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December 12, 2008
Noble metal nanoparticles for water purification: A critical reviewThin Solid Films
Professor Pradeep’s Research Group
DST Unit on Nanoscience
IIT Madras
Content of the review article
1. Introduction
2. Drinking water purification – a historical perspective
3. Need for nanomaterials in water purification – the need to look at molecular technologies
4. Noble metal nanoparticle based chemistry
4.1 Synthesis protocols
4.2 Origin of reactivity
4.3 Heterogeneous catalysis - methods for nanoparticle deposition on support
4.4 Drinking water purification: Novel reactions at the nano-scale
4.4.1 Chemistry of organic compounds with noble metal nanoparticles
4.4.2 Detection of pesticides in drinking water with noble metal nanoparticles
4.4.3 Chemistry of heavy metal ions with noble metal nanoparticles
4.4.4 Detection of heavy metals in drinking water with noble metal nanoparticles
4.4.5 Chemistry of micro-organisms with noble metal nanoparticles
5. Case study: Nanoparticles based chemistry for pesticides removal
6. Other nanomaterial based approaches for water purification
7. Commercial interests in drinking water purification
8. Environmental implications of the use of noble metal nanoparticles
9. Summary and conclusions
10. Acknowledgements
11. References
Introduction – relationship of life and human civilization with
water
- Water has been the most vital component of life during its existence on earth for last 3.5 billion years.
- The earliest form of life appeared in sea water (3.5 billion years ago) and
transferred to land only 380 million years ago.
- Despite of this transfer to land, an ocean, in terms of fluidic composition, continues to exist within us. Similarly keeping a very high proportion of living organisms’ body weight as water (~70%), Nature has iterated the vitality of water
for life.
- Water is one of the purest signs of prosperity, health, serenity, beauty, artistry, purity and many other attributes. Leonardo Da Vinci had described water as “the
vehicle of nature" ("vetturale di natura”).
- The Nile was the lifeline of the Egyptian civilization. The Indus Valley civilization flourished on the banks of the Indus river.
Noble metals in human life
- Gold and silver belong to the family of “metals of antiquity”, having their history with mankind dating back to 6,000 BC and 4,000 BC respectively. They have been
associated with the gods, with immortality, and with wealth across the human civilizations.
- Use of noble metals in medicines is aplenty: swarna bhasma, tears of the sun,
arthritis and anti-bacterial.
Drinking water purification – a historical perspective
Year
1804 Setup of world's first city-wide municipal water treatment plant (Scotland, sand-filter technology)
1810 Discovery of chlorine as a disinfectant (Humphrey Davy)
1852 Formulation of Metropolis Water Act (England)
1879 Formulation of Germ Theory (Louis Pasteur)
1902 Use of Chlorine as disinfectant in drinking water supply (calcium hypo chlorite, Belgium)
1906 Use of ozone as disinfectant (France)
1908 Use of Chlorine as disinfectant in municipal supply, New Jersey
1914 Federal regulation of drinking water quality (USPHS)
1916 Use of UV treatment in municipal supplies
1935 Discovery of synthetic ion exchange resin (Adams, Holmes)
1948 Nobel Prize to Paul Hermann Müller (insecticidal properties of DDT)
1959 Discovery of synthetic reverse osmosis membrane (Yuster, Loeb, Sourirajan)
1962 Publishing of Silent Spring, first report on harmful effects of DDT (Rachel Carson)
1965 World's first commercial RO plant launched
1974 Reports on carcinogenic by-products of disinfection with chlorine
Formulation of Safe Drinking Water Act (USEPA)
1975 Development of carbon block for drinking water purification
1994 Report on use Zerovalent Iron for degradation of halogenated organics (Gillham, Hannesin)
1997 Report on use Zerovalent Iron nanoparticles for degradation of halogenated organics (Wang, Zhang)
1998 Drinking Water Directive applied in EU
2000 Adoption of Millennium Declaration during the UN Millennium Summit (UN Millennium Development Goals)
2003 Report on use Noble metal nanoparticles for degradation of pesticides (Nair, Tom, Pradeep)
2004 Stockholm Convention, banning the use of persistent organic pollutants
2007 Launch of world's first nanotechnology based domestic water purifier (Pradeep, Eureka Forbes Limited)
Milestone
Important milestones in the history of water purification (1800-2007)multiple sources from internet
Review of major contaminants in drinking water
- Incidence of Gout due to leaded wine and rum- Use of lead in paints and discharge in environment
Delays in physical/ mental development, Kidney problem, high blood pressure
>300,000 US children and 65% of Shanghai children have high lead concentration
Egypt, EU, USA, Thailand, China, Cambodia
15 ppb- Old piping lines,
mineral weathering, paint
Lead
- ~30% of the mercury in US comes from abroad e.g. China- Unilever plant, Kodaikanal(India). Minamata, Niigata (Japan), River Nura(Kazakhstan).
Neurotoxicant, tremors, respiratory failure, gastrointestinal failures, and kidney damage
~630,000 infants are born with high Hg content in the blood every year (EPA)
Indonesia, China, Africa, Philippines, Japan, Kazakhstan, USA, Brazil, Australia, Taiwan, EU
- 2 ppb- Industrial pollution,
dental filling, Food (fish)
Mercury
- 1 in 100 people (Conc: 0.05 mg/l) and 10 in 100 people (Conc: 0.5 mg/l) die due to cancer in long-term
High blood pressure, glucosuria, hyperpigmentation, keratoses, cancer
65 million (Asia)Bangladesh, India, China,
Pakistan, Nepal, Myanmar, Vietnam
10 ppb- Geological originArsenic
- In 1999, a union of 1,200 scientists, doctors and lawyers announced their opposition to water fluoridation (USA)
- Dental and skeletal fluorosis, Muscle fibre regeneration, nervous system malfunction
62 million (India)Asia, Mexico, Australia,
Argentina, Africa, New Zealand
- 2 ppm
- Geological origin, mineral weathering, coal mining
Fluoride
- 25 million pounds of TCE were released into the U.S. environment by manufacturing plants in 1995
CCl4: High toxicity to liver and kidney, carcinogenic.TCE: Lung/liver tumor
- ~180 million people in US consume chloraminatedwater
Japan, Central Asia, Arabian Peninsula, Sweden, Poland, Germany, USA, Egypt, China
CCl4: 5 ppbTCE: 5 ppbTTHMs: 80 ppb
Chlorination, effluents, home insecticide
Halogenated organics
Pesticide contamination in soft drinks, the Union Carbide Bhopal tragedy (India)
Cancer, cardiovascular/ reproductive/ neurological disorders, Liver/kidney problems
Poisoning: 28 million agricultural workers in the developing countries. ~18,000 deaths.
US, Kenya, Egypt, India, European Union, Africa, China, Australia
DDT: 1 ppbCarbofuran: 40 ppbSimazine: 4 ppb
- Farming, effluents, home use
Pesticides
RemarksHealth effectsPopulation at riskAffected countriesPermissible
limitsOriginMajor pollutant
Review of major drinking water contaminants, their health impacts and a few associated eventsmultiple sources from internet
Important reasons for use of nanotechnology in drinking water
purification
10
100
50
100
50
50
200
0
50
100
150
200
1950
1960
1970
1980
1990
2000
Year
Concentration (in ppb)
Lead
Arsenic
Membrane preparation
Synthetic lipid bilayer
Calculated non-mediated diffusion
Intact human erythrocyte
D-Glucose
Permeability coefficient (cm.s-1
)
D-Mannitol
2.4 X 10-10
4.4 X 10-11
4 X 10-9
2 X 10-4
3 X 10-9
5 X 10-9
Science, 2001, 2353-57 Nature, 2008, 301-10
Origin of nobility at bulk scale
79Au
Z60 100
<r>
rel/<r>
non-rel, for 6s
1
80
0.95
0.9
0.85
(a) Ni(111) Cu(111) Pt(111) Au(111)
Projected DOS (arb. units)
-10
-50
5
ε(eV) H 1s-d
antibonding
H 1s-d bonding
(b)
Acc. Chem. Res., 1979, 276-81 Nature, 1995, 238-40
Origin of reactivity at nanoscale
400 600 800 10000.0
0.2
0.4
0.6
(a)
(c)
(b)
Intensity (arb. u
nits)
Wavelength (nm)(a) (b) (c) (d)
s
p
UV Visible IR
Abso
rban
ce
Fermi
bands
Metallic
absorption
Inter-band
absorption
Plasmon
Wavelength (nm)
Surface plasmon
absorption
(ii)
(i)
(iii)
(a)
UV Visible IR
Abso
rban
ce
UV Visible IR
Abso
rban
ce
Z(E)
E
D1d(E)
E
nz = 1
nz = 2
nz = 3
nz = 4
D2d(E)
E(b)
(c)
(d)
D0d(E)
E(e)
A
20nm
A
20nm
Gold Bullet. (submitted) Adv. Mat.,2008, 980-83 Langmuir 2008, 4589-99
Phys. Rev. A, 1976, 2287-98
Catal. Today, 2002, 63–78
Origin of re
activity at nanoscale (continued)
J. Phys. Chem., 1993, 5457-71
Nature, 1998, 396, 444–446
Phys. Chem. Chem. Phys., 2007, 725–30
Drinking water purification: Novel reactions at the nano-scale
Chemistry of organic compounds with noble metal nanoparticles
Chem. Mater., 1998, 444-50J. Phys. Chem. B, 1998, 8364-66
Environ. Sci. Techno. 1995, 1511-17
Drinking water purification: Novel reactions at the nano-scale
Chemistry of organic compounds with noble metal nanoparticles
(b)
Intensity (arb. u
nits)
a
b
2 Theta (degree)10 30 50 70
Wavelength (nm)1800 1600 1400 1200 1000
12881550
(c)
Intensity (X10
-3)
0
4
8
12
400 600 800 10000.0
0.5
1.0
1.5
Abso
rban
ce
Wavelength (nm)
p
o
ba(a)
A B
Curr. Sci., 2003, 1560-64
Wavenumber (cm-1)
3000 2000 1000
Transm
ittance (a.u.)
a
b
c
400 600 800 10000.0
0.2
0.4
ba
Abso
rban
ce
Wavelength(nm)400 600 800
0.00
0.05
0.10
b-e
a
Abso
rban
ce
Wavelength (nm)
(B)(A)
a
b
c(C)
J. Environ. Monit., 2003, 363–65 J Nanosci Nanotechnol. 2007, 1871-7
Drinking water purification: Novel reactions at the nano-scale
Detection of pesticides in drinking water with noble metal nanoparticles
a b c d e fa b c d e fa b c d e fa b c d e f
BB CCa b c
(A)
(B)400 500 600 700 800 900
0.0
0.1
0.2
0.3 f
e
d
c
b
a
Ab
so
rban
ce
Wavelength (nm) Wavelength (nm)400 600 800
Abso
rban
ce
0
0.1
0.2
0.3
a
b
c
de
f
(c)(C)
J. Environ. Health (submitted)
Drinking water purification: Novel reactions at the nano-scale
Chemistry of heavy metal ions with noble metal nanoparticles
(A)
Abso
rban
ce
Wavelength (nm)300 400 500 600
(A)
Abso
rban
ce
Wavelength (nm)300 400 500 600
2θ (degrees)30 50 70 806040
Intensity
a
bc
d
(111) (200) (220) (311)
(311)(220)(200)(111)
(200) (220)(311)
(222)
(400)(331)
(420)
(311)(220)(200)(111)
(111)
(B)
2θ (degrees)30 50 70 806040
Intensity
a
bc
d
(111) (200) (220) (311)
(311)(220)(200)(111)
(200) (220)(311)
(222)
(400)(331)
(420)
(311)(220)(200)(111)
(111)
(B)
J. Colloid Interf. Sci. 2006, 415–18
Ag (s) + H+ + Cl- → AgCl (s) + H2 E°= -0.22 V
The non-reactivity of bulk silver can again be understood from the absence of driving
force for the reaction. However, at the nano-scale, the feasibility of the reaction (i.e. E
> 0) confirms the increasing reducing nature of the silver nanoparticle surface.
Drinking water purification: Novel reactions at the nano-scale
Chemistry of heavy metal ions with noble metal nanoparticles
200 400 6000.00
0.05
0.10
(viii)(ix)
(ii)
(i)
Wavelength (nm)
Absorban
ce
(a) (b)
Ag → Ag + e- E°oxidation = -0.8 V Hg2+ + 2e-
→ Hg E°reduction = 0.85 V
2Ag + Hg2+→ Hg + 2Ag+ E°= 0.05 V
Chem. Mater., 1998, 444-50
Agn + Cu2+→ Agn-1 + Ag+ + Cu+
followed by similar reaction of Agn-1,Cu+ + Agn+m → Cu2+ + Ag-
n+m
Ag+ + Ag-n+m → Agn+m+1
Chem. Phys. Lett., 1989, 473-76
J. Phys. Chem., 1992, 2411-14
Drinking water purification: Novel reactions at the nano-scale
Chemistry of heavy metal ions with noble metal nanoparticles
C
20nm
Wavelength (nm)300 500 700 900
Abso
rban
ce
0
0.2
0.4
0.6A BA Bba
ab
C
20nm
Wavelength (nm)300 500 700 900
Abso
rban
ce
0
0.2
0.4
0.6A BA Bba
ab
20 nm
(A)
100nm
(B)
(C)
+++++
+
+*
*
b
+
+
(100) (002)
(101)
(102
)
(110)
(103)
(112)(201)(004)
(222)
(111
)
(111)
(200)
(220)
(311
)(222)
a
2θ (degrees)30 50 70 806040
Intensity
+++++
+
+*
*
b
+
+
(100) (002)
(101)
(102
)
(110)
(103)
(112)(201)(004)
(222)
(111
)
(111)
(200)
(220)
(311
)(222)
a
2θ (degrees)30 50 70 806040
Intensity
(D)
Gold Bullet. (submitted)
Chem. Mater., 1998, 444-50
Drinking water purification: Novel reactions at the nano-scale
Detection of heavy metal ions with noble metal nanoparticles
Raman Shift (cm-1)300 500 700 900
SERS In
tensity
(a) Ag sputtered filmAg sol (citrate)Ag sol (PVP)CubesCuboctahedraOctahedra
Particle shape
Na 2HSO
4detec
tion (ppb)
0
100
200
2000
(c)
SERS In
tensity
Raman Shift (cm-1)500 600 700 800 900 1000
AsIII + AsV
AsV(d)
Raman Shift (cm-1)300 500 700 900
SERS In
tensity
PVPBTHDTMDA
(b)
Ange
w.
Che
m. In
t. E
d.
2008,
645
6 –
60
Inorg
. C
he
m. 2
008,
47,
293
4-2
936
Drinking water purification: Novel reactions at the nano-scale
Chemistry of micro-organisms with noble metal nanoparticles
Concentration of silver (µg)0 40 80 0 40 80
0 40 80 0 40 80log(1+X)
0
2
4
6
8
0
2
4
6
8
0
2
4
6
8
0
2
4
6
8
AgNO3
R2 = 0.98
Rod
R2 = 0.9689
Sphere
R2 = 0.9878
Triangle
R2 = 1
(B)
Concentration of silver (µg)0 40 80 0 40 80
0 40 80 0 40 80log(1+X)
0
2
4
6
8
0
2
4
6
8
0
2
4
6
8
0
2
4
6
8
AgNO3
R2 = 0.98
Rod
R2 = 0.9689
Sphere
R2 = 0.9878
Triangle
R2 = 1
(B)
20 nm
(C)a b
c d
a b
c d
a b
c d
a b
c d
(A) AgNO3 Rod
Sphere Triangle
Other nanomaterial based approaches for water purification
Iron-based nanoparticles
Binding energy (eV)859 856 853 850
Counts (X 104)
0
0.6
1.2
1.8
2.4
Ni2+ Ni0
24 hrs
3 hrs
1 hr
15 min
(b) (c)
100 nm
(a)
Carbon nanotubes
0 sec 15 sec 30 sec
45 sec 60 sec 80 sec
Pt wire(a) (b)
Commercial interests in drinking water purificationiw
Product Name Nanomaterial utilized Contaminants removal Adsorption capacity Product life Product price
Aquaguard Gold Nova, Eureka
Forbes Limited
Silver nanoparticles supported on
alumina
Pesticides and halogenated organics- 6000 liters $50
Adsorbia Titania nanoparticles
Arsenic and disinfection
12-15 gm As(V) and 3-
4 gm As(III) per kg of
adsorbent
- -
AD33, Adedge Technologies, Inc. Iron oxide nanoparticles Heavy metals including arsenic, lead,
chromium, zinc, copper- 3,800-11,400 liters $50
Nanoceram, Argonide Electropositive alumina nanofibers
on a glass filter substrate
Disinfection, natural organic matter,
turbidity, salt, radioactivity, heavy metals - -$3-10 per sq m
2,
$75 per filter
ArsenX, SolmeteX, Inc. Hydrous iron oxide nanoparticles on
polymer substrate
Arsenic, vanadium, chromium, uranium 38 mg of Arsenic per
gm of adsorbent-
$0.07-0.20 per
1,000 liters
(amortized due to
reusability)
Nanopore, Nanovation AG Membrane filters based on ceramic
nanopowder supported on alumina
Disinfection
- - -