removal of heavt metals by cn ts
TRANSCRIPT
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Removal of Heavy Metals by using Carbon Nanotube
By
Ashish Gadhave
M.Tech
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• Introduction» Heavy Metals in
Wastewater» Other Adsorbents
» Carbon Nanotubes
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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
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Other Adsorbents• Many adsorbents have been studied for removal of heavy
metals Activated CarbonHuskOlive Stone wasteMordeniteCrab shell
• BUT low adsorption capacity• Researchers are putting efforts to investigate new
adsorbent
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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
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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
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Adsorption sites
1)Internal Sites
2)Interstitial Channels
3)Grooves
4)External Surface
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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
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Functionalization• Functionalization plays very important role in
adsorption properties of CNTs
• Functionalization adds –OH, -C=O, -COOH groups.
• Functionalization aims for easy processing.
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SEM image.A. Non functionalized B. Functionalized
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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
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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).
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Adsorption PerformanceAdsorption Isotherm
Adsorption MechanismEffect of pH
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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
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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
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Adsorption Mechanism
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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)n2-n ↔ [CNT-O-M(OH)n
2-n]1-n
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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
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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.
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• 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
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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.
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Thank You