Application of carbon nanotubes in water desalination

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Application of carbon nanotubes in water desalination

  1. 1. Application of Carbon Nanotubes in Water Desalination Ankit Kumar Singh Department of Materials Science & Engineering
  2. 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. 3. Carbon nanotube sheets
  4. 4. Synthesis of CNT sheetsOxidation 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. 5. Characterization of CNT sheetsBulk CNT sheet SEM and TEM image of CNT sheet Ref: Tofighy et.al., Desalination 2010, Vol. 258, 182-186
  6. 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. 7. Carbon Nanotube Membranes
  8. 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. 9. Ref: Holt et.al., Science 2006, Vol 312, 1034-1037
  10. 10. Ref: Hinds et.al., Science 2004, Vol 303, 62-65
  11. 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 layersRef: Kim et.al., Nano Letts. 2007, Vol 7, 2806-2811
  12. 12. Vertically-alignedCarbon nanotube membranes
  13. 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 CNTdetached by water etching membrane membrane glued onto it Ref: Miao Yu et.al., Nano Letters 2009, Vol. 9, 225-229
  14. 14. SEM image of cross section of as SEM image of cross section of grown CNT forest dense CNT membraneSEM 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. 15. Properties of CNT membranes Membrane properties As grown Dense membraneCNT inner diameter, nm 3.0 3.0Thickness, µm 750 750Morphology CNT and interstitial poresDensity, g/cm3 0.010 0.21CNT density, 1010 CNT/cm3 14 290Avg. distance between CNTs, nm 28 6CNT volume occupancy, % 1 21 Removal of Nano-Gold Particles from DI waterMembrane 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. 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. 17. Ion exclusion by Carbon Nanotube pores
  18. 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. 19. Ref: Fornasiero et. al., Proceedings of National Academy of Science 2008, 17250-17255
  20. 20. Desalinator
  21. 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°CModification 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. 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. 23. TEM image of MWCNTs Raman spectrum of MWCNTsXRD pattern of MWCNTs Desalination curves of MWCNTs Ref: Zhang et. al., Mat. Chem. & Phys. 2006, Vol. 97, 415-417
  24. 24. Thank you

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