Sorption of Organic Electrolytes and Surfactants from Natural Waters by Heterogeneous Membranes

The widespread use of surfactants increasingly requires the development and application of reliable methods for the demineralization of wastewaters, preventing environmental pollution. One of the most reliable and effective methods of demineralization of wastewaters is the electrodialysis method. Studying the behavior of large organic ions in the membrane is important for modeling cell membranes and purification of medicinal and biological preparations. The sorption characteristics of the MA-40 and MK-40 ion-exchange membranes in solutions of simple and organic electrolytes, and in a solution of the surfactant were investigated. It was found that the sorption of organic ions by membranes is mainly of an ion-exchange nature. The moisture content and elasticity of the membranes decreases in solutions of organic electrolytes, during the sorption of which the membrane becomes brittle. A study showed that in the solutions of organic electrolytes, the MA-40 membrane retains high electrochemical activity, while the MK-40 in a solution of the surfactant completely loses it. From the data obtained in this work, it is shown that organic ions do not present a hazard when water is desalted by electrodialysis, whereas sorption of surfactant ions leads to membrane poisoning.

Characterization of MK-40 Membrane Modified by Layers of Cation Exchange and Anion Exchange Polyelectrolytes

Coating of ion exchange membranes used in electrodialysis with layers of polyelectrolytes is a proven approach that allows for the increasing of the limiting current, the suppressing of sedimentation, the controlling of the intensity of generation of H+ and OH− ions, and also the improving of monovalent selectivity. However, in the case when two materials with the opposite sign of the charge of fixed groups come in contact, a bipolar boundary is created that can cause undesirable changes in the membrane properties. In this work, we used a MK-40 heterogeneous membrane on the surface of which a layer of polyethyleneimine was applied by adsorption from a solution as a model of heterogeneous membranes modified with oppositely charged polyelectrolyte. It was found that, on one hand, the properties of modified membrane were beneficial for electrodialysis, its limiting current did not decrease and the membrane even acquired a barrier to non-selective electrolyte transport. At the same time, the generation of H+ and OH− ions of low intensity arose, even in underlimiting current modes. It was also shown that despite the presence of a layer of polyethyleneimine, the surface charge of the modified membrane remained negative, which we associate with low protonation of polyethyleneimine at neutral pH.

Heterogeneous ZIF-L membranes with improved hydrophilicity and anti-bacterial adhesion for potential application in water treatment

Heterogeneous Zn/Co-ZIF-L membranes were prepared through the successive growth of Zn-ZIF-L and Co-ZIF-L on the macroporous ceramic supports, and the obtained heterogeneous membranes showed improved hydrophilicity and anti-bacterial adhesion.