THWRC Awarded Proposal 515UHH0050H

Project Number:       515UHH0050H

Title:                           Multifunctional Graphene-oxide Nanocomposite Beads for Removal of Water

                                     Contaminants in Packed Bed Columns

Lead PI:                     Debora Rodrigues

Awarded Amount:    $31,000

ABSTRACT

The World Health Organization has estimated that about 11% of the world’s population does not have access to clean water and that about 1.6 million deaths annually are caused by contaminated water. Graphene oxide (GO) has recently been shown to be a promising material for water treatment since it has anti-microbial properties and excellent capability to adsorb positively charged heavy metals and chemicals from water. The polyethylenimine (PEI) polymer, on the other hand, has amino groups that have the potential to adsorb negatively charged chemicals. Hence, the combined use of these two materials for water treatment would maximize the removal of different types of contaminants. However, like GO, PEI disperses well in water and is very difficult to recover from water. Hence, it is not viable to use them in their pure forms for water treatment purposes. In order to solve this problem, in the present project, we suggest the embedment of these materials in a polymer that can form porous hydrogels, i.e. chitosan (CS).

The overarching objective of this research is to incorporate graphene oxide (GO) in a miscible polymer blend of chitosan (CS) and  polyethylenimine (PEI) to synthesize nanocomposite polymer beads and to investigate the anti-microbial and heavy metal removal adsorption properties of this new multifunctional nanocomposite for potential application in water treatment. Our central hypothesis is that the addition of small, well-dispersed amounts (1% – 5%) of GO in a CS-PEI polymer blend will generate an advanced functional material with anti-microbial properties and more binding sites for adsorption of negatively and positively charged heavy metals compared to the individual constituents of the nanocomposite. The project will be divided into four tasks: (1) Synthesize highly performing GO-CS/PEI nanocomposite beads; (2) Determine the adsorption capacity and parameters affecting heavy metal adsorption by the nanocomposite beads; (3) Investigate the anti-microbial properties of the beads; and (4) Measure microbial and heavy metal removal by the nanocomposite beads in packed columns. The information gained from this research will advance our understanding on potential applications of carbon-based nanocomposites, and lead to a new water treatment material.

In order to address these tasks, we will employ different procedures. In task 1, we will synthesize beads with different concentrations of GO and PEI embedded in the CS matrix. We will use different methods of dispersion and homogenous incorporation of nanoscale GO in the polymer blend of CS-PEI matrix. The thermal stability and dispersion of the nanomaterials will be also investigated in the resulting nanocomposite beads. In task 2, batch experiments will be performed with two heavy metals (i.e. chromium hexavalent and copper) to better understand the mechanisms of adsorption of the nanocomposite beads, as well as the effects of pH, bead size and contact time on heavy metal removal. The adsorption experiments will be conducted individually and under competitive conditions with different pH and contact times. Desorption and adsorption will be also investigated to determine the reusability of the beads. For task 3, we will determine the effects of nanocomposites on Gram-positive (e.g. Bacillus subtilis and Enterococcus faecalis) and Gram-negative (e.g. E. coli and Pseudomonas fluorescens) bacteria and on mixed microbial communities from freshwater. The anti-microbial assays will determine effects of contact time and effects of GO concentration on microbial inactivation by the nanocomposite. Lastly, in task 4, The graphene oxide-nanocomposite beads with the best anti-microbial and heavy metal removal performance in the batch studies will be investigated in packed bed columns with different heights and flow rates with contaminated freshwater sources to determine the best conditions for heavy metal adsorption and microbial removal in a packed bed column.