| dc.description.abstract | The preparation of inorganic molecularly imprinted polymers (IMIPs) with high caffeine adsorption and selectivity has been developed using caffeine as the model compound via sol-gel process. The IMIPs were prepared by alkoxysilanes (functionality=4) with or without adding silane coupling agents (functionality=3 or 2). In sol-gel process the hydroxyl groups were produced after hydrolysis of alkoxysilanes and silane coupling agents. These hydroxyl groups promoted the interaction between caffeine and inorganic matrix. Sol-gels are mainly inorganic-based. Therefore, caffeine can be removed by extraction or calcination. The influence on IMIPs prepared by these two removing caffeine methods is also reported. In addition, the influence on caffeine adsorption and selectivity of IMIPs prepared by introducing pore-forming agent, lactic acid, or base catalyst is discussed. Because the flexible matrix and lower degrees of cross-linking were achieved by adding silane coupling agent in the sol-gel process, caffeine could be easily captured in the network of IMIPs. Therefore, in our study the influence on IMIPs prepared by adding different silane coupling agent or adding two kinds of silane coupling agent in the system is also discussed. In addition, the organic molecularly imprinted polymers (MIPs) using functional monomer, methacrylic acid (MAA), and crosslinking agent, ethylene glycol dimethacrylate (EGDMA), were also prepared by solution polymerization as compared with IMIPs.
Competition adsorption experiments between caffeine (CAF) and structure analogous molecule, theophylline (TH), are determined by High-Performance Liquid Chromatography (HPLC) analysis. Porosity measurements of imprinted polymers are performed using Accelerated Surface Area and Porosimetry (ASAP). The surface micro-structure of imprinted polymer is obtained by Scanning Electron Microscape (SEM).
The pore structure of inorganic matrix was obtained via introducing pore-forming agent, lactic acid, into sol-gel process. Hence, the interaction of caffeine and binding sites were promoted. The best caffeine adsorption (20.6μmol/g) of IMIP was obtained. In addition, the high selectivity (4.14) of IMIP was achieved via introducing base catalyst into sol-gel process. It is worth noting that the caffeine adsorption of IMIP with template removed by calcination is two times that by extraction without sacrificing the selectivity of IMIP.
The selectivity of IMIPs prepared by adding silane coupling agent (functionality=3 or 2) into sol-gel process was increased obviously. In addition, the selectivity of IMIPs was also influenced by different step of calcination temperature. The best selectivity (48) of IMIP prepared with methyltrimethoxysilane (MTMOS) was obtained and the temperature of calcination for the second step was 300℃. In addition, the selectivity of IMIP with caffeine prepared with MTMOS was 8 to 34 times than that of blank IMIP without caffeine.
The caffeine adsorption of IMIP prepared by alkoxysilanes with two kinds of silane coupling agent was increased when the more amounts of dimethyldiethoxysilane (DMDEOS) was added. In addition, the caffeine adsorption of IMIPs prepared under pH=5 and pH=6 is higher than that prepared under pH=4. The higher caffeine adsorption of IMIP and the high values of BET surface area of IMIPIn addition, the ratio of micro- and meso-pore structure of IMIP is an very important factor to prepare IMIPs. The best selectivity of IMIP is 36.7 and the meso-pore surface area and micro-pore surface area are 52.7m2/g and 137.2m2/g, respectively.
The caffeine adsorption of MIPs prepared by solution polymerization was increased when the more amounts of solvent was added. The caffeine adsorption of MIPs prepared by solution polymerization was 10 times than that of MIP prepared by bulk polymerization.. In addition, the selectivity of MIPs prepared by solution polymerization was not changed very clear. The caffeine adsorption and selectivity of MIPs are 11~15μmol/g and about 1.2, respectively.
Not only caffeine adsorption but also selectivity of IMIPs prepared by sol-gel process are better than MIPs prepared by solution polymerization. | en_US |