Highly permeable Al₂O₃ microfiltration membranes with holey interior structure achieved through sacrificial C particles

Abstract

Alumina (Al2O3) microfiltration membranes with holey interior structure exhibit the combined desirable properties of both superior permeability and good retention performance. These membranes are purposely made to consist of a holey intermediate layer with a thickness in the range 12.9‐15.5 μm and a top filtration layer of very thin thickness in the range 1.8‐2.8 μm, fabricated by cosintering with sacrificial carbon (C) particles. The holey structure in the intermediate layer, which can be well controlled by regulating the amount of C particles added to Al2O3 particles, contains plenty of holes of 1‐5 μm in size, thereby possessing much reduced water flow resistance. The thin top filtration layer, which contains uniformly distributed nanopores of 90‐100 nm in size, functions as the selective layer, thereby ensuring a good retention performance. At the C particle content of 30 wt. %, the Al2O3 membrane with holey interior structure demonstrates a super‐high pure water flux (3358 Lm‐2h‐1), which is almost twice that of the membrane without holey interior structure (1697 Lm‐2h‐1), while the mechanical strength and retention performance are well maintained.

Overcoming the Trade-off between Water Permeation and Mechanical Strength of Ceramic Membrane Supports by Interfacial Engineering

“…These large pores in the ceramic support can contribute to the open porosity, thereby improving the water permeability. 23 Therefore, the much-improved water permeance of these ceramic supports was attributed to the thin barrier layer (1.33 mm) and the unique porous microstructure.…”

“…In this circumstance, additional intermediate layers are required prior to the deposition of the top filtration layer in the membrane preparation. 23 In this work, alumina powders with an average particle size of ∼10 μm were selected as the starting material, and kaolin, a type of low-cost natural clay, was introduced to modify the interfaces in the alumina powder matrix. The alumina particles were mostly of an asymmetric plate-like morphology (Figure S1a), the randomly stacking of which would benefit the formation of large pores and the improvement in mechanical strength due to the interlocks, 24 while kaolin was in the form of nanoflakes (Figure S1b).…”

“…However, these larger particles require a higher sintering temperature to bond together, and the thus-formed supports tend to show rough surface and large surface pores. In this circumstance, additional intermediate layers are required prior to the deposition of the top filtration layer in the membrane preparation …”

“…The porous structure near the surface and channels was constructed by the partially sintered coarse alumina particles (Figure d), while additional large holes were observed in the middle region (Figure e). These large pores in the ceramic support can contribute to the open porosity, thereby improving the water permeability . Therefore, the much-improved water permeance of these ceramic supports was attributed to the thin barrier layer (1.33 mm) and the unique porous microstructure.…”

Rational Design and Porosity of Porous Alumina Ceramic Membrane for Air Bearing

“…This is because the spaces generated by particle accumulation will form micropores after sintering and the existence of pores increases the porosity. The articles also illustrate this point [27,28]. When porous ceramic membranes are sintered at high temperature, the green body shrinks significantly, resulting in the decrease in or even disappearance of pores.…”