聚乙烯亚胺改性介孔氧化硅载体孔结构的调控机理

Mechanism of regulating pore structure of polyethyleneimine modified mesoporous silica foam

以三嵌段共聚物聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(P123)为模板,硅酸四乙酯(TEOS,C_(8)H_(20)O_(4)Si)为硅源合成了比表面积高达712.5 m^(2)/g,孔体积为2.44 cm^(3)/g的新型介孔氧化硅载体(MCF).通过正电子湮没寿命谱(PALS)以及常规表征手段;例如N2吸附脱附、透射电子显微镜、热重分析、傅里叶变换红外光谱等系统研究了聚乙烯亚胺(PEI)改性MCF对纳米尺度孔结构的影响.结果表明,合成的MCF具有明显的无序介孔结构,孔与孔之间通过窗口相互连接形成了一个连续的、具有良好热稳定性的多孔通道网络,同时可以直观看到有机胺PEI已被成功引入到MCF通道中.为了更全面地评估材料孔径的变化情况,通过高灵敏度、可探测亚纳米量级的正电子湮没技术研究正电子在PEI负载MCF中的湮没机制,发现存在τ_(3)和τ_(4)两个长寿命分量,表明样品中存在微孔和介孔.同时由于PEI分子的引入,导致τ_(3)和τ_(4)呈明显的下降趋势,之后利用正电子在纯气体中的湮没率公式校正PALS所测得的寿命来计算所得孔尺寸,发现孔尺寸随着有机分子PEI的填充而逐渐减小,这将为探究聚乙烯亚胺改性MCF孔结构的调控机理以及有机分子改性介孔分子筛材料体系的孔结构表征提供新的思路.

A novel mesoporous silica foam(MCF)with a specific surface area of 712.5 m^(2)/g and a pore volume of 2.44 cm^(3)/g is synthesized by using triblock copolymer poly(ethylene oxide,polypropylene oxide and ethylene oxide,P123)as template and TEOS(C_(8)H_(20)O_(4)Si)as silicon source.The effect of polyethylenimide(PEI)modified MCF on nanoscale pore structure is studied by positron annihilation lifetime spectroscopy(PALS)and conventional characterization methods,such as N_(2) adsorption desorption,transmission electron microscopy,thermogravimetric analysis and Fourier transform infrared spectroscopy.The results show that the synthesized MCF has an obvious disordered mesoporous structure,and a continuous porous network with window connection between the pores is formed.Meanwhile,it can be seen directly that PEI is successfully introduced into MCF pore channels.In order to evaluate the pore size and its distribution more comprehensively,the mechanism of positron annihilation which is highly sensitive to nanometer scale open volumes in PEI loaded MCF is studied.It is found that there are two long life components τ_(3) and τ_(4),indicating the micropores and mesopores co-existing in the sample.Furthermore,the introduction of PEI molecules results in a significant decrease in τ_(3) and τ_(4),and the lifetime values are then corrected by using the positron annihilation rate formula in pure gas to calculate the pore size.The results show that the pore size gradually decreases with the filling of the organic molecule PEI.This provides a new insight into the mechanism of regulating the pore structure of MCF by polyethyleneimine modification,as well as the characterization of pore structure in organic-modified mesoporous molecular sieves.