Synthesis of Polyoxometalates

SYNTHESIS OF KEGGIN AND SANDWICH-TYPE POLYOXOMETALATES FOR ENVIRONMENTAL APPLICATIONS

Katherine Aldrich

Hang Zuo

Northeastern University, Boston MA

Chemical Engineering

NORTHEASTERN SUMMER EXCHANGE Previous Internships at Genzyme Corporation and Waters Corp.

Genzyme-Biologics and Biological Engineering

Waters-Process Engineering

New in-sight into a different area of Chemical Engineering

Upon returning to Boston, internships at Alkermes and Henkel

Use experience gained at NTU in Material Science to apply in industrial

setting

ENVIRONMENTAL CONCERN: WASTE WATER1,2

River polluted with red dye1 Clean Lake2

ENVIRONMENTAL CONTAMINANTS3

Phenol

Azo Dyes

Sulfur containing compounds

WET AIR OXIDATION (WAO)

Oxygen oxidizes organic compounds into carbon dioxide and water

High Temperatures and Pressures

High Operating Costs

Used for waste streams that cannot be burned or undergo

biological treatment4

CATALYTIC WET AIR OXIDATION (CWAO)

Addition of a catalyst

Reaction takes place under milder temperatures and pressures

Two types of heterogeneous catalysts

-Transition Metal Oxides (Fe, Sn, Mn)

-Supported Nobel Metals (Pt, Pd, Ru)

Major advantages of CWAO are lower operating costs and

increased degradation of organic pollutants4

PROBLEMS WITH CWAO

Three Major Problems

1. High Cost of Noble Metals

2. Incomplete Oxidation of Phenols to Carbon Dioxide

-Intermediate products can be more toxic than original pollutant

3. Catalyst Deactivation

These three problems have prevented successful implementation of CWAO

Need for stable and recyclable catalyst4

POLYOXOMETALATES AS A CATALYST

Transition metal oxide clusters in the highest

state of oxidation

Includes Mo (VI), W (VI), and V (V)

Well-defined structures

-Keggin Type POM

-Sandwich Type POM4

Keggin Structure of (H5PV2Mo10O40 )5

PROBLEMS WITH POMS AS CATALSYTS

Low surface area

High solubility in water

Results in

-Low Efficiency

-Inability to recycle catalyst

-Toxic Waste Generation

Goal: Generate an efficient and recyclable catalyst using POMs6

SURFACTANTS AND MICELLES

Spontaneously form micelles

Water concentration decreases from the

surface to the core

Completely hydrophobic core

Surfactant outer layer and POM core

POM is in a completely water free zone6

Water concentration decreases from the outer layer to the core7

PURPOSE1. Synthesis Polyoxometalates H5PV2Mo10O40 and Na12[WZn3(H2O)2(ZnW9O34)2]

2. Addition of surfactant CTAB to H5PV2Mo10O40

3. Characterization using SEM, XRD, FTIR, UV-VIS, TGA and GC-MS.

Scanning Electron Microscope (SEM)

SYNTHESIS OF POLYOXOMETALATES Molybdovanadophosphoric acid (H5PV2Mo10O40)

Zinc(II)-Substituted POM (Na12[WZn3(H2O)2(ZnW9O34)2])

Simple procedure, but difficult to synthesize

NaZnW POM was synthesized multiple times

H5PV2Mo10O40 NaZnW POM

SYNTHESIS OF H5PV2MO10O40

1. Sodium Metavanadate

2. Disodium Phosphate

3. Sulfuric acid

4. Sodium molybdate dihydrate

Extracted using ethyl ether

Washed, filtered and allowed to crystalize8

Extraction Flask for POM using Ethyl Ether

SEM IMAGE AND EDX OF H5PV2MO10O40

FTIR ANALYSIS OF H5PV2MO10O40

• Band at1060 is the P-O vibration• 958 is M-O• 866 is inter-octraheral M-O-M• 784 is the intra-octrahedral M-O-M• Water bands at 3400cm-1 and 1620cm-14

THERMOGRAVIMETRIC ANALYSIS (TGA)

From 50-100°C, most of the water evaporated

Very little water attached to the crystal

XRD OF H5PV2MO10O40

XRD From Literature4

Experimental XRD

ADDITION OF CTAB TO H5PV2MO10O40

Cetyltrimethyl ammonium bromide(CTAB)

Micelles trap environmental contaminants

High concentration of substrate near the POM

FTIR OF CTAV2

Note the lack of water band at 3400cm-1

CATALYTIC ACTIVITY OF CTAB AND H5PV2MO10O40

Structure of Reactive Black 5 Dye

• Measured the catalytic activity of CTAV2

• 9.2E-4M CTAV2 (0.3 g)

• Sulfur-containing Reactive Black 5

• Mixed solid CTAV2 with liquid Reactive Black 5 (25 ppm,

100 mL)

• Samples at 0min, 3 min, 10 min, 20 min, 30 min, 45

min, 60 min, 90 min and 120 min

• Analyzed with UV-VIS Spectroscopy

UV-VIS GRAPH FOR REACTIVE BLACK 5 DYE DEGRADATION

• Blue light has a wavelength of 475

nm

• Red light has a wavelength of 650

nm

• Rapid absorbance of dye into CTAV2

• Within 10 min, absorbance

decreases from 0.45 to 0.17

• No change after 45min

REACTIVE BLACK 5 DYE REMOVAL

At 30 min, 95% of the dye has been removed from solution

Point of catalyst saturation

After 30 min, the percent of dye removal decreases to 85%

Some dye was released from catalysts resulting in a decrease of dye removal

Stabilizes after 90 min

1. Sodium Tungstate Dihydrate

2. Nitric Acid at 80-85°C

3. Zinc Nitrate Hexahydrate

Filtered and allowed to crystalize

Needle-shaped crystals9

Synthesis of NaZnW POM (Na12[WZn3(H2O)2(ZnW9O34)2])

Drop by drop addition of nitric acid

SEM IMAGES

Batch 1 Batch 2 Batch 3

Batch 2 Batch 3

EDX of Zn POM

Batch 2

XRD of

Na12[WZn3(H2O)2(ZnW9O34)2]

)

Batch 3

XRD of

Na12[WZn3(H2O)2(ZnW9O34)2]

)

FTIR ANALYSIS

• Peak at 1384 is NO3

• Batch 2 failed

• Broad peak at 1384cm-1 for

Batch 2

• POM was not fully synthesized

as reactant NO3 is still present

Thermogravimetric Analysis (TGA) of NaZnW POM

9.3%

2.5%

• Between 50-100°C, free water

evaporated

• Between 100-300°C, water that was

bonded to the crystal evaporated

• Sharp drop at 350°C indicates

breakdown on POM structure

CONCLUSIONS

H5PV2Mo10O40 was successfully synthesized and the characterization

aligned to literature results

CTAV2 removed 90% of dye from solution

Temperature and pH greatly effects synthesis of Zinc(II)-Substituted POM

Only Batch 3 Zinc(II)-Substituted POM was successful

ACKNOWLEDGEMENTS

We would like to thank Professor Webster for organizing this exchange with NTU and also Professor Dong Zhili for agreeing to

host us in his lab.

A very special thank you to Yao Lei and Shun Kuang. They were incredibly helpful in running experiments and also in introducing us to the Singapore Culture. The experience would not have been the

same without them.

REFERENCES

1. Daily Mail. “The River That Did Run Red.” 2012. http://www.dailymail.co.uk/news/article-2199800/The-river-DID-run-red-Residents-Chinese-city-left-baffled-Yangtze-turns-scarlet.html

2. US EPA. EPA’s Clean Lake Program. 2013. http://water.epa.gov/type/lakes/cllkspgm.cfm3. Sigma-Aldrich. http://www.sigmaaldrich.com/singapore.html4. Zhao,S. Wang, X. “Catalytic wet air oxidation of phenol with air and micellar molybdovanadophosphoric

polyoxometalates under room condition.” Elsevier Journal. l 97 (2010) 127–1345. Arichi, J. Pereira, M. Synthesis of Keggin-type polyoxometalate crystals. Solid State Sciences. Elsevier Journal. (2010)

1866–18696. Shah,A. Mujahid, A. “Micelle directed synthesis of (C19H42N)4H3(PW11O39)nanoparticles and their catalytic

efficiency for oxidative degradation of azo dye.” J Sol-Gel Sci Technol (2012) 63:194–1997. Centre For Distance Engineering Education Programme. 2013.

http://www.cdeep.iitb.ac.in/nptel/Core%20Science/Engineering%20Chemistry%201/Slide/lect1/1_5.htm

8. TSIGDINOS , G. HALLADA, J. Molybdovanadophosphoric Acids and Their Salts. I. Investigation of Methods of Preparation and Characterization.” Apvil 3, 1967

9. Lai, G. Luo, J. “Zinc-Substituted Polyoxometalate for Oxidative Desulfurization of Dibenzothiophene.” Petroleum Science and Technology. 19 May 2014