Novel process for facile preparation of mesoporous silica-based materials with controllable pore structure from coal fly ash

Abstract

Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches. Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method. In this paper, facile preparation of mesoporous silica with controllable pore structure from fly ash by the template-free process via two steps of mineral phase transformation and selective acid etching was proposed. The influence of crystalline structure and acid etching degree on structure of as-synthesized mesoporous silica materials was revealed, as well as mechanism of crystalline structure transformation and pore structure formation. The results show that mullite and quartz could be transformed into acid-soluble kaliophilite when fly ash reacted with K2CO3 at temperature of 800–1100 °C. The hexagonal kaliophilite would be transformed into orthorhombic KAlSiO4–O1 phase when the temperature is controlled at 1100 °C. Mesoporous silica with specific surface area of 475.93 m2/g and 642.57 m2/g could be synthesized from activated fly ash with kaliophilite and KAlSiO4–O1 phase crystalline structure. By controlling the degree of acid etching, mesoporous silica materials with different pore structures can be obtained. This paper provides a cost-effective and large-scale process for the preparation of mesoporous silica materials with controllable pore structure from solid waste fly ash.