Enhanced desalination via functionalized carbon nanotube immobilized membrane in direct contact membrane distillation

In this paper, for the first time we report the development of carbon nanotube immobilized membrane (CNIM) on porous polypropylene support for direct contact membrane distillation (DCMD) desalination application. We also describe the effect of specific interaction of functional group of carbon nanotubes (CNTs) with water moisture on the enhancement of water vapor flux in DCMD via alteration of polar-non polar nature of membrane surface. The incorporation of carboxylic acid (-COOH) functional group on carbon nanotubes alters the hydrophilic-hydrophobic interaction of water moistures with the membrane surface that provides additional pathway for enhanced water vapor transport. The water vapor flux was obtained 36.8 kg/m² h at 70 °C for CNT-COOH-PP, which is 51.5% higher than unmodified polypropylene membrane at salt concentration 10,000 ppm in feed. The salt rejection was found greater than 99.9% at salt concentration 10,000 ppm in feed solution. An increase in mass transfer coefficient about 1.5 times was also observed for CNT-COOH-PP membrane. The CNIM also exhibits higher thermal stability at elevated temperatures.