The size modulation of hollow mesoporous carbon spheres synthesized by a simplified hard template route

Hollow mesoporous carbon spheres (HMCSs) have been prepared by a simplified replication route from a solid silica core/mesoporous silica shell aluminosilicate (SCMS-Al) template, which was synthesized by directly incorporating aluminum species into the mesoporous framework during template synthesis. The size of HMCSs can be tuned between 80 and 470 nm by simply changing the diameters of SCMS-Al. The HMCSs have uniform mesopores with a narrow pore size distribution (3.4-4.1 nm), and high surface area, (890-1150 m²/g) and total pore volumes (0.75-1.15 cm³/g). The techniques of N₂ sorption isotherms, TEM, EDX and SEM were used to characterize the as-synthesized spheres.     

High-performance carbon nanotube-implanted mesoporous carbon spheres for supercapacitors with low series resistance

Carbon nanotube-implanted mesoporous carbon spheres were prepared by an easy polymerization-induced colloid aggregation method using gelatin as a soft template. Scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption measurements reveal that the materials are mesoporous carbon spheres, with a diameter of ∼0.5–1.0 μm, a specific surface area of 284 m²/g and average pore size of 3.9 nm. Using the carbon nanotube-implanted mesoporous carbon spheres as electrode material for supercapacitors in an aqueous electrolyte solution, a low equivalent series resistance of 0.83 Ω cm² and a maximum specific capacitance of 189 F/g with a measured power density of 8.7 kW/kg at energy density of 6.6 Wh/kg are obtained.     

Direct template synthesis of mesoporous carbon and its application to supercapacitor electrodes

A direct templating method which is facile, inexpensive and suitable for the large scale production of mesoporous carbon is reported herein. A meso-structure surfactant/silicate template was made in a solution phase and resorcinol-formaldehyde as a carbon precursor was incorporated into the template solution. After aging, carbonization and hydrofluoric acid (HF) etching, mesoporous carbon was obtained. Using X-ray diffraction, scanning and transmission electron microscopy and nitrogen sorption, the synthesis mechanism of the mesoporous carbon was elucidated. According to the small angle X-ray scattering measurements, the surface became smoother after the removal of the silica, indicating that the silica was mostly located at the pore surface of the carbon. Also, the calculation of the pore volume demonstrated that the silica was transferred into the pores of the carbon without structural collapse during HF etching. When the prepared mesoporous carbon was applied to a supercapacitor electrode, the rectangular shape of the cyclic voltammogram was less collapsed, even at a high scan rate, which is indicative of its high rate capability. This was due to the low resistance of the electrolyte in the pores (3.8 Ω cm²), which was smaller than that of conventional activated carbon electrodes and even comparable to that of ordered mesoporous carbon electrodes. This improved performance was probably due to the well developed mesoporosity and high pore connectivity of the prepared mesoporous carbon.     

Sol-gel synthesis of titania hollow spheres

TiO₂ hollow spheres are prepared by a convenient sol-gel method at room temperature. The products were characterized by XRD, FESEM, TEM and FT-IR. It was found that these spheres are hollow inside with outer diameters of 200-500 nm. The average mesoporous diameter is about 9.8 nm. And the BET surface area and specific pore volume are about 161.9 m²/g and 0.441 cm³/g, respectively.     

Palladium supported on functionalized mesoporous silica as an efficient catalyst for Heck reaction

Pd nanoparticles supported in functionalized mesoporous silica were prepared. Mesoporous silica support was modified with [3-(2-aminoethyl aminopropyl)] trimethoxysilane. Palladium ions were grafted onto the functionalized mesoporous silica and reduced with hydrazine hydrate to obtain the Pd nanoparticles supported on functionalized mesoporous silica. The Pd loading in the nanocomposite of Pd supported on the functionalized mesoporous silica is 4.30 wt%. CO chemisorption analysis on the nanocomposite shows a Pd dispersion as high as 35% and a Pd surface area of 156 m²/g. The surface area, pore size, and pore volume decrease slightly with the incorporation of the Pd nanoparticles into the functionalized mesoporous silica. Pd supported on the functionalized mesoporous silica with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Heck carbon-carbon coupling reaction. The catalyst can be reused for at least six recycles in air with only a minor loss of activity.     

Templated synthesis of nanosized mesoporous carbons

Mesoporous carbon materials formed by nanosized particles have been synthesized by means of a nanocasting technique based on the use of mesostructured silica materials as templates. We found that the modification of the chemical characteristics of the surfactant employed allows mesostructured silica materials with particle sizes <100 nm to be synthesised. The mesoporous carbons obtained from these silica materials retain the structural properties of the silica used as template and consequently they have a particle size in the 20-100 nm range. These carbons exhibit large BET surfaces areas (up to 1300 m² g⁻¹) and high pore volumes (up to 2.5 cm³ g⁻¹), a framework confined porosity made up of uniform mesopores (3.6 nm) and an additional textural porosity arising from the interparticle voids between the sub-micrometric particles. The main advantage of nanometer-sized mesoporous carbons in relation to the micrometer-sized carbons is that they have enhanced mass transfer rates, which is important for processes such as adsorption or catalysis.     

Synthesis of hollow silica spheres SBA-16 with large-pore diameter

Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent, tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH₄F. The size of these spheres is in the range of 10 to 30 μm. The shell is about 700 nm thick and consists of large pores, ~ 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m²/g. The formation mechanism of the silica hollow spheres is discussed.     

Synthesis and characterization of ordered mesoporous silicon carbide with high specific surface area

Ordered mesoporous silicon carbide with a high specific surface area was prepared using poly(methlysilylene)ethynylene by utilizing mesoporous silica SBA-15 as a template which was etched off after pyrolysis in an argon atmosphere. The obtained sample is mainly composed of randomly oriented β-SiC crystallites, and it exhibits an ordered mesoporous structure, a high surface area of 511 m²/g, a large pore volume of 0.61 cm³/g, and narrow pore-size distributions of 4 nm. The rough surface and high order of the material that result from the strong interconnections of the SiC products are the main reasons for such high surface areas. The mesoporous ceramics have stability even after re-treatment at 900 °C for 2 h under an air atmosphere.     

A dual template method for synthesizing hollow silica spheres with mesoporous shells

PS/silica core/shell composites were synthesized by the modified Stöber method using polystyrene spheres and cetyltrimethylammonium bromide as dual templates under room temperature. The silicate species and the templates were self-assembled to form mesoporous silica shell on the surface of the PS spheres. Hollow silica spheres with mesoporous shell were obtained by removing the polymer core and the templates through calcination. The hollow silica spheres showed high specific surface area of 1099.5 m²/g and narrow pore size distribution centered at 2.31 nm.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Mesoporous indium oxide synthesized via a nanocasting route

The synthesis of crystalline mesoporous indium oxide by using a mesoporous carbon (CMK-3) as hard template is described. Transmission electron microscopy (TEM) exhibits the presence of mesoporous structure in our sample and the corresponding wide-angle X-ray diffraction (XRD) pattern confirmed the crystalline wall of sample. N₂ adsorption measurement exhibits the synthesized crystalline mesoporous indium oxide possesses a specific surface area of 39 m²/g and the total pore volume of 0.17 cm³/g, and the corresponding pore size distribution curve reveals the presence of a mesopore of 7.0 nm in maximum. Our work demonstrates that the maintenance of the ordered structure of carbon template is very significant for obtaining high quality replicas via the nanocasting route.     

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.     

Mesoporous nickel (or cobolt)-doped silica-pillared clay: Synthesis and characterization studies

The metals-doped silica-pillared clay (SPC) materials with ordered pore structure in the gallery were obtained by a surfactant-directed assembly of silica species in the interlayer space of natural montmorillonite (MMT). The novel method afforded SPC derivatives with basal spacings of 4.4-4.5 nm, BET specific surface areas of 382.4-472.6 m²/g, pore volumes of 0.64-0.71 cm³ g⁻¹ and uniform pores (3.6 nm) between the layers. The main nickel and cobalt species was tetrahedrally coordinated Ni²⁺ or Co²⁺ in the gallery silica framework. Our results indicate that surfactant plays a decisive role in pore formation, because in acts as a micelle-like template during the hydrolysis of TEOS. In particular, the formation of metal-ammonia complex and rapid adsorption by surfactant in galleries controls metal species outflow from interlayers and contributes to the formation of metal species containing firm silica-pillars.     

Simple synthesis of hollow carbon spheres from glucose

Hollow carbon spheres were prepared by the reaction between glucose and Zn particles at 550 °C. Scanning and transmission electron microscopies reveal that most of the spheres are about 1-2 µm in diameter, similar to the sizes of the Zn particle. The shells of the spheres are comprised of numerous hollow nanospheres with the diameter of 10-100 nm. The specific surface area of the spheres is 207 m²/g. The Zn particles act as both the reactant and the template for the micron-scale spheres, and the H₂ bubbles generated during the reaction as the template for the hollow nanospheres.     

Honeycomb-like graphitic ordered macroporous carbon prepared by pyrolysis of ammonium bicarbonate

Honeycomb-like graphitic macroporous carbon (HGMC) was synthesized by means of pyrolysis of NH₄HCO₃ using Mg powder as reductant in an autoclave at 550 °C. The characterization of structure and morphology was carried out by X-ray diffraction (XRD), Raman spectrum, field-emission scanning electron microscopy (FESEM), and (High-resolution) transmission electron microscope [(HR)TEM]. The results of nitrogen adsorption-desorption indicate that the products are macropore materials with the pore size of 1-3 μm, and the Brunauer-Emett-Teller (BET) surface area was 14 m²/g. As a typical morphology, the possible growth process of HGMC was also investigated and discussed. The experimental results show that the in situ formed MgO microparticles play a template role during the HGMC formation.     

Synthesis of spheroidal ordered mesoporous carbon materials from silica/P123/butanol composites

Spheroidal ordered mesoporous carbon materials with diameter of 2–10 μm were synthesized by direct carbonization of silica/triblock copolymer P123/butanol composites using P123 and butanol as the structure-directing agents and carbon precursors. The morphologies, structures and pore characteristics of the carbon materials were investigated by scanning and transmission electron microscopes, X-ray diffraction, and nitrogen sorption. It was found that the material possesses a cubic ordered mesoporous structure with Ia3d symmetry. The butanol addition directly affects the carbon morphology and pore structure. When the mass ratio of butanol to P123 is 0.5:1, the product exhibits a perfectly spheroidal morphology with a specific surface area of 1236 m² g⁻¹ and a total pore volume of 1.26 cm³ g⁻¹. The formation mechanism of the spheroidal ordered mesoporous carbon materials is discussed briefly.     

Synthesis and characterization of ordered mesoporous silica by using polystyrene microemulsion as templates

A simple room temperature synthesis of pure mesoporous silica by using a homemade and functional template: polystyrene microemulsion is reported. The process consists of HCl-catalysed sol-gel reactions of tetraethyl orthosilicate (TEOS) in polystyrene microemulsion, followed by removal of the template via solvent extraction or calcining. X-ray diffraction, Transmission Electron Microscope and N₂ adsorption-desorption isotherms are then used to characterize the mesostructure. The results indicate that the synthesized mesoporous silica has a large BET surface area with more than 900 m²/g, large pore volume with more than 0.8 cm³/g and ordered mesopore-structure. This provides a possible way to control the meso-structure and pore size of mesoporous materials via potential functional templates.     

Preparation of high nickel-containing MCM-41-type mesoporous silica via a modified direct synthesis method

A method with modifying tetraethyl orthosilicate (TEOS) with nickel species has been developed for the synthesis of mesoporous silica with high nickel content (11.8 wt.% of Ni or even higher). With the method, MCM-41-type materials were obtained with high BET surface area reaching 868 m²/g and pore volume up to 0.73 cm³/g. The materials were characterized by means of X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N₂ adsorption, Fourier transform infrared and X-ray photoelectron spectroscopy. Nickel species were incorporated into the silica frameworks. The mesostructures still remain after activation using H₂ at 773 K.     

Synthesis of mesoporous hydroxyapatite using a modified hard-templating route

Mesoporous polycrystals of hydroxyapatite-calcium are synthesized via a modified hard-templating route. The structure properties of hydroxyapatite-calcium are characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. Wide-angle X-ray diffraction and Fourier transform infrared spectroscopy measurements reveal that the crystalline grains consist of highly crystalline pure hydroxyapatite phases. Transmission electron microscopy results show that rod-like hydroxyapatite-calcium grains with an average diameter of about 100 nm long and about 20 nm wide are uniformly distributed, which are also observed with an average pore size of 2-3 nm. Based on N₂ adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of mesoporous hydroxyapatite-calcium are 2.73 nm, 42.43 m² g⁻¹ and 0.12 cm³ g⁻¹, respectively.     

New mesoporous silica/carbon composites by in situ transformation of silica template in carbon/silica nanocomposite

Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3?nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8?nm) and macropores (ca 300?nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909?m²/g) and large pore volume (ca 0.73?cm³/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.