| Due to the advantages of light weight, high specific surface area(SSA), large porosity, strong adsorption capacity, chemical stability, porous carbon materials have been one of the hot points in the international research fields and have potential applications in various fields such as hydrogen storage and supercapacitors. Applications in different fields put forward different requirements on porous carbon materials’ pore and phase structure: physisorption adsorption of hydrogen storage normally need high SSA, large pore volume and suitable pore size(0.6-0.9 nm); electrode materials for electrochemical energy storage require high SSA, hierarchical pore structure and good conductive properties. Therefore, improving the SSA and conductivity, regulating the pore structure and aperture size of porous carbon materials are the key to realizing the application of porous carbon materials. Among the various porous carbon materials, porous carbon spheres have received special attention due to the controllable morphology and pore structure. The main content of this article is the preparation, graphitization, structure regulation and characterization of discrete microporous carbon, mainly divided into the following aspects:(1) We used poly(styrene-divinylbenzene)(PS-DVB) which were prepared via soap-free emulsion polymerization reaction as raw material and CCl4, C2H4Cl2 as crosslinking agent for secondary crosslinking and carbonization, which is a new method to prepare highly monodisperse and discrete carbon spheres. The pore structure of carbon spheres can be controlled by changing the the amount of DVB, and the number and order of the hypercrosslingking reaction. The obtained samples are characterized by FESEM, TEM, XRD, Raman, FT-IR, nitrogen adsorption desorption, hydrogen adsorption, etc. The results show that the secondary crosslinked carbon spheres have good monodispersity and discreteness, and changing the order of the hypercrosslingking reaction has no effect on the morphology; the SSA of carbon spheres prepared by using dichloroethane in the first place are bigger than that of using tetrachloromethane; the secondary crosslinked carbon spheres have higher SSA and pore volume than single crosslinked carbon spheresl; the SSA, pore volume and pore size of carbon microspheres increase with the increase of the content of DVB, which suggests that higher crosslinking density can effectively reduce the crosslinked microspheres’ volume shrinkage in the carbonization process. The BET of these carbon microspheres is about 400-500 m2g-1, and the average pore size of the microspheres is about 0.67-0.70 nm, which are beneficial parameters for the hydrogen storage.Hydrogen storage quantity increased with the increase of SSA and micropore pore volume.(2) The pore structure of carbon spheres can be adjusted by changing the structure of precursor, that is to say porous carbon spheres are prepared by crosslinking and carbonizing the hollow microspheres precursors; the pore structure of carbon spheres can be also adjusted by changing the crosslinking temperature. Specifically, first of all, hollow microspheres were prepared through dissolving cores of solid core-shell PS-DVB spheres with CCl4, then porous carbon spheres are prepared by super crosslinking at different temperatures using Cl CH2CH2 Cl as crosslinking agent, anhydrous Fe Cl3 as catalyst and carbonizing. The obtained samples are characterized by FESEM, TEM, XRD, Raman, FT-IR, nitrogen adsorption desorption, etc. The SEM and TEM images demonstrate that after changing the precursor, the as-prepared carbon spheres still process solid sturcture with little change of the surface morphology. The nitrogen adsorption–desorption isotherms of the carbon spheres show that the BET of the carbon spheres which is crosslinked at 0 ℃is larger than that of at 40 ℃; the micropore volume of prepared carbon spheres represents a significant share of total pore, which is beneficial for hydrogen storage.(3) As electrochemical electrode materials, porous carbon materials should not only have high specific surface area and entrance, but also have suitable hierarchical pore structure and good electrical conductivity. In order to improve the electrical conductivity and construct multilevel pore structure of porous microspheres, this paper used solid PS-DVB microspheres as raw material for crosslinking and carbonization, which developed a simple method to construct graphite network structure in the porous carbon and realized the coexistence of porous carbon and graphite multiple function structure. Practically speaking, the PS microspheres was treated with hypercrosslinking procedure with Cl CH2CH2 Cl as crosslinking agent, anhydrous Fe Cl3 as catalyst; the hypercrosslinked microspheres were washed with a certain amount of acetone(using the solvation effects) so as to not keep part of the iron; finally, low degree of graphitization of carbon spheres were obtained by carbonizating. At the same time, we also studied the influence of the content of DVB, super crosslinking temperature, carbonization temperature on the phase structure and pore structure of the samples. The obtained samples are characterized by TGA/DSC, FESEM, TEM, XRD, Raman, FT-IR, nitrogen adsorption desorption, etc. The results show that we successfully prepared porous graphitized carbon spheres. The change of the content of DVB, super crosslinking temperature and carbonization temperature all have a certain effect on the structure of graphitized carbon spheres. From the XRD and Raman spectra we know that the graphitization degree of the sample is not high. The results of nitrogen adsorption show that the proportion of the microporous volume of carbon spheres is larger, and the specific surface area is between 407 m2 g-1 and 528 m2 g-1.(4) In order to achieve highly graphitized carbon spheres, and further improve the carbon conductive performance and reduce the graphitization temperature, the researchers developed a method for preparing highly graphitized hierarchical porous carbon spheres at low temperature. The experimental scheme is improved on the basis of(3). In order to precipitate and load most of the Fe Cl3 in the internal and external of hole of super crosslinked PS microsphere, the hypercrosslinked microspheres was washed with toluene(Fe Cl3 does not dissolve in toluene), and the highly graphitized porous carbon spheres were obtained after carbonization. The obtained samples are characterized by TGA/DSC, FESEM, TEM, XRD, Raman, FT-IR, nitrogen adsorption desorption, electrochemical workstation, etc. Results show that the highly graphitized carbon spheres were achieved at low temperature(600 ℃); the narrow graphite ribbons of part of the porous amorphous carbon form a three-dimensional network structure. The results, such as XRD, Raman, etc., showed that the degree of graphitization decreasing with the increase of the amount of carbon spheres DVB; the sample carbonized at 700 ℃had the highest degree of graphitization; the degree of graphitization of the carbon spheres crosslinking at 60 ℃was higher than that prepared at 40 ℃. Nitrogen adsorption results demonstrated that the samples were all having a specific surface area and pore volume. The electrochemical test results showed that the electrochemical performance of the samples had been greatly improved; the sample that the content of DVB was 40% had better electrochemical performance and the capacitance reached 105 F / g.Graphitized carbon spheres keep characteristics of high SSA and pore structure of non graphitized carbon spheres. This carbon spheres with porous structure, high SSA, network structure of graphite, meet the construction requirements of the carbon material in electrochemistry applications. As a novel multifunctional single material, the samples are expected to be good electrochemical materials... |
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