Facile synthesis of ordered mesoporous carbons with high thermal stability by self-assembly of resorcinol-formaldehyde and block copolymers under highly acidic conditions

The effect of phenols reactivity with formaldehyde on the formation of ordered mesoporous carbons has been investigated. A strategy to accelerate the polymerization of phenolic resins by using strongly acidic conditions is proposed. The self-assembly of resorcinol-formaldehyde and block copolymers (e.g., F127) under highly acidic concentrations (e.g., 1.5 M HCl) is probably driven by the I+X-S+ mechanism and hydrogen bonding and affords a highly reproducible approach for synthesis of ordered mesoporous carbons. The synthesis can be readily scaled up with no change in sample quality. The carbon material obtained (denoted as C-ORNL-1) exhibits highly ordered hexagonal mesostructure, with a typical BET surface area of approximately 600 m2/g, pore size of 6.3 nm, and pore volume of approximately 0.60 cm3/g. One of the unique structural features of C-ORNL-1 is its high thermal stability; it can be graphitized at 2600 degrees C while considerable mesoporosity is maintained.     

Organic acid-assisted soft-templating synthesis of ordered mesoporous carbons

A series of soft-templated ordered mesoporous carbons (OMCs) was synthesized by using resorcinol and formaldehyde as carbon precursors, triblock copolymer Pluronic F127 as a soft-template, and an organic acid (acetic, benzoic, citric, oxalic, or succinic) as a polymerization reaction catalyst. The aforementioned organic acids were strong enough to facilitate the formation of ordered mesophases by the block copolymer template used and to catalyze the polymerization reaction of resorcinol and formaldehyde in this template. The use of weak organic acids instead of strong inorganic acids such as HCl eliminated inorganic anions from the reaction environment and resulted in high surface area OMCs. Basically, the resulting carbons showed the surface areas and pore volumes comparable to those reported for the carbons prepared under similar conditions but in the presence of strong inorganic acids. Electron microscopy analysis proved the presence of ordered mesopores, whereas thermogravimetric analysis showed a good thermal stability of these carbons.     

Controlled synthesis of highly dispersed platinum nanoparticles in ordered mesoporous carbons

A novel route has been developed to fabricate ordered carbon mesoporous materials with well-dispersed, highly stable Pt nanoparticles of ca. 2-3 nm on the pore walls using platinum acetylacetonate as the co-feeding carbon and Pt precursor.     

A family of ordered mesoporous carbons derived from mesophase pitch using ordered mesoporous silicas as templates

A variety of ordered mesoporous carbons (OMCs) were synthesized using ordered mesoporous silicas (OMSs) as hard templates and the mesophase pitch (MP) as a carbon precursor. The synthesis included the mixing of OMS with MP, the infiltration of OMS with MP at 450–550?°C and the carbonization of MP in OMS/MP composite followed by the dissolution of the OMS template. OMCs with structures of two-dimensional hexagonal arrays of nanorods and three-dimensional arrays of nanospheres were obtained through the replication of silica templates, including large-pore SBA-15, KIT-6, large-pore FDU-12 and SBA-16. In particular, 2-D hexagonal array of carbon nanorods (CMK-3 carbon) with (100) interplanar spacing of ～13 nm as well as an array of carbon nanospheres arranged in the face-centered cubic structure with the unit-cell parameter of 33 nm were successfully prepared. The specific surface areas of the resulting carbons were up to 400 m²/g, and the total pore volumes were up to 0.43 cm³/g, with the highest values achieved when the MP infiltration temperature was 500?°C. The OMCs exhibited narrow mesopore size distributions. As inferred from XRD, the frameworks of OMCs featured semi-graphitic structures even though moderate carbonization temperature (850?°C) was employed.     

Facile synthesis for ordered mesoporous gamma-aluminas with high thermal stability

The facile synthesis of highly ordered mesoporous aluminas with high thermal stability and tunable pore sizes is systematically investigated. The general synthesis strategy is based on a sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous aluminas possess a highly ordered 2D hexagonal mesostructure, which is resistant to high temperature up to 1000 degrees C. Ordered mesoporous structures with tunable pore sizes are obtained with various precursors, different acids as pH adjustors, and different block copolymers as templates. These mesoporous aluminas have large surface areas (ca. 400 m2/g), pore volumes (ca. 0.70 cm3/g), and narrow pore-size distributions. The influence of the complexation ability of anions and hydro-carboxylic acid, acid volatility, and other important synthesis conditions are discussed in detail. Utilizing this simple strategy, we also obtained partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor. FTIR pyridine adsorption measurements indicate that a large amount of Lewis acid sites exist in these mesoporous aluminas. These materials are expected to be good candidates in catalysis due to the uniform pore structures, large surface areas, tunable pore sizes, and large amounts of surface Lewis acid sites. Loaded with ruthenium, the representative mesoporous alumina exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.     

Nitrogen-doped cobalt nanoparticles/nitrogen-doped plate-like ordered mesoporous carbons composites as noble-metal free electrocatalysts for oxygen reduction reaction

In this work, nitrogen-doped cobalt nanoparticles/nitrogen-doped plate-like ordered mesoporous carbons(N/Co/OMCs) were used as noble-metal free electrocatalysts with high catalytic efficiency. Compared with OMCs with long channel length, due to more entrances for catalytic target accessibility and a short pathway for rapid diffusion, the utilization efficiency of cobalt nanoparticles inside the plate-like OMCs with short pore length is well improved, which can take full advantage of porous structure in electrocatalysis and increase the utilization of catalysts. The active sites in N/Co/OMCs for oxygen reduction reaction(ORR) are highly exposed to oxygen molecule, which results in a high activity for ORR. By combination of the catalytic properties of nitrogen dopant, incorporation of Co nanoparticles, and structural properties of OMCs, the N/Co/plate-like OMCs are highly active noble-metal free catalysts for ORR in alkaline solution.     

Facile synthesis of ordered mesoporous molybdenum carbide electrocatalysts for high-performance hydrogen evolution reaction

In this study, a simple method was designed to prepare ordered mesoporous carbons embedded with molybdenum without any extreme conditions. We prepared three different ordered molybdenum carbide materials with mesoporous structures to explore the influence of the structure of molybdenum-based materials on the HER catalytic efficiency. The ordered mesoporous molybdenum carbide catalysts (CMK-3-MoCx, fCMK-3-MoCx, CMK-8-MoCx) were characterized by SEM, TEM, XRD, nitrogen adsorption-desorption and XPS. The HER is catalyzed efficiently on the three electrocatalysts, fCMK-3-MoCx shows the best HER electro-catalytic performance with a small onset potential of −0.06 V vs. RHE, a low tafel slope of 66 mV dec⁻¹ and a small over-potential value of 89 mV at 10 mA cm⁻². This excellent performance on HER is due to its high specific surface area and highly ordered mesoporous structure that resulted in excellent proton transport efficiency and high electron transfer rate. Our results provide a new research direction for the application of flat ordered mesoporous structures in catalysis.     

Synthesis of ordered mesoporous carbons with channel structure from an organic-organic nanocomposite

Mesoporous carbons with ordered channel structure (COU-1) have been successfully fabricated via a direct carbonization of an organic-organic nanocomposite.     

Facile synthesis of ordered magnetic mesoporous gamma-Fe2O3/SiO2 nanocomposites with diverse mesostructures

On the basis of a sol–gel process, a facile, low cost, and one-step approach for preparing ordered magnetic mesoporous γ-Fe₂O₃/SiO₂ nanocomposites by an evaporation-induced self-assembly (EISA) approach is presented. Various mesostructured silica materials (P6mm or Im3m) incorporated with different amounts of iron oxide (n_Si/n_Fe=9/1, 8/2, 7/3, respectively) were synthesized and characterized by XRD, TEM, N₂-sorption analyses, and superconducting quantum interference device (SQUID) magnetometer. The HCl-leaching experiments together with TEM micrographs and nitrogen sorption analysis suggested that most of the γ-Fe₂O₃ domains of several nanometers were embedded in the silica walls, rather than dispersed in the mesopores, which could cause the significant pore clogging reported in some studies. The release behaviors of lysozyme from these magnetic porous nanocomposites were investigated for the possible application of drug targeting and control release. The influence of iron precursors was also studied and a possible mechanism was proposed. The hydrolysis of Fe³⁺ ions under weakly acidic conditions and the induced formation of SiOFe bonds may account for the synthesis of this kind of nanocomposite. These multifunctional nanostructured materials would have a wide range of applications in toxin removal, catalysis, waste remediation, and biological separation as well as novel drug-carrier technologies.     

Facile synthesis of highly ordered mesoporous ZnTiO3 with crystalline walls by self-adjusting method

Highly ordered mesoporous ZnTiO(3) with crystalline walls was directly prepared by a sol-gel process combined with evaporation induced self-assembly in ethanol, using amphiphilic triblock copolymers as structure directing agents. The whole process is self-adjusting to organize the network-forming metal oxide species without additional acid or base. The mesoporous material is pure cubic-phase ZnTiO(3) and has large surface area (up to 134 m(2)/g), large pore volume (0.17 cm(3)/g), and narrow pore size distribution (3-4.5 nm). The optic behavior was systematically studied, which is very helpful to understand the mesoporous ZnTiO(3) material either in fundamental study or for potential applications in optics and catalysis. This work provides a "self-adjusting" approach to fabricate the mesoporous functional materials with diverse compositions: the diverse hydrolysis-condensation kinetics of various metal oxides is homogenized to yield stable multicomponent precursors. The development of such a simple, versatile, and reproducible method is important for applications in practice.     

Facile synthesis of thick ordered mesoporous TiO2 film for dye-sensitized solar cell use

Crack-free thick ordered mesoporous TiO₂ films with excellent optical quality have been synthesized by combination of “Doctor Blade” technique and a two-step evaporation induced self-assembly (EISA) method. By employing the as-synthesized mesoporous film with the thickness of 7 μm as the photoanode in dye-sensitized solar cell (DSC), a solar conversion efficiency of 6.53% has been obtained at 30 mW cm⁻² light intensity.     

Sn–Co–C composites obtained from resorcinol-formaldehyde gel as anodes in lithium-ion batteries

Sn–Co–C composites have been prepared by using the resorcinol/formaldehyde polymerization method combined with the carbothermal reduction of metal oxides during carbonization. Homogeneously dispersed metal/carbon composites were identified by electron microscopy. Scanning electron microscopy images revealed the presence of carbonaceous particles with inclusions of metal agglomerates, and the X-ray diffraction patterns revealed the presence of tin and cobalt–tin phases. The introduction of small amounts of cobalt led to higher capacities as compared to coke and cobalt-free samples. The sample with a Sn/Co molar ratio of 85:15 and a higher, initial metal oxide-to-resorcinol ratio was able to maintain capacity values near 380 mAh/g after 30 cycles. The instability of cobalt–tin phases on cycling was not a hindrance for the electrochemical behavior. Charge transfer resistance values were kept low during cycling for cobalt-containing composites.     

Preparation of activated ordered mesoporous carbons with a channel structure

Activated ordered mesoporous carbons with a channel structure (AOMCs-CS) were successfully prepared by imposing CO(2) activation on ordered mesopore carbon C-FDU-15. It is found that the continuous carbon framework of the precursor C-FDU-15 plays an important role in keeping the order structure of the resulting AOMCs-CS. The mild activation (e.g., 31 wt % burnoff) does not impair the order degree. After that, the order degree gradually decreases with further increasing burnoff. However, the basic hexagonal mesostructure of C-FDU-15 can still be found in the AOMCs-CS when the burnoff is up to 73 wt %, although many carbon walls are punched and thus many larger mesopores and marcropores are generated. With increasing burnoff, the surface area and volume of micropores increase first and then decrease, and the surface area and volume of mesopores continuously increase. The highest measured Brunaruer-Emmett-Teller (BET) surface area, micropore volume, and total pore volume of the AOMCs-CS reach 2004 m(2)/g, 0.50 cm(3)/g, and 1.22 cm(3)/g, respectively.     

Sol-gel synthesis of ordered mesoporous alumina

Well-ordered mesoporous alumina materials with high surface area and a narrow pore size distribution were synthesized using a sol-gel based self assembly technique.     

Adsorption of bulky molecules of nonylphenol ethoxylate on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore sizes were prepared using ordered mesoporous silica SBA-15 as hard templates. The OMCs possess abundant mesopores with narrow pore size distribution, on which the adsorption behavior of bulky molecules of nonylphenol ethoxylate (NPE) were investigated. The isotherms of NPE on OMCs can be fitted by Langmuir adsorption model, evidenced by the adsorption data. The surface area of the pores larger than 1.5 nm is a crucial factor to the adsorption capacity of NPE, whereas the most probable pore diameter of OMCs is crucial to the adsorption rate of NPE. The adsorption temperature has more significant effects on adsorption rate than the adsorption capacity. Theoretical studies show that the adsorption kinetics of NPE on OMCs can be depicted with the pseudo-second-order kinetic model. In addition, thermodynamic parameters of adsorption were evaluated based on the equilibrium constants related to the equilibrium of adsorption at different temperatures.     

Nitric acid oxidation of ordered mesoporous carbons for use in electrochemical supercapacitors

Ordered mesoporous carbon materials with high microporosity were synthesized by a low temperature autoclaving of citric acid-catalyzed polymerized resorcinol/formaldehyde in the presence of the triblock copolymer F127 and were activated by nitric acid oxidation. The materials were used as electrode materials in electrochemical supercapacitors. A bimodal pore size distribution of 2.1–2.3 and 5.3 nm with a surface area of 465–578 m² g^?1 and pore volume of 0.44–0.54 cm³ g^?1 was obtained with the retention of an ordered mesoporous structure after nitric acid (2 M) treatment. The introduced functional groups produced a pseudocapacitance, which resulted in an increase in the specific capacitance. The electrochemical capacitance of the resulting mesoporous carbons showed a marked increase after 3 h of nitric acid activation, exhibiting a high value of 295 F g^?1 at the scan rate of 10 mV s^?1 in 6 M KOH aqueous solution and good cycling stability with specific capacitance retention over 500 cycles.     

Thermodynamic and neutron scattering study of hydrogen adsorption in two mesoporous ordered carbons

Two mesoporous ordered carbon materials (MOCs) have been synthesized from silica templates by using sucrose as the carbon precursor. The textural characterization using Ar, N2, and CO2 adsorption combined with neutron diffraction showed that the two samples exhibit a significant microporous volume close to 0.5 cm3/g and an ordered network of mesopores. For both MCM48 and SBA15 templated carbons, adsorption first proceeds with the filling of micropores and then by the filling of mesopores with an adsorption energy close to the enthalpy of vaporization of bulk hydrogen. The hydrogen isosteric heat of adsorption in the micropores (6-8 kJ/mol) is significantly larger than that on the graphite surface (approximately 4 kJ/mol) but still too small for a reasonable use of these MOCs as hydrogen adsorbents for storage at room temperature. The neutron scattering study showed that the structure at 10 K of the adsorbed deuterium phase is poorly organized; it exhibits short and medium range orders of about 13 angstroms in micropores and about 20 angstroms in mesopores, respectively. The average distance between adsorbed molecules decreases with coverage by about 10%. In the mesopores, the diffracted line is consistent with a pseudohexagonal packing.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.