MXene-based membranes for water treatment: preparation, properties, and application

The existence of life on Earth depends on the availability of water. Rapid population growth, industrial development, and shortage of freshwater resources have made human society face the global challenge of water shortage, and it is expected that the world's water demand will increase by 20-30% from now until 2040. To overcome this problem, different processes have been used to purify water, and among these processes, membrane separation can be a suitable technology to meet this challenge due to the high quality of produced water, simplicity of operation, ability to operate under mild conditions, and low energy consumption. The common technologies for water treatment like distillation require high energy consumption and these technologies can not meet the global demand for fresh water. Among the different membrane processes, reverse osmosis is an efficient technology to remove salt ions from brackish water to obtain potable water. In membrane separation methods, the selection of the appropriate material as a membrane is so important because the physical, chemical, and mechanical properties, and separation performance (water flux, selectivity and, salt rejection) of the membrane are strongly dependent on the selected material type. Hence, researchers are still interested in the use of new materials to improve membrane performance. MXene nanosheets (transition metal carbides and nitrides) are a new category of two-dimensional materials with graphene-like structures that have unique properties, including large surface area, narrow interlayer spacing, high hydrophilicity, and surface functionality, suitable physical, chemical, and mechanical properties for membrane applications. Mxene compounds are important both as new pure membrane structures and also as nanomaterials to improve the properties of polymers in membrane processes. To this end, in the present paper, comprehensive information has been introduced on MXene compounds, including their synthesis, surface functionality, and membrane fabrication, with a focus on water treatment technology.