Silica Nanofibrous Membranes for the Separation of Heterogeneous Azeotropes

Nanofibrous materials produced through electrospinning are characterized by a high porosity, large specific surface area, and high pore interconnectivity and, therefore, show potential for, e.g., separation and filtration. The development of more inert nanofibers with higher thermal and chemical resistance extends the application field to high-end purification. Silica nanofibrous membranes produced by direct electrospinning of a sol-gel solution without a sacrificing carrier, starting from tetraethoxysilane, meet these challenging requirements. After electrospinning the membrane is highly hydrophobic. Storage under dry conditions preserves this property. Oppositely, a superhydrophilic membrane is obtained by storage under high humidity (month scale). This switch is caused by the reaction of ethoxy groups, present due to incomplete hydrolysis of the precursor, with moisture in the air, resulting in an increased amount of silanol groups. This transition can be accelerated to hour scale by applying a heat treatment, with the additional increase in cross-linking density for temperatures above 400 degrees C, enabling applications that make use of hydrophobic and hydrophilic membranes by tuning the functionalization. It is showcased that upon designing the water repellent or absorbing nature of the silica material, fast gravity-driven membrane separation of heterogeneous azeotropes can be achieved.

通过电纺丝生产的纳米纤维材料的特征在于高孔隙率，大的比表面积和高的孔互连性，因此显示出例如分离和过滤的潜力。具有更高的耐热性和耐化学性的更多惰性纳米纤维的开发将应用领域扩展到高端纯化。从四乙氧基硅烷开始，在不牺牲载体的情况下，通过直接电纺溶胶-凝胶溶液生产的二氧化硅纳米纤维膜可以满足这些挑战性的要求。静电纺丝后，该膜是高度疏水的。在干燥条件下储存可保留此特性。相反，通过在高湿度（月规模）下储存获得超亲水膜。这种转换是由于前体不完全水解而产生的乙氧基与空气中的水分反应所致，从而导致硅烷醇基团数量增加。通过进行热处理，可以将这种转变加速到小时刻度，并且对于温度高于400摄氏度的情况，交联密度的额外增加将使通过调节功能性利用疏水性和亲水性膜的应用成为可能。结果表明，通过设计二氧化硅材料的疏水性或吸收性，可以实现非均相共沸物的快速重力驱动膜分离。

Published: 2018

Journal ：ADVANCED FUNCTIONAL MATERIALS

Impact Factor：16.723

Paper link: https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201804138