Low-cost Templating Preparation Of Mesoporous Carbons With Controllable Structure And Their Adsorption Performance

Mesoporous carbons (MCs) have recently aroused great interest due to their well-developed porous structure, good electronic conductivity, excellent thermal and chemical stability, which are extensively applied in various fields such as adsorption, separation, catalysis, and electrochemical energy storage. By careful controlling the pore structure and morphology, MCs can achieve better performance for the specific application requirements. However, the preparation of the MCs is usually costly and the porous structures are beyond controlling. Furthermore, the obtained MCs are usually in the form of powders or irregular particles, which greatly limit their applications. Therefore, developing a low-cost and facile preparation method of mesoporous carbons with controlled pore structure and morphology is of great significance.Here in this work, mesoporous carbons with controlled pore structure were synthesized via a facile templating method using low-cost hydrolyzed water glass (sodium silicate) as pore-directing precursor. The mixture of carbon precursor (resorcinol-formaldehyde) sol and home-made silica sol followed by sol-gel process generated a dual polymer/silica hydrogels. After ambient drying, carbonization and HF etching, mesoporous carbons with developed mesoporous structure were obtained. The effect of hydrolysis temperature and hydrolysis time of water glass and the weight ratio of resorcinol-formaldehyde polymer to silica on the structure of MCs were investigated systematically. It was found that as-prepared MCs had disordered mesoporous channels fully replicated from the initial colloidal silica networks. The average mesopore size can be precisely controlled in 6-12 nm by tuning the hydrolysis time and hydrolysis temperature, while the total pore volume can be adjusted in the range of 1.1-2.3 cm3/g by changing the weight ratio of polymer to silica.Furthermore, with the assistant of spray drying technology, mesoporous carbon microspheres (MCMs) were produced in large-scale. The pore structure of MCMs can be turned by adjusting the hydrolysis conditions, including the hydrolysis temperature and time, the concentrations of water glass and the mass ratio of resorcinol-formaldehyde polymer to silica. It was found that the silica framework could restain the volume shrinkages in the process of drying and carbonization, improving the porosity of MCMs. The as-prepared MCMs possessed large surface area (>1000 m2/g), large pore volume (1-2.1 cm3/g) and a narrow pore size distribution.Finally, the VB12 adsorption behavior on MCMs was investigated. Owing to the developed mesoporous structure, the MCMs demonstrated outstanding adsorption capacity of VB12 as high as 606 mg/g, among highest value reported in the literatures. It was found that the mesopore size and pore volume had significant influences on the adsorption performance of VB12. In general, the equilibrium adsorption capacity increased with the increase of pore volume or the decrease of mesopore size. The equilibrium adsorption capacity firstly increased and then decreased, with the increasing of the adsorption temperature. The equilibrium adsorption isotherms of VB12 on MCMs were fitted with type Ⅰ adsorption isotherm, which could be simulated well by the Langmuir model. The adsorption rate of VB12 on MCMs was quite fast, which could be fitted with the pseudo second-order kinetics model.