Ceramic tubular nanofiltration membranes with tunable performances by atomic layer deposition and calcination

Ceramic nanofiltration (NF) membranes are of particular significance for molecular separations under harsh conditions. However, they are usually manufactured by the sol-gel process which frequently suffers from low efficiency and poor control in the membrane properties. Herein we demonstrate an efficient and more controllable strategy to produce ceramic tubular NF membranes based on atomic layer deposition (ALD). Tubular ceramic membranes with pore size of ~5 nm are used as the substrates, on which titanium alkoxide (titanicone) is ALD-deposited. Subsequent calcination in air degrades the organic moieties in titanicone, thus converting the dense layer of titanicone into a microporous layer of TiO₂. This microporous TiO₂layer serves as a thin separation layer delivering the NF size-sieving function. The thickness of the TiO₂layer can be readily tuned by changing the ALD cycle numbers, and correspondingly the original substrate membranes are progressively tightened with rising ALD cycles, and the membrane with 300 cycles exhibits a molecular-weight-cut-off (MWCO) of ~680 Da and water permeability of 30 L m⁻² h⁻¹ bar⁻¹. Such a water permeability is higher than many other ceramic tubular membranes with similar MWCOs because of the ultrathin nature of the microporous TiO₂layer established by titanicone deposition and calcination.