Hydraulic Performance Modifications of a Zeolite Membrane after an Alkaline Treatment: Contribution of Polar and Apolar Surface Tension Components

Abstract

Hydraulic permeability measurements are performed on low cut-off Na-mordenite (MOR-type zeolites) membranes after a mild alkaline treatment. A decrease of the hydraulic permeability is systematically observed. Contact angle measurements are carried out (with three polar liquids) on Na-mordenite films seeded onto alumina plates (flat membranes). A decrease of the contact angles is observed after the alkaline treatment for the three liquids. According to the theory of Lifshitz-van der Waals interactions in condensated state, surface modifications are investigated and a variation of the polar component of the material surface tension is observed. After the alkaline treatment, the electron-donor contribution (mainly due to the two remaining lone electron pairs of the oxygen atoms present in the zeolite extra frameworks) decreases and an increase of the electron-receptor contribution is observed and quantified. The contribution of the polar component to the surface tension is attributed to the presence of surface defaults, which increase the surface hydrophilicity. The estimated modifications of the surface interaction energy between the solvent (water) and the Na-mordenite active layer are in good agreement with the decrease of the hydraulic permeability observed after a mild alkaline treatment.

The effect of PEG length on the size and guest uptake of PEG-capped MIL-88A particles

“…Here, we used the analytical approach of Prud'homme, using the same assumptions, except for the core which we take to be composed of magnetite (Fe 3 O 4 ) only and the surface is covered with PEG. We also applied other parameters for the surface tensions using MOFs 28 and zeolites 29 instead of magnetite at the core. These calculations (not shown here) led to brush density predictions that are of the same order of magnitude as for the magnetite particles.…”

Synthesis of mono- and bi-layer MFI zeolite films on macroporous alumina tubular supports: Application to nanofiltration

“…There are two types of defects: extraframework cations corresponding to the presence of aluminum sites, and surface Si-OH groups which appear when Si-O-Si surface network is terminated by an oxygen atom [65]. As it was shown in previous works [66,67], the formation of hydroxyl groups and the adsorption of water molecules generate the formation of an ultrapolar layer on the membrane surface, which is at the origin of mass transfer limitation. The hydration of the small amount of sodium cations located in the pores of the zeolite also leads to a slight decrease of the water flux (end of the conditioning process), because it affects the mobility of the water molecules inside the zeolite porosity (intracrystaline).…”

Modification of the Selectivity Properties of Tubular Ceramic Membranes after Alkaline Treatment

“…As the electric properties of the material did not change after treatment, only a significant modification of dielectric effect was able to explain the observed results. The increase of hydraulic properties of the membranes after the alkaline treatment can be explained by a decrease of the surface hydrophilicity [ 22 ]. The fluoride ions in the water were less deformable, and the interaction energy with a hydrophilic surface was maximal.…”

“…For example, Yang et al [ 21 ] observed an increase of hydraulic performances of a TiO 2 -doped alumina membrane compared to the alumina homogeneous membrane, owing to a modification of hydrophilic properties. Dutournié et al [ 22 ] observed a decrease of the hydraulic performances of a zeolitic membrane after a chemical treatment. Contact angle investigations have shown that the decrease of membrane hydraulic performances is correlated with an increase of surface hydrophilicity.…”