Synthesis of nanoporous carbon with controlled pore size distribution and examination of its accessibility for electric double layer formation

A new template approach is reported for the synthesis of nanoporous carbon. In contrast with previous template methods, the present one combines the synthesis of template, the introduction and formation of carbon into one step. This is achieved by simultaneous pyrolysis of Fe(CO)₅ and C₂H₂ to form the Fe template in situ with the formation of carbon. Additionally, by simply supplying Fe(CO)₅ and C₂H₂ at different ratios, the proportion and particle size of the Fe template can be altered. Consequently, nanoporous carbons with different pore sizes can be prepared after the Fe particles have been removed by HCl treatment. Under the present experimental conditions, a microporous carbon is demonstrated having a surface area of 602 m²/g and pore sizes mainly in the range of 0.5–1.2 nm, and a mesoporous carbon having a surface area of 880 m²/g and pore sizes mainly in the range of 2–10 nm. As an example for potential applications, the presence of mesopores in the mesoporous carbon is shown to have larger capacitance values than the microporous carbon. This may result from the fact that the presence of mesopores facilitates the electrolyte migration into the carbon interior.     

Controlling the textural parameters of mesoporous carbon materials

The mesoporous carbon materials prepared by inorganic templating technique using mesoporous silica, SBA-15 as a template and sucrose as a carbon source, have been systematically investigated as a function of sucrose to mesoporous silica composition, with a special focus on controlling the mesoporous structure, surface morphology and the textural parameters such as specific surface area, specific pore volume and pore size distribution. All the materials have been unambiguously characterized by XRD, N₂ adsorption–desorption isotherms, high-resolution transmission electron microscopy, high-resolution field emission scanning electron microscopy, and Raman spectroscopy. It has been found that the porous structure, morphology and the textural parameters of the mesoporous carbons materials, CMK-3-x where x represent the sucrose to silica weight ratio, can be easily controlled by the simple adjustment of concentration of sucrose molecules. It has also been found that the specific surface area of the mesoporous carbon materials systematically increases with decreasing the sucrose to silica weight ratio. Moreover, the specific pore volume of the materials increases from 0.57 to 1.31 cm³/g with decreasing the sucrose to silica weight ratio from 5 to 1.25 and then decreases to 1.23 cm³/g for CMK-3-0.8. HRTEM and HR-FESEM also show a highly ordered pore structure and better surface morphology for CMK-3-1.25 as compared to other materials prepared in this study. Thus, it can be concluded that the sucrose to silica weight ratio of 1.25 is the best condition to prepare well ordered mesoporous carbon materials with good textural parameters, pore structure and narrow pore size distribution.     

Mesoporous silica from rice hull ash

In the synthesis of mesoporous materials, the use of a template with an adequate porosity is normally favoured. As far as silica is concerned, many sophisticated procedures directed towards this goal have been published. It is already well documented that rice hull contains relatively pure silica after combustion of the residual organic matter. The authors of this contribution have recently demonstrated that large surface area silicates react with glycerol around 200 °C to give depolymerized silica with a chemical composition similar to that of poly‐alkoxides. The interest in this so‐called depolymerization is to allow easy formation of reactive gels which retain the memory of the porous structure of the original starting material. Rice hull ash (RHA), obtained after combustion of the organic residues at 500 °C, gives a silica characterized by mesopores with an average diameter about 3.5 nm. It is shown that RHA reacts with glycerol at 200 °C to form gels which, after hydrolysis and calcination, retain the mesoporous character. The hydrolysis procedure and especially, the pH is important for the distribution of the mesoporosity. The very simple reaction of a by‐product of the food industry with glycerol, a “green reagent”, gives a mesoporous solid silica in the form of a reactive gel, with many potential uses. Its use in a new procedure for the synthesis of a supported ZSM‐5 zeolite has been demonstrated. Copyright © 2007 Society of Chemical Industry     

Synthesis of mesoporous MFI zeolite by dry gel conversion with ZnO particles and the catalytic activity on TMB cracking

A facile synthesis method for mesoporous MFI zeolite (MMZ) has been developed. MFI zeolite was synthesized by a dry gel conversion in the presence of ZnO nanoparticles with a size of 20 nm. The as-synthesized MFI zeolite included crystalline layered zinc silicate and already possessed 5–15 nm mesopores. After calcination, MMZ/zinc silicate composite was treated with hydrochloric acid to remove unreacted ZnO particles. The micropore (1–2 nm) volume was increased after the HCl treatment, suggesting that ZnO nanoparticles (1–2 nm) remained during crystallization as well as zinc silicate. The catalytic activity of MMZ on 1,3,5-trimethylbenzene (TMB) cracking was compared with that of conventional MFI nanocrystals with a size of 80–100 nm. The conversion of TMB on MMZ was much higher than that on the MFI nanocrystals even though crystal size of MMZ is larger than the conventional MFI zeolite. These results suggest that acid sites on the internal surface of mesopores of MMZ contribute to the high conversion of TMB.     

Atomistic simulations for adsorption and separation of flue gas in MFI zeolite and MFI/MCM-41 micro/mesoporous composite

Adsorption of pure CO₂ and N₂ and separation of CO₂/N₂ mixture in MFI zeolite and MFI/MCM-41 micro/mesoporous composite have been studied by using atomistic simulations. Fully atomistic models of MFI and MFI/MCM-41 are constructed and characterized. A bimodal pore size distribution is observed in MFI/MCM-41 from simulated small- and broad-angle X-ray diffraction patterns. The density of MFI/MCM-41 is lower than MFI, while its free volume and specific surface area are greater than MFI due to the presence of mesopores. CO₂ is preferentially adsorbed than N₂, and thus, the loading and isosteric heat of CO₂ are greater than N₂ in both MFI and MFI/MCM-41. CO₂ isotherm in MFI/MCM-41 is similar to that in MFI at low pressures, but resembles that in MCM-41 at high pressures. N₂ shows similar amount of loading in MFI, MCM-41 and MFI/MCM-41. The selectivity of CO₂ over N₂ in the three adsorbents decreases in the order of MFI>MFI/MCM-41>MCM-41. With increasing pressure, the selectivity increases in MFI and MFI/MCM-41, but decreases in MCM-41. The self-diffusivity of CO₂ and N₂ in MFI decreases as loading increases, while in MFI/MCM-41, it first increases and then drops.     

Highly dispersed gold nanoparticles assembled in mesoporous titania films of cubic configuration

Highly dispersed Au nanoparticles (NPs) of average size of 9–12 nm were successfully assembled in mesopores of titania thin films, through H₂-reduction of . The well organized mesoporous nanostructure was characterized by using small-angle X-ray scattering, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, secondary ion mass spectroscopy and UV–vis spectrophotometry. Au NPs embedded in the mesoporous nanostructure exhibited enhanced thermal stability, up to 450 °C, which is attributed to the spatial confinement effect of the mesopores with cubic configuration. An obvious surface plasmon resonance was observed at 570 nm in the UV–vis absorption spectra of Au NPs embedded in the mesoporous thin films. The red shift and broadening of plasmon band observed for Au NPs are accounted for by the interaction between Au NPs and mesoporous titania framework. The mesoporous TiO₂/Au nanocomposite films show optically allowed direct transition of titania, where the incorporation of Au NPs evidently reduces the bandgap of titania.     

Chiral (Salen) Cobalt Complexes Encapsulated in Mesoporous MFI as an Enantioselective Catalyst for Asymmetric Ring Opening of Terminal Epoxides

MFI structural zeolite (ZSM-5 and Sililcalite) was treated with hot NaOH solution to make mesoporous channels in the microporous crystals. Inner mesopore size could be controlled by changing the concentration of NaOH solution. The pore structure of alkaline-treated MFI zeolite was studied by instrumental analysis. To obtain the cage type mesopores, Ti-coating on the outside MFI crystals before alkaline treatment was investigated to be the most effective. Co(III) salen complexes monomers were successfully encapsulated in mesoporous MFI-type zeolite by “ship-in-a-bottle” method. The heterogeneous catalyst could be applied in asymmetric ring opening of terminal epoxides by phenol derivatives. It showed very high enantioselectivity with yield in the catalysis.     

钙钛矿复合氧化物的介孔化及用于CH4催化燃烧

利用有序介孔立方相(Ia3d)乙烯基三乙氧基硅烷(TEVS)为模扳,通过纳米组装法在硅基硬模板的介孔中填入La - Fe -柠檬酸络合物,经焙烧和碱洗去除硅基模板,制备具有有序介孔结构且高比表面积的LaFeO3钙钛矿(ABO3),并与软模板法和自燃烧法制备的LaFeO3钙钛矿催化荆作对比,运用XRD、TEM和BET对合...     

Effect of Mesoporous Silica Buffer Layer on the Orientation of MFI Zeolite Membranes

Growth of MFI zeolite membranes on porous α-alumina substrates with and without precoated mesoporous silica buffer layer has been performed by in situ crystallization. A preferentially b -oriented MFI membrane can be prepared on a mesoporous silica-coated substrate. A membrane with a randomly oriented and eventually [ h 0 h ]-oriented top layer is obtained on an uncoated α-alumina substrate. The chemical properties of the substrate are suggested to have significant effects on the membrane orientation.     

A simplified preparation of mesoporous carbon and the examination of the carbon accessibility for electric double layer formation

Mesoporous carbon was prepared from resol-type phenol-formaldehyde resin using mesoporous silica as template. By filling the resin into the pores of the template, followed by resin carbonization and template dissolution, mesoporous carbon preparation can be significantly simplified. Small-angle X-ray diffraction reflected the long-range ordering of the pores in the carbon. TEM and N₂-adsorption analysis showed that the carbon contained mesopores of different sizes and a high proportion of micropores. Electrochemical cyclic voltammetry was conducted in H₂SO₄ to examine the surface accessibility of the carbon for double layer formation. Microporous activated carbon, also from the resol resin, was prepared for comparison. Although the pore sizes are different, the double-layer capacitances per unit area for both carbons are similar at low potential sweep rates. However, the capacitance decline with the sweep rate was less significant for the mesoporous carbon. Upon gasification of the carbons to increase their surface area, the ultimate capacitance per unit carbon area was enhanced and the enhancement was slightly larger for the mesoporous carbon. It is suggested that the presence of mesopores has facilitated the electrolyte migration into carbon interior. A two-electrode capacitor assembled with the mesoporous carbon was shown to have a small resistance and still exhibited a capacitive behavior at high potential sweep rates.     

Improved performance of mesoporous zeolite single crystals in catalytic cracking and isomerization of n-hexadecane

Mesoporous zeolite single-crystal catalysts exhibit the hitherto most pronounced activity enhancement over conventional zeolite catalysts in slurry-phase catalytic cracking and isomerization of n-hexadecane. This improved performance of both pure and Pt-loaded mesoporous MFI single crystals is attributed to enhanced mass transport via the extended non-crystallographic intracrystalline mesopores to and from active sites located inside the zeolite micropores.     

Efficient adsorption and photocatalytic degradation of organic pollutants diluted in water using the fluoride-modified hydrophobic titanium oxide photocatalysts: Ti-containing Beta zeolite and TiO2 loaded on HMS mesoporous silica

Using the F⁻ media, the hydrophobic zeolite and mesoporous silica can be synthesized. These hydrophobic porous materials exhibit the high ability for the adsorption of organic compounds diluted in water and become the useful supports of photocatalyst. The hydrophobic Ti-Beta(F) zeolite prepared in the F⁻ media exhibited high efficiency than the hydrophilic Ti-Beta(OH) zeolite prepared in OH⁻ media for the liquid-phase photocatalytic degradation of 2-propanol diluted in water to produce CO₂ and H₂O. The TiO₂ loaded on the hydrophobic mesoporous silica HMS(F) (TiO₂/HMS(F)), which was synthesized using tetraethyl orthosilicate, tetraethylammonium fluoride as the source of the fluoride and dodecylamine as templates, also exhibited the efficient photocatalytic performance for the degradation. The amount of adsorption of 2-propanol and the photocatalytic reactivity for the degradation increased with increasing the content of fluoride ions on these photocatalysts. The efficient photocatalytic degradation of 2-propanol diluted in water on Ti-Beta(F) zeolite and TiO₂/HMS(F) mesoporous silica can be attributed to the larger affinity for the adsorption of propanol molecules on the titanium oxide species depending on the hydrophobic surface properties of these photocatalysts.     

含氟体系中MFI型分子筛膜的制备及其乙醇/水分离性能

以氟化铵为矿化剂、四丙基溴化铵为模板剂,在负载晶种的钇稳定氧化锆(YSZ)中空纤维支撑体表面合成了MFI型分子筛膜,并用于乙醇/水的分离;系统考察了氟硅比(n_NH4F/n_SiO2)、合成时间等条件对膜分离性能的影响,在n_NH4F/n_SiO2为0.8、合成时间为8 h下合成出高性能膜,其通量达8.2 kg·m^-2·h^-1、乙醇/水分离因子为47;同时研究了MFI型分子筛膜在乙醇/水体系中的分离稳定性,揭示出该方法所合成膜表面无Si-OH,从而避免了Si-OH与乙醇反应而带来膜分离性能的下降.     

Simple synthesis of hierarchically structured partially graphitized carbon by emulsion/block-copolymer co-template method for high power supercapacitors

Hierarchical structure with macropores interconnecting mesopores of carbon material can remarkably improve the rate performance of electric double layer capacitor. However, pre-formed hard templates such as silica particles or polymer beads have been used in most synthetic procedures for them, resulting in an increase of manufacturing cost and time. Herein, we report novel method for synthesizing hierarchically structured macro/mesoporous partially graphitized carbon (MMPGC) for high power supercapacitor electrode material without pre-formed hard template. Instead of hard template, emulsion/block co-polymer co-template was used for generating macropores and mesopores, respectively. As a supercapacitor electrode material, MMPGC showed higher capacity retention at high current than ordered mesoporous carbon, which is characterized by cyclic voltammetry, galvanostatic charge–discharge. In addition, the effect of macropores and partially graphitized wall on reducing resistance of supercapacitor electrode was analyzed in detail with electrochemical impedance spectroscopy fitting method.     

Extraction of nano-porous silica from hydrosodalite produced via modification of low-grade kaolin for removal of methylene blue from wastewater

BACKGROUND: This work employs low-grade kaolin as raw material in the economical production of nano-porous silica with extended surface area via the hydrothermal acidification of intermediate zeolite composite to remove methylene blue from wastewater. Hydrosodalite fabricated through the modification of meta-kaolin (MK) with sodium aluminate (NaAlO₂) was used as a precursor in the hydrothermal acidification step. RESULTS: The direct conversion of MK to zeolite composite generating a low crystalline phase, containing quartz which was eliminated in the acidification step, exhibited a strong affinity towards dye adsorption. It was indicated that the NaAlO₂/MK ratio could influence the hydrosodalite crystallization as well as adsorption efficiency of the nano-porous silica obtained from acidification of zeolite composite. The nano-porous silica formation involved the ion extraction from hydrosodalite cabbage-like particles, depending on crystallinity of intermediate zeolite composite. CONCLUSION: The mesoporous silica represented the appropriate adsorptive behavior when produced from precursor modified with lower NaAlO₂ content, NaAlO₂/MK = 0.24, attributed to superior specific surface area, 420 m² g⁻¹, with average pore diameter about 3.3 nm. The equilibrium data was better correlated by Redlich–Peterson isotherm. Compared to the surface area of silica powders fabricated from high grade kaolins, Al₂O₃/SiO₂, > 0.83, by the acid-etched strategy, the mesoporous silica produced from the low-grade kaolin by the template free method indicates higher value. © 2020 Society of Chemical Industry     

等级孔β沸石的制备与表征

对β沸石进行碱处理,得到具有介孔-微孔等级孔结构的β沸石,采用N₂吸附-脱附、FT-IR、XRF、NMR、XRD和TEM等手段进行表征。结果表明,碱度、温度和处理时间是β沸石孔结构的主要影响因素,随着碱度、温度和处理时间的增加,介孔比表面积先增加后降低,微孔比表面积和结晶度不断降低,平均孔径不断递增。在碱度0.5 mol·L^-1、温度50 ℃和处理时间5 h条件下,可以得到介孔孔径集中的β沸石。研究发现,介孔的产生是OH^-选择性地与沸石晶体中的硅反应,将部分骨架硅脱除而成,并对沸石的微孔结构造成破坏所致。     

Synthesis and properties of mesoporous carbons with high loadings of inorganic species

A series of mesoporous carbons with high loading of silica has been synthesized by acid-catalyzed polymerization of resorcinol and formaldehyde in the presence of tetraethyl orthosilicate (TEOS), colloidal silica (silica source) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (soft template) followed by carbonization. This synthesis route can be considered as a combination of soft-templating and hard templating strategies. The resulting mesoporous silica-carbon composites contained spherical silica colloids in addition to uniformly distributed silica originated from TEOS. Dissolution of silica led to high surface area carbons, which in addition to the primary mesopores formed by thermal degradation of block copolymer template possessed spherical mesopores after dissolution of silica colloids and fine pores after removal of TEOS-generated silica species. This approach can be used to incorporate other inorganic nanoparticles into mesoporous carbons with extra microporosity created after dissolving TEOS-generated silica species.     

Investigation on the morphology of hierarchical mesoporous ZSM-5 zeolite prepared by the CO2-in-water microemulsion method

A series of hierarchical mesoporous ZSM-5 zeolites with different morphology were successfully synthesized by the CO₂-in-water microemulsion method, and mesoporosity was formed without organotemplate. The different synthesis conditions, including silica alumina molar ratio, stirring time and compressed CO₂ pressure, were systematically investigated to discuss the influence of these conditions on the morphology of ZSM-5 zeolite. The resulting samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP) and nitrogen adsorption-desorption measurement. XRD results indicated that compressed CO₂ route for the synthesis of MFI zeolites had a fast crystallization rate and good crystallinity. SEM images showed that the ZSM-5 hierarchical mesoporous ZSM-5 zeolite had a uniform chain-like crystal morphology, whereas silicalite-1 displayed a monodisperse crystal morphology. In addition, the nitrogen adsorption-desorption measurement provided sufficient evidence for the presence of hierarchical mesopores in ZSM-5 zeolite.     

Characterization of acidic property of sulfo-group functionalized microporous and mesoporous silica by adsorption microcalorimetry

Sulfo-group functionalized microporous and mesoporous silica based-on a MCM-41 framework which showed solid acid property were synthesized and characterized by adsorption microcalorimetry. Both the sulfo-functionalized microporous and mesoporous silica (Micro-SO₃H and Meso-SO₃H) were prepared by the oxidation of thiol group (–SH) included mesoporous silica which was obtained through the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples have an ordered two-dimensional hexagonal pore array similar to that of MCM-41 as depicted from the XRD patterns. Nitrogen adsorption also shows that both microporous and mesoporous silica have pore characteristics similar to MCM-41, i.e. high surface area and high pore volume. However, pore regularity, surface area and pore volume decreased as the MPTMS loading increased. Solid-state ²⁹Si NMR indicated that the sulfo groups were successfully incorporated into both microporous and mesoporous silica frameworks. This sulfo-functionalized porous silica have high NH₃ uptakes and high differential heats of NH₃ adsorption, suggesting the presence of strong acidic sulfo groups on the silica surface. Acid catalyses of the samples were characterized by the isomerization reaction of but-1-ene to cis, trans-but-2-ene.     

Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method

Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N₂ atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m²/g (0.31 cm³/g)–250 m²/g (0.16 cm³/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions.