Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.     

高结晶规则大孔硅的制备和应用

ＦＳＭ－１６,ＭＣＭ－４１和ＳＢＡ－１５等具有高规则二维六角晶格的多孔硅可用不同硅源和表面活性剂合成,其孔径可达１０,１５或３０ｎｍ,可用具有不同熔基链长的表面活性剂和膨胀剂控制。其结晶规则性随孔径的增大而降低。用层状硅土Ｋａｎｅｍｉｔｅ制备的ＦＳＭ－１６和来自水玻璃的ＭＣＭ－４１,其表面阴离子度比用四甲氧基硅烷（ＴＭＯＳ）制备的ＳＢＡ－１５高得多。如将在等电点以下呈阴离子性的生物酶插入硅孔,则由于离子间的相互作用和氢键结合力,可得到结合得十分稳定的生物／无机陶瓷结合体。以此结合体为有机酸化反应的催化剂,反应的活性很高。     

Synthesis of Highly Ordered Large Size Mesoporous Silica and Effect of Stabilization as Enzyme Supports in Organic Solvent

The FSM-16, MCM-41 and SBA-15 type hexagonal mesoporous silica materials having a highly arrange in order of the 2-dimensional structure were synthesized by using different silicon sources and surfactants. In the 2-dimensional silicate framework, pore size can be uniformly controlled by the combined use of the surfactants having different alkyl chains length and swelling agents (triisopropyl benzene). Pore-diameter of FSM-16 and MCM-41 can be expanded to 100 A, SBA-15 is 150 A. Crystal regularity decreased with increasing the pore-diameter in the FSM-16 derived from Kanemite (silicon source) and MCM-41 from water glass, its anionic char-acteristics on the pore wall may be higher than SBA-15 derived from oligomeric tetramethoxysilane (TMOS) is also reported. We have successfully used FSM-16 and MCM-41 as immobilizing agents of enzyme having cationic residues under isoelectric point. The level of adsorption of enzymes in the FSM-16 and MCM-41 was relatively high, but was low in the SBA-15 support. The mechanism of enzyme adsorption in mesopore was suggested to be the ionic interactions. In aqueous solutions, horseradish peroxidase (HRP) immobilized in FSM-16 containing 89A mesopore showed the highest loaded amounts(183mg/mg FSM),then a FSM-16 of pore-diameter 30 A only loaded a litter amounts (28mg/mg FSM) on the outside surface. The catalytic activity in organic solvent is high when HRP was immobilized in FSM-16 and MCM-41, but is low in case of SBA- 15.     

Adsorption myoglobin over mesoporous silica molecular sieves: Pore size effect and pore-filling model

The present work describes the adsorption of myoglobin over mesoporous materials with different pore diameters (SBA-15 and MCM-41) from buffered solutions. The Langmuir-type adsorption of myoglobin occurs with monolayer coverage on the inner surface of the mesoporous channels. These adsorbents were thoroughly characterized by X-ray diffraction, nitrogen adsorption/desorption and FT-IR spectroscopy before and after the myoglobin adsorption. The amount of myoglobin adsorbed significantly depends on the specific pore volume and/or the pore diameter of the mesoporous silica adsorbents. These experimental results were analyzed using pore-filling models, suggesting that myoglobin molecules are well-packed in the SBA-15 pores. FT-IR spectra before and after the adsorption confirm the structural stability of the adsorbed myoglobin.     

Removal of patulin from aqueous solutions by propylthiol functionalized SBA-15

Propylthiol functionalized SBA-15 silica was investigated to detoxify aqueous solutions contaminated with the regulated mycotoxin patulin. Micelle templated silicas with a specific pore size were synthetically modified to possess propylthiol groups, a functional group known to form Michael reaction products with the conjugated double bond system of patulin. BET surface area analysis indicated the propylthiol functionalized SBA-15 possesses channels with the pore size of 5.4 nm and a surface area of 345 m(2)g(-1). Elemental analysis indicates the silicon/sulfur ratio to be 10:1, inferring one propylthiol substituent for every ten silica residues. The propylthiol modified SBA-15 was effective at significantly reducing high levels of patulin from aqueous solutions (pH 7.0) in batch sorption assays at room temperature. The material was less effective at lower pH; however heating low pH solutions and apple juice to 60 °C in the presence of propylthiol functionalized SBA-15 significantly reduced the levels of patulin in contaminated samples. Composite molecular models developed by semi-empirical PM3 and empirical force field methods support patulin permeation through the mesoporous channels of propylthiol functionalized SBA-15. Density functional study at the B3LYP/6-31G(d,p) level predicts the proposed patulin adducts formed by reaction with the thiol residues exhibit less electrophilic properties than patulin. It is demonstrated the use of propylthiol functionalized SBA-15 is a viable approach to reduce patulin levels in aqueous solutions, including contaminated apple juice.     

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.     

Mesoporous silica with controlled porous structure and regular morphology

A new procedure for the synthesis of mesoporous silica with controlled porous structure and regular morphology was developed. It is based on the precipitation from a homogeneous environment using cetyltrimethylammonium bromide as a structure directing agent. The decrease in pH, which causes the formation of solid particles, is achieved by the hydrolysis of ethyl acetate. The procedure enables to obtain not only the MCM-41 mesoporous molecular sieve with a very high degree of pore ordering and phase purity, but also materials of a new type, viz. bimodal silicas containing both the MCM-41 mesopore system with a pore size of about 3 nm and a system of larger mesopores with sizes ranging from 10 to 30 nm. Owing to their structural properties and regular worm-like morphology, bimodal silicas are promising materials for applications in separation processes or as supports for bulky molecules or nanoparticles.     

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.     

2-羟基-1-萘甲醛功能化SBA-15吸附剂的制备及其对Cr(III)的吸附性能

为去除水体中Cr(III)的污染, 本研究利用席夫碱反应原理制备了2-羟基-1-萘甲醛功能化SBA-15吸附剂(Q-SBA-15)。通过不同测试手段对所制备样品的形貌、孔道结构、元素组成和表面化学状态进行了系统表征。结果表明, SBA-15经2-羟基-1-萘甲醛修饰后, 其比表面积和孔径明显减小, 但表面形貌和晶体结构没有明显变化。为研究Q-SBA-15对Cr(III)的吸附性能, 详细分析了溶液pH和离子强度的影响, 以及吸附动力学、吸附等温线、吸附热力学和再生性能。结果表明, Q-SBA-15对Cr(III)吸附过程遵循准二级吸附动力学模型和Langmuir模型。当吸附温度为 40 ℃、pH为6、吸附时间为120 min时, Q-SBA-15对Cr(III)的吸附容量最大, 达到102.3 mg/g。Q-SBA-15对Cr(III)的吸附作用主要依靠其表面官能团与Cr(III)的配位螯合作用, 且为自发吸热过程。再生实验表明Q-SBA-15具有良好的重复使用性。该Q-SBA-15吸附剂在去除Cr(III)方面具有潜在的应用价值。     

Mesoporous silicates as nanoreactors for carbon nanotube production in the absence of transition metal catalysts

Carbon nanotubes were produced from either a template or the polymer-filled pore systems of mesoporous silicates of various structures and dimensions by heat treatment in the absence of air. Successful synthesis was done when the template molecules contained little or no oxygen. For SBA-15 material, where the structure-directing molecule used for synthesis of mesoporous silicate was polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, no carbon nanostructures were formed. A peculiar carbon nanostructure was generated from the template for pore expanded MCM-41. To demonstrate carbon nanotube formation from polymer in the mesoporous silicates, the mesopores of MCM-41, MCM-48, and SBA-15 silicates were filled with divinyl-benzene polymer and then graphitized at 1300 K. The polymer was successfully transformed into carbon nanotubes for the MCM class silicate but not the SBA-15 silicate.     

Mesoporous silica nanoparticles inhibit cellular respiration

We studied the effect of two types of mesoporous silica nanoparticles, MCM-41 and SBA-15, on mitochondrial O 2 consumption (respiration) in HL-60 (myeloid) cells, Jurkat (lymphoid) cells, and isolated mitochondria. SBA-15 inhibited cellular respiration at 25-500 microg/mL; the inhibition was concentration-dependent and time-dependent. The cellular ATP profile paralleled that of respiration. MCM-41 had no noticeable effect on respiration rate. In cells depleted of metabolic fuels, 50 microg/mL SBA-15 delayed the onset of glucose-supported respiration by 12 min and 200 microg/mL SBA-15 by 34 min; MCM-41 also delayed the onset of glucose-supported respiration. Neither SBA-15 nor MCM-41 affected cellular glutathione. Both nanoparticles inhibited respiration of isolated mitochondria and submitochondrial particles.     

Taguchi optimization approach for Pb(II) and Hg(II) removal from aqueous solutions using modified mesoporous carbon

Using the Taguchi method, this study presents a systematic optimization approach for removal of lead (Pb) and mercury (Hg) by a nanostructure, zinc oxide-modified mesoporous carbon CMK-3 denoted as Zn-OCMK-3. CMK-3 was synthesized by using SBA-15 and then oxidized by nitric acid. The zinc oxide was loaded to the modified CMK-3 by the equilibrium adsorption of Zn(II) ions from aqueous solution followed by calcination to convert zinc nitrate to zinc oxide. The CMK-3 had porous structure and high specific surface area which can accommodate zinc oxide in a spreading manner, the zinc oxide connects to the carbon surface via oxygen atoms. The controllable factors such as agitation time, initial concentration, temperature, dose and pH of solution have been optimized. Under optimum conditions, the pollutant removal efficiency (PRE) was 97.25% for Pb(II) and 99% for Hg(II). The percentage contribution of each controllable factor was also determined. The initial concentration of pollutant is the most influential factor, and its value of percentage contribution is up to 31% and 43% for Pb and Hg, respectively. Our results show that the Zn-OCMK-3 is an effective nanoadsorbent for lead and mercury pollution remediation. Langmuir and Freundlich adsorption isotherms were used to model the equilibrium adsorption data for Pb(II) and Hg(II).     

Influence of mesoporous fillers with PP-g-MA on flammability and tensile behavior of polypropylene composites

The effect of mesoporous silica MCM-41 and SBA-15 as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (PP-IFR) were studied, and the IFR system mainly consisted of the ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythriol (PER) as a carbonization agent. The mesoporous MCM-41 and SBA-15 were incorporated into flame retardant formulation at four different concentrations (1, 3, 5, 8 wt.%) to investigate the synergism between the flame retardant materials. A synergistic effect in flame retardancy was best when a suitable amount of SBA-15 was used in combination with APP and PER.     

Adsorption of duplex DNA on mesoporous silicas: possibility of inclusion of DNA into their mesopores

It is well known that a silica surface cannot adsorb duplex DNA in common aqueous solution (not chaotropic solution) because of the electrostatic repulsion of the silica surface and polyanionic DNA. However, we recently found that when duplex DNA in phosphoric acid form (or in acidic solution) was used, DNA was successfully adsorbed into mesoporous silicas even in low-salt aqueous solution. The adsorption behaviors of DNA into mesoporous silicas were influenced by the pore diameter sizes. Mesoporous silicas with 2.80- or 3.82-nm peak pore diameters adsorbed DNA the best in diluted NaCl solution. Formation of the hydrogen bond between P(O)OH groups in DNA and adsorbed water, SiOH groups, or both on silica surfaces is regarded as a main factor in this adsorption. The coincidence of the pore sizes and DNA diameter realizes this unique adsorption promoted by the effect of encompassing DNA with the inner surface of mesoporous silica. Although there is no clear direct evidence for including duplex DNA in the mesopores yet, this adsorption technique is expected to provide a new tool for DNA science, because DNA in the pore size 2-5 nm in diameter has to be in unusual disentangled thread form.     

Synthesis of 3-dimensional mesoporous silica using a di-block copolymer template

Exploring polymeric surfactants as templates for synthesizing ordered mesoporous silicas has become increasingly important for both academic interests and industrial applications. In this work, we employed C₁₆EO₄₀, a di-block copolymer polyethylene-poly(ethylene oxide), as template in an attempt to synthesize a modified 3-dimensional wormhole mesoporous silicas (WMS-39). In addition, various synthesizing conditions were investigated, including pre-hydrolysis time of TEOS, reaction temperatures and the ratios of TEOS to template. The products were characterized using powder XRD, TEM, ²⁹Si MAS NMR and nitrogen adsorption measurements. The characteristics of as-synthesized mesoporous silica were compared with SBA-15, a highly ordered mesoporous silica, prepared using non-ionic tri-block copolymers of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) as templates. The WMS-39 materials have a BET surface area of 600–970 m²/g and narrowly distributed pore diameter around 3.9 nm. The morphology of WMS-39 was found to be wormhole framework as indicated in TEM diagrams. Thermal transformation of the as-synthesized mesoporous materials were carefully analyzed with TGA/DTA. Findings obtained from this work enable us to propose a modified assembly mechanism of mesoporous silicas.     

Synthesis of mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal mesoporous silica from rice husk ash

The mixed-phase bimodal mesoporous silicas (BMS) were simply synthesized via sol-gel technique using rice husk ash-derived sodium silicate as a silica source, and Pluronic P123 and cetyltrimethyl ammonium bromide (CTAB) as the pore structure-directing agents. The gel solution composition in the synthesis process was based on SiO₂:Pluronic P123:CTAB:HCl:H₂O molar ratio of 1:0.088:0.088:4:200. The effect of mixing sequences of starting materials on BMS structures was investigated. The phase separation among SBA-15, SBA-3-like porous silica and xerogel was found when the gel solutions of SBA-15 and SBA-3-like were prepared separately in the primary stage, whereas the mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal porous silica was successfully synthesized when CTAB was added into the SBA-15 gel solution and the secondary micelle structure was formed inside the primary SBA-15 framework.     

Synthesis of nano titania particles embedded in mesoporous SBA-15: characterization and photocatalytic activity

Supported nanocrystalline titanium dioxide (TiO2) has been prepared by a post-synthesis step via Ti-alkoxide hydrolysis through the use of mesoporous SBA-15 silica. TiO2/SBA-15 composites with various TiO2 loading have been prepared and characterized by X-ray diffraction, nitrogen adsorption, Fourier transform infrared spectroscopy and diffusive reflective UV-vis spectroscopy. The addition of mesoporous SBA-15 prevents the anatase to rutile phase transformation and the growth of crystal grain. TiO2 did not block the SBA-15 pores, and their surface was fully accessible for nitrogen adsorption. Calcination in air of the composites up to 800 degrees C did not change the nanocrystal phase and slightly increased the domain size from 5.0 to 7.5 nm, indicating that the anatase TiO2 grains in the mesostructures have a relatively high thermal stability and proper pore diameter allows controlling the size of obtained titania particles. The TiO2/SBA-15 composites prepared by this study showed much higher photodegradation ability for methylene blue (MB) than commercial pure TiO2 nanoparticles P-25. Experimental results indicate that the photocatalytic activity of titania/silica mixed materials depends on the adsorption ability of composite and the photocatalytic activity of the titania, and there is an optimal ratio of Ti:Si, too high or low Ti:Si ratio will lower the photodegradation ability of the composites.     

有序介孔氧化硅孔道氧化锰团簇组装研究

以有序介孔氧化硅MCM-41为主体材料,通过浸渍法及后续热处理工艺,在孔道中组装氧化锰的团簇粒子,并对其进行结构表征。通过XRD、HR—TEM、XPS及N2吸附表明氧化锰的团簇粒子已经成功组装到MCM-41有序孔道中。通过对不同孔径有序介孔材料的氧化锰团簇粒子的组装,表明随着孔道中组装量的增加,350nm附近光致发光强度增强,吸收边发生红移,同时1000nm附近吸收带宽化。     

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.     

Functionalized diatom silica microparticles for removal of mercury ions

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (–SH or –NH₂) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g⁻¹ for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.