Alkaline-oxidized MXene composite membrane of ultra high flux and advanced rejection performance for water purification

MXene is a metal-carbon/nitrogen compound material with a two-dimensional layered structure. As a new form of two-dimensional material, it has great potential in the field of water purification because of its properties of high permeability and hydrophilicity. In this study, a MXene composite membrane was prepared by in-situ oxidation of titanium dioxide on the MXene surface by an alkaline oxidation method. A series of characterizations of the prepared MXene composite membrane was carried out. Scanning electron microscopy showed that with an increasing degree of oxidation, the extent of agglomeration of MXene nanosheets increased, thus generating more water channels that are conducive to the transport of water molecules, and an increasing water flux. The penetration performance, interception performance, and stability of the MXene composite membrane were tested. The effect of different concentrations of KOH on the properties of the composite membrane was investigated. It was found that the flux of the composite membrane increased with alkali concentration by 4.6–28.8 times the flux without exposure to alkali. It was found that the rejection rate of the composite membrane for pollutants (dyes, humic acid, bovine serum albumin protein) decreased only slightly with increasing alkali concentration, and was ≥94% of the pure MXene membrane rejection rate in all cases. The rejection performance of the composite membrane was related to the size and charge properties of the pollutant molecules. The results of the stability tests showed that the composite membranes had a high degree of physical and flux stability in a range of aqueous solutions.