Material CMK-3 Research Articles

Modified CMK-3 carbon materials for efficient removal of roxarsone

Roxarsone adsorption from water using ordered mesoporous carbon CMK-3 (P_CMK-3) and CMK-3 carbon modified with thiourea (TU_CMK-3) or diclofenac (SD_CMK-3) was studied. The adsorption of roxarsone occurred at low pH. The adsorption was fast; in the case of SD_CMK-3 and TU_CMK-3 materials, the adsorption equilibrium was achieved within 2 min, whereas in the case of P_CMK-3 material, within 30 min. The adsorption capacities towards roxarsone were 130, 99, and 200 mg/g for P_CMK-3, TU_CMK-3, and SD_CMK-3, respectively. Coexistence of 20 mg/L Ca2+, Mg2+, Fe3+; Cl-, HCO3–, SO42-, NO3–, and PO43- ions did not significantly hinder the adsorption of roxarsone onto SD_CMK-3 material. The NaOH solution application enabled virtually complete roxarsone desorption from the SD_CMK-3 surface. It was found that the adsorption of roxarsone on the SD_CMK-3 material is a complex process occurring as a result of the electrostatic interaction of anionic forms of roxarsone with a positively charged surface, hydrogen bonds, and the interactions between carbon and the aromatic ring in roxarsone. Adsorption is accompanied by partial reduction of –ONO2 groups in the roxarsone molecule and partial transformation of organic As contained in the roxarsone molecule to As(V).

A sustainable route for production of graphene oxide-contained nanostructured carbons from rice husk waste and its application in wastewater treatment

Agricultural biomass, such as rice husk (RH), is a renewable source of bioenergy. However, a large amount of RH ash (RHA) is generated after the thermal conversion of RH. The main component of RHA is silica (>85 wt%). This study used recyclable RHA as a mesoporous SBA-15 template source. Next, ordered mesoporous carbon/ graphene oxide (RH-CMK-3/GO) composites were synthesized through the direct carbonization of GO, sucrose, and an SBA-15 template. Experimental data demonstrated that GO was successfully conjugated on the surface of CMK-3. The RH-CMK-3/GO exhibited a highly ordered mesostructure, which was not affected by the incorporation of GO. Compared with bare RH-CMK-3, the RH-CMK-3/GO had an enhanced surface area and pore volume. The composite exhibited a highest pore volume of 1.143 cm 3/g, a surface area of 1138 m2/g, and a pore diameter of 3.68 nm. The RH-CMK-3/GO revealed a higher ability for the adsorption of rhodamine B (RhB) than did the SBA-15, SBA-15/GO, and pure CMK-3 materials. The removal of RhB increased with increases in the composite dosage, solution pH and temperature, and carbonization temperature and time and a decrease in the initial RhB concentration. Moreover, the RH-CMK-3/GO exhibited a highest removal efficiency of 100%. The thermodynamics, kinetics, and isotherm adsorption data for the RH-CMK-3/GO composite exhibited satisfactory fitting for the endothermic, pseudo-second-order, and Langmuir models, respectively. Moreover, the composite exhibited good reusability. These results suggest that RHA can be effective for the fabrication of valuable mesoporous carbon nanocomposites and the elimination of organic contaminants from wastewater.

Amine‐ and Amide‐Functionalized Mesoporous Carbons: A Strategy for Improving Sulfur/Host Interactions in Li–S Batteries

AbstractLithium–sulfur (Li–S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill‐suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two‐step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li–S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor.

Oxidative esterification of furfural by Au nanoparticles supported CMK-3 mesoporous catalysts

Furfural which is derived from the hemicellulose fraction of abundant lignocellulose has received significant attention to many researchers as its valorization yields useful products such as fine chemicals and transportation fuels. Methyl 2-furoate is one of the important valorized products of furfural as it finds applications in flavor and fragrance industries. Methyl 2-furoate is generally obtained by oxidation followed by esterification of furfural but under acidic and corrosive conditions. Uniform rods of CMK-3 mesoporous materials were successfully synthesized by using nanocasting method. Au nano particles were impregnated into the pores of CMK-3 by wet impregnation method followed by hydrogen reduction at high temperature (673K). All the catalysts were thoroughly characterized by various analytical techniques. Homogeneous dispersion of Au nano particles ≈3nm size was found over CMK-3 materials. Qualitative and quantitative analyses of Au were made by XPS and ICP techniques. The effect of impregnating metal ions (Ni, Pt and Pd) and supports (SBA-15, graphite, graphene, MWCNT, activated carbon and TiO2) was studied on the catalytic conversion of furfural. Among them, Au/CMK-3 catalyst was found to be the best. Among the Au/CMK-3 catalysts, 5% Au/CMK-3 catalyst showed remarkable conversion of furfural (99.7%) with very high selectivity towards methyl 2-furoate (99.6%). The stability and reusability of the 5% Au/CMK-3 catalyst was found to be very good even after five catalytic cycles.

Characterization of nanostructured carbon CMK-3 by means of Monte Carlo simulations

A structural model of mesoporous carbon (CMK-3) prepared from the templating of SBA-15 silica materials named M_CMK3 and a mixed geometry model, representing the porous space as a collection of slit, cylindrical and M_CMK3 pores, is theoretically evaluated, developed and applied to the characterization of an experimental sample [1]. By using the Monte Carlo simulation method (off lattice), families of N2 adsorption isotherms are generated for cylindrical, slit and M_CMK3 geometries corresponding to different pore sizes. Then, the three geometric families of isotherms (kernels) are used to fit the experimental N2 adsorption data corresponding to CMK-3 materials, allowing for the determination of the micro and mesopore volume and the corresponding Pore Size Distribution (PSD). The same experimental data were fit using different mixed geometry models, and from the analysis of the effect of different kernels on the resulting PSD, it is concluded that the proposed mixed geometry model can capture in more detailed the textural and energetic features of nanostructured carbon CMK-3. Finally, using a virtual solid and pseudo-experimental adsorption data, the importance of the pore geometry and its effects on the PSD and isosteric enthalpy of adsorption are studied.

Molecular modelling of ionic liquids in the ordered mesoporous carbon CMK-5

We performed classical molecular dynamics simulations of the ionic liquids (ILs) [dmim+][Cl−] and [emim+][NTf2−], confined in a model CMK-5 material, which consists of amorphous carbon nanopipes (ACNPs) arranged in a hexagonal array. We compare our findings against the behaviour of the same ILs inside an isolated ACNP (i.e. no IL adsorbed on the outer surface of the ACNP) and inside a model CMK-3 material (which is similar to CMK-5, but is formed by amorphous carbon nanorods). Our results indicate that the presence of IL adsorbed in the outer surface of an uncharged ACNP in CMK-5 affects the dynamics and the density of an IL adsorbed inside the ACNP and vice versa. ILs adsorbed outside the nanopipes in CMK-5 (i.e. with IL also adsorbed inside the nanopipes) have faster dynamics and remain closer to the carbon surfaces when compared to the same ILs adsorbed on CMK-3 materials. The trends are IL-specific: [dmim+][Cl−] has slower dynamics when inside an isolated ACNP than when inside the ACNPs in CMK-5, but in contrast, [emim+][NTf2−] moves faster when it is inside an isolated ACNP than when it is inside the ACNPs in CMK-5 (i.e. with IL adsorbed outside the nanopipes).

First evidence of interconnected micro and mesopores in CMK-3 materials

The porous structure and the pore interconnections of mesoporous carbon of CMK-3 type have been studied by means of hyperpolarized 129Xe NMR spectroscopy. Parallel studies of purely microporous carbon and CMK-3 have unambiguously revealed the presence of micropores inside the CMK-3 structure. In addition, 129Xe 2D-exchange NMR experiments have clearly shown direct exchange of Xe atoms between the micro and the mesoporosity. This indicates the presence of micropores inside the carbon rods constituting the mesoporous structure of CMK-3 materials.

MnO2-Embedded-in-Mesoporous-Carbon-Wall Structure for Use as Electrochemical Capacitors

We present an in situ reduction method to synthesize a novel structured MnO(2)/mesoporous carbon (MnC) composite. MnO(2) nanoparticles have been synthesized and embedded into the mesoporous carbon wall of CMK-3 materials by the redox reaction between permanganate ions and carbons. Thermogravimetric analysis (TG), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), and cyclic voltammetry were employed to characterize these composite materials. The results show that different MnO(2) contents could be introduced into the pores of CMK-3 treated with different concentrations of potassium permanganate aqueous solution, while retaining the ordered mesostructure and larger surface area. Increasing the MnO(2) content did not result in a decrease in pore size from the data of nitrogen sorption isotherms, indicating that MnO(2) nanoparticles are embedded in the pore wall, as evidenced by TEM observation. We obtained a large specific capacitance over 200 F/g for the MnC composite and 600 F/g for the MnO(2), and these materials have high electrochemical stability and high reversibility.

A structure of MnO 2 embedded in CMK-3 framework developed by a redox method

A new in situ reduction method has been developed to synthesize a novel structured MnO 2/mesoporous carbon composites with MnO 2 nanoparticles embedded in the wall of ordered mesoporous carbon CMK-3 materials. KMnO 4 was easy to be reduced into MnO 2 in a short time in the presence of carbon, meanwhile the carbon atoms on the surface were oxidized into C–OH, C O and COOH species, making the surface more hydrophilic, and permanganate ions more readily to access, which leads to the embedded structure. The MnO 2/CMK-3 composite materials were characterized using thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) spectroscopy. The results show that different MnO 2 contents could be introduced into the pores of CMK-3 treated with an aqueous solution of potassium permanganate, while retaining the ordered mesostructure and larger surface area. Increasing the MnO 2 content did not result in a decrease in pore size from the data of nitrogen sorption isotherms, indicating that MnO 2 nanoparticles are embedded in the pore wall, as evidenced by TEM observation.

Iron oxide modified mesoporous carbons: Physicochemical and catalytic study

Series of iron oxide supported on CMK-1 and CMK-3 materials obtained by impregnation from aqueous or organic media are studied by TPR, XAFS, Moessbauer spectroscopy and methanol decomposition as a catalytic test. More highly dispersed iron oxide particles are obtained using ethanolic impregnation medium, but their dispersion is affected to a low extent by the support pore structure. On the basis of the combined results on the state and reductive phase transformations of the loaded iron oxide particles, more accessible CMK-3 in comparison with CMK-1 pore structure is assumed.