Large-scale Synthesis Of Mesoporous Carbon Microspheres By A Spray Drying Method And Their Adsorption Performance

Mesoporous carbon materials have recently aroused great interest due to their well-developed porous structure, good electronic conductivity and excellent thermal and chemical stability, which were extensively applied in the fields of adsorption and separation, catalysts, and electrochemistry. However, the obtained mesoporous carbons are usually in the form of powders or irregular particles. For practical applications, except for the porous structure, the control of the morphology is also highly required. Microspheres show unique advantages because of their uniform stacking density, excellent mechanical properties, good fluidity, low resistance and fast adsorption/desorption rate. However, large-scale synthesis of mesoporous carbon microspheres (MCMSs), especially with controllable structure and fine morphology is still a challenge.In this thesis, MCMSs with controllable structure and fine morphology have been synthesized in large scale via a facile spray drying method using resorcinol and formaldehyde as carbon source and silica sol as hard template. The adsorption behavior of Vitamin B12 was investigated to explore its potential as a biomaterial adsorbent. In addition, the surface chemistry of MCMSs was modified by nitrogen doping via using melamine as one of precursors, which is hoped to further improve their adsorption performance. The major conclusions are summarized as follows:(1) MCMSs were prepared via a spray drying method using resorcinol and formaldehyde as carbon source and silica sol as hard template. The morphology could be carefully controlled by changing inlet temperature, concentration of the precursor, feed flow rate and addition amount of PVA. The optimum conditions for the preparation of MCMSs were determined as the pre-reaction time of 1 h, the precursor concentration of 7.5 w/v%, inlet temperature of 120 ℃, feed flow rate of 750 ml/h and spray pressure of 0.4 MPa. The mesoporous structure could be precisely tuned by adjusting the mass ratio of organic precursor and silica sol (RF/SiO2) and the size of silica nanoparticle. The pore volumes and the specific surface area of the obtained microspheres prepared from different RF/SiO2 ratios could be controlled in the range of 1.7-2.7 cm3/g and 825-1220 m2/g, respectively, while the average pore size could be controlled to 7-22 nm by using the silica sol with different sizes.(2) The Vitamin B12 adsorption behaviors were investigated with respect to as-prepared MCMSs. Owing to the developed mesoporous structure, the MCMSs exhibited excellent adsorption kinetic with 90% of total adsorption capacity in the initial 10 min. The equilibrium adsorption capacities of VB12 over these MCMSs were in the range of 325.8-495.7 mg/g. It was found that the adsorption capacity was mainly depended on the pore volume of the adsorbents while they had similar pore sizes. In addition, the adsorption capacity decreased with the increasing pore size for the adsorbent with the similar pore volume.(3) Nitrogen doped MCMSs were prepared by employing melamine as one of precursors. The addition approach of melamine into RF precursors was strongly affected the final nitrogen content doped in the materials, in which step-by-step mixing process showed obviously higher nitrogen content (3.3-9.8 wt%) than these from direct mixing process (2.7-4.8 wt%) at the same precursor composition. The addition of melamine could also adjust the mesoporous structure of the MCMSs due to different carbonization yields. Here the total pore volume could be turned in the range of 1.7-3.6 cm3/g. These nitrogen doped MCMSs exhibited excellent adsorption capacity for Cr6+ with the highest adsorption capacity of 361.3 mg/g, and the adsorption was endothermic and spontaneous process based on the thermodynamic calculation. The adsorption capability was strongly dependent on the pore volume, surface area and nitrogen content, among which the pore volume played a major role. In general, the adsorption capability increased with the increasing pore volume and surface area, while nitrogen doping could also facilitate the improvement of adsorption capacity.