Preparation And Adsorption Property Of Molecularly Imprinted Polymer On The Surface Of Porous Carbon Nanospheres

On the route of the development of desulfurization, the surface molecular imprinting technique is an emerging adsorption desulfurization in which the template molecules are imprinted on the surface of matrix to create molecular cavities which are complementary to the template in size, shape and spatial arrangement of functional groups, realizing special adsorption towards a targeted molecule. Dwing to the introduction of the porous structure, porous carbon nanospheres (PCNSs), with higher BET surface and higher reaction activity than carbon microspheres (CMSs), can be used as matrix with increased surface area and improved reactivity when raw material is biomass. As-obtained PCNSs can eliminate the surface activation step and improve the reactivity of grafting, so as to overcome the difficulty of modification in the process of preparing surface molecularly imprinted materials.The moleculary imprinted polymers (MIPs) were prepared by surface imprinting using dibenzothiophene (DBT) as template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the crosslinker and porous carbon nanospheres (PCNSs) modified with silane coupling agent as carrier material. PCNSs were prepared by hydrothermal method using glucose as raw materials, followed by annealing. Then PCNSs were modified by y-(methacryloxy)propyl trimethoxysilane (KH-570). The influences of KH-570content on silanization and methacrylic acid content on crosslinking reaction were researched. The samples were characterized by electron microscopy, infrared spectroscopy, X-ray diffraction, thermogravimetry and pore size analysis. The combining characteristic of MIPs for DBT was studied preliminarily with static adsoption methods with the aid of gas chromatography. The results are as follows:(1) PCNSs with regular shape, uniform size, high BET surface and good solvent dispersion were synthesized at180℃by hydrothermal method combined with annealing using aqueous glucose solution as raw materials. In this process, the effects of glucose concentration (0.025,0.125,0.250,0.300,0.500,0.700mol/L) and reaction time (8,12,14,20,28,36h) on the morphologies and sizes of the product were investigated. The optimum parameters were:0.250mol/L glucose solution, reaction time28h,180℃. The results show that PCNSs, with the size of160nm and a specific surface area of468.3m2·g-1, had the pore sizes of1.1nm, and several kinds of oxygen-containing functional groups including hydroxyl, carbonyl and carboxyl group on their surfaces, were prepared at optimum conditions. As-obtained PCNSs eliminated the procedure of surface activation and improved the grafting reactivity, thus overcoming the difficulty of modification in the process of preparing surface molecularly imprinted materials. The experiments of adsorption and selectivity also show that the imprinted polymer had higher adsorption efficiency and higher selectivity.(2)KH-570was used as silane coupling agent to modify PCNSs. The effect of KH-570content (0.5,1.0,1.5mL) was considered to select suitable silanization parameter. The optimum parameters for silanization were:PCNSs0.3g, reaction time2h,65℃, pH≈5, ethanol45mL, water15mL, KH-5701.0 mL. The silanized PCNSs kept the original morphology and exhibited high grafting rate.(3)MAA was then grafted on the surface of silanized PCNSs to prepare MIPs for adsorbing dibenzothiophene. The amount of MAA (1.0,1.5,2.0mL) for grafting poly-merization was optimized. The results show that the appropriate amount of MAA (0.2g of silanied PCNSs) was1.0mL, together with the following conditions, reaction temperature, reaction time and the of initiator were70℃,10h,6%of MAA, respectively, in20mL of chloroform. The particles of product had a regular spherity.(4)The adsorption properties of obtained DBT MIPs-PCNSs were evaluated with the aid of gas chromatography. The results show that:the adsorption capacity of DBT on MIPs-PCNSs was376mg/g, which was higher than that of non-imprinted polymers (NIPs-PCNSs,240mg/g), the recognition factor was2.1and the adsorption equilibrium time was3h at25℃. The pseudo first and second order kinetic models all provided correlation for the kinetic adsorption of DBT onto MIPs-PCNSs. Selective adsorption experiments suggest that MIPs-PCNSs had better selective recognition for DBT, with a selectivity factor2.0. For the recovery of DBT,98.6%of DBT was desorpted and the MIPs were repeated for use for six times, with a10%decrease in saturated adsorption for each cycle.