Assessing the Efficacy and Safety of a New Class of Water Filtration Membranes Composed of Nano Scale Cellulose

EPA Grant Number: FP917828
Title: Assessing the Efficacy and Safety of a New Class of Water Filtration Membranes Composed of Nano Scale Cellulose
Investigators: Connors, Eoghan Leif
Institution: The State University of New York at Stony Brook
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2015 through August 31, 2018
Project Amount: $132,000
RFA: STAR Graduate Fellowships (2015) RFA Text |  Recipients Lists
Research Category: Academic Fellowships

Objective:

Hypothesis:

  1. The rate of cellulose nanofibers (CNFs) released into water passing through the membranes can be related to membrane properties including: (1) the size of CNFs used in barrier layer; (2) the pore size of the electrospun mid-layer scaffold; and (3) the thickness of the CNF barrier layer and the mid-layer scaffold.
  2. Membrane properties (described above) can be optimized to maximize their performance for removing pollutants while minimizing CNF release.
  3. Post disposal release of CNFs to the environment during use and post disposal can be quantified using established techniques using a novel chamber to capture and measure the release of nanomaterials.

Approach:

Hierarchical nanofibrous membranes will be produced by electrospinning a poly (acrylonitrile) (PAN) nanofibrous scaffold onto a non-woven poly (ethylene terephthalate) (PET) support and subsequently coating the scaffold with a thin barrier layer of CNFs using solution casting. A variety of these membranes will be produced with systematically varied properties including: (1) the size of CNFs used in barrier layer; (2) the pore size of the electrospun mid-layer scaffold; and (3) the thickness of the CNF barrier layer and the mid-layer scaffold. Large CNFs will be produced using multi-pass high pressure homogenization and traditional TEMPO oxidation, while ultrafine CFNs will be produced using TEMPO/ NaBr/ NaClO oxidation. The pore size of the PAN mid-layer scaffold will be altered by manipulating the parameters of electrospinning. Lastly, the thickness of the PAN mid-layer scaffold and CNF barrier layer will be controlled by altering the duration of electrospinning and the gap of the solvent casting knife respectively. The release of CNF’s from a variety of membranes will be monitored while repeatedly passing high purity HPLC grade water through the membranes. The filtrate water collected after flowing through the membranes will be concentrated using low temperature vacuum evaporation to avoid any decomposition of CNF. The content of CNF in the concentrated solutions will be quantified using conductometric titration to determine the number of carboxylate groups in solution and total organic content (TOC) analysis. The carboxylate content and TOC can then be compared to the known contributions from each CNF to determine the rate of their release from the membranes. To verify that the contribution to TOC of the filtrate comes from CNFs a background TOC will be established for water flowed through the PAN/PET scaffold to eliminate contributions from these carbon containing polymers. Additionally, dynamic light scattering and small angle X-ray scattering will be performed to screen for the presence of CNFs and their aggregates. A potential roadblock would be if the amount of CNF in the filtrate is below the detection limit of these techniques. To solve this potential setback, sulfur be introduced on the surface of CNFs via silane coupling or click chemistry to determine CNF concentration based on sulfur content using highly sensitive inductively coupled plasma- atomic emission spectroscopy. Changes to the surface structure of the CNF barrier layer will be studied using atomic force microscopy and scanning electron microscopy, while any changes to surface chemistry will be evaluated using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy. Finally, the release of CNFs from the membranes and changes in their surface structure/chemistry post disposal will be investigated using a custom built chamber for simulating environmental exposures to humidity and UV radiation exposure. The ultrafiltration

Expected Results:

It is expected that membrane properties will correlate to the rate of CNF release during water filtration and post disposal. It is unclear weather smaller CNFs will have a greater chance of being ""picked up"" by the water and leeching out or if larger CNFs will be less evenly distributed and supported within the membrane leading to a greater rate of release. It is expected that the larger the pore size the greater rate of release of CNFs due to larger void space although it is also possible that the increased surface area due to smaller pore size could result in a greater rate of release of CNFs.

It is likely that a greater thickness of the CNF barrier layer and the mid layer scaffold will result in a slower the rate of CNF release.

A trend of increasing efficacy of filters with smaller CNFs, smaller pore size, and larger membrane layers is expected. Additionally, altering the surface chemistry of the CNFs with functional groups known to promote chemical adsorption should lead to improved removal of chemical contaminants such as lead (II). Although these results are anticipated, it is important to consider the effects of membrane properties on the flux of water through the membrane as well as the release of CNFs in order to determine the optimal composition for achieving maximum filtration with minimal leaching of nanomaterials.

Supplemental Keywords:

Water, Filtration, Membrane, Cellulose, Nanomaterial, Environmental Health and Safety

Progress and Final Reports:

  • 2016
  • 2017
  • Final