This document discusses several applications of carbon nanotubes (CNTs) in water desalination. It describes how CNT sheets, membranes, and vertically-aligned CNTs can be used to remove salt from water. CNT sheets are synthesized and characterized, showing their ability to adsorb salt. CNT membranes are prepared using different encapsulation methods and shown to have nanopores that can selectively filter ions. Vertically-aligned CNT membranes are grown via CVD and densified to form porous structures for desalination. Multi-walled CNT electrodes are also tested in a desalination device, demonstrating salt removal from water.

1. Application of Carbon Nanotubes in
Water Desalination
Ankit Kumar Singh
Department of Materials Science & Engineering

2. Different techniques for water desalination
using CNTs
• Carbon Nanotube Sheets
• Carbon Nanotube Membranes
• Vertically-aligned Carbon Nanotubes
• Ion exclusion by Carbon Nanotube pores
• Desalinator

3. Carbon nanotube sheets

4. Synthesis of CNT sheets
Oxidation of the CNT sheets
• CNT sheets immersed in conc. HNO3 for 20h
• Washed using DI water and dried at 110°C for 24h
• CNT sheet dimensions: 4cm2 wide and 2mm thick
Ref: Tofighy et.al., Desalination 2010, Vol. 258, 182-186

5. Characterization of CNT sheets
Bulk CNT sheet SEM and TEM image of CNT sheet
Ref: Tofighy et.al., Desalination 2010, Vol. 258, 182-186

6. Effect of initial salt concentration on adsorption
uptake for the oxidized CNT sheets
Ref: Tofighy et.al., Desalination 2010, Vol. 258, 182-186

7. Carbon Nanotube Membranes

8. 1) 2) 3)
1) Si3N4-encapsulated membrane
2) Polystyrene-encapsulated membrane
3) Filtration-assisted assembly membrane
Ref: Noy et.al., Nanotoday 2007, Vol 2, 22-29

9. Ref: Holt et.al., Science 2006, Vol 312, 1034-1037

10. Ref: Hinds et.al., Science 2004, Vol 303, 62-65

11. a) bright-white spots (indicated by
arrows) represent open nanotube
pores
b) encapsulated SWNT bundle having
inner diameter of 4 nm
c) The individual SWNT with an inner
diameter of 1.5 nm, encapsulated by
additional graphite layers
Ref: Kim et.al., Nano Letts. 2007, Vol 7, 2806-2811

12. Vertically-aligned
Carbon nanotube membranes

13. Preparation of high density, vertically aligned carbon
nanotube membranes
Vertically aligned CNT In-situ water etching to Soaking & evaporating
forest through CVD detach the CNT forest to densify CNT forest
SEM image of CNT forest Photograph of dense CNT Porous filter and CNT
detached by water etching membrane membrane glued onto it
Ref: Miao Yu et.al., Nano Letters 2009, Vol. 9, 225-229

14. SEM image of cross section of as SEM image of cross section of
grown CNT forest dense CNT membrane
SEM image of top surface of CNT Pore size distribution of as-grown CNT
membrane forest and dense CNT membrane
Ref: Miao Yu et.al., Nano Letters 2009, Vol. 9, 225-229

15. Properties of CNT membranes
Membrane properties As grown Dense membrane
CNT inner diameter, nm 3.0 3.0
Thickness, µm 750 750
Morphology CNT and interstitial
pores
Density, g/cm3 0.010 0.21
CNT density, 1010 CNT/cm3 14 290
Avg. distance between CNTs, nm 28 6
CNT volume occupancy, % 1 21
Removal of Nano-Gold Particles from DI water
Membrane Water flux Water flux with 12800 ppb Au Au concentration in
Kg/m2.h.bar particles, Kg/m2.h.bar filtrate, ppb
M1 2130 44 72
M2 2740 80 35±2
Ref: Miao Yu et.al., Nano Letters 2009, Vol. 9, 225-229

16. Advantages of VA-CNT over CNT composite membrane
• Higher CNT porosity (20%)
• Interstitial pore size <=> CNT pore size (3nm)
• No sealing material
• Membrane fabrication simplified
• Additional permeation
Ref: Miao Yu et.al., Nano Letters 2009, Vol. 9, 225-229

17. Ion exclusion by Carbon Nanotube pores

18. • CNT membranes
• Functionalized with carboxylic
• Groups filling of Si3N4 matrix
• Supported by silicon chip
• Cross-section SEM image
• Gap-free coating of Si3N4
• Photograph of membrane sides
• Time variation of the permeate
volume per unit area of free
standing membrane
• 0.6mM K3Fe(CN)6 solution
• Nanofiltration cell showing
the column of feed solution
1. P = 0.69 bar 2. CNT membrane
3. permeate solution 4. feed
5. permeate
• Electrophoresis chromatogram
Ref: Fornasiero et. al., Proceedings of National Academy of Science 2008, 17250-17255

19. Ref: Fornasiero et. al., Proceedings of National Academy of Science 2008, 17250-17255

20. Desalinator

21. Preparation of MWCNTs
• Methane Chemical Vapor Deposition performed in quartz tube
• Nickel-silica binary aerogel catalyst
• Reduction with H2 for 30 min @ 680°C
• Reduction with CH4 for next 90 min @ 680°C
Modification of MWCNTs
• Sample A: =>Raw MWCNTs
• Sample B: =>Sample A + 20% HNO3 with ultrasonic for 2h
=> washed with distilled water
=> dried for 24h @ 100°C
• Sample C: =>Sample A + HNO3 + H2SO4 for 0.5h
=> washed with distilled water
=> dried for 24h @ 100°C
• Sample D: =>Sample B
=> oxidized in air for 0.5h @ 600°C
• Sample E: =>Sample B
=> ball milled @ 1200 rpm for 2 h
Ref: Zhang et. al., Mat. Chem. & Phys. 2006, Vol. 97, 415-417

22. Preparation of MWCNT electrodes
• Mixture of MWCNTs and binders (4:1 by wt.)
• Pressed under 25 MPa @ 150°C for 15 min
• Binders => phenolic resin + urotropine (9:1)
• Tablet carbonized @ 850°C for 2h in N2 atmosphere
• Electrode dimensions: 115mm X 75mm X 1mm
Flow rate: 10 ml/min
Voltage: 1V DC
Ref: Zhang et. al., Mat. Chem. & Phys. 2006, Vol. 97, 415-417

23. TEM image of MWCNTs Raman spectrum of MWCNTs
XRD pattern of MWCNTs Desalination curves of MWCNTs
Ref: Zhang et. al., Mat. Chem. & Phys. 2006, Vol. 97, 415-417

24. Thank you