In situ embedment and growth of anhydrous and hydrated aluminum oxide particles on polyvinylidene fluoride (PVDF) membranes

Surface modification of polyvinylidene fluoride (PVDF) membranes was successfully performed by doping anhydrous and hydrated aluminum oxide particles (γ-alumina, boehmite and gibbsite) through in situ particle embedment and subsequent crystal growth under a hydrothermal environment. The approach of particle embedment involves the dispersion of anhydrous or hydrated aluminum oxide particles in the water phase during PVDF membrane precipitation, and the result was found to strongly depend on the change of free energy in particle–membrane interaction. The embedment of γ-alumina nanoparticles is thermodynamically favorable, but the embedment of boehmite or gibbsite particles is less favorable, especially when using hydrophilic polyvinylpyrrolidone (PVP) additive within the membrane cast solution. The approach of 105 °C hydrothermal treatment initiates the growth of gibbsite on embedded γ-alumina nanoparticles, and the treatment duration determines the coverage of gibbsite particles on PVDF membrane. The overall hydrophilicity of membranes increases with the embedment of γ-alumina and the growth of gibbsite. An increase of membrane resistance was not observed with γ-alumina embedment, but the excessive growth of gibbsite particles may reduce membrane permeability. The Escherichia coli attachment result shows that the surface doping of aluminum oxide particles can greatly reduce E. coli adhesion to the membrane surface, suggesting the positive effect on the reduction of bio-fouling. The success of this PVDF membrane modification method has also provided a promising strategy to manipulate the surface property of other polymer membranes by inorganic materials.