Synthesis of polymer supported nanoscale zerovalent iron and its

SYNTHESIS OF POLYMER SUPPORTED-NANO SCALE ZEROVALENT IRON AND ITS USE IN WATER

PURIFICATION

By Dhiraj DuttaM.Sc. 4th Semester(Organic Special)

Enroll no. – 136209022Session – 2013-2015

OBJECTIVES

• To synthesize nanoscale zero-valent iron.• To stabilize nZVI by entrapping with a

polymer (Alginate).• Characterization of nZVI.• To account for the removal of

– arsenic(III), – chromium(VI), – fluoride, – nitrate, and – a dye (Rhodamine B) in water by alginate supported

nZVI in presence of natural adsorbent straw charcoal.

INTRODUCTION

• Nanotechnology in Ground water remediation– Nanotechnology is the engineering and art of manipulating matter at

the nanoscale (1–100 nm).– Nanotechnology sector have been widely studied to protect the

environment by pollution control, treatment and as a remedial measure to long term problems such as contaminated waste sites.

– Site Remediation:• In situ: • Ex situ:

NANOSCALE ZERO-VALENT IRON (nZVI)

• Most widely used species for Nanoremediation.• Diameter ranges from 10 – 100 nm.• Core shell type structure.• The core primarily consists of zero-valent or

metallic iron whereas a mixed valent (i.e. Fe2+ and Fe3+) oxide shell is formed as a result of oxidation of metallic iron.

• More surface area and more no. of reactive sites.

• Moreover, it also possess dual properties of reduction and absorption.

DRAWBACKS OF BARE nZVI

• nZVI particles expose vigorous tendency to agglomerate into larger solid particles.

• Separation of non-supported nZVI particles from the aqueous phase is still a difficult task.

• Also because of its high reactivity, it is difficult to store.

POLYMER SUPPORTED nZVI

• Alginate• Sodium Alginate• Calcium Alginate

CONTAMINANTS IN WATER

• Arsenic• Chromium• Fluoride• Nitrate• Dye (Rhodamine B)

• Arsenic– Natural abundance is high.– Exists in two states: +3 and +5.– Highly toxic.– Mostly contaminated in ground and surface water.– Can cause melanosis, leuko-melanosis, Arsenicosis,

skin cancer, cancer of lungs and bladder.– EPA permissible level – 0.010 mgL-1

• Chromium– Exists in two states: +3 and +6.– Among which +6 is toxic.– Vastly contaminated from disposal of waste in water.– Highly toxic.– Can cause allergic dermatitis.– EPA permissible level – 0.1 mgL−1

• Fluorides– Highly abundant in nature.– Exists in -1 state.– Mostly contaminated in water due to both natural

and human activities.– Highly toxic.– Can cause dental fluorosis and skeletal fluorosis, etc.– EPA permissible level - 1 mgL−1

• Nitrate– Highly abundant in nature.– Mostly contaminated in water due to both natural

and human activities.– Can cause methemoglobinemia, stomach cancer,

colorectal cancer, pancreatic cancer, etc.– EPA permissible level – 10 mgL−1

• Dye (Rhodamine B)– Extensively used in industries for coloring.– Most of them have toxic effects.– Rhodamine B is a basic dye, most extensively used in

paper printing, textile dyeing, and leather industries.– Contaminated in water via disposal from industries.– Can cause coughing, sore throat , breathing problem

and chest pain if inhaled ;and irritation of the gastrointestinal tract if swallowed.

PREVIOUS WORKS

• “Entrapment of iron nanoparticles in calcium alginate beads for groundwater remediation applications”, worked out by Achintya N. Bezbaruah et. al. 2009. for the first time used calcium alginate encapsulated nZVI for ground water remediation taking a model contaminant nitrate. They also showed the efficacy of alginate encapsulated nZVI over bare nZVI in ground water remediation.

• “Ca–alginate-entrapped nanoscale iron: arsenic treatability and mechanism studies” , worked out by Achintya N. Bezbaruah et. al. 2011. again used calcium alginate encapsulated nZVI for the removal of Arsenic from aqueous solution.

METHODOLOGY

• Synthesis of nZVI:– ZVI Nanoparticles can be synthesized in aqueous solutions by the

reduction of ferric iron (Fe3+) or ferrous iron(Fe2+) with sodium borohydride

METHODOLOGY

• Synthesis of Ca-Alginate supported NZVI:

CHARACTERIZATION OF nZVI

• SEM Analysis:

(a) SEM image of alginate bead entrapped with nZVI. The section was taken through the center of the bead, (b), (c) SEM image of alginate bead surface after nZVI entrapment showing pores, (d), (e), (f) Higher magnification SEM image.

CHARACTERIZATION OF nZVI

• X-Ray Diffraction:

REMOVAL OF ARSENIC

• Hypotheses:

– Arsenic removal from nZVI is generally attributed to surface

precipitation and adsorption.

• Determination of concentration of Arsenic solution:

– Silver diethyl dithiocarbamate(SDDC) method

REMOVAL OF ARSENIC

• Estimation of Arsenic:– SDDC Method:

• In Flask: 25 ml sample + 7.5 ml conc. HCl + 1ml KI + 0.5 ml SnCl2

• In Scrubber Tube: Glass wool + few drops of Lead Acetate.

• In Absorber Tube: SDDC dissolved in Pyridine solution.

Scrubber tube

Absorber tube

• Zinc is added to the Flask for development of AsH3 which passes through the scrubber tube to the absorber tube forming a red complex with SDDC in pyridine.

• It shows λmax at 535 nm.

– SDDC method Explanation:• KI in Presence of HCl is used for pre reduction of As(V) to As(III)

so that they don’t interfere leading to undesired results.• Arsenic in presence of Zinc gets reduced to arsine, AsH3 in the

generator tube.• Arsine then passes through glass wool soaked with lead acetate in

order to remove sulfide which may be present in solution.• Arsine is then absorbed by SDDC in pyridine, forming a red

complex in the absorber tube.

REMOVAL OF ARSENIC

• Determination of maximum wavelength (λmax):

REMOVAL OF ARSENIC

• Preparation of Calibration curve:– Four standard arsenic(III) solutions having different concentration of 1,

2, 3, and 4 ppm were prepared.

REMOVAL OF ARSENIC

• Column Analysis:– Straw charcoal was packed in a column of cross

section(50cm x 20mm) having height 2 cm followed by packing of dried Alginate encapsulated nZVI beads (containing ~2 g of nZVI) having height of 10.5 cm. So a total height of (2+10.5) = 12.5 cm.

• Effect of Contact time:– The Standard As(III) solution of concentration

3 ppm was allowed to percolate through the columns. The concentration of As(III) in the eluent was recorded after 1 hr, 2 hr, 24 hr, 48 hr, and 72 hr and following results are obtained:

Time (hr) Concentration (ppm)

Percentage Removal (%)

1 1.803 39.902 1.165 61.16

24 0.349 88.3648 0.162 94.6072 0.118 96.06

1 2 24 48 720

20

40

60

80

100

120

39.9

61.16

88.3694.6 96.06

Percentage Removal of Arsenic

Time (hr)

% R

emov

al o

f Ars

enic

REMOVAL OF CHROMIUM

• Hypotheses:

– Chromium (VI) removal from nZVI is generally attributed to its

reduction from its toxic form +6 to its non toxic form +3 state.

– Chromium (III) may be removed through the precipitation or co-

precipitation in terms of mixed Fe(III) and Cr(III) hydroxide.

• Determination of concentration of Chromium solution:

– Direct spectroscopic method

REMOVAL OF CHROMIUM

• Estimation of Chromium(VI):– Direct Spectroscopic method:

• Chromium (VI) solution are directly poured in the 1 cm cell and Absorbance is measured at 373 nm.


λmax = 373 nm

REMOVAL OF CHROMIUM

• Preparation of Calibration curve:– Four standard chromium(VI) solutions having different concentration

of 1, 2, 3, and 4 ppm were prepared.

REMOVAL OF CHROMIUM



• Effect of Contact time:– The Standard Cr(VI) solution of concentration

3 ppm was allowed to percolate through the columns. The concentration of Cr(VI) in the eluent was recorded after 5 min, 15 min, 30 min, 45 min, 60 min, 90 min and 120 min; and following results are obtained:

Time (min) Concentration (ppm)


5 1.163 61.2315 1.075 64.1630 1.006 66.4645 0.957 68.1060 0.928 69.0690 0.919 69.56

120 0.909 69.705 15 30 45 60 90 120

0

10

20

30

40

50

60

70

80

90

100

61.2364.16 66.46 68.1 69.06 69.56 69.7

Percentage Removal of Chromium

Time (min)

% R

emov

al o

f Chr

omiu

m

REMOVAL OF FLUORIDE

• Hypothesis:– Fluoride removal by nZVI is attributed to adsorption .

• Determination of concentration of Fluoride solution:– Zirconium-alizarin method

REMOVAL OF FLUORIDE

• Estimation of Fluoride:– Zirconium-alizarin method:

• In this method fluoride reacts with Zr-Alizarin S lake to form ZrF6

2- and the colour of the dye lake becomes progressively weak with the increase in the amount of fluoride.


Zr-Alizarin Red S lake

REMOVAL OF FLUORIDE


REMOVAL OF FLUORIDE

• Preparation of Calibration curve:– Four standard fluoride solutions having different concentration of 1, 2,

3, and 4 ppm were prepared.

REMOVAL OF FLUORIDE



• Effect of Contact time:– The Standard fluoride solution of concentration

3 ppm was allowed to percolate through the columns. The concentration of fluoride in the eluent was recorded after 5 min, 15 min, 30 min, 45 min, 60 min, 90 min and 120 min; and following results are obtained:



5 2.75 8.3415 2.48 17.3330 1.96 34.6745 1.45 51.6760 1.121 62.6390 0.757 74.76

120 0.559 81.375 15 30 45 60 90 120

0

10

20

30

40

50

60

70

80

90

8.34

17.33

34.67

51.67

62.63

74.76

81.37

Percentage Removal of Fluoride

Time (min)

% R

emov

al o

f Flu

orid

e

REMOVAL OF NITRATE

• Hypothesis:– Nitrate removal by nZVI is attributed to the deoxidization or reduction

of nitrate to ammonium.

• Determination of concentration of Arsenic solution:– Phenol-disulphonic acid method

REMOVAL OF NITRATE

• Estimation of Nitrate:– Phenol-disulphonic acid method:

• Nitrate reacts with phenol disulphonic acid and produces a nitro-derivative which in alkaline solution develops yellow colour due to rearrangement of its structure.

• The colour produced follows Beer’s law and is intensity proportional to the concentration of NO3 present in the sample.


REMOVAL OF NITRATE


REMOVAL OF NITRATE

• Preparation of Calibration curve:– Four standard nitrate solutions having different concentration of 1, 2,

3, and 4 ppm were prepared.

REMOVAL OF NITRATE



• Effect of Contact time:– The Standard nitrate solution of concentration

3 ppm was allowed to percolate through the columns. The concentration of nitrate in the eluent was recorded after 5 min, 15 min, 30 min, 45 min, 60 min, 90 min and 120 min; and following results are obtained:



5 2.542 15.3315 1.965 34.5030 1.584 47.2045 1.303 56.5660 1.075 64.1690 0.891 70.34

120 0.830 72.33

5 15 30 45 60 90 1200

10

20

30

40

50

60

70

80

90

100

15.33

34.5

47.2

56.56

64.1670.34 72.33

Percentage Removal of Nitrate

Time (min)

% R

emov

al o

f Nitr

ate

REMOVAL OF DYE (RHODAMINE B)

• Hypothesis:– Rhodamine B dye removal by nZVI is atributed to reduction or

degradation.

• Determination of concentration of Rhodamine B solution:– Direct Spectroscopic method.


• Estimation of Rhodamine B dye:– Direct spectroscopic method:

• Rhodamine B solution are directly poured in the 1 cm cell and Absorbance is measured at 555 nm.


• Preparation of Calibration curve:– Four standard rhodamine B solutions having different concentration of

1, 2, 3, and 4 ppm were prepared.




• Effect of Contact time:– The Standard rhodamine B solution of

concentration 3 ppm was allowed to percolate through the columns. The concentration of rhodamine B in the eluent was recorded after 1 hr, 2 hr, 24 hr, 48 hr, and 72 hr; and following results are obtained:

Time (hr) Concentration (ppm)


1 1.476 50.802 1.262 57.93

24 0.997 66.7648 0.917 69.4372 0.869 71.03

1 2 24 48 720

10

20

30

40

50

60

70

80

50.8

57.93

66.7669.43 71.03

Percentage Removal of Rhodamine B

Time (hr)

% R

emov

al o

f Rho

dam

ine

B

RESULT SUMMARY

Contaminant Contact Time (hr)

Initial concentration

(ppm)

Final concentration

(ppm)Percentage

Removal

Arsenic 72 3 0.118 96.06

Chromium 2 3 0.909 69.70

Fluoride 2 3 0.559 81.37

Nitrate 2 3 0.830 72.33

Rhodamine B 72 3 0.869 71.03

CONCLUSION

• In this study, nZVI particles supported on alginate polymer were successfully synthesized, characterized and applied for the removal of model contaminants – (i) Metal ions – arsenic, chromium; (ii) Anions – fluoride, nitrate; and (iii) Dye – rhodamine B.

• The characterization results clearly show that the present synthesis method would be useful to synthesize alginate entrapped nZVI and could solve the stability issue of nZVI for its multipurpose applications in environmental remediation and water purification.

• The above experimental results indicate that polymer (alginate) encapsulated nZVI can be efficiently used for the removal of arsenic, chromium, fluoride, nitrate, and rhodamine B.

• The presence of straw charcoal in the column enhances the removal process and also ensures no passage of Fe(II) and Fe(III) in to the eluent.

FUTURE PLANS

• TEM has to be taken for Characterization of alginate encapsulated nZVI.

• Different parameters has to be studied for column analysis like variation of

pH, dosage’s of nZVI, initial concentration of contaminated solution.

• To study the removal of contaminated pesticides in water by alginate

encapsulated nZVI .

• Also, to study the removal efficiency of microorganisms in water by

alginate encapsulated nZVI.

• To study the efficacy of remediation by nZVI in presence of additive

supports such as surfactants or other polyelectrolytes.

Thank You

Synthesis of polymer supported nanoscale zerovalent iron and its

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