Capacitive deionization (CDI) is an emerging desalination and water treatment process, which efficiently removes hardness or any ionic species in water/wastewater through electro-sorption. Compared to conventional desalination technologies, such as thermal evaporation or membrane process, many advantages of CDI have been reported, including lower energy consumption, less chemical usage, and lower fouling potential.

In addition to intrinsic deionization performance, CDI also has great potential for selective ion removal by adopting ion-selective polymer coating. In our lab, we mainly focus on selective removal of multivalent ions over monovalent ions, such as scalants (Ca²⁺, SO₄^2- etc.) or toxic heavy metals (Cr (VI), As (V) etc.). This selective desalination process will be a significant improvement not only for local communities, but also for nationwide water and energy industries. For example, produced water from oil and gas industries have been disposed to injection wells, and significant amount of fresh water has been used for hydraulic fracturing. If the CDI process sufficiently removes fouling-forming multi-valent ions from produced water, treated water can be reused for continuous fracturing, that saves huge amount of water (resource) and energy (trucking waters). Another possible application would be cooling water treatment. When the blowdown water can be reused after treatment, it will save about 15% of the makeup water (Zhang et al., 2007, Zhang et al., 2008, Altman et al., 2012, Wang et al., 2014).