A versatile sol–gel route to monolithic oxidic gels via polyacrylic acid template

Abstract

A versatile sol–gel route (dispersed inorganic sol–gel, DIS method) was developed to prepare diverse monolithic gels and, ultimately, monolithic aerogels by simply using the reagents of inorganic salt solution, polyacrylic acid (PAA), and propylene oxide (PO). The preliminary study on the gelation processes of diverse ions including Li⁺, Al³⁺, Ca²⁺, Ti⁴⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Zr⁴⁺, Mo⁵⁺, Cd²⁺, and Ta⁵⁺via both DIS and epoxide addition method (EA method, without adding PAA) indicates that PAA facilitates the formation of monolithic gels, instead of precipitates or cracking gels. The formation mechanism of DIS method was studied by comparing the hierarchic microstructure and pore texture of the chromia gels via DIS and EA method. Conversion of DIS-derived and EA-derived chromia gels to the aerogels was accomplished by the supercritical fluid drying in order to maintain the nanoporous structure of the gels. At last, it is suggested that PAA acts as both dispersant and template in the sol–gel reaction, which not only provides steric hindrance, but also guides the gelation during the gelation processes of hydration, hydrolysis, nucleation & growth, and crosslinkage & formation.