(42v) Development and Characterization of Carbon Nanotube Membranes for Membrane Distillation

Membrane distillation (MD) is an attractive separation process that uses hydrophobic membranes and is driven by the vapor pressure difference across the membrane. Membrane distillation is an emerging technology for water desalination, industrial wastewater treatment, radioactive waste treatment, removal of volatile organic compounds, and concentrating organic solutions. Further development of MD technology depends on the development of cost-effective, robust, and scalable membranes with the desired characteristics, including optimized porosity, high hydrophobicity, the proper surface chemistry, high thermal stability, and good mechanical properties.

This work was aimed at the development of carbon nanotube (CNT) composite membranes that can be utilized for both conventional MD and high-temperature (e.g., >120 °C) separation applications. Composite membranes were prepared by growing CNT, by the chemical vapor deposition method, on various metallic and ceramic substrates, including stainless steel and Hastelloy C alloy meshes, nickel foam, and quartz filter paper. Substrates were subjected to different pretreatments before the carbon deposition stage to create active sites or adjust pore openings. Pretreatments included acid treatment using concentrated HCl at 25 °C, air oxidation at 500-800 °C, surface treatment by Argon plasma, iron or nickel catalyst deposition by solution coating or sputtering, and nickel coating by electroless nickel solution. Membranes were characterized by scanning electron microscopy, Raman spectroscopy, water contact angle measurement, and other characterization methods. A commercially available Teflon membrane and a CNT buckypaper were characterized and tested for comparison purposes. A direct-contact MD configuration was used for the desalination tests. Characterization results indicated that prepared composite CNT membranes are highly hydrophobic and composed of CNT and other carbon materials grown on the substrate materials. Work is in progress to evaluate the performance of developed membranes for MD application. Properly optimized CNT composite membranes can potentially be used for water desalination and other separation applications, particularly at elevated temperatures, where existing polymer-based membranes may fail.