During the pre-discussion, students were asked to answer the following questions based on articles assigned for reading:

1. What fraction of the world’s population lacks clean drinking water?

1.2 billion people lack access to clean drinking water, 1/6 of the world’s population!

2. List four methods for producing potable water and briefly describe each.

Disinfection: The chemical or photochemical treatment of water to kill harmful waterborne pathogens. These pathogens are a major cause of death worldwide and have the worst effects in third world countries. Common chemicals used for disinfection include chlorine and halogenated species. Unfortunately, many of the common methods of disinfection create toxic byproducts.

Decontamination: The detection and removal of harmful substances from water. Decontamination is a longstanding practice, but problems exist. “Two key problems are that the amount of suspected harmful agents is growing rapidly, and that many of these compounds are toxic trace quantities. To detect their presence and remove them in the presence of safe and natural constituents that are 3 to 9 orders of magnitude more concentrated is challenging, expensive, and unreliable at present”. (Shannon et. Al 2008)

Desalinization: Typically the use of reverse osmosis to reduce the salt concentration of salty water to safe levels. Reverse osmosis is a process in which water is forced against a concentration gradient through a selectively permeable membrane to remove ions and molecules. Currently, it is a highly energy intensive method that is utilized only in locations of significant water distress. Other methods of desalinization include forward osmosis and thermal distillation.

Reuse and Reclamation: The capture and treatment of used water, such as, but not limited to, wastewater, irrigation water and industrially utilized water. It is an emerging method for water treatment that holds significant promise for the future. “A large part of the cost of water for human use is pumping, transport and storage (particularly in developing countries whose citizens often spend substantial time acquiring water). Thus recovering water at or close to the point of use should be very efficient.” (Shannon et. Al 2008)

3.  Explain two strategies for improving salt rejection while maintaining high water flux in RO membranes.

Carbon Nanotube Membranes: The creation of RO membranes from carbon nanotubes can improve salt rejection while maintaining high water flux. The carbon nanotubes uniform pore diameter and hydrophobic nature allow high water flux. The size selective nature of the carbon nanotubes, as well as their potential to be chemically manipulated can result in increased salt reject.

Ion Channels: Driven by the study of ion channels in biological cells, which have the ability to actively transport ions out of solution while maintaining high water flux, the synthesis of ion channels into RO membranes is being explored.

 

4.  Explain the boundary condition of fluid/solid interface in the case of water flowing through a carbon nanotube.  Why is the relevant to membrane design?

Engineering on the nanoscale means thinking in the nanoscale. A carbon nanotube’s diameter is tiny and is almost completely occupied by a single water molecule! This means that the interactions between the inner walls of the carbon nanotube and the water molecule heavily impact how effectively the water molecule can flow through the nanotube. Due to the hydrophobic nature of the carbon nanotubes water is repelled from the walls of the carbon nanotube. Therefore, slip is possible and high water flux can be achieved through the nanotube.

5. Draw a scheme for vertical ordering of SWCNTs into a membrane using surfactant templating.

See Published work (2)

Figure 1. Proposed scheme for the fabrication of vertically aligned SWNT polymer nanocomposite thin-film: (1) sequestration of SWNT into cylindrical micelle mesophase; (2) magnetic field alignment of cylindrical micelles; (3) polymerization of mesophase to form a polymer thin-film embedded with vertically aligned SWNT. (Mauter et al. 2010)  

6.  List and briefly describe three applications of carbon-based nanomaterials other than high flux RO membranes.

Sorption of Environmental Contaminates: The high surface to volume ratio, controlled pore size and manipulatable surface chemistry renders nanoparticles highly effective sorbents. “In addition to serving as direct sorbents, carbonaceous nanomaterials have also been employed as high surface area scaffold for oxides or macromolecules with intrinsic sorbent capacity. Covalent chemistry opens synthesis routes for nanoscaffolds tailored to absorb or complex ions, metals, and radionuclides in solution.” (Mauter et Al. 2008)

Antimicrobial Agents: Many nanomaterials are inherently antimicrobial, because their unique dimensions allow them to block cell wall formation in bacteria. Further, antimicrobial agents, such as silver, can be chemically linked to nanomaterials and subsequently utilized for microbial treatment. These antimicrobial agents can be utilized in wastewater treatment.

Renewable Energy: Carbon based nanotechnology can be applied to a broad array of renewable energy. Applications include proton exchange membranes in fuel cells, radiation counters in nuclear power plants, low volume storage units for hydrogen gas and inexpensive and durable organic cells for solar power.

Bibliography

1)      Mauter, Meagan S., and Menachem Elimelech. “Environmental Applications of Carbon-Based Nanomaterials.” Environmental Science & Technology 42.16 (2008): 5843-859. Print.

2)      Mauter, Meagan S., Menachem Elimelech, and Chinedum O. Osuji. “Nanocomposites of Vertically Aligned Single-Walled Carbon Nanotubes by Magnetic Alignment and Polymerization of a Lyotropic Precursor.” ACS Nano (2010): 101018090626039. Print.

3)      Shannon, Mark A., Paul W. Bohn, Menachem Elimelech, John G. Georgiadis, Benito J. Mariñas, and Anne M. Mayes. “Science and Technology for Water Purification in the Coming Decades.” Nature 452.7185 (2008): 301-10. Print.