Preparation of fibrous porous materials by chemical activation 1. ZnCl_2 activation of polymr-coated fibers

摘要

Fiborous porous materials (FPM_s) have been prepared by coating a glass fiber with a solution of polymre and ZnCl_2, followed by stabilization in air and heat treatment in N_2. The ZnCl_2 was then removed by washing with D.I.water and HCl. Four kinds of polymers, a phenolic resin, polyacryonitrile, poly(vinyl alcohol) and cellulose, were used to prepare solutions with ZnCl_2. The result s showed that ZnCl_2 acts as a dehydration agent to promote the thermal cross-linkig of polymer at a much lower temperature, leading to FPMs having much highr char yields and very high surface areas. The porosity was created in part by dissolution of the ZnCl_2 left in the charred coating. The activation temperature and ZnCl_2 concentration play an important role in porosity development. In the early stage of heating, the specific surface area, micropore and mesopore volumes increased with increasing temperature. As the activation temperature increases above 450 deg C. ZnCl_2 begins to volatilize out of the coating, and further charring and aromatization of the coating results in a dimensional contractioon leading to a decrease in the micropore volume. It was observed that the specific surface area, as well as micropore and mesopore volumes, increased with incresing ZnCl_2 concentration. Pore size analysis showed that the FPMs actiated with ZnCl_2 were mainly microporous. For FPMs activated with concentrated ZnCl_2 (66 wt.%), there is a remrakable and large mesopore size distribution in addition to the typical micropore size distribution. In addition, such FPMs have very high specific surface area, more than 1600 for PAN-based on 2500 m~2/g of coating for cellulose-based FPMs.