Mesoporous Carbon-silica Nanocomposites Research Articles

Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

Natural rubber as a renewable carbon source for mesoporous carbon/silica nanocomposites.

This study is the first report on the preparation of mesoporous carbon/silica (MCS) nanocomposites with tunable mesoporosity and hydrophobicity using natural rubber (NR) as a renewable and cheap carbon source. A series of mesoporous nanocomposites based on NR and hexagonal mesoporous silica (HMS) were prepared via an in situ sol–gel process and used as precursors; then, they were converted into MCS materials by controlled carbonization. The NR/HMS precursors exhibited a high dispersion of rubber phase incorporated into the mesostructured silica framework as confirmed by small-angle X-ray scattering and high-resolution transmission electron microscopy. An increase in the carbonization temperature up to 700 °C resulted in MCS nanocomposites with a well-ordered mesostructure and uniform framework-confined wormhole-like channels. The NR/HMS nanocomposites possessed high specific surface area (500–675 m2 g−1) and large pore volume (1.14–1.44 cm3 g−1). The carbon content of MCS (3.0–16.1 wt%) was increased with an increase in the H2SO4 concentration. Raman spectroscopy and X-ray photoelectron spectroscopy revealed the high dispersion of graphene oxide-like carbonaceous moieties in MCS materials; the type and amount of oxygen-containing groups in obtained MCS materials were determined by H2SO4 concentration. The enhanced hydrophobicity of MCS nanocomposites was related to the carbon content and the depletion of surface silanol groups, as confirmed by the water sorption measurement. The study on the controlled release of diclofenac in simulated gastrointestinal environment suggests a potential application of MCS materials as drug carriers.

Ultrasensitive electrochemical immunosensor for procalcitonin with signal enhancement based on zinc nanoparticles functionalized ordered mesoporous carbon-silica nanocomposites

Abstract A novel and sensitive strategy for procalcitonin (PCT) determination was developed based on zinc nanoparticles-functionalized ordered mesoporous carbon-silica nano-composites (OMCSi-Zn). This strategy combined an effectively designed trace tag and a simple immunosensor. The large amount of OMCSi-Zn materials as label greatly amplified the detection signals for the electrochemical detection of proteins, while the good biocompatibility of graphene-chitosan as sensor matrix retained excellent stability and accelerated electron transfer for the sandwich-type immunoassay. Without metal preconcentration, the zinc nanoparticles loading on the ordered mesoporous carbon-silica nano-composites (OMCSi) could directly be detected through electrochemical voltammetries, while the immunoreaction had a close relationship with the distinct voltammetric peaks. The proposed method exhibited high sensitivity and good stability for PCT detection, possessing an improved linear response range from 0.05 pg/mL to 80 ng/mL, with a detection limit of 0.013 pg/mL (S/N = 3). Moreover, the serum samples from clinic were accurately detected with the proposed method, indicating that the developed immunoassay possessed excellent potential application in clinical diagnostics for PCT.

Morphology control of mesoporous silica-carbon nanocomposites via phase separation of poly(furfuryl alcohol) and silica in the sol–gel synthesis

Due to the different rates of silica alkoxide hydrolysis and furfuryl alcohol polymerization, hydrophobic poly(furfuryl alcohol) network became incompatible with hydrophilic silica network, PFA-rich spheres were formed in the sol–gel process. The presence of the amphiphilic triblock copolymers P123 could help reduce the degree of phase separation. Slower drying rate, higher aging temperature, and higher C/SiO2 ratio accelerated the polymerization of FA and tend to aggregate more PFA spherical domains. However, in the sample with a fast increased viscosity, the temperature effect would be small since the PFA is hard to agglomerate, leading a homogenous mesoporous structure. If the C/SiO2 ratio is quite high to get a more hydrophobic system, there will be no phase separation too. The understanding of the phase separation of poly-furfuryl alcohol-silica systems offers great opportunities in controlling of the mesoporous carbon-silica nanocomposites. Schematic diagrams of the formation of PFA/silica hybrids: during the sol–gel process, once an alkoxide molecule is hydrolyzed, the resulting hydroxy groups make the molecule more polar, which are more hydrophilic. At the same time, FA polymerized to form PFA oligomers, which are hydrophobic. The incompatibility between these two precursors could be reduced by the amphiphilic triblock copolymers P123, because the long PEO chains are hydrophilic while the PPO block is hydrophobic. Either homogenous or phase separated PFA/silica/P123 can be obtained by tailoring the chemical ratio and the sol–gel process parameters.

Promoting effect of surface acidities on efficiency of copper modifier for ordered mesoporous carbon-SiO2-Al2O3 nanocomposites in adsorptive desulfurization

The ordered mesoporous carbon-silica-alumina nanocomposites (MCSAs) with different ratios of Si/Al (10, 20 and 100) were synthesized by a multi-component co-assembly method followed by pyrolysis at high temperatures. The Si/Al ratio has an important effect on the acidic characteristics of the nanocomposite. The pyridine FT-IR results show that the nanocomposite with a Si/Al ratio of 100 has maximum amount of Brønsted acid sites. This may be because more non-framework Al-O-Si species are generated in the MCSA samples with lower Si/Al ratio due to the dealumination of the precursor in an acidic media during the surfactant-based assembly procedure and/or partial dealumination occurring during high temperature calcination. The copper-modified MCSAs were prepared by incipient wetness impregnation followed by calcination. The desulfurization performance of the as-prepared adsorbents was evaluated by the selective adsorption of dibenzothiophene (DBT) as a model sulfur compound from model fuels at ambient conditions. The dispersion extent of copper species increases with the increase of Brønsted acid sites, which results in a higher selectivity for DBT in competition with benzene. Compared with our previously prepared ordered mesoporous carbon-silica nanocomposite (MCS), the promotion effect of aluminum incorporation on the desulfurization selectivity is demonstrated. Moreover, the ordered mesoporous carbon-alumina nanocomposite (MCA) was also prepared. Its ordered mesostructure partially collapsed and the micropore volume is increased after copper incorporation, resulting in a good enhancement in sulfur capacity and selectivity.

Enhanced adsorption selectivity of dibenzothiophene on ordered mesoporous carbon-silica nanocomposites via copper modification

In this study, copper-modified ordered mesoporous carbon-silica nanocomposites (MCSs) were synthesized by incipient wetness impregnation of copper nitrate. The desulfurization performance of the as-prepared adsorbents was evaluated by the selective adsorption of dibenzothiophene (DBT) as model sulfur compound from model fuels at ambient conditions. For comparison, the adsorptive desulfurization capacity for copper species supported on pure silica SBA-15 and pure carbonaceous CMK-3 was also investigated, respectively. The results indicate that MCS with 10wt.% of copper performed highest selectivity for DBT in competition with benzene. The significantly enhanced desulfurization performance of MCS could be attributed to its hybrid mesoporous carbon-silica nature which is favorable for high dispersion extent of copper and synergistic effect between the carbon substrate and the supported copper species.

Effects of Synthesis Process on Luminescence Properties and Structure of Mesoporous Carbon–Silica Nanocomposite

Effects of Synthesis Process on Luminescence Properties and Structure of Mesoporous Carbon–Silica Nanocomposite

Effects of Synthesis Process on Luminescence Properties and Structure of Mesoporous Carbon–Silica Nanocomposite

The effects of hydrolysis and polycondensation reactions for synthesizing light-emitting mesoporous carbon–silica (MPCS) nanocomposite on the structure, chemical bonding state, and luminescence properties of MPCS were investigated by controlling the concentration (0.02 to 5 M) of HCl, which was used as a catalyst for hydrolysis and polycondensation. The progress of hydrolysis and polycondensation reactions provides a nanometer-order pore/wall structure and results in a strong light-emitting property. The pore/wall structure was obtained using HCl at concentrations of 0.2 M and higher, but it became disordered with increasing HCl concentration (2 and 5 M). The luminescence color of the MPCS nanocomposite can be changed from yellowish-white to bluish-white by changing the concentration of HCl.

Synthesis and microwave absorbing properties of FeNi alloy incorporated ordered mesoporous carbon–silica nanocomposite

Ordered mesoporous carbon–silica/FeNi nanocomposite were prepared by a sol–gel method and following sintering process. The electromagnetic parameters were measured in the 0.5–18GHz range. Compared with ordered mesoporous carbon–silica composite, the permittivity of ordered mesoporous carbon–silica/FeNi nanocomposite decreases, while the permeability almost remains unchanged. The optimal reflection loss of ordered mesoporous carbon–silica/FeNi nanocomposite can reach −45.6dB at 11.1GHz for a layer thickness of 3.0mm. The enhanced microwave absorption of the mesoporous carbon–silica/FeNi nanocomposite is due to better balance between the complex permittivity and permeability, geometrical effect, as well as multiple reflections by the ordered mesoporous structure.

White light emitting Mesoporous Carbon-Silica Nanocomposite

Visible photoluminescence (PL) from oxidized mesoporous carbon-silica nanocomposite (MPCS) prepared by the triconstituent co-assembly method is reported. White PL from MPCS was observed by naked eye at room temperature. Oxidation effects on carbon-silica bonding states and transmittance were investigated. PL intensity decreased with decreasing of carbon dangling bond density by oxidation at above 500 °C. The transmittance of MPCS at excitation and emission wavelengths increased with increasing of oxidation temperature. It is concluded that PL intensity is determined by the balance between PL related carbon density and transmittance. We proposed an additional wet oxidation that can increase PL intensity by the increase of transmittance under suppressing carbon desorption.

White Light Emission from Mesoporous Carbon–Silica Nanocomposites

White Light Emission from Mesoporous Carbon–Silica Nanocomposites

White Light Emission from Mesoporous Carbon–Silica Nanocomposites

Visible photoluminescence properties of mesoporous nanocomposites of carbon and silicon dioxides prepared using the triconstituent co-assembly method is reported. Intense white-light emission from the nanocomposites was observed at room temperature, under 370-nm light irradiation after proper carbon desorption by air-oxidation. We observed that the shapes of the luminescence spectra, especially in the green-yellow region, were highly dependent on the oxidation condition of the samples.

Selective Adsorption Behavior of Cu(II) and Cr(VI) Heavy Metal Ions by Functionalized Ordered Mesoporous Carbon

An ordered mesoporous carbon silica nanocomposite was synthesized by the evaporation induced triconstituent co assembly method, wherein a soluble resol polymer was used as an organic precursor, tetraethoxysilane was used as an inorganic precursor, and the triblock copolymer F127 was used as the template. After the removal of silica with HF, ordered mesoporous pure carbon (OMC) was obtained. X ray diffraction (XRD), N2 adsorption desorption isotherms (BET), and transmission electron microscopy (TEM) showed that the OMC product had a highly ordered structure with a large pore size of 6.4 nm, a pore volume of 2.13 cm3·g-1, and a high surface area of 1330 m2·g-1. The OMC was subsequently functionalized with ethylenediamine by treatment with nitric acid and thionyl chloride to obtain a functionalized ordered mesoporous carbon (C NH2(m)), m is the mass (g) of the added ethylenediamine. Fourier transform infrared (FTIR) spectroscopy showed that the amino group was successfully grafted onto the surface of the OMC. TEM images showed that C NH2(m) had a highly ordered mesoporous structure. OMC and C NH2(m) were used as adsorbents for the selective adsorption of Cu(Ⅱ) and Cr(Ⅵ) ions from the aqueous solution. C NH2(9.0) had a higher adsorption capacity for Cu(Ⅱ) of 495.05 mg·g-1 versus 213.33 mg·g-1 for the OMC and a lower adsorption capacity for Cr(Ⅵ) of 68.21 mg·g-1 versus 241.55 mg·g-1 for the OMC, indicating its significantly favorable potential for the selective adsorption of Cu(Ⅱ).

One-pot synthesis of ordered mesoporous carbon–silica nanocomposites templated by mixed amphiphilic block copolymers

Mixed amphiphilic block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO–PPO–PEO) and polydimethylsiloxane-poly(ethylene oxide) (PDMS–PEO) have been successfully used as co-templates to prepare ordered mesoporous polymer–silica and carbon–silica nanocomposites by using phenolic resol polymer as a carbon precursor via the strategy of evaporation-induced self-assembly (EISA). The ordered mesoporous materials of 2-D hexagonal (p6m) mesostructures have been achieved, as confirmed by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and nitrogen-sorption measurements. Experiments show that using PDMS–PEO as co-template can enlarge the pore sizes and reduce the framework shrinkage of the materials without evident effect on the specific surface areas. Ordered mesoporous carbons can then be obtained with large pore sizes of 6.7 nm, pore volumes of 0.52 cm3/g, and high surface areas of 578 m2/g. The mixed micelles formed between the hydrophobic PDMS groups and the PPO chains of the F127 molecules should be responsible for the variation of the pore sizes of the resulting mesoporous materials. Through the study of characteristics of mesoporous carbon and mesoporous silica derived from mother carbon–silica nanocomposites, we think mesoporous carbon–silica nanocomposites with the silica-coating mesostructure can be formed after the pyrolysis of the PDMS–PEO diblock copolymer during surfactant removal process. Such method can be thought as the combination of surfactant removal and silica incorporation into one-step. This simple one-pot route provides a pathway for large-scale convenient synthesis of ordered mesostructured nanocomposite materials.

Triconstituent Co-assembly to Ordered Mesostructured Polymer−Silica and Carbon−Silica Nanocomposites and Large-Pore Mesoporous Carbons with High Surface Areas

Highly ordered mesoporous polymer-silica and carbon-silica nanocomposites with interpenetrating networks have been successfully synthesized by the evaporation-induced triconstituent co-assembly method, wherein soluble resol polymer is used as an organic precursor, prehydrolyzed TEOS is used as an inorganic precursor, and triblock copolymer F127 is used as a template. It is proposed for the first time that ordered mesoporous nanocomposites have "reinforced concrete"-structured frameworks. By adjusting the initial mass ratios of TEOS to resol, we determined the obtained nanocomposites possess continuous composition with the ratios ranging from zero to infinity for the two constituents that are "homogeneously" dispersed inside the pore walls. The presence of silicates in nanocomposites dramatically inhibits framework shrinkage during the calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. Combustion in air or etching in HF solution can remove carbon or silica from the carbon-silica nanocomposites and yield ordered mesoporous pure silica or carbon frameworks. The process generates plenty of small pores in carbon or/and silica pore walls. Ordered mesoporous carbons can then be obtained with large pore sizes of approximately 6.7 nm, pore volumes of approximately 2.0 cm(3)/g, and high surface areas of approximately 2470 m(2)/g. The pore structures and textures can be controlled by varying the sizes and polymerization degrees of two constituent precursors. Accordingly, by simply tuning the aging time of TEOS, ordered mesoporous carbons with evident bimodal pores at 2.6 and 5.8 nm can be synthesized.