In Situ Recrystallization of Silica Template for Synthesis of Novel Microporous ZSM-5/Hollow Mesoporous Carbon Composites

Abstract

Silica-based nanocasting synthesis of a nanostructured carbon replica inevitably involves the disposal of silica waste and toxic etchant after the time-consuming and costly etching processes for selective removal of silica template from a carbon/silica composite to produce the silica-free carbon replica, not only resulting in chemical waste, but also posing serious environmental concerns. Instead of removal of the silica template, the in situ recrystallization transformation of the silica into more useful functional nanostructured silica offers an attractive alternative to the problem of handling silica waste and toxic etchants. In this work, the novel composites composed of microporous zeolite ZSM-5 crystals and hollow core-mesoporous shell carbon (HCMSC) capsules are synthesized for the first time by such transformation process of sacrificial silica template in the carbon/solid core-mesoporous shell silica (SCMSS) composite through hydrothermal process under alkaline condition. Compared to the commercial filter materials, the zeolite/HCMSC composite (BET surface area: 532-600 m(2)/g) possessing a wide range of pore sizes, i.e., micropores from zeolites, mesopores from the outer shells, and macropores from the hollow core of the carbon capsules reveals the outstanding adsorption capacity for the typical malodorous acetaldehyde. Therefore, the recrystallization approach will be appealing as a simple, economical, environmentally benign, and efficient direct synthesis process for the preparation of new multifunctional composite materials for many advanced applications such as removal of volatile organic compounds, separation, energy storage, and catalysis. Recrystallization transformation approach of sacrificial silica in silica/carbon composites is reported for the first time for the formation of new composite materials composed of microporous ZSM-5 zeolite and hollow mesoporous carbon capsules. That is, the silica template waste is utilized to produce a new highly desirable crystalline microporous ZSM-5 silica material by this approach. The composite demonstrated high adsorption capacity for acetaldehyde.