Hemicellulose, Starch and Chitosan Based Gels

Abdus Salam, Joel J. Pawlak, Richard A. Venditti

Abstract

Arsenic and other heavy metal contamination in water is a significant world-wide health threat.     In this research low-cost, sulfur-free, green, water-insoluble materials with heavy metal remediation properties were produced from renewable resources such as starch, hemicellulose, citric acid and chitosan. Synthesized starch or hemicellulose citrate-chitosan foams were flexible, porous, and elastic.  The foams arsenic uptake in water was significantly greater than five different commercial metal remediating agents.  The mercury and lead uptakes with the foams were similar to a commercial sulfur based product, Sorba Tech 450, but cadmium and selenium uptake were comparatively lower. Xylan citrate-chitosan was also shown to take up potassium iodide similar to its ability to take up sodium chloride.  This may have application to water clean-up required in a nuclear crisis with water contaminated with radioactive iodide. The complexation of  arsenic with oxygen and nitrogen of the starch citrate-chitosan foam has been shown with TOF SIMS.

Introduction

The remediation of heavy metal laden waters is a pressing problem.    As water quality standards continue to tighten, many industries, such as coal mining, metal manufacturers, electronics and others, will be required to remove greater portions of dissolved metals in waste water before discharging.   In addition, water contamination with heavy metals, especially arsenic, mercury and lead, are a significant challenge to a large portion of the world’s population.   Arsenic is a naturally occurring trace element found in rocks, soils, and the water in contact with them. Arsenic has long been recognized as a toxic element, which can contribute to skin, bladder, and other cancers. There are many locations across the world where the groundwater contains naturally high concentrations of arsenic^.1-6The US Environmental Protection Agency recently revised the maximum contaminant level (MCL) for arsenic in drinking water from 0.05 to 0.01 mg/L, the current World Health Organization standard. The MCL of 0.05 mg/L had been the standard since 1942.⁷Also, in the US and Canada, concentrations of Pb, Hg, Cd and Se in ground and industrial waters are significantly higher than EPA Standards.⁸

     Another serious problem facing the world is the contamination of drinking water during a nuclear disaster.  Iodine 131 is a radioactive isotope that is produced during the radioactive decay of Uranium.  Iodine 131 can form salts in water and be taken up through ingestion of water of contaminated foods.   During the Fukashima nuclear crisis in Japan, radiation that is 3000 times or more of the acceptable limits has been detected in the sea water near the site.  While iodine 131 has a half-life of just over 8 days, its potential negative health effects merit the development of strategies to remove it from the drinking water.

In the market are available inorganic or petroleum based metal chelating agent such as silica, clays, thiol-compounds, carbon disulfide mixed iron powder, etc.^9-10  Often these materials carry an active layer of molecules (eg.,  sulfonated compounds) that bind dissolved metals.    However, the sulfur itself in some of these materials may be included in the water phase with its own detrimental effects. ¹¹These materials also have little affinity for the counter-ion and thus are not effective for taking up negatively charged species.

Both ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) have an extremely strong complexing capacity with certain dissolved toxic heavy metals, resulting in precipitates. The strong complexation occurs because of the affinity of the heavy metal with the lone pair electron of nitrogen and oxygen atoms in these compounds.¹² However, it is difficult to separate these small precipitated particles from the water phase. 

As alternatives to these materials many researchers have attempted to developcarbohydrate derivative based metal chelating agents through chemical modification such as grafting or cross linking with vinyl monomer¹³, ammonium molybdate¹⁴, etc.    Many of these materials are toxic themselves or have poor metal complexing performance relative to existing commercial metal chelating agents. ^13-16

Hemicelluloses represent about 20-35% of lignocellulosic biomass in trees and plants and are estimated to account for one-third of all renewable organic carbon available on earth.¹⁷Hemicelluloses are a broad class of carbohydrate materials that are shorter chains than cellulose and exhibit some branching.¹⁸Often, hemicelluloses are found as organic wastes or byproducts of renewable forest and agricultural products.  For instance, in the pulp and papermaking process, significant quantities of hemicellulose are solubilized and burned for energy.  It can be estimated that the amount of hemicellulose currently burned in the paper industry worldwide is on the order of 100 millions of tons per year. 

Starch is another renewable polymer that is widely abundant and readily available in a number of commercial forms.  The low cost and commercial availability of starch in the market attracts researchers attempting to develop new functional starch derivatives for industrial applications.^19-20  The disadvantage of using starch relative to hemicellulose is that starch is a food product, whereas hemicellulose is not.

Chitosan is alsoa carbohydrate polymerbut derived from chitin, a waste material produced in the fishing industry from crab, shrimp and other shell fish.  Chitosan is a beta 1, 4 linked polymer of glucose with amino groups primarily located in the two positions.  Derivatives of chitosan have been found to inhibit the growth of a wide variety of bacteria and fungi.^21-22

In previous research, it was found that hemicellulose-citrate or starch citrate combined with chitosan under the proper reaction conditions, developed hydrogel foams that displayed increased water and saline absorption²⁴.  In that study, it was determined that the materials had an affinity for salt adsorption.²⁵In the current investigation, the metal uptake (arsenic, lead, mercury, cadmium and selenium) of these materials is described.  Also, the uptake of salts such as sodium chloride and potassium iodide is examined. 

Table 1: Effect of arsenic loading onto hemicelluloses/starch citrate-chitosan and commercial metal chelating agents. (Absorbent 0.025g, Solution 50ml and Soaking time 6 minutes)

 

Sample	Initial Concentration (µg/L)	Final Concentration (µg/L)	Metal Loading (mg/g)
Hemicellulose citrate-chitosan	50100 26200 12700 4950 100.8	45700 21100 11000 4310 91.5	10.2 8.8 3.4 1.28 0.019
Starch citrate-chitosan	50100 26200 12700 4950 100.8	45400 22200 10600 4030 47.6	9.4 8.0 4.2 1.84 0.095
Sorbatech 450	50100 26200 12700 4950 100.8	45600 24300 11900 4900 92.2	9.0 3.8 1.6 0.10 0.017

 

Figure 5: TOF SIMS High Mass Resolution Spectra of Control (-) and Arsenic exposed (-) starch citrate-chitosan foam.

1. Chatterjee, A.; Das, D.; Mandal, B.K.;Chowdhury, T.R.; Samanta, G.; Chakraborti, D.
Analyst 1995, 120, 643–650.

2. Del Razo, L. M.; Arellano, M. A.; Cebrián, M. E. Environ Pollut. 1990, 64, 143–53.

3. Morton, W.; Starr, G.; Pohl, D.; Stoner, J.; Wagner, S.; Weswig, P. Oregon Cancer 1976, 37, 2523–2532.

4. Matisoff, G.; Khourey, C.J.; Hall, J.F.; Varnes, A.W.; Strain, W.H. Ground Water 1982, 20, 446–455.

5. Welch, A.H.; Lico, M.S.; Hughes, J.L. Ground Water 1988, 26, 333–347.

6. Nikolaidis, P.N.; Dobbs, M. G; Lackovic, A. J. Water Res. 2003, 37, 1417-1425.

7. Karadede, H.; Ünlü, E. Chemosphere 2000, 41, 1371-1376.

8. Kim, S. J.; Chah, S.; Yi, J. Korean J. chem. Eng. 2000, 17, 118-121.

9. Lezzi, A.; Cobianco, S.; Roggero, A.; J. of Polym. Sci. Part A: Polym. Chem. 2000, 32, 1877-1883.

10. Matthew, M.; Matlock, M. M.; Henke, R. K.; Atwood, A. D. J. of Hazardous Materials 2002, 92, 129-142.

11. Sola, I.; Ausio, X.; Simo, R.; Grimalt, O. J.; Ginebreda, A. Chromatography 1997, 778, 329-335.

12. Sillanpaa, M.; Oikari, A. Chemosphere 1996, 32, 1485-1497.

13. Khalil, I. M.; Abdel-Halim, G. M. Starch/Stärke 2001, 53, 35–41.

14. Dambies, L.; Vincent, T.; Guibal, E. Water Res. 2002, 36, 3699-3710

15. Kim, B.S. Lim, S.-T. Carbohyd. Polym. 1999, 39, 217–223.

16. Khalil, I. M.; Abdel-Halim, G. M. Carbohyd. Res. 2000, 324, 189-199

17. Ebringerova, A.; Hromadkova, Z. Biotechnol. & Genetic Eng. Rev. 1999, 16‚325-346.
18. Prade, R. A. Biotechnol. & Genetic Eng. Rev. 1995, 13‚ 101-131.
19. Jenkins, P. J.; Donald, A.M. J. Biological Macromolecules, 1995, 17, 315-321.
20. Mauro, D. J.; Abbas, I. R.; Orthoefer, F. T. Corn 2003, 605–634.
21. Liu, H.; Du, Y.; Yang, J. ; Zhu, H. Carbohydr. Polym. 2004, 55, 291-297.
22. Lim, S.H.; Hudson, S. M. Carbohydr. Res. 2004, 339, 313-319.
23. Salam, A.; Pawlak, J. J.; Venditti, A. R.; El-tahlaw, K. Cellulose 2011, 18,1033-1041.
24. Salam, A.; Pawlak, J. J.; Venditti, A. R.; El-tahlaw, K. Carbohydr. Polym. 2011, 84, 1221–1229.
25. Salam, A.; Pawlak, J .J.; Venditti, A. R.; El-tahlaw, K. Biomacromolecules 2010, 11, 1453–1459.
26. Haider, S.; Park, S.Y. J. Membrane Sci. 2009, 328, 90-96.
27. Langmuir, I. J. Am. Chem. Soc. 1918, 40, 1361–1403.
28. Belu A. M.; Graham D. J.; Castner D. G. Biomaterials, 2003, 24, 3635 – 3653.
29. Yukio, F. Y.; Saito, N.; Nonaka, H.; Suzuki, A.; Nakanaga, T.; Fujimoto, T.; Kurokawa, A.; Ichimura, S. Surf. Interface Anal. 2011, 43, 245–248.
30. Elson, M. C.; Davies, H. D.; Hayes, R. E. Water Res. 1980, 14, 1307-1311.