Adsorption of perfluorooctanoic acid (PFOA) using graphene-based materials Supriya Lath (PhD Student, The University of Adelaide) Prof. Mike McLaughlin Dr. Divina Navarro Prof. Dusan Losic Dr. Anu Kumar (UofA, School of Agriculture Food & Wine) (UofA, School of Agriculture Food & Wine; CSIRO Land & Water) (UofA, School of Chemical Engineering) (CSIRO Land & Water) University of Adelaide 1
PFOA (Perfluorooctanoic acid) Applications hydrophobic fluorinated tail anionic polar head University of Adelaide 2
Concerns and Challenges Bioaccumulation; long-range transport Exposure through soil, water, dust Linked with human and animal health Phased out, but ubiquitous Resistant to degradation; stable University of Adelaide 3
Remediation Strategies for PFOA & PFASs Biological (PFOA resistant to degradation) Remediation Physical & Chemical (scope for in situ and ex situ) Photocatalysis Sonochemical degradation Advanced oxidation Adsorptive immobilisation (in situ) e.g. activated carbon Thermal (energy intensive; ex situ only) University of Adelaide 4
Graphene Materials Single layer of graphite 2-D carbon sheet High surface area Versatile surface chemistry Graphite Graphene (single layer) (stacked carbon layers) University of Adelaide 5
Project Aims Develop graphene-based materials with capabilities for immobilisation of PFOA. Evaluate efficiency of prepared materials for PFOA-sorption, and compare with a commercial remediation agent. effect of ph effect of ionic strength effect of PFOA concentration University of Adelaide 6
Materials Used Commercial adsorbent: RemBind TM (mixture of activated C, gibbsite and kaolinite) RemB Prepared graphene adsorbents: Graphene oxide Iron-modified graphene GO FeG University of Adelaide 7
Synthesis of GO & FeG GO, oven dry at 30 0 C Δ 50 0 C, 15 hrs Ice + 30% H 2 O 2 Multiple wash cycles with HCl, water & ethanol (centrifuge, decant) Graphite + KMnO 4 + conc. H 2 SO 4 : H 3 PO 4 (9:1) FeG hydrogel FeG aerogel Freeze-dry Hydrothermal reduction Self-assembly FeSO 4.7H 2 O Δ 90 0 C 8 hrs Well-exfoliated GO suspension (2 mg/ml) Marcano, D. C., et al. (2010). "Improved Synthesis of Graphene Oxide." ACS Nano 4(8): 4806-4814. Cong, H.P., et al. (2012). "Macroscopic Multifunctional Graphene-Based Hydrogels and Aerogels by a Metal Ion Induced Self-Assembly Process." ACS Nano 6(3): 2693-2703. University of Adelaide 8
Structural Characterisation GO: SEM and TEM images 100 μm 2 μm FeG: SEM and TEM images Idealised Structure of Graphene Oxide iron oxide particles (goethite mineral) Additional characterisation: XRD spectra FTIR spectra 100 μm 0.2 μm University of Adelaide 9
Surface Characterisation Specific surface area (25 C) Surface zeta potential (25 C) Adsorbent Specific surface area GO 434.6 m 2 /g FeG 242.4 m 2 /g RemB 123.4 m 2 /g Kaolinite 1 ~ 25 m 2 /g 1 Avena, Marcelo J., et al. (2001). "Methylene blue dimerization does not interfere in surface-area measurements of kaolinite and soils." Clays and clay minerals 49.2: 168-173. University of Adelaide 10
Experimental methods & PFOA analysis Radiochemical Analysis: Isotopically labelled ( 14 C) PFOA, (ARC Inc., USA) Liquid scintillation β-counting measures 14 C activity. Specific activity = 2035 MBq/mmol Weigh adsorbents Spike PFOA solutions (10 mm CaCl 2 background electrolyte) Shake (48 hrs), centrifuge, remove aliquot for analysis Note: PFOA concentration calculations were corrected for any sorption that occurred on the reaction vessels during batch sorption. University of Adelaide 11
% PFOA adsorbed PFOA sorption: equilibrium time 100 90 80 70 60 50 40 30 20 10 0 RemB FeG GO 0 12 24 36 48 60 72 84 96 Sorption time (hours) Time: 0 96 hrs Initial [PFOA] ~ 30 ng/ml ph 5.5 10 mm CaCl 2 background 25 C University of Adelaide 12
% PFOA adsorbed PFOA sorption: effect of ph 100 90 80 70 60 50 RemB (PZC = 5.7) FeG (PZC = 7.1) ph: 3 9 Initial [PFOA] 100 ng/ml 10 mm CaCl 2 background 48hrs 25 C 40 GO 30 20 10 0 2 3 4 5 6 7 8 9 10 ph of solution University of Adelaide 13
% PFOA adsorbed PFOA sorption: effect of ionic strength 100 80 RemB FeG 0 100 mm CaCl 2 background Initial [PFOA] 20 ng/ml ph 5.5 48hrs 60 25 C 40 GO Background electrolyte Elec. conductivity ms/cm = ds/m 20 10 mm CaCl 2 2.11 (non-saline soil) 0 0 20 40 60 80 100 CaCl 2 background electrolyte (mm) 25 mm CaCl 2 4.93 (saline soil) 50 mm CaCl 2 9.24 (landfill leachate) University of Adelaide 14
Amt. of PFOA adsorbed (ng/mg) PFOA sorption: effect of concentration (isotherm) 1200 1000 800 RemB FeG Initial [PFOA] 0 650 ng/ml 10 mm CaCl 2 background ph 5.5 48hrs 600 400 GO 25 C 200 0 0 20 40 60 80 100 120 Eqlbm PFOA Conc, Ce, ng/ml University of Adelaide 15
Summary GO & FeG successfully adsorbed PFOA FeG > GO Surface area did not correlate with sorption performance Effect of ph and ionic strength Efficiency of GO with in ph FeG & RemB resistant to changes No saturation of binding sites to concentrations up to 650 μg/l PFOA Binding related to non-ionic interactions with surfaces Hydrophobic interactions Possible role of Important role of minerals Fe, Al, Si University of Adelaide 16
Acknowledgements Prof. Mike McLaughlin Prof. Dusan Losic Dr. Divina Navarro Dr. Anu Kumar (UofA, School of Agriculture Food & Wine) (UofA, School of Chemical Engineering) (UofA, School of Agriculture Food & Wine) (CSIRO Land & Water) Dr. Richard Stewart (Ziltek Pty. Ltd.) Funding: Australian Postgraduate Award and Ziltek Soil Science Scholarship (Ziltek Pty. Ltd.) University of Adelaide 17