Solid Core Mesoporous Shell Silica Research Articles

An alternative HCMS carbon catalyst in bromine reduction reaction for hydrogen-bromine flow batteries

In this study, significantly active hollow core mesoporous shell (HCMS) carbon catalysts are synthesized for the hydrogen-bromine flow battery cathode electrode. As an alternative to cathode catalysts such as Pt/C or carbon black, high surface area HCMS carbons are synthesized and its effect on hydrogen-bromine flow battery performance has been investigated for grid-scale energy storage for the first time. HCMS carbon is synthesized by template replication of the solid core mesoporous shell silica spheres. By changing the amount of TEOS (1 mL, 6 mL, 10 mL) used during silica template formation, carbons with different core/shell structures have been produced (HCMS1, HCMS6, HCMS10). Structural characterizations of the synthesized cathode catalysts have been performed with SEM, TEM, and N2 adsorption analyses. Electrochemical characterization of catalysts has been performed by cyclic voltammetry analyses and flow battery performance tests. 0.50 W/cm2 peak power density obtained with HCMS1 carbon is promising compared to Pt-based catalysts and commercial carbons.

Carminic Acid Linked to Silica Nanoparticles as Pigment/Antioxidant Bifunctional Excipient for Pharmaceutical Emulsions.

The incorporation of pigments and natural polyphenols into inorganic matrices, resulting in a hybrid material that improves the resistance and chemical stability of the pigments and the antioxidant capacity of the materials, has been of great interest to the pharmaceutical, chemical and food industries. The aim of this work was to prepare and characterize a bifunctional pigment–antioxidant nanomaterial-based carminic acid-decorated solid core-mesoporous shell silica nanoparticles, evaluating its properties as a pigment, its antioxidant capacity and its properties as a chemical stabilizer of emulsions. The chemical stability of oil-in-water (O/W) Pickering emulsions was evaluated determining the stability of vitamin E solubilized in the oil phase. Carminic acid was attached through the action of coupling ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) agents, and the resulting spherical and homogeneous nanoparticles showed a diameter close to 175 nm. A notorious change of emulsion color was observed by the addition of the nanomaterial. Emulsions showed an attractive pink color, and when the pH was adjusted to pH 3 and pH 9, a change in color was observed, analogous to carminic acid in solution. The nanomaterial incorporation also improved chemical stability, decreasing vitamin E consumption to 9.26% of the initial value, demonstrating an important antioxidant effect of the developed nanomaterial.

Iron promoted nitrogen doped porous graphite for efficient oxygen reduction reaction in alkaline and acidic media

Nitrogen doped porous graphite with trace iron and hollow spherical shape is synthesized by using glucose as carbon source, dopamine hydrochloride as N source, Fe(NO3)3 as Fe source and solid core mesoporous shell silica sphere as template. The glucose and dopamine is carbonized to N-doped carbon; the silica template produces porous and hollow shape with much edges or intrinsic defects; and the addition of Fe increases pore diameter, graphitization degree, total N and pyridinic N content. The characterizations confirm that the doping N leads to active sites for oxygen reduction reaction; the Fe forms active NFe species yet electrochemically unstable, which is removed at last. The intrinsic graphite defect and its synergistic effect with doping N are also believed to favor ORR. The material with the above features corresponds to superior oxygen reduction activity in both alkaline and acidic media to commercial Pt/C. The as-synthesized material with few Fe also shows excellent stability due to the graphitized matrix and little metal with excellent anti-methanol and anti-CO performances. The durability of catalysts is also confirmed by using graphite as counter electrode to exclude the impact of dissolution of Pt counter electrode and its re-deposition on the working electrode.

Metal-free mesoporous carbon with higher contents of active N and S codoping by template method for superior ORR efficiency to Pt/C

Carbon materials with more exposed N or S atoms result in higher activity for oxygen reduction reaction. In this paper, mesoporous carbon based materials with 5.3 at% of N and 7.1 at% of S are synthesized (defined as porous-S-N-C). The solid core mesoporous shell silica as template results in mesoporous structure of the porous-S-N-C which favors mass transfer and higher doping (both increase by ∼20%) and exposing of active N and S atoms. The electrochemical characterization results show that the mesoporous structure and the S modification favor much to the N-C based catalysts in catalyzing ORR. Typically, the porous-S-N-C has a 3.99 electron transfer number at 0.4 V, and higher ORR efficiency, much better CO tolerance, much better methanol tolerance and much higher electrochemical stability than commercial Pt/C. This novel method of improving the contents of doped and exposed N and S atoms is imagined to be applied to preparation of other high-content-heteroatom doped materials.

Small-sized Pt particles on mesoporous hollow carbon spheres for highly stable oxygen reduction reaction

Mesoporous hollow carbon spheres (HCSs) are prepared using glucose as carbon source and solid core mesoporous shell silica spheres (SCMSSs) as templates. Pt particles are then loaded on the HCSs as electrocatalyst and used for oxygen reduction reaction (ORR) in acidic media. Physical measurements display that the HCSs have high surface area (1163m2g−1), large pore volume (2.8cm3g−1) and mesoporous structure (9.8nm in diameter), which are favorable for uniform dispersion and stable loading of small-sized Pt particles, and efficiently improve the mass transfer in catalytic reactions. Cyclic voltammogram measurements show that the mass current density on Pt/HCS electrocatalyst (192.2 mA mgPt−1) is 1.7 times as high as that of commercial Pt/C (TKK) for ORR. Furthermore, the mesopores of HCSs give Pt/HCS more electrocatalytic stability due to stronger physical interaction force.

Smaller Pt particles supported on mesoporous bowl-like carbon for highly efficient and stable methanol oxidation and oxygen reduction reaction

Bowl-like carbons (BLCs) with mesoporous structure are prepared using glucose as carbon source and solid core mesoporous shell silica spheres (SCMSSs) as templates. Pt particles are then loaded on the BLCs as electrocatalyst and used for both methanol oxidation and oxygen reduction reaction (ORR) in acidic media. Physical measurements display that the BLCs are formed due to flowing of melted glucose along the mesoporous shell of the SCMSSs. Moreover, the BLCs with high surface area (1108.3 m2 g−1), large pore volume (2.7 cm3 g−1) and mesoporous structure (9.4 nm in diameter) are beneficial for uniform dispersion and stable loading of smaller noble metal particles, and efficiently improve the mass transfer in catalytic reactions, compared to carbon powders. Cyclic voltammogram measurements show that the mass current densities on Pt/BLC electrocatalyst are 2.6 times (1846mAmgPt−1) for methanol oxidation and 1.6 times (180.6mAmgPt−1) for ORR as high as that of commercial Pt/C (TKK). Furthermore, the mesopores give Pt/BLC more electrocatalytic stability due to stronger physical interaction force.

Titanium Containing Solid Core Mesoporous Silica Shell: A Novel Efficient Catalyst for Ammoxidation Reactions

Novel titanium containing solid core mesoporous shell silica has been synthesized by using octadecyltrichloro silane and triethylamine. The synthesized material was characterized by various physicochemical techniques. The mesoporous character of the material has been revealed from PXRD studies. The presence of octadecyltrichloro silane and triethylamine in the sample has been confirmed from EDAX studies. TG/DTA analysis reveals the thermal characteristics of the synthesized material. The presence of titanium in the frame work and its coordination state has been studies by UV-vis DR studies and XPS analysis. Chemical environment of Si in the framework of the material has been studied by 29 SiMASNMR studies. The surface area of the material is found to be around 550 m 2 g �1 and pore radius is of nano range from BET analysis. The spherical morphology and particle size of the core as well as shell has been found to be 300 nm and 50 nm respectively from TEM analysis. The catalytic application of this material towards the synthesis of caprolactam from cyclohexanone in presence of hydrogen peroxide through ammoxidation reaction has been investigated. The optimum conditions for the reaction have been established. The plausible mechanism for the formation of core silica and conversion of cyclohexanone has been proposed.

Structural and Catalytic Properties of a Novel Vanadium Containing Solid Core Mesoporous Shell Silica Catalysts for Gas Phase Oxidation Reaction

Structural and Catalytic Properties of a Novel Vanadium Containing Solid Core Mesoporous Shell Silica Catalysts for Gas Phase Oxidation Reaction

Smart synthesis of hollow core mesoporous shell carbons (HCMSC) as effective catalyst supports for methanol oxidation and oxygen reduction reactions

The present paper describes an easy and quick synthesis of hollow core mesoporous shell carbon (HCMSC) simply templated from unpretreated solid core mesoporous shell silica using a cheap precursor like sucrose. Physical characterizations showed uniform spherical carbon capsules with a hollow macroporous core of ca. 305- and 55-nm-thick mesoporous shell, forming a well-developed 3-D interconnected bimodal porosity. High specific surface area and large pore volume were also confirmed, suggesting the obtained HCMSC as a promising catalyst support. HCMSC-supported Pt (nominal 20 wt.%) with an average Pt particle size of 1.9 nm was synthesized by wet impregnation, and a signal of strong interaction between carbon support and platinum was confirmed by X-ray photoelectron spectroscopy. In cyclic voltammetry and linear sweep voltammetry tests, the Pt/HCMSC electrode showed significantly higher electrocatalytic activity for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) if compared with commercial Pt/Vulcan catalyst. The durability tests by cyclic voltammetry showed for the Pt/HCMSC a lower electrochemical active surface area loss than the commercial one in acidic solution. All the primary tests suggested that the Pt/HCMSC, due to its particular structure and the high dispersion of noble metal particles, is a promising catalyst for fuel cell applications, for MOR and ORR.

Highly Stable and Magnetically Recyclable Mesoporous Silica Spheres Embedded with FeCo/Graphitic Shell Nanocrystals for Supported Catalysts

We have synthesized highly stable and magnetically recyclable mesoporous silica spheres embedded with FeCo-graphitic carbon shell nanocrystals (FeCo/GC@MSS) by a simple one-step chemical vapor deposition (CVD) method. Solid core-mesoporous shell silica spheres with an average diameter of ∼400 nm are used as supports not only for the synthesis of the FeCo/GC nanocrystals but also for catalysts after the synthesis of the FeCo/GC@MSS. The FeCo/GC nanocrystals in the mesoporous silica spheres exhibit superparamagnetism with ultrahigh saturation magnetization up to 215 e.m.u./metal g at room temperature. The FeCo/GC@MSS is chemically stable against acid etching and oxidation, which enable the FeCo/GC@MSS to be used as a support for an acid catalyst, phosphomolybdic acid (PMA). We have shown that PMA-loaded FeCo/GC@MSS works as an excellent recyclable reagent system that catalyzes propargylation of 1,3-diphenyl-2-propyn-1-ol with phenol.

Effect of the templates on the synthesis of hollow carbon materials as electrocatalyst supports for direct alcohol fuel cells

Hollow carbon hemispheres (HCHSs) have been synthesized by the aid of polystyrene spheres (PSs) or solid core mesoporous shell silica (SCMSS) as templates. A possible formation mechanism is presented. Scanning and transmission electron microscopic measurements show that the HCHSs have uniform morphologies and high Brunauer–Emmett–Teller surface areas. The high surface areas are beneficial for the dispersion of precious metal nanoparticles. Pd nanoparticles deposited on HCHSs show uniform particle distribution and exhibit excellent performance for alcohol electrooxidation. The ratios of the peak current densities of the ethanol oxidation on Pd/HCHS-PS or Pd/HCHS-SCMSS to Pd/C are 2.74 and 3.35, respectively. The hemispherical structure results in an improvement in the mass transfer and higher alcohol concentrations can be used to increase the energy density of direct alcohol fuel cells.

Synthesis of mesoporous hollow carbon hemispheres as highly efficient Pd electrocatalyst support for ethanol oxidation

The synthesis procedure of the highly mesoporous hollow carbon hemispheres (HCHs) using glucose as carbon source and solid core mesoporous shell silica (SCMSS) as template and the formation mechanism of the HCHs have been presented. The HCHs show an ultrahigh surface area of 1095.59 m 2 g − 1 and an average mesopore size of 9.38 nm. The hemispherical structure with large mesopores also results in the improvement in the mass transfer and therefore more concentrated ethanol solution can be used to increase the energy density. The additional advantage of the HCHs compared to the hollow carbon spheres is that they can provide the similar surface area at reduced volume. The current densities of ethanol oxidation on Pd nanoparticles supported on HCH (Pd/HCH) electrocatalyst are three times as many as on Pd/C at the same Pd loadings.

Titanium-Doped Solid Core-Mesoporous Shell Silica Particles: Synthesis and Catalytic Properties in Selective Oxidation Reactions

AbstractNear monodisperse spherical particles composed of a nonporous silica core covered by a Ti-doped hexagonally arranged mesoporous silica shell, Ti-SCMS, as well as spherical submicron-size particles of Ti-MCM-41, have been synthesized for the first time and characterized by elemental analysis, N 2 adsorption, XRD, TEM and DR-UV spectroscopy. The mesoporous Ti,Si-shell has a thickness of about 45 nm and incorporates isolated Ti centers in tetrahedral coordination. Catalytic properties of Ti-SCMS and Ti-MCM-41 have been studied in selective oxidation of three representative bulky organic substrates, 2,3,6-trimethylphenol, methyl phenyl sulfide and caryophyllene, with aqueous H 2 O 2 in MeCN medium. Ti-SCMS appeared to be more active and selective in the H 2 O 2 -based selective oxidation reactions compared to Ti-MCM-41, thus demonstrating an advantage of conducting a catalytic process in a thin mesoporous Ti,Si-shell.Graphical AbstractNear monodisperse spherical silica particles with a solid inert core covered by a well-ordered mesoporous shell, containing site-isolated Ti centers, have been synthesized, characterised and found to be highly active in selective oxidations with H 2 O 2 .[IMAGE]

Direct grafting of ε‐caprolactone on solid core/mesoporous shell silica spheres by surface‐initiated ring‐opening polymerization

AbstractPoly(ϵ‐caprolactone) (PCL) was formed on Solid core/mesoporous shell (SCMS) silica surface by surface‐initiated ring‐opening polymerization (SI‐ROP). The SI‐ROP of ϵ‐caprolactone was achieved by heating a mixture of SCMS silica, ϵ‐caprolactone and the tin(II) 2‐ethylhexanoate [Sn(Oct)2] in a anhydrous toluene for 20 h at different temperatures viz. 40, 60, and 80°C. The PCL grafted SCMS silica was characterized by fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X‐ray, differential scanning calorimetry and scanning electron microscopy (SEM). The FTIR spectroscopic analysis reveals the formation of ester linkage between PCL and hydroxyl terminated SCMS silica. TGA investigation shows increase in PCL content on SCMS silica surface with increase in reaction temperature. The SEM photographs clearly show the formation of PCL polymer on the SCMS silica surface without altering the spherical nature of SCMS silica. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008