SBA-15 Silica Template Research Articles

Revealing the competitive effect of N2 and H2O towards CO2 adsorption in N-rich ordered mesoporous carbons

The incorporation of heteroatoms improves CO2 adsorption on carbon-based materials, but it can also provide some hydrophilic character to the bare-carbon frameworks, making the hypothesis of competitive CO2/H2O adsorption not negligible. In this respect, the CO2 capture is here evaluated through a deep characterization of the sorption properties of N-rich ordered mesoporous carbons under dry and moisture conditions, and in CO2/N2 gas mixtures. The nanocasting strategy is used to obtain N-rich CMK-3-type carbons in one pot by impregnating D-glucosamine hydrochloride, a carbon/nitrogen source, into an SBA-15 silica template followed by pyrolysis treatment at 600, 750, and 900 °C. The fine-tuning of the pyrolysis treatment aims to find the right proportion of micropores and N content, which are important features for selective CO2 adsorption. The highest surface amount of N (11.3 at.%), in particular of the pyridinic type, enhances the CO2/N2 selectivity (1.03 mmol/g of adsorbed CO2 from a 20% CO2 in N2), but also the undesired increment in the H2O uptake. CO2 uptake under competitive CO2/H2O conditions is better preserved with 8.3 at.% of surface nitrogen (1.55, 1.52, 0.61, and 0.89 mmol/g of CO2 at a relative humidity of 0, 25, 50, and 75%, respectively). Interestingly, the N-CMK-3 materials retain their capture properties over repetitive adsorption-desorption cycles in pure CO2. In this respect, a TGA-FTIR study is performed to monitor the reusability of the sorbents after CO2 capture from moist flue gases to assess the effectiveness of the reactivation procedure towards the removal of the adsorbed species.

Nanoporous carbon nitride with a high content of inbuilt N site for the CO2 capture

We report the nanoconfinement-mediated graphitic nanoporous carbon nitride (gNPCN) adsorbents with a high content of inbuilt basic nitrogen (N) (48%) by X-ray photoelectron spectroscopy (XPS) for efficient CO2 adsorption. The gNPCNs (gNPCN-150 and gNPCN-130) are synthesized using the mesoporous SBA-15 silica template and a single carbon-nitrogen (C–N) precursor (guanidine hydrochloride). The various adsorbents were utilized for investigating the influence of pore size (PS), surface area (SA), and type of adsorbent for CO2 adsorption performance. The capacity for CO2 capturing of gNPCN-150 reached 23.1 mmol/g at 0 °C under 30 bar pressure. This CO2 capturing capacity value was higher than the capacity gNPCN-130, SBA15, activated carbon (AC), and multiwalled carbon nanotube (MWCN) under identical conditions. The gNPCN materials exhibited superior CO2 adsorption ability that is ascribed to the presence of the highly organized mesoporosity, inbuilt high content of basic N site for adsorbing more CO2 through acid-base interaction, and tunable surface-structural properties. Moreover, the synthesis strategy is remarkably flexible in selecting C–N sources. This study features graphitic high-ordered nanoporous CN materials as a resourceful platform towards the efficient CO2 capture.

Synthesis and characterization of Co-Mo bimetallic carbides

Co-Mo carbides were prepared by impregnation with aqueous solution of metal salts and sucrose into ordered mesoporous SBA-15 silica template using carbothermal hydrogen reduction. Bimetallic Co-Mo carbide obtained by using carbothermal hydrogen reduction of Co-Mo precursors is formed when the Co-Mo molar ratio is 1.0. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Electrochemical characterization of obtained materials w?re performed by cyclic voltammetry in acid solution.

Synthesis of highly porous LaCoO3 catalyst by Nanocasting and its performance for oxygen reduction and evolution reactions in alkaline solution

Highly porous LaCoO3 perovskite was synthesized by a nanocasting method using a mesoporous silica template and subsequently applied as a bifunctional catalyst for the oxygen reduction and evolution reactions in alkaline solution. The La-Co citrate complex was mixed a porous SBA-15 silica template, and then, calcinated at 650 °C to prepare a LaCoO3/SBA-15 composite. Highly porous LaCoO3 was prepared by treating this composite with NaOH to remove the SBA-15 silica template. The obtained LaCoO3 showed a very rough surface, high surface area, and relatively small particle size compared with LaCoO3 prepared by the sol-gel method. The catalytic performance of the highly porous LaCoO3 for the oxygen reduction and evolution reactions was electrochemically measured in alkaline solution. LaCoO3 prepared by the nanocasting exhibited higher cell performance than that prepared by sol-gel method due to its larger surface area.

Influence of carbon precursor on porosity, surface composition and catalytic behaviour of CMK-3 in oxidative dehydrogenation of propane to propene

Ordered mesoporous CMK-3 carbon replicas were synthesized by infiltration of mesopores present in a SBA-15 silica template with two different carbon precursors, i.e. sucrose and poly(furfuryl alcohol). The obtained composites were carbonized under an inert gas atmosphere at 550, 650, 750 and 850 °C, and the template was etched with a HF solution. The final carbon replicas were analyzed by various physicochemical techniques, including low-temperature N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and tested as catalysts in the oxidative dehydrogenation of propane (ODP) at 450 °C. Both series of materials differed strongly with respect to their porosity, but showed very similar surface composition determined by XPS. Higher porosity of CMK-3 prepared using the sucrose precursor influenced propane conversion and selectivity to propene. Furthermore, oxygen containing groups (e.g. carbonyl-type) were found to be less sensitive to the type of carbon precursor than to the ODP reaction conditions.

N-doped ordered mesoporous carbon supported PdCo nanoparticles for the catalytic oxidation of benzyl alcohol

A highly ordered nitrogen doped mesoporous carbon was prepared by passing acetonitrile as carbon and nitrogen source over a mesoporous SBA-15 silica template at 900 °C by using a CVD bubbling method. The silica template was removed by etching with HF, followed by filtration, washing and functionalization with HNO3 to give N-CMK-3 (N = 11.3 wt%). This material exhibited good mesostructural ordering (XRD analysis), a high surface area (885 m2/g) and a large pore volume (1.70 cm3/g). Addition of a monodispersed colloidal solution of PdCo (d = 3.3 nm), Pd (4.2 nm) or Co (10.5 nm) nanoparticles to N-CMK-3 as support gave highly uniform and well dispersed nano-sized Pd, PdCo and Co nanoparticle supported catalysts. The synthesized catalysts were activated with H2 (5%)/Ar at 400 °C to remove capping agents. These activated PdCo, Pd and Co/N-CMK-3 catalysts were tested for benzyl alcohol oxidation under solvent free conditions using oxygen as an oxidant at different temperatures (110–140 °C) and times (1–8 h) and compared with an equivalent carbon (Vulcan XC-72) supported catalyst. In the aerobic oxidation of alcohols, the PdCo/N-CMK-3 showed similar activity to the Pd/N-CMK-3 catalyst but only using 50% of the amount of Pd in a PdCo catalyst. An important role of Co is to reduce the bulk Pd content of the catalyst. This can be explained by a core-shell structure for the PdCo catalyst. The catalytic oxidation of a range of benzyl alcohols (no solvent, O2 as oxidant, 130 °C) in the presence of PdCo/N-CMK-3 typically gave aldehydes with conversions in the range 87–99% (selectivity 99%) after 5 h. The catalyst also retained its selectivity and activity after four recycles.

Mesoporous SnO<sub>2</sub> by Nanocasting Route Using Various Silica Templates for Gas Sensing Application

Mesoporous SnO2 was successfully synthesized via nanocasting route using various silica matrices likely KIT-6, SBA-15 and SBA-16 as hard templates. The chemical and structural properties of these materials were characterized by means of XRD, N2 adsorption-desorption and TEM analyses. All replica products exhibited well-defined mesoporous structures and large surface areas as well as highly crystalline frameworks. Sensors were fabricated from the as-prepared mesoporous SnO2 replicas and used to test the response to 1000 ppm of ethanol vapour at different operating temperatures. The results showed that the mesoporous SnO2 sensors nanocasted from KIT-6, SBA-15 and SBA-16 silica templates exhibits excellent gas response as compared to a bulk SnO2 material, suggesting the potential application of the sensor for detecting ethanol vapour. Maximum sensitivity (~ 18.7) was reached at 300 °C using mesoporous SnO2 sensor nanocasted from KIT-6 silica. It can be explained by the large surface area and well-defined mesostructure of SnO2(KIT-6), which lead to highly effective surface interaction between the ethanol molecules and the surface active sites.

Fe and N Functionalized-Ordered Mesoporous Carbon with Different Morphologies: Role of Fe on Surface Properties and Electrocatalytic Activity

Because of their high energy conversion efficiency, low pollution, low operating temperature, high power density, and wide range of applications, fuel cells have received a plethora of attention. Oxygen reduction reaction (ORR) takes place usually on Pt loaded on different carbon supports, but their large-scale commercial application has been precluded mainly by the high cost of the requisite noble metal. To overcome all the drawbacks of Pt or Pt-based catalysts, various efforts have been devoted to find its proper substitute. Heteroatom-doped carbon catalysts, due to their high stability, excellent electrocatalytic performance, and economic viability over costly Pt-based catalysts are being pioneered as a suitable alternative. Although heteroatom-doped porous carbon materials have evolved as one of best possible solutions in this regard, the probable synergy of heteroatom doping and textural properties has not been well investigated yet in details. In this work, a detailed investigation is carried out on Fe and N-functionalized ordered mesoporous carbon (FeN-OMC) as electrocatalyst ORR in both alkaline and acidic media. The FeN-OMCs with different morphology are synthesized by pyrolysis of iron phthalocyanine-infiltrated corresponding SBA-15 silica templates. The as-synthesized FeN-OMC materials show excellent electrocatalytic ORR activity with nearly four electron transfer process. While the activity in alkaline media is nearly equal to or better than commercial Pt catalyst in terms of onset potential and diffusion-limited current density, it closely follows in acidic media, which is a tremendous achievement for non-precious metal catalysts developed till date. The most interesting observation is that not only heteroatom, but textural properties also affect catalytic activity profoundly. The physical presence of Fe species may be necessary in the synthesis of active heteroatom-doped carbon for high ORR activity, but may be not necessary any more for the as-prepared doped carbon to play as electrocatalyst for ORR. Despite of being prepared with similar Fe and N content, the catalytic ability of FeN-OMC materials is gradually increased with decrease in mesopore channel length with maximum activity in thin platelet FeN-OMC. These observations demonstrate that structural morphology in addition to heteroatom and other textural properties, has significant synergistic influence on ORR catalysis in heteroatom-doped carbon materials.

White-light photoluminescence and photoactivation in cadmium sulfide embedded in mesoporous silicon dioxide templates studied by confocal laser scanning microscopy

SBA-15 and SBA-16 silica templates have been infiltrated with CdS by means of nanocasting using a hybrid precursor. The morphology and structure of both the SiO2@CdS nanocomposites and the silica-free CdS replicas have been characterized. The three-dimensional nanocrystalline CdS networks embedded in SBA-15 and SBA-16 silica templates exhibit broad photoluminescence (PL) spectra over the entire visible range, together with enhanced PL intensity compared to silica-free CdS replicas. These effects result from the role silica plays in passivating the surface of the CdS mesostructures. Furthermore, photoactivation is eventually observed during continuous illumination because of both structural and chemical surface modifications. Owing to this combination of properties, these materials could be appealing for solid-state lighting, where ultra-bright near-white PL emission is indispensable.

Ordered mesoporous boron-doped carbons as metal-free electrocatalysts for the oxygen reduction reaction in alkaline solution

Ordered mesoporous boron-doped carbons (BOMCs) were prepared by co-impregnation and carbonization of sucrose and 4-hydroxyphenylboronic acid into SBA-15 silica template. Nitrogen sorption, small angle X-ray diffraction (XRD), and transmission electron microscopy (TEM) reveals that BOMCs possess highly ordered mesoporous structure, uniform pore size distribution, and high surface area. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that B atoms can be successfully doped into the framework of OMCs. Due to the desirable characteristics of BOMCs, BOMCs are highly active, cheap, and selective metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline solution. Although B content is a key factor in determining ORR activity, the ORR activity of BOMCs is also dependent on the surface area. The high surface area of BOMCs facilitates the exposure of the active sites for ORR. BOMCs may be further exploited as potentially efficient and inexpensive metal-free ORR catalysts with good long-term stability in alkaline solution.

N-doped carbon nanowires synthesized from l-arginine for electrochemical application

N-doped carbon nanowires are synthesized by a simple impregnation method under low carbonization temperature. l-Arginine is adopted as carbon sources and nitrogen sources and SBA-15 is employed as hard template. The obtained carbon nanowires possess uniform and ultrafine diameter of around 6.5nm, in good accord with the pore size of the SBA-15 silica template. The probable mechanism is proposed that l-arginine is elongated to form long chains in the pore of SBA-15 through dehydration–condensation reaction. The as-synthesized carbon nanowires contain heteroatoms such as nitrogen and oxygen, which are very helpful to the pseudo-capacitance and the wettability of carbon materials. The experimental results demonstrate that N-doped carbon nanowires exhibit superior performance in supercapacitance properties.

Humidity Sensing Property of Mesoporous Indium Oxide

In this paper, mesoporous indium oxide has been synthesized by the hard template route from the SBA-15 silica template. The results characterized from XRD, and N2 adsorption-desorption demonstrated that the synthesis can be controlled successfully in nanometer (meso-structure) scale. The obtained sample was investigated as humidity sensing material by coating on a ceramic plate, and the humidity sensing performance can be enhanced up to more than three orders of magnitude without any doping. Further testing proved that it is a promising humidity sensing material and can be widely used, and a possible mechanism was also provided.

Influence of the preparation method on the morphology of templated NiCo2O4 spinel

The synthesis of NiCo2O4 spinel by several nanocasting strategies (i.e., multi-step nanocasting, one-step nanocasting and soft-templating), in which nickel and cobalt nitrates are used as precursors and Pluronic P123 as surfactant, is explored. First, in the multi-step nanocasting, the effect of the impregnation method (evaporation, solid–liquid and two-solvent) of the SBA-15 silica template on the morphology of NiCo2O4 replica is investigated. The evaporation method seems to be the best choice to obtain mesoporous NiCo2O4 powder which, after calcination at 375 °C and subsequent template removal, displays the highest surface area (93.1 m2/g). We have also checked the feasibility of the one-step nanoscating approach for the synthesis of ordered NiCo2O4 arrays, though this methodology entails severe difficulties, mainly related to the different decomposition temperature of the nitrate precursors and the P123 surfactant. Finally, randomly oriented, aggregated NiCo2O4 nanoparticles are obtained by means of P123 surfactant-assisted soft-templating approach.

Novel ice structures in carbon nanopores: pressure enhancement effect of confinement

We report experimental results on the structure and melting behavior of ice confined in multi-walled carbon nanotubes and ordered mesoporous carbon CMK-3, which is the carbon replica of a SBA-15 silica template. The silica template has cylindrical mesopores with micropores connecting the walls of neighboring mesopores. The structure of the carbon replica material CMK-3 consists of carbon rods connected by smaller side-branches, with quasi-cylindrical mesopores of average pore size 4.9 nm and micropores of 0.6 nm. Neutron diffraction and differential scanning calorimetry have been used to determine the structure of the confined ice and the solid-liquid transition temperature. The results are compared with the behavior of water in multi-walled carbon nanotubes of inner diameters of 2.4 nm and 4 nm studied by the same methods. For D(2)O in CMK-3 we find evidence of the existence of nanocrystals of cubic ice and ice IX; the diffraction results also suggest the presence of ice VIII, although this is less conclusive. We find evidence of cubic ice in the case of the carbon nanotubes. For bulk water these crystal forms only occur at temperatures below 170 K in the case of cubic ice, and at pressures of hundreds or thousands of MPa in the case of ice VIII and IX. These phases appear to be stabilized by the confinement.

MESOPOROUS CARBON POWDER GAS SENSORS FOR DETECTION OF CARBON MONOXIDE

This article reports a new class of silicon-based microgas sensors utilizing hexagonally-ordered mesoporous carbon powders (MCPs) as the sensitive film. The mesoporous carbon powders featuring high-specific surface area are replicated by the SBA-15 silica template and immobilized between Cr electrodes on a 9 × 9 cm silicon chip by using a.c. dielectrophoresis (DEP) process at room temperature. The silicon sensor platform comprises Cr microheaters embedded in a dielectric thin membrane manufactured by microelectromechanical systems back-etching techniques. It is shown that MCPs can be satisfactorily aligned along electric fields and accumulated to the electrode area. Investigations into CO detection are carried out to verify gas-sensitive characteristics of the MCP nanofilm. Our experimental results disclose the mesoporous carbon powders are successfully chemoresistive to CO , and demonstrate distinct resistance change with respect to ppm-level variation. In addition, response time, recovery time, and reproducible sensing behavior are experimentally obtained.

Microfabrication and chemoresistive characteristics of SBA-15-templated mesoporous carbon gas sensors with CMOS compatibility

We describe a new class of silicon-based gas sensors that employ gas-sensitive films made of hexagonally ordered mesoporous carbon nanopowders. The mesoporous carbon powders (MCPs) are replicated by the SBA-15 silica template and immobilized between interdigitated Cr electrodes on a 300 μm × 300 μm active area using an alternating current dielectrophoresis (DEP) process at room temperature. The silicon sensor platform comprises Cr microheaters embedded in a dielectric thin membrane formed by conventional back-etching techniques with microelectromechanical systems (MEMS) manufacturability and complementary metal oxide semiconductor (CMOS) compatibility. It is observed that MCPs can be satisfactorily aligned along electric fields and accumulated to the electrode region. Comprehensive investigations are carried out to evaluate the gas-sensitive characteristics of MCP nanoparticles to gases such as O 2 and NH 3 for the first time. Experimental results disclose that the amorphous carbon powders are chemoresistively sensitive to oxidising and reducing gas species, and demonstrate distinct resistance change with gas concentrations in ppm-level. Fast response times estimated as ∼100 s for O 2 and ∼90 s for NH 3 and reproducible response behaviour are observed. The measured characteristics reported in this paper make MCPs a competitive alternative to carbon nanotubes (CNTs) because of their superior porosity, high specific surface area and cost-effective immobilization process.

Synthesis and Electrochemical Property of Boron-Doped Mesoporous Carbon in Supercapacitor

Mesoporous carbon with homogeneous boron dopant was prepared by co-impregnation and carbonization of sucrose and boric acid confined in mesopores of SBA-15 silica template. Low-level boron doping shows catalytic effect on oxygen chemisorption at edge planes and alters electronic structure of space charge layer of doped mesoporous carbon. These characteristics are responsible for substantial improvement of interfacial capacitance by 1.5−1.6 times higher in boron-doped carbon than that in boron-free carbon with alkaline electrolyte (6 M KOH) and/or acid electrolyte (1 M H2SO4). This finding should be very useful for developing new doped carbon electrode materials for supercapacitors.

Polypyrrole-Based Nitrogen-Doped Carbon Replicas of SBA-15 and SBA-16 Containing Magnetic Nanoparticles

Polypyrrole-based ordered mesoporous carbons (OMCs) were synthesized via chemical vapor infiltration of pyrrole into pores of the SBA-15 and SBA-16 silica templates containing iron(III) chloride catalyst (FeCl3). After carbonization of polypyrrole at 800 °C and etching of the silica templates with hydrofluoric acid solution, nitrogen-doped and graphitic OMCs with incorporated magnetic nanoparticles were obtained. These materials were analyzed by CHNS elemental analysis, thermogravimetry (TG), nitrogen adsorption, small and wide angle powder X-ray diffraction (XRD), Raman spectroscopy, scanning, and transmission electron microscopy (TEM). The resulting carbon replicas retained the crystallographic symmetry of the silica templates: namely, P6mm in the case of the SBA-15 template, and Im3m in the case of the SBA-16 template. The uniformity, size, and volume of ordered mesopores in the carbon replicas were affected by structural properties of the templates used as shown by analysis of nitrogen adsorption isotherms and pore size distributions. A better infiltration of carbon precursor was achieved for the templates with larger pores, which resulted in the carbon replicas of improved adsorption and structural properties. Elemental analysis revealed the presence of nitrogen in the carbon replicas studied in the range of 3−8 wt %, whereas TG analysis of the replica samples in air gave about 2−5% residue, which was identified as hematite (Fe2O3). The presence of graphitic domains was confirmed by characteristic TG oxidation profile above 400 °C, the D and G bands on the Raman spectra, and the intense reflections on the wide angle XRD patterns. Powder XRD also showed the presence of extra-framework magnetic iron (α-Fe) and iron carbide (Fe3C) nanoparticles having crystallite size in the ranges of 40−80 and 20−40 nm, respectively. TEM images also revealed that these nanoparticles were larger than the carbon rods and pore widths of the SBA-15 carbon replica, which is in good agreement with the XRD-based estimation. The in situ EDS analysis of carbon rods and spheres showed that iron was present in the carbonaceous framework, which does not exclude the existence of much smaller nanoparticles, below 5 nm.

Synthesis of Nanowire and Hollow LiFePO4 Cathodes for High-Performance Lithium Batteries

The synthesis of nanowire and hollow LiFePO4 cathodes using the hard templates KIT-6 and SBA-15 is reported for high-performance lithium batteries. The two-dimensional hexagonal SBA-15 silica template with P6mm symmetry is used for the template that contains parallel cylindrical pores arranged with hexagonal symmetry, which serves to organize the wires into parallel bundles. On the other hand, three-dimensional cubic arrangement of pores in KIT-6 silica with Ia3d symmetry yields hollow morphology with mesopores. After impregnation of the template into a solution or after coating on the template with a solution consisting of LiFePO4 precursors, the silica template is removed and is subsequently fired at 700 °C. Electrochemical cycling of both the nanowire and hollow LiFePO4 cathodes demonstrates excellent rate capability even above 10C rate, showing >89% capacity retention of the initial capacity. Among them, the rate capability of the hollow cathode at 15C is higher than that of the nanowire cathode, show...

Mesoporous carbons as low temperature fuel cell platinum catalyst supports

Platinum catalysts supported on ordered mesoporous carbons (OMC) are described. The mesoporous carbon support, CMK3 type, was synthesised as an inverse replica of a SBA-15 silica template. The platinum catalysts (i.e. Pt 20 wt% and Pt 10 wt%, respectively), obtained through a conventional wet impregnation method, have been investigated to determine their structural characteristics and electrochemical behaviour. The electro-catalytic performance towards the oxygen reduction reaction (ORR) was compared to those of commercial Pt/C-Vulcan XTC72R (E-Tek) catalysts with the same Pt wt%, under the same experimental conditions. The two catalyst samples have allowed the effect of the variation of both the Pt to Nafion and Pt to the supporting carbon ratios to be studied. Electrochemical tests have been carried out in three different systems: a catalyst ink deposited on a glassy carbon rotating disk electrode (RDE), a gas diffusion electrode (GDE) in a three-electrode cell with H2SO4 as the electrolyte and a complete PEM single fuel cell. The first results indicate that the OMC performs slightly less well than commercial carbon supports, mainly in the complete fuel cell system. The data from the cell tests indicate a less effective distribution of Nafion on the OMC surface which, probably, decreases the platinum utilisation and the proton conductivity.