Synthesis and characterization of transition metal and metal oxide nanoparticles inside mesoporous carbon CMK-3

Transition metal oxides were synthesized inside the pore system of mesoporous carbon CMK-3. By a wet impregnation, drying and calcination procedure iron, copper, nickel, cobalt, manganese and zinc oxides were formed almost exclusively within the mesopores. A reduction into the metal forms with regard to structural array in the case of zinc oxide and a reduction to manganese(II) oxide for manganese(IV) oxide was accomplished by hydrogen. Powder X-ray diffraction (PXRD), Raman spectroscopy and transmission electron microscopy (TEM) proved the preservation of the host structure during impregnation and reduction procedures. The formation of nanosized metal oxides inside the mesopore system was confirmed with PXRD and TEM. Nitrogen physisorption measurements still revealed micro- and mesoporosity for the host/guest compounds. A reduction of the surface areas and pore sizes in contrast to the host structure being an indication of the coating of the inner surfaces of the carbon walls is shown as well. Infrared and X-ray absorption spectroscopy (XAS) carried out in fluorescence mode confirm the formation of the respective oxides and metals. Furthermore, the existence of small, disordered nanoparticles was proved by XAS investigations and information on the local structure of the metals and metal oxides was obtained from these measurements.     

Improving the electrocapacitive properties of mesoporous CMK-5 carbon with carbon nanotubes and nitrogen doping

Nitrogen-containing carbon composite materials composed of mesoporous carbon CMK-5 and carbon nanotubes (CNTs) were prepared by the chemical vapor deposition method with Fe(NO₃)₃-impregnated SBA-15 as template and pyridine as the carbon precursor. The Fe nanoparticles confined in the channels of SBA-15 induced the formation of mesoporous carbon characteristic of CMK-5, whereas Fe particles homogeneously dispersed on the external surface of SBA-15 served as catalysts for CNTs growth. The contents of CNTs, the N doping level and the microstruture of the carbon composite were closely related to the initial Fe/Si atomic ratio in SBA-15 template. Incorporation of CNTs in the composite was found to substantially reduce the electric resistance, leading to the composite materials exhibiting excellent rate-performance. A maximum specific capacitance of 208 F/g and a power density of 10 kW/kg were achieved in 6.0 mol/L KOH aqueous electrolyte when these carbon composites were applied as supercapacitor electrodes. Moreover, the composite electrode also exhibited good electrochemical stability with no capacitance loss after 1000 cycles of galvanostatic charge-discharge process.     

介孔炭CMK-3吸附剂对噻吩类硫化物的吸附性能

研究了采用硬模板法制备的介孔炭CMK-3吸附剂对模拟油中噻吩(TS)、苯并噻吩(BT)及二苯并噻吩(DBT)的吸附性能。采用X射线衍射、氮气吸附-脱附及透射电子显微镜对介孔炭CMK-3吸附剂进行了表征。结果表明,介孔炭CMK-3具有有序的孔道结构,比表面积、平均孔直径和平均孔容分别为1 232 m~2/g、4.878 nm和1.502 cm~3/g。同时探讨了介孔炭CMK-3对TS、BT及DBT的吸附动力学和热力学规律。结果表明,与Freundlich吸附等温模型相比,CMK-3吸附剂对TS、BT及DBT的吸附等温线更符合Langmuir吸附等温模型;吸附为放热过程,CMK-3对TS、BT及DBT的吸附焓变分别为-11.53,-19.74,-26.10 k J/mol。CMK-3吸附剂对TS、BT及DBT的吸附符合二级动力学模型,吸附活化能分别为37.53,34.42,47.67 k J/mol。     

介孔炭CMK-3吸附剂对噻吩类硫化物的吸附性能

研究了采用硬模板法制备的介孔炭CMK-3吸附剂对模拟油中噻吩(TS)、苯并噻吩(BT)及二苯并噻吩(DBT)的吸附性能。采用X射线衍射、氮气吸附-脱附及透射电子显微镜对介孔炭CMK-3吸附剂进行了表征。结果表明,介孔炭CMK-3具有有序的孔道结构,比表面积、平均孔直径和平均孔容分别为1 232 m²/g、4.878 nm和1.502 cm2/g、4.878 nm和1.502 cm³/g。同时探讨了介孔炭CMK-3对TS、BT及DBT的吸附动力学和热力学规律。结果表明,与Freundlich吸附等温模型相比,CMK-3吸附剂对TS、BT及DBT的吸附等温线更符合Langmuir吸附等温模型;吸附为放热过程,CMK-3对TS、BT及DBT的吸附焓变分别为-11.53,-19.74,-26.10 k J/mol。CMK-3吸附剂对TS、BT及DBT的吸附符合二级动力学模型,吸附活化能分别为37.53,34.42,47.67 k J/mol。     

Activation of carbon nanofibres for hydrogen storage

The present study was aimed to investigate different methods of activation of carbon nanofibres, CNF, in order to determine the beneficial effect on the hydrogen sorption capacities of increasing the surface area. Two activation systems were used: physical activation with CO₂ and chemical activation with KOH. A range of potential adsorbents were thus prepared by varying the temperature and time of activation. The structure of the CNF proved more suitable to activation by KOH than by CO₂, with the former yielding higher surface area carbons (up to 1000 m² g⁻¹). The increased surface area, however, did not correspond directly with a proportional increase in hydrogen adsorption capacity. Although high surface areas are important for hydrogen storage by adsorption on solids, it would appear that it is essential that not only the physical, but also the chemical, properties of the adsorbents have to be considered in the quest for carbon based materials, with high hydrogen storage capacities.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

Rapid preparation,characterization and hydrogen storage properties of pure and metal ions doped mesoporous MCM-41

Pure and Ni²⁺, Fe³⁺, Co²⁺ and Cr³⁺ ions doped mesoporous MCM-41 samples were prepared rapidly in reflex condensers under microwave irradiation for about 1 h. Those materials were characterized by XRD, HRTEM, and N₂ adsorption at 77 K. Hydrogen sorption determinations at 77 K showed that a small amount of Ni²⁺ ions’ doping improved the hydrogen storage capacity from 0.44 wt.% of pure MCM-41 to 0.53 wt.% for the 2%Ni²⁺–MCM-41 at a pressure of 1 bar.     

CMK-3 nanostructured carbon: Effect of temperature and time carbonization on textural properties and H2 storage

Abstract

CMK-3 carbons were synthesized varying the carbonization conditions and studying the effect of the templates calcined at different temperatures. The textural characterization of different SBA-15 templates calcined at 350, 450, and 550?°C shows a variation of the specific surface area below 10%. Based on the results, the SBA-15 obtained at 350?°C (the more affordable condition) was used as the final template for the CMK-3 synthesis. The results show that varying the time (from 2 to 6?h) and the temperature (from 600 to 900?°C) on the carbonization step, the textural, structural, and morphological properties of the carbons do not vary in a meaningful way. Thus, a CMK-3 carbon synthesized (using as template an SBA-15 calcined at 350?°C) obtained at 600?°C during 2?h was chosen to be used as adsorbent in hydrogen storage in order to stablish the relationship between the textural properties and its performance. Regarding the hydrogen storage, capacities of 15?mg H₂ g^?1 (1.5% w/w), and up to 28?mg H₂ g^?1 (2.8% w/w) were obtained at 1 and 10?bar, respectively. At high pressure, an important influence of the large micropores and narrow mesopores on the hydrogen adsorption was found.     

Direct synthesis of ordered mesoporous carbon applied in hydrogen storage

In this work, we present a direct, novel and low cost method for the preparation of an ordered mesoporous carbon (OMC). OMC was successfully synthesized by the carbonization of the silica/triblock copolymer/sucrose composite in the presence of sulfuric acid. The resulting material was characterized by XRD, N₂ sorption analysis and TEM techniques. The novel synthesis technique improved significantly the H₂ storage properties (3.78 wt%) compared with that of CMK-3 synthesized using the nanocasting strategy (2.2 wt%) at 77 K and 10 bar.     

In situ synthesis and hydrogen storage properties of PdNi alloy nanoparticles in an ordered mesoporous carbon template

Organized mesoporous carbon has been used as a nanoreactor to prepare PdNi metallic particles using an incipient wetness method starting from Pd and Ni salts. The final composite material consists of nanosized metallic particles of an alloy with composition Pd_0.60Ni_0.40 highly dispersed within the carbon host structure. The thermodynamic hydrogenation properties of both the PdNi-free OMC and the Pd_0.60Ni_0.40-OMC composite have been determined by hydrogen isotherm sorption measurements. The introduction of the palladium–nickel alloy into the carbon matrix does not increase the hydrogen storage capacity at 77 K and 2 MPa, since the hydrogen uptake is mainly attributed to physisorption on the carbon surface. However, at room temperature and moderate pressure (0.5 MPa), the filling of the OMC with nanocrystalline Pd_0.60Ni_0.40 results in larger hydrogen uptake than that of the PdNi-free OMC.     

Calculation of XRD patterns of simulated FDU-15, CMK-5, and CMK-3 carbon structures

XRD patterns of model structures of the ordered mesoporous carbon materials FDU-15, CMK-5, and CMK-3 have been calculated. The structure models had been derived by filling tubular (CMK-5), rod-like (CMK-3), or channel wall (FDU-15) spaces in a given unit cell with carbon atoms. The generated carbon sites then have been used for the calculation of the XRD patterns. It could be shown that XRD patterns of CMK-5 materials vary substantially with variation of the tube diameter and carbon wall thickness. For a certain range of tube diameters, the XRD patterns do not resemble those of CMK-3 or FDU-15. The carbon material FDU-15 is isostructural to the silica SBA-15, CMK-3 is the negative replica of SBA-15. XRD patterns of CMK-3 and FDU-15 models also vary with varying rod or pore diameter but the changes are not as significant as for different CMK-5 models. As expected, the XRD patterns of FDU-15 and CMK-3 resemble each other very much for a given lattice parameter if the rods of CMK-3 are of the same size as the pore diameters of FDU-15.     

Iron (III) oxide nanoparticles within the pore system of mesoporous carbon CMK-1: intra-pore synthesis and characterization

Iron (III) oxide nanoparticles were synthesized inside the pore system of mesoporous carbon CMK-1. This intra-pore synthesis was carried out using several cycles of wet impregnation, drying and calcination procedures. The existence of iron (III) oxide nanoparticles within the pore system was proved by powder X-ray diffraction, nitrogen physisorption, preservation of the host structure by Raman spectroscopy and transmission electron microscopy. Finally, the local structure of the iron oxide was determined by X-ray absorption spectroscopy.     

Template synthesis of CMK-3 nanostructured carbon material and study of its properties

Mesostructured carbon has been obtained by template synthesis. SBA-15 mesostructured silicate has been used as a template. The effect of the properties of a template on the ordering of a replica has been studied. It has been shown with the use of X-ray diffraction, gas adsorption, and electron microscopy that there are evident correlations of the conditions of synthesis of a template with the ordering of a carbon replica, which can be guided by the synthesis of materials. The ordering of a replica significantly depends on the mesopore volume of the initial template and thickness of the pore wall. One should use templates with the highest possible mesopore volume and minimal wall thickness to obtain highly ordered replicas. These templates can be prepared during the treatment of synthesized materials at temperatures close to 100°C. It has been determined that, when there is SBA-15, the presence of micropores is a necessary condition for the preparation of carbon replicas that retain the structure of the template.     

High sensitive simultaneous determination of catechol and hydroquinone at mesoporous carbon CMK-3 electrode in comparison with multi-walled carbon nanotubes and Vulcan XC-72 carbon electrodes

The simultaneous voltammetric determination of catechol (CC) and hydroquinone (HQ) has been achieved at a mesoporous carbon CMK-3 modified electrode in phosphate buffer solution (pH 7.0). At the electrode both CC and HQ can cause a pair of quasi-reversible and well-defined redox peaks and their peak potential difference increases. In comparison with multi-walled carbon nanotubes (MWCNTs) and Vulcan XC-72 carbon modified electrodes the CMK-3 modified electrode shows larger peak currents and higher adsorbed amounts for the two dihydroxybenzene isomers. This is related to the higher specific surface area of CMK-3. Under the optimized conditions, the linear concentration ranges for CC and HQ are 5 × 10⁻⁷ to 3.5 × 10⁻⁵ M and 1 × 10⁻⁶ to 3 × 10⁻⁵ M, respectively. In the presence of 5 μM isomer, the linear concentration range of CC (or HQ) is 5 × 10⁻⁷ to 2.5 × 10⁻⁵ M (or 5 × 10⁻⁷ to 2.0 × 10⁻⁵ M). The sensitivity for CC or HQ is 41 A M⁻¹ cm⁻² or 52 A M⁻¹ cm⁻², which is close to that without isomer. The detection limits (S/N = 3) for CC and HQ are 1 × 10⁻⁷ M after preconcentration on open circuit for 240 s.     

Ni- and CuNi-modified activated carbons and ordered mesoporous CMK-3 for furfural hydrotreatment

In this paper, various carbon materials such as activated carbons and mesoporous carbon material CMK-3 modified with nickel and copper, are investigated in the production of a potential biofuel 2-methylfuran with furfural hydrotreatment. Deep characterization of the prepared catalysts revealed differences in pore size, surface area, and metal particle size. Furthermore, the acidity of the catalysts varied significantly affecting the product distribution. Very high activity and selectivity towards 2-methylfuran was achieved with two steam activated carbons (Norit RB4C and Darco) and ordered mesoporous carbon material CMK-3 modified with copper and nickel. 2-Methylfuran yield as high as 60.2% was achieved with 5/5 wt% CuNi/RB4C in 2 h at 230 °C. The operation in slurry phase was observed to promote the reaction towards 2-methylfuran.     

Magnesiothermal synthesis of nanostructured SiC from natural zeolite (clinoptilolite) and mesoporous carbon CMK-1

Magnesiothermal synthesis of nanosized SiC has been successfully achieved from a mixture of the natural zeolite clinoptilolite and a high-surface area mesoporous carbon CMK-1, synthesized by impregnating a mesoporous silica template MCM-48 with sucrose, followed by carbonization in argon and removal of the silica template. Magnesium powder was used to initiate the self-combustion reaction. Removal of the alkaline and alkaline earth exchangeable cations from the clinoptilolite by ion exchange with NH₄⁺ was essential for a good yield of product, which is also dependent on the use of excess of carbon. TEM confirmed the nanostructure and size of the 15–25 nm SiC product crystallites.     

Detailed structure of the hexagonally packed mesostructured carbon material CMK-3

Detailed investigation of the ordered mesoporous CMK-3 carbon using XRD structural modeling based on the continuous electron density representation and the Rietveld technique allowed deriving comprehensive and consistent information on the material anatomy. The electron density distribution map agrees with carbon ‘bridges’, which seem to be attributed to the material interconnecting carbon nanorods in the CMK-3 mesostructure. These carbon ‘bridges’ are supposed to be derived from former complementary mesopores of the SBA-15 template used.     

Synthesis and properties of P-doped mesoporous carbon

Journal of Applied Electrochemistry - The modification of mesoporous carbon (MC) with phosphoric acid as the phosphorus source is an effective mean of increasing the electroactive center. In this...     

Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbide-derived carbon (DUT-19) as catalysts. X-ray diffraction and N₂ physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition.