Polyacrylamide-coated MCM-48 mesoporous silica spheres: synthesis,characterization and drug delivery study

Mesoporous type-MCM-48 silica was grafted with polyacrylamide (PAAm) by using an azo-type initiator. The effect of monomer and initiator concentrations, reaction time, and temperature were evaluated to determine the optimal grafting conditions. Functionalized MCM-48 silicas were characterized by X-ray diffraction (XRD), infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which confirmed the grafting process. According to XRD, SEM and TEM results, PAAm-modified MCM-48 silica did not show changes in its morphology and mesostructure by comparing with pristine MCM-48. Also, modified silicas were tested as delivery system using nalidixic acid as drug model. MCM-48-PAAm silicas were able to load more significant amounts of nalidixic acid than the unmodified MCM-48, and showed a sustained delivery behaviour, releasing about 80% of drug.     

Adsorption performance of mesoporous silicas towards a cationic dye. Influence of mesostructure on adsorption capacity

The dye adsorption performance of four mesoporous silicas with different structure and textural properties, MCM-41, MCM-48, SBA-15 and mesocellular silica foam (MCF), was studied and compared by using toluidine blue O (TBO) as dye model in aqueous solution. These materials were characterized by X-ray diffraction (XRD), small-angle X-ray scattering, nitrogen adsorption-desorption analyses, and transmission electron microscopy (TEM). The effect of some parameters such as adsorbent dosage, contact time, temperature, and pH on the TBO removal in aqueous solution was studied. Results showed that adsorption capacity raised when adsorbent dosage, contact time and pH solution were increased while an increase in temperature decreased the adsorption of TBO. Langmuir, Freundlich and Temkin isotherm models were employed to elucidate the adsorption mechanism while the adsorption rate data were analyzed according to the pseudo-first and second-order kinetic models. Results showed that adsorption of TBO onto MCM-48, SBA-15, and MCF fitted well the Freundlich isotherm model while the kinetic studies showed that adsorption process could be better described by the pseudo-second-order model for all mesoporous silicas. Finally, some solvents were evaluated to carried out dye desorption from the TBO-loaded mesoporous silicas founding that acetic acid was the most efficient.     

介孔SiO2薄膜的制备与表征

采用浸涂法,以载玻片为基底,十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,丙三醇为成膜干燥控制剂,制备出有序的介孔SiO2薄膜.利用X射线衍射仪(XRD)、红外光谱(IR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对其结构进行表征.XRD测试结果表明,合成的薄膜具有MCM-41介孔结...     

Sonochemical assisted preparation of ZnS–ZnO/MCM-41 based on blast furnace slag and electric arc furnace dust for Cr (VI) photoreduction

Iron/steel making industry is a weed that produces large quantities of slag and dust. The objective of the present study was to develop a procedure for obtaining and characterizing photocatalysts derived from this waste for chromium remediation. The MCM-41 was synthesized via sodium silicate (Na₂SiO₃) derived from Blast Furnace Slag (BFS), and ZnO and ZnS were synthesized based on zinc extracted from Electric Arc Furnace Dust (EAFD). Subsequently, ZnO/ZnS were sono-chemically loaded on the MCM-41 and were tested for the Cr (IV) photoreduction. The resultant ZnO, ZnS, MCM-41, and composites were characterized by X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), N2adsorption–desorption isotherms, Fourier-transform infrared (FT-IR) spectrometry, Dynamic Light scattering, and Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A regular hexagonal structure of typical mesoporous MCM-41 had been proven by small-angle XRD, HRTEM, and N2 adsorption–desorption. The photoreduction activity of ZnS–ZnO/MCM-41 nanocomposite has obvious efficiency compared to ZnO and ZnO/MCM-41, achieving a 94% photoreduction of Cr (VI) in 180 min under UV irradiation. The slight activity loss after 4 cycles (84.7%) reveals the good photoreduction properties of catalysts. Based on these results, ZnS–ZnO/MCM-41 composite material seems to be high efficiency, green, stable, environment, and economical alternative to be used as a photocatalyst for the reduction of Cr (VI).     

Octadecyl grafted MCM-41 silica spheres using trifunctionalsilane precursors – preparation and characterization

MCM-41 silica spheres were prepared via the pseudomorphic route. Subsequent surface modification of the mesoporous silica spheres was achieved by two silylating agents, n-octadecyltrihydridosilane and n-octadecyltrimethoxysilane, which provided different surface coverages. The MCM-41 pore structure, surface properties and morphological features were examined by small angle X-ray scattering, nitrogen adsorption–desorption and scanning electron microscopy. The investigations revealed an influence of the silica source on the mesoporous structure, as reflected by a higher long-range order for the pores in MCM-41 spheres prepared from Kromasil silica. Surface modification is accompanied by a reduction of the surface area, pore diameter and pore volume of the MCM-41 materials, whereas the spherical morphology of the spheres is retained. The degree of grafting and cross-linking of the alkylsilanes was determined by ²⁹Si NMR spectroscopy. A higher degree of alkyl chain grafting was observed for the solvent extracted MCM-41 spheres and for samples prepared via surface polymerization.FTIR and ¹³C NMR spectroscopies were employed to study the conformational behaviour and mobility of the grafted octadecyl chains. The conformational order was found to strongly depend on the history of the MCM-41 supports (calcination, solvent extraction) and on the actual surface modification procedure. In general, a lower conformational order was observed for the present mesoporous alkyl modified silica spheres as compared to conventional C₁₈ modified silica gels which is mainly attributed to the lower surface coverage.     

Effects of different structure-directing agents (SDA) in MCM-41 on the adsorption of CO2

CO₂ capturing technologies have attracted significant attention in order to limit emissions and reduce their negative effect on the environment. Mesoporous silica materials (MCM-41) are easily recyclable, affordable, and thermally and mechanically stable, providing added benefits in CO₂ capture. However, further studies are necessary to characterize the effects of MCM-41 pore size, adsorption temperature and surface silylation on CO₂ adsorption efficiency. In this work, mesoporous silica is synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n + 1 N(CH₃)₃Br, n = 14, 16 and 18) as structure-directing agents, and the adsorption capacity of CO₂ on TTMCM-41 (C₁₇H₃₈NBr), CTMCM-41 (C₁₉H₄₂NBr), DTMCM-41(C₂₁H₄₆NBr) samples was measured gravimetrically at room temperature and pressure up to 40 bar. The silica structures were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy (TEM). The XRD, N₂ adsorption–desorption and TEM measurements indicated the presence of a well-ordered hexagonal array with uniform mesostructures. The mesoporous silica obtained, denoted as TTMCM-41, CTMCM-41 and DTMCM-41, had distinct physical properties, such as BET surface area, hexagonal unit cell, pore volume, pore diameter and pore wall thickness. CTMCM-41 exhibited an adsorption capacity (0.58 g CO₂/g adsorbent) of more than DTMCM-41 (0.48 g CO₂/g adsorbent) and TTMCM-41 (0.42 g CO₂/g adsorbent). The results suggest that CTMCM-41 can be a better mesoporous adsorbent for CO₂ adsorption .     

Adsorption of toluene on mesoporous materials from waste solar panel as silica source

The adsorption of toluene was tested with MCM-41 and mesoporous silica materials (S-MCM) synthesized from waste solar panel. X-ray powder diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) were applied to characterize the prepared samples. In addition, the adsorption capacities of MCM-41 and S-MCM were almost the same which was observed according to the breakthrough experiments. The adsorption capacity of toluene in S-MCM was 57, 104, 200 and 277 mg g^− 1 for initial toluene concentrations of 250 to 1500 ppm respectively. The effects of the operation parameters, such as contact time and initial concentration on adsorption performance, were also tested in this study.     

Influence of the reaction conditions on the thermal stability of mesoporous MCM-48 silica obtained at room temperature

The thermal stability of MCM-48 silicas synthesized at room temperature under basic conditions using cetyltrimethylammonium bromide (CTAB) as template was evaluated as a function of the reaction time, CTAB/TEOS and H₂O/ethanol molar ratios and ammonium hydroxide (NH₄OH) concentration in the initial gel composition. Samples were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that synthesis conditions affect the structural and thermal properties of the MCM-48 silicas. These silicas exhibited a size from 200 to 500 nm with spherical morphology.     

Bifunctional mesoporous Cu–Al–MCM-41 materials for the simultaneous catalytic abatement of NOx and VOCs

This study explored the possibility of using waste organic solvent as the source of volatile organic compound (VOC) and it served as a reducing agent of selective catalytic reduction (SCR) deNO_x process, in which the VOC itself can be catalytically oxidized on the mesoporous Cu and/or Al substituted MCM-41 catalysts. The synthesized Cu–Al–MCM-41 catalysts were extensively characterized by powder low-angle X-ray diffraction (XRD), N₂ adsorption–desorption measurements, transmission electron microscopy (TEM), UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), ²⁷Al magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR), electron paramagnetic resonance spectroscopy (EPR) and inductively coupled plasma–mass spectrometer (ICP–MS) analysis. The XRD, TEM and N₂ adsorption–desorption studies clearly demonstrated the presence of a well ordered long range hexagonal array with uniform mesostructures. The Cu–Al–MCM-41 materials showed a better long-term-stability than that of copper ion-exchanged H–ZSM-5 (Cu–ZSM-5) zeolite. The Cu–Al–MCM-41 material was found to be an efficient catalyst than that of Cu–MCM-41 without aluminum for the simultaneous catalytic abatement of NO_x and VOCs, which was attributed to the presence of well dispersed and isolated Cu²⁺ ions on the Cu–Al–MCM-41 catalyst as observed by UV–Vis DRS and EPR spectroscopic studies. And the presence of aluminum (Al³⁺ ions) within the framework of Cu–Al–MCM-41 stabilized the isolated Cu²⁺ ions thus it led to higher and stabilized activity in terms of NO_x reduction.     

Characteristics of vanadium-substituted mesoporous silica with wormhole framework structure: effects of vanadium content

Vanadium-substituted wormhole framework structure (V-WMS) mesoporous silicas (V-WMS) with various Si/V ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfactant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), N₂ adsorption–desorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy. V-WMS samples shown characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. These mesoporous V-WMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. An absorption band of FT-IR at ca. 960 cm⁻¹ was assigned to the vibration of Si–O–V linkages. These samples also showed one strong UV–visible absorbance with overlapping maxima at about 255 nm. The results show that vanadium was incorporated into the structure of wormhole mesoporous silica (WMS). However, for V-WMS with high vanadium content (Si/V < 25), a broad shoulder in XRD pattern was observed at about 3–4°, suggesting the presence of impurity phase of vanadium species in the sample. The efforts in preparing V-WMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active vanadium centers.     

Preparation and characterization of Pd/Si-MCM-41 with high hydrogenation activity

The pure silica mesoporous molecular sieve MCM-41 was synthesized under hydrothermal conditions. Pd/Si-MCM-41 was prepared by the incipient wetness impregnation of pure silica MCM-41 with PdCl₂ as precursor. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms at 77 K, inductively coupled plasma (ICP) spectroscopy measurements. The formation of Pd particles reduced the crystalline character of Si-MCM-41, but the structure of Si-MCM-41 framework was retained. The designed Pd/Si-MCM-41 mesoporous material was used as catalysts for hydrogenation of rosin, and showed excellent catalytic performance. Such outstanding catalytic performance should be attributed to the proper size of Pd particles and its high dispersion.     

Ag(Ⅰ)Schiff碱配合物改性MCM-41分子筛的制备和表征

以3-氨丙基三乙氧基硅烷(3-aminopropyltriethoxysilane,APS)为偶联剂,用共缩聚的方法合成了氨基官能化的MCM-41介孔分子筛(amino-functionalized mesoporous MCM-41,AP-MCM-41),在分子筛孔道和表面共价偶联Ag(Ⅰ)Schiff碱配合物。采用X射线衍射、Fourier红外光谱、紫外-可见光谱、氮气吸附/脱附、元素分析和透射电子显微镜对所制备的样品进行了表征。结果表明:Ag(Ⅰ)Schiff碱配合物被成功嫁接到了分子筛的孔道和表面上,而且嫁接后的MCM-41仍然具有较好的孔径分布和有序结构,比表面积达到712.59m2/g,最可几孔径为3.41nm,具有典型的介孔材料特征。透射电子显微镜观察显示具有明显的孔道结构,并且较为规整。紫外-可见光谱显示,金属配位后,样品的相应的归属峰发生了明显的漂移,说明Ag(Ⅰ)Schiff碱配合物已嫁接到MCM-41表面并形成牢固的结构。     

MCM-41介孔碳材料的合成及其电化学性能研究

该文以十六烷基三甲基溴化铵（CTAB）为模板剂,可溶性淀粉(Starch)为碳源,通过软模板法一步合成了高度有序的介孔碳材料。通过热重分析（TG）、X-射线衍射（XRD）、N2吸附-脱附和透射电子显微镜（TEM）等对材料的结构进行了表征。结果表明：当模板剂与可溶性淀粉质量比为m(CTAB):m(Starch)=1.0：1.5,650 ℃焙烧碳化3 h,并用氢氟酸去除二氧化硅后,所得到的MCM-41有序介孔碳材料（OMC-650）的比表面积为985 m2/g,平均孔径为孔径分布均匀,平均孔径为2.5 nm。XRD和TEM分析表明,OMC-650具有典型的MCM-41结构特征,有序性良好。以OMC-650作为工作电极,氧化汞为参比电极,铂为辅助电极,用6 M•L-1 KOH做电解液,测其比电容为150 F/g,且经过1000次循环后,其比电容仍为138 F/g,为原电容的92%,说明所合成的材料具有良好的电容稳定性。     

Preparation of highly dispersed TiO2 in hydrophobic mesopores by simultaneous grafting and fluorinating

TiO₂ photocatalysts highly dispersed in the MCM-41 mesoporous silica material were synthesized using two different TiO₂ precursors of TiF₄ and (NH₄)₂TiO(C₂O₄)₂. The catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), UV–vis absorption, X-ray photoelectron spectroscopy (XPS), and Ti K-edge X-ray absorption fine structure (XAFS). The hydrophobic properties and catalytic activities of photocatalysts with different TiO₂ precursors and loading amount were examined by adsorption and degradation of iso-butanol diluted in water. The results showed that the TiO₂ loaded MCM-41 prepared from TiF₄ exhibited higher photocatalytic activity than from (NH₄)₂TiO(C₂O₄)₂. The fluorine-modified hydrophobic pore walls formed in the impregnation process using TiF₄ as well as highly dispersed TiO₂ nanoparticles play a crucial role for the high photocatalytic efficiency.     

13X微孔沸石和MCM-41介孔材料的合成及用于处理含Cd2+废水

以天津蓟县钾长石矿粉为主要原料,经选矿、煅烧、水热处理等工艺成功合成了13X微孔沸石. 以气相氧化硅、氢氧化钠、十六烷基三甲基溴化铵等为主要原料,在水热条件下合成了MCM-41有序介孔材料. 采用XRD和N2吸附-脱附等手段对合成的13X沸石和MCM-41介孔材料的物相、比表面积、孔径、孔体积等进行了分析对比. 在此基础上,对13X沸石和MCM-41介孔材料处理含Cd2+废水的效果和机理进行了对比研究,确定了不同分子筛用量、不同初始pH值、不同混合时间下13X沸石和MCM-41介孔分子筛对水中Cd2+的吸附率和吸附量. 研究发现,尽管MCM-41的比表面积和孔径远大于13X沸石,但其对水中Cd2+的处理效果却低于13X沸石,这与13X沸石和MCM-41的孔道结构类型、化学组成、表面荷电性质等有关.     

介孔氧化硅固载Yb(OTf)3的制备及催化葡萄糖生产乳酸

采用溶剂法和焙烧法制备了SBA-15和MCM-41两类介孔氧化硅,并以此为载体制备固载型三氟甲基磺酸镱(Yb(OTf)₃)催化剂。通过小角X射线衍射(SAXD)、氮气吸附/脱附、²⁹Si固体核磁共振光谱(NMR)、透射电子显微镜(TEM)及热重分析(TG)等方法对载体及催化剂进行表征,研究其在葡萄糖制备乳酸反应中的催化性能。结果表明：溶剂法制备的氧化硅表面羟基含量比焙烧法高,负载的磺酸基团和三氟甲基磺酸镱都更多,催化活性更高;SBA-15的平均孔径比MCM-41的大3 nm左右,这使得SBA-15具有更好的传质性能以及Yb(OTf)₂-SBA-15具有更好的催化性能。以Yb(OTf)₂-SBA-15-S为催化剂,在2 MPa N₂压力、190 ℃下反应60 min,乳酸的收率达到42.35%。     

Factors affecting Hg(II) adsorption on hybrid nanostructured silicas: influence of the synthesis conditions

This paper reports the synthesis, characterization and mercury adsorption behaviour of new organic–inorganic hybrid nanostructured silicas obtained by co-condensation, molecular imprinting and post-synthesis routes. N₂ adsorption–desorption measurements, XRD, FT-IR, MAS NMR, SEM, TEM and elemental analysis were used to characterize the physico-chemical properties of the hybrid nanostructured materials. The materials were studied for Hg(II) adsorption in aqueous medium at pH 3 and compared with unmodified nanostructured silica. Mercury adsorption was higher in the hybrid material prepared by the co-condensation method that reached a mercury uptake of 134 mg Hg/g. The best mercury adsorption efficiency was observed for the hybrid material prepared by molecular imprinting route. The synthetic route employed clearly affects the textural properties of the silica, the amount of organic ligand attached onto the support and mercury adsorption behaviour.     

Novel utilization of MCM-22 molecular sieves as supports of cobalt catalysts in the Fischer–Tropsch synthesis

Cobalt catalysts (2–10 wt% Co) supported on silica-rich MCM-22 zeolites have been prepared by impregnation with aqueous Co(NO₃)₂ solutions. The catalysts are characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption, solid state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalytic properties for the Fischer–Tropsch synthesis (FTS) at 280 °C, 12.5 bar and H₂/CO = 2 are evaluated. The catalysts supported on MCM-22 exhibit the highest selectivity to long-chain (C₅₊) hydrocarbons when MCM-22 supports are synthesized with the appropriate Si/Al ratio.     

Investigation of equilibrium and kinetic parameters of methylene blue adsorption onto MCM-41

Mesoporous MCM-41 was synthesized at room temperature using tetraethoxysilane (TEOS) with cetyltrimethylammonium bromide (CTAB) and employed as an effective adsorbent for the adsorption of methylene blue dye from aqueous solution. The as-synthesized MCM-41 was calcined at 250 and 550°C to study the relation between the surface area and pore volume with surfactant removal. The synthesized MCM-41 was characterized using thermo gravimetric analysis (TGA), X-ray diffraction (XRD) patterns, nitrogen adsorption/desorption isotherms and Fourier transform infrared (FT-IR) spectroscopy. The MCM-41 calcined at 550°C showed higher surface area (1,059 m² g^?1) with pore volume of 0.89 ml g^?1 and was used for the investigation of adsorption isotherms and kinetics. The experimental results indicated that the Freundlich and Redlich-Peterson models expressed the adsorption isotherm better than the Langmuir model. In addition, the influence of temperature and pH on adsorption was also investigated. The decrease in temperature or the increase in pH enhanced the adsorption of dye onto MCM-41. A maximum adsorption capacity of 1.5×10^?4 mol g^?1 was obtained at 30°C. The kinetic studies showed that the adsorption of dye on MCM-41 follows the pseudo-second-order kinetics.     

Mesoporous Tin-Triflate Based Catalysts for Transesterification of Sunflower Oil

Unimodal porous system (denoted as SnTf-MCM-41) and bimodal porosity (denoted as SnTf-UVM-7) were prepared in a two-step synthesis. The triflic acid was incorporated into previously synthesized Sn-containing porous silicas. Chemical analysis was carried out by electron probe microanalysis (EPMA), textural properties were determined by transmission electron microscopy (TEM) and from nitrogen adsorption–desorption isotherms (77 K), while structural characterization by X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. The structural characterization provided evidences on the direct interaction of triflate with incorporated tin species. The acidity of these catalysts was determined from the ammonia chemisorption measurements. The catalysts have been tested for transesterification of sunflower oil under both microwave and ultrasound activation. These experiments showed a direct reaction between the acidity of the catalysts and catalytic performances. No leaching of the triflate species or catalyst deactivation have been detected over several runs.