The document discusses using carbon nanotubes (CNTs) to remove heavy metals from wastewater. It notes that extensive industrialization has increased heavy metals in wastewater, which are toxic. While other adsorbents have been used for removal, CNTs have higher adsorption capacity due to their large surface area and interaction with pollutants. The document examines the structure and types of CNTs, as well as their characterization and ability to adsorb heavy metals through functional groups on their surface. Key factors affecting adsorption include surface acidity, pH, and temperature. The document concludes that CNTs are effective and future work could further enhance their adsorption properties and cost-effectiveness.

1. Removal of Heavy Metals
by using Carbon Nanotube
By
Ashish Gadhave
M.Tech

2. •Introduction
»Heavy Metals in
Wastewater
»Other Adsorbents
»Carbon Nanotubes

3. Heavy Metals in Wastewater
• Extensive industrialization and improper disposal
are prime factors responsible for release of heavy
metals into environment.
• In India, only 60% of wastewater is being treated
(CPCB, 2011)
• Almost all heavy metals are toxic to living beings
e.g. Cd- nausea, cancer
Pb- gastrointestinal disorder, abdominal pain
Ni- cancer of
lungs, bones, weakness, headache

4. Other Adsorbents
• Many adsorbents have been studied for removal of heavy
metals
 Activated Carbon
Husk
Olive Stone waste
Mordenite
Crab shell
• BUT low adsorption capacity
• Researchers are putting efforts to investigate new
adsorbent

5. Carbon Nanotubes
• With emergence of nanotechnology, research
has been initiated to exploit the unusual and
unique properties of carbon nanotubes (CNTs).
• It is first invented by Dr. Ijima in 1991.
• Made by rolling up of graffin sheet to form
CNT.
• Two types
A. SWCNTs
B. MWCNTs

6. Adsorption
Properties of CNTs
• Highly porous and hollow
• Large specific surface area, light mass density
and strong interaction between CNTs and
pollutant
• Adsorption properties mainly depend on
adsorption sites

7. Adsorption sites
1)Internal Sites
2)Interstitial
Channels
3)Grooves
4)External Surface

8. Continues…
• Adsorption reaches equilibrium much faster on
external sites than on internal sites under same
conditions of temperature and pressure.
• Fraction of opened and unblocked nanotubes can
considerably influence the overall adsorption
capacity.
• The opened CNTs provide more adsorption sites
than closed ones

9. Functionalization
• Functionalization plays very important role in
adsorption properties of CNTs
• Functionalization adds –OH, -C=O, -COOH
groups.
• Functionalization aims for easy processing.

11. SEM image.
A. Non functionalized B. Functionalized

12. CNTs Characterization
• There is no direct correlation between metal ion
adsorption capacity of CNTs and BET surface
area, pore volume
• Surface total acidity influences the adsorption
capacity of CNTs [Report table no 1].
• Adsorption of heavy metals onto the CNTs are
mainly controlled by the strong interactions
between the metal ions and hydrophilic surface
functional groups

13. Metal
Ion
Adsorbent SA PV MPD STA STB qmax
Pb (II)
CNT/HNO3/
Xylene Fe
47 0.18 3.4 1.63 14.8
CNT/HNO3/
Benzene Fe
62 0.26 3.2 1.65 11.2
Ni (II)
SWCNTs 577 1.15 7.98 0.54 0.23 9.22
SWCNT/NaOCl 397 0.46 4.62 4.42 0.35 47.85
Cd (II)
CNT/HNO3 154 0.58 3.6 4.04 5.1
Ag-MWCNT 101 0.27 10.98 4.69 0.1 16.95
Zn (II)
SWCNTs 590 1.12 7.6 11.23
SWCNT/NaOCl 423 0.43 4.12 43.66
SA = BET surface area (m2/g), PV = pore volume (cm3/g),
MPD= mean pore diameter (nm), STA= surface total acidity (mmol/g),
STB = surface total basicity (mmol/g), qmax = maximum adsorption capacity (mg/g).

14. Adsorption Performance
Adsorption Isotherm
Adsorption Mechanism
Effect of pH

15. Adsorption Isotherm
• The metal ion adsorption equilibrium are
commonly correlated with the Langmuir or the
Freundlich equations.
• Several researchers depicted that metal ion
adsorption on CNTs can be well fitted in
Langmuir equation.
• whereas some researchers reported that sorption
of heavy metals on CNTs can be correlated with
both Langmuir and Freundlich equations

16. Metal
Ion
Adsorbent parameters Initial conc. of
metal ion
Qmax (mg/g)
Pb (II) CNTs/MnO2 pH= 7, t= 2hr 30 ppm 78.74
CNTs/ HNO3 pH= 5, T= 298K 80 ppm 35.6
Cu (II) Dispersed MWCNT pH= 5.6 10 ppm 67.8
Undispersed MWCNTs pH= 5.6 10 ppm 51.3
Cd (II) Amino modified
MWCNTs
pH= 6, T= 318K 5 ppm 31.45
Activated alumina-
CNT
pH= 7.5 250 ppm 229.9
Ni (II) SWCNT/NaClO T= 298K 60 ppm 47.86
Qmax= adsorption capacity, t= contact time, T= Temperature

17. Adsorption Mechanism

18. Possible Adsorption Reactions
• Step I
 Protonation and deprotonation of CNTs:
CNT-OH + H+ ↔ CNT-OH2
+
CNT-OH ↔ CNT-O- + H+
• Step II
 Adsorption of divalent metal ions on CNTs
CNT-OH2
+ + M2+ ↔ [CNT-OHM2+]2+ + H+
CNT-O- + M(OH)n
2-n ↔ [CNT-O-M(OH)n
2-n]1-n

19. Effect of pH
• pH plays very important role in adsorption of metal ions.
• When the solution pH is higher than pHPZC (a pH value,
called ‘point of zero charge’, at which the net surface charge
is zero), the negative surface charge provides electrostatic
interactions that are favourable for adsorbing metal ions.
• The decrease of pH leads to neutralization of surface
charge, thus, the adsorption of metal ions should decrease.
• pH also affects metal ion species and competing
complexation reactions, and influences adsorption capacity

20. Future Work
• Much progress has been made over the last few years in
adsorption applications of CNTs.
• In spite of high costs, using CNTs as adsorbents maybe
advantageous in future because the high adsorption
capacities of CNTs compared to other media may offset
their high cost.
• There are still a lot of works to do to enhance CNT
adsorption properties in future.

21. • The surface modification to enhance the dispersion
property of CNTs in solution can greatly increase the
interaction of CNTs with metal ions.
• The practical use of CNTs as sorbents in water and
wastewater treatment depend upon the continuation of
research into the development of a cost-effective way of
CNT production and the toxicity of CNTs and CNT
related materials

22. Conclusion
• CNTs can be used as effective adsorbent for removal of
heavy metal ions.
• The adsorption capacities of metal ions to different
CNTs follow roughly the order: Pb2+ >Ni2+ >Cu2+ >Cd2+
• The adsorption mechanism appears mainly attributable
to chemical interaction between the metal ions and the
surface functional groups.
• Process parameters such as surface total acidity, pH and
temperature play a key role in determining sorption rate
of metal ion onto CNTs.

23. Thank You