Ground water & surface water quality in rural & urban areas are affected by natural & anthropogenic contamination. These water resources are being contaminated by pervasive Low Molecular Weight Organic Compounds (LMWOCs) which are not effectively removed by the current wastewater technologies. The US Environmental Protection Agency (USEPA) is focused on the removal of many classes of LMWOCs from drinking water & wastewater including; disinfection byproducts (DBP) precursors, pharmaceuticals, personal care products, heavy metals & perfluoroalkylated substances. In order to address removal of these pervasive compounds, an anion exchange resin polymer (AEP) functionalized Single Walled Carbon Nanotubes (SWCNTs) in the form of nanoresin has been developed. The large surface area of SWCNTs increases the availability of active ion exchange sites of the AEP. These nanoresins have higher & faster adsorption capacity compared to other current commercialized materials like magnetic ion exchange resins, DOWEX, etc.
This nanoresin was synthesized by modified activator regenerated electron transfer atom transfer radical polymerization technique in aqueous media. The hydrodynamic diameter of the purified AEP & nanoresins were 1.660 ± 0.10 nm & 194.9 ± 11.3 nm, respectively. The ratio between D & G bands, measured using Raman Spectroscopy, increased by 100% compared to pristine carbon nanotubes which is indication of covalent functionalization of the AEP. The proton nuclear magnetic resonance of the growing AEP showed 99.8% conversion from monomer to polymer in 69.30 hours. The scanning electron microscopy of nanoresin films fabricated on mixed ester cellulose (MCE) membrane for performance testing showed a smooth morphology of mesh of SWCNTs with conformal polymer coating. The step height of the fabricated film determined under atomic force microscopy was 142.31 nm. The measured membrane resistance of the thickest nanoresin film was determined to be κm = 2.1x1011 m-1 which is smaller than typical ultrafiltration membranes with κm = 2x1012 m-1.
We demonstrate the removal of several types of pharmaceuticals (viz., tetracycline hydrochloride and carbenicillin disodium), pesticides (viz., bentazon, terbacil, and bromacil), DPBs (viz., bromoacetic acid and choloroacetic acid) and PFAS (viz., perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS)), from water via adsorption capacity measurements. The percentage removal of PFOA and PFOS, for a starting concentration between 2-4 mg/L of contaminant, was 92.67% and 95.8%, respectively. The regeneration studies performed upto 20 cycles, showed a slope of -0.23 ± 0.18% per cycle which demonstrates that the nanoresin could be regenerated. The green synthesis of nanoresin, the ability to remove different classes of pervasive contaminants & the regeneration capacity corroborate an effective & sustainable solution to water purification & enhancement of water quality.