| Mesoporous carbon spheres, due to their excellent chemical and thermal stability, good biocompatibility, unique structure of aperture, high specific surface area, large pore volume and good thermal conductivity, have attracted technological interests for their potential applications in drug delivery, adsorption, catalytic carrier and lithium ion electrode materials. So far, the template method, chemical vapor deposition method and hydrothermal method have been successfully used in preparing mesoporous carbon spheres. However, there are various shortcomings in the synthetic methods, such as the complexity of the synthetic steps, the need to advance the template synthesis, the carbon spheres easily bonding, which greatly limite the application of mesoporous carbon spheres in many fields.Herein, we report a simple one-step method to successfully and controllably synthesize a series of mesoporous carbon spheres with high specific surface area, large pore size, large pore volumes and especially well dispersity, including starch-base bimodal mesoporous carbon spheres, furfuryl alcohol-base mesoporous carbon spheres and Fe-magnetic mesoporous carbon spheres. Modification of the mesoporous carbon spheres were carried out by H2O2 and HNO3. The mesoporous carbon spheres were evaluated via N2 sorption analysis, scanning electron microscopy, X-ray diffraction, Thermo Gravimetric/ Differential Thermal Analysis, Raman spectroscopy and Infrared Spectroscopy. Carbamazepine(CBZ), Naproxen(Nap), neutral red(NR) were selected as the model to investigate the adsorption and release behavior of molecules on mesoporous carbon spheres. The details were as follows:(1) The synthesis of starch-base bimodal mesoporous carbon spheres and CBZ release. Starch-base bimodal mesoporous carbon spheres were synthesized by a simple one-pot method, in which biomass corn starch was used as carbon precursor, silica nanoparticles were used as template precursor. The experimental results showed that the starch concentration played an important role in the morphology and pore structure of carbon spheres, what could adjust the mesoporous structure, tunable mesopore volume, and specific surface area of the crabon spheres. The carbon spheres showed a bimodal pore system when the starch concentration was above 20%. The specific surface areas and pore volumes of the carbon spheres reach a maximum of 753 m2/g and 2.25 cm3/g respectively at 30% of the starch concentration. Besides, the carbon spheres showed good dispersion and became intact and smooth. The SEM images showed a spherical morphology and a particle size of 13 μm to 18 μm. The surface of the carbon spheres became much more intact and smooth as the starch concentration increased. However, the carbon spheres became aggregation when the starch concentration was 60%. CBZ, due to its poor watersolubility and low release rate, was selected as the model drug and loaded onto the asprepared carbon spheres to investigate its release behavior. The experimental results showed that the dissolution rate was significantly increased after CBZ loading onto the carbon spheres than the pure CBZ, which could be explained by the noncrystalline state improved dispersibility, and nanoscale size of CBZ in the pore channels of the the carbon spheres. The drug release behaviors were well simulated by a simple index equation:)1(kteay--(28), a is the maximum cumulative release fraction of CBZ, and k is the release rate constant related to solvent accessibility and diffusion coefficient. Both a and k increase with the increasing surface area and pore volumes of the carbon spheres.(2) The synthesis and modification of furfuryl alcohol-base mesoporous carbon spheres and the adsorption of NR. Furfuryl alcohol-base mesoporous carbon spheres were synthesized by a simple one-pot method, in which furfuryl alcohol was used as carbon precursor, silica nanoparticles were used as template precursor, and oxalic acid as catalyst. The experimental results showed that the furfuryl alcohol amount had effects on the morphologies and structural parameters of the materials. The specific surface area and the total pore volumes decreased with the increasing amount of furfuryl alcohol. The specific surface areas and pore volumes of the carbon spheres reached a maximum of 806.5 m2/g and 0.97 cm3/g respectively when the amount of furfuryl alcohol was 1 m L. In order to examine the relationship among the pore structure, adsorption ability and hydrophilicity of the carbon spheres, the carbon spheres were modified by H2O2 and HNO3. Fourier transform infrared(FTIR) spectroscopy showed that the carboxy group was grafted onto the surface of the carbon spheres. The surface area and pore volume of H2O2-treated carbon increased to 810.8 m2/g and 1.29 cm3/g respectively, but decreased to 593.9 m2/g and 0.54cm3/g, respectively after HNO3 oxidation. The reason could be explained that HNO3 was a strong oxidant and the increase in additional mass or/and structural collapse could lead to the decrease in specific surface area and pore volume after oxidation treatment. NR was selected as the adsorption model and loaded onto the as-prepared carbon spheres to investigate its adsorption behavior. The results showed that the adsorption behaviors were well simulated by the Langmuir adsorption isotherm: qKcc Kq)1/(m(10)(28), qm represented the saturation adsorption capacity and K represented the Langmuir constant. The saturation adsorption capacities of NR onto CS-H2O2, CS-HNO3, and CS-1 were 274.7, 227.3, and 204.5 mg/g, respectively. The improvement in the adsorption amount is related to the surface area, high pore volume and hydrophilicity which played an important role in adsorption capacities.(3) The synthesis of Fe-magnetic mesoporous carbon spheres and the release of Nap. Femagnetic mesoporous carbon spheres were synthesized by a simple one-pot method, in which furfuryl alcohol was used as carbon precursor, silica nanoparticles as template, Fe(NO3)3·9H2O as magnetic precursor, and ionic liquids as solvent. The experimental results showed that the amount of Fe(NO3)3·9H2O played an important role in the morphology and pore structure of carbon spheres. The specific surface area and the total pore volumes decreased with the increasing amount of Fe(NO3)3·9H2O. The specific surface areas and pore volumes of the carbon spheres reached a maximum of 653.4 m2/g and 1.27 cm3/g respectively when the amount of Fe(NO3)3·9H2O was 1.2 mmol. The SEM results showed a spherical morphology and a particle size of 15 μm to 20 μm. Nap, due to its poor water-solubility and low release rate, was selected as model drug and loaded onto the as-prepared carbon spheres to investigate its release behavior in p H=5.0, 6.8, and 8.0. The experimental results showed that the dissolution rate was significantly increased after Nap loading onto the carbon spheres than the pure Nap, which could be explained by the noncrystalline state improved the dispersibility of Nap in the pore channels of the carbon spheres. Within the scope of the study, the release behaviors of Nap increased with the increasing of p H. The release behaviors reached maximum when the p H = 8.0. This phenomenal was closely related to the structure of Nap and the release rate of drug release rate could be adjusted by varying the p H.The overall innovation of the present study lies in: A simple one-pot method was first used for the controllable synthesis of a series of starch-base bimodal mesoporous carbon spheres, furfuryl alcohol-base mesoporous carbon spheres and Fe-magnetic mesoporous carbon spheres. Synthesis of the silica template and impregnation were completed in situ in one pot so that the presynthesis of the silica template and additional impregnation steps are no longer necessary. The influence of various carbon precursors on the structural parameters of the resultant carbon spheres was investigated. Furthermore, functionalization was carried out by introducing magnetic sorces and oxidizing agent. The synthesized materials with high specific surface area, large pore volume and well dispersion can enhance their release and adsorption ability. |
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