPEG) was made using poly ethylene glycol as the pore former, while the other (CSRF) was produced using Pluronic^® F127 as the soft template by organic–organic self-assembly. The CPEG and CSRF carbons were estimated from nitrogen physisorption experiments to be micro- and mesoporous, respectively. Platinum nanoparticles were deposited on each carbon as well as on Vulcan XC-72 carbon by the formic acid reduction method. The physicochemical properties of electrocatalysts were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX), and their electrochemical features were examined using cyclic voltammetry, chronoamperometry, and impedance spectroscopy. It was found that higher methanol oxidation peak current densities as well as lesser charge transfer resistance at electrode/electrolyte interface were obtained for Pt supported on CSRF as compared to those on Vulcan XC-72 carbon, owing to the higher specific surface area and larger total pore volume (696 m² g⁻¹ and 0.60 cm³ g⁻¹, respectively) together with superior electrical conductivity of mesoporous CSRF. On the other hand, the lower surface area and pore volume of microporous CPEG substrate confined Pt nanoparticles deposition and thus made CPEG-supported Pt an inefficient methanol oxidation electrocatalyst.     

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.     

Synthesis of mesoporous silica materials (MCM-41) from iron ore tailings

Highly ordered mesoporous materials were successfully synthesized by using the iron ore tailings as the silica source and n-hexadecyltrimethyl ammonium bromide as the template. The samples were detail characterized by powder X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and N₂ physisorption. The as-synthesized materials had high surface area of 527 m² g⁻¹ and the mean pore diameter of 2.65 nm with a well-ordered two-dimensional hexagonal structure. It is feasible to prepare mesoporous MCM-41 materials using the iron ore tailings as precursor.     

Laccase immobilized on methylene blue modified mesoporous silica MCM-41/PVA

The mesoporous silica sieve MCM-41 containing methylene blue (MB) provides a suitable immobilization of biomolecule matrix due to its uniform pore structure, high surface areas, good biocompatibility and nice conductivity. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the MB modified MCM-41/PVA composite film has been developed. Laccase from Trametes versicolor is assembled on a composite film of MCM-41 containing MB/PVA modified Au electrode and the electrode is characterized with respect to transmission electron microscopy (TEM) and scanning electron microscopic (SEM), Cyclic voltammetry (CV), response time, detection limit, linear range and activity of laccase. The laccase modified electrode remains good redox behavior in pH 4.95 acetate buffer solution, at room temperature in present of 0.1 mM catechol. The response time (t_90%) of the modified electrode is less than 4 s for catechol. The detection limit is 0.331 µM and the linear detect range is about from 4.0 µM to 87.98 µM for catechol with a correlation coefficient of 0.99913(S/N = 3). The apparent Michaelis–Menten (K_M^app) is estimated using the Lineweaver–Burk equation and the K_M^app value is about 0.256 mM. This work demonstrated that the mesoporous silica MCM-41 containing MB provides a novel support for laccase immobilization and the construction of biosensors with a faster response and better bioactivity.     

Silica materials recovered from photonic industrial waste powder: its extraction, modification, characterization and application

This study explored the possibility of recovering waste powder from photonic industry into two useful resources, sodium fluoride (NaF) and the silica precursor solution. An alkali fusion process was utilized to effectively separate silicate supernatant and the sediment. The obtained sediment contains purified NaF (>90%), which provides further reuse possibility since NaF is widely applied in chemical industry. The supernatant is a valuable silicate source for synthesizing mesoporous silica material such as MCM-41. The MCM-41 produced from the photonic waste powder (PWP), namely MCM-41(PWP), possessed high specific surface areas (1082 m²/g), narrow pore size distributions (2.95 nm) and large pore volumes (0.99 cm³/g). The amine-modified MCM-41(PWP) was further applied as an adsorbent for the capture of CO₂ greenhouse gas. Breakthrough experiments demonstrated that the tetraethylenepentamine (TEPA) functionalized MCM-41(PWP) exhibited an adsorption capacity (82 mg CO₂/g adsorbent) of only slightly less than that of the TEPA/MCM-41 manufactured from pure chemical (97 mg CO₂/g adsorbent), and its capacity is higher than that of TEPA/ZSM-5 zeolite (43 mg CO₂/g adsorbent). The results revealed both the high potential of resource recovery from the photonic solid waste and the cost-effective application of waste-derived mesoporous adsorbent for environmental protection.