Controllable synthesis of hierarchical porous mullite fiber network for gas filtration

The hierarchical network was prepared by firing the mixture of mullite fiber and a kind of active powder which was made up of alumina gel, silica gel and AlF3 powder. During which, the smooth surface of mullite fiber was coated with the secondary structure which was controllable by adjusting the firing temperature or by changing the mass ratio of active powder/mullite fiber. The secondary structure created new pore size distribution for the network. Some new pores with diameters of about 1 μm were found in the modified network, while the network constructed by the smooth mullite fiber only had pores with diameters of about 50 μm. Because of the introduction of the secondary structure, the particle filtration efficiency of the network substantially increased. The filtration efficiency for the 0.5 μm particles increased from 12.9% to 94.2%. The filtration efficiency for the 0.3 μm particles also increased from 0.6% to 56.6%.