Atmospheric Pressure Alkaline Etching of MFI Zeolite Under Mild Temperature Toward Hollow Microstructure and Ultralow k Film

Constructing a hollow structure inside zeolite is very helpful for improving its performance. Unlike the conventional alkaline etching technique usually operated at high temperature (typically 170 °C) and high pressure (autogenerated in autoclave), here, it is discovered that zeolite MFI nano-box can be achieved under mild etching conditions of atmospheric pressure and low temperature of 80 °C, making it very attractive for energy conservation and practical applications. A hollow-structure formation mechanism of protection-dissolution etching is demonstrated by characterizing MFI crystals obtained under different etching time, temperature, and etchant concentration. The utilization of template agent-free secondary growth leads to the successful fabrication of a continuous b-oriented hierarchical MFI zeolite film with desired microstructure of embedded cavities and opened pores. The advantage of the newly constructed film is highlighted by its ultralow k value accompanied with high mechanical strength.