Spray-drying Synthesis Of Mesoporous/Hollow Carbon Microspheres And Their Applications

Mesoporous carbon microspheres (MCMs) and hollow carbon microspheres (HCMs) have attracted great interests in the development of materials science, environment science, bioscience and aerospace field etc, due to the unique physical structures and surface chemistry such as large BET surface, developed porosity, low bulk density, low flow resistance, high conductivity, good resistance and chemical stability. However, the currently developed strategies for the synthesis of these carbons spheres suffer from the comparatively complex, time-consuming and high-cost procedures, which inevitably hinder their practical applications. Thus, it is of great interest to develop a direct, low-cost and highly efficient method for the large-scale synthesis of mesoporous carbon microspheres and hollow carbon microspheres.In this thesis, mesoporous carbon microspheres (MCMs) and hollow carbon microspheres (HCMs) were prepared by a spray drying method, respectively. The fabrication procedures were optimized and exhibited good controls in the external morphology, porous structures and the natural properties. The main results are summarized as following:(1) The mesoporous carbon microspheres have been synthesized by spray drying method using resorcinol (R) and formaldehyde (F) as carbon source and silica sol (SiO2) as hard template. The factors including solution concentration, inlet temperature and feed speed are systematically optimized to control the morphology of MCMs. The as-obtained MCMs have a good spherical morphology and a narrow particle size distribution of 1 to 20 μm. The mesoporous structure could be precisely turned by adjusting the mass ratio of RF/SiO2 and the size of silica nanoparticle. The specific surface area and the pore volumes of the obtained microspheres could be adjusted in the range of 928-1220 m2/g and 1.5-2.7 cm3/g, respectively, and the pore size could be controlled by using silica sol with different sizes.(2) The MCMs were used for removing Cr6+ from waste water. Various factors influencing the adsorption of Cr6+ including pH, adsorption temperature and contact time were studied. As the adsorption process was pH dependent, it showed maximum removal efficiency of Cr6+ at pH 3.0. The adsorbing capacities could reach ca.60 mg/g at the end of 1 h, and the adsorption equilibrium is acquired till the end of 24 h. Pseudo-second-order model was found to best represent the kinetics of Cr6+ adsorption. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models, and Qm value was as high as 165.3 mg/g. Furthermore, Fe3O4-loaded MCMs were prepared to rapidly separate the adsorbent from the solution by a simple magnetic process. Fe3O4-loaded MCMs had a high adsorption capacity of 156.3 mg/g, and a good regeneration ability with a capacity of 123.9 mg/g for the fifth adsorption-desorption cycle. Owing to their good magnetic response, the Fe3O4-loaded MCMs could be easily separated from the solution by magnetism.(3) After surface coating with the polyvinyl alcohol (PVA), the resultant MCMs were employed as low-density fillers for lightweight phenolic-based composites prepared by hot-pressing method. Coating with PVA could lead to the surface closed of the MCMs with an egg-shell like structure, in which the surface had a smooth and non-porous structure while the bulk still maintained developed mesoporous network. While using the fillers for the composites, the density of composites decreased from 1.36 g/cm3 to 1.12 g/cm3 with the increase of the MCMs content from 0 to 10 wt.%. Meanwhile, the compressive strength of the composites increased significantly from 106 MPa to 168 MPa (at 5 wt.% MCMs). More importantly, the dielectric constant of the composites increased from 4-3.6 of pure resin to 10.4-9.1 of the composites consisting of 10 wt.% MCMs in the frequency range of 102-107 Hz. Combined the advantages of decreasing the density, improving the mechanical properties and increasing the dielectric properties, the MCMs could be served as a new kind of multifunctional fillers for various potential applications, particularly for low-density microwave absorption material.(4) To achieve the required morphology, the factors of influencing the products morphology and purity including RF concentration, PVA content, NaHCO3 content, inlet temperature and feed speed are systematically optimized. The as-obtained HPMs have a low bulk density of 0.089 g/cm3, narrow particle size distribution of 15 to 80 μm with a mean size of 37 μm, a high floatation ratio of 96.3% and high mechanical strength. Followed by a simple carbonization, HCMs with a bulk density of ca.0.1 g/cm3 and particle size distribution of 15 to 80 μm with a mean size of 23 μm can be achieved. A series of syntactic foam consisting of HPMs and HCMs as fillers and phenolic resin as matrix are prepared via a hot-press molding. While using the fillers for the syntactic foam, the density of syntactic foams decreased from 1.31 g/cm3 to 0.48 g/cm3 with the increase of the MCMs content from 0 to 30 wt.%. The maximum compressive strength of the syntactic foam was still 19 MPa with the content of 30 wt.%. The microscopic structure of the syntactic foam and the fractured surfaces after compression testing were observing, and the mechanism of compression fracture was analyzed.