Nhlane, Dineo Sonia2021-04-282021-04-282020https://hdl.handle.net/10539/31039A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science, 2020Acid mine drainage (AMD) exerts significant negative environmental effects by contaminating fresh water sources and potentially affecting human health. Thin film nanocomposite (TFN) membranes provide an opportunity for treatment of metal-ion-contaminated water due to their enhanced adsorption capacity for heavy metal ions, increased water permeation and anti-fouling properties. The aim of this study was to assess the applicability of GO containing membranes for removal of Hg(II) and U(VI) ions from AMD-contaminated waters. GO nanosheets were prepared via modified Hummer’s method. Thiol-functionalised GO nanosheets were then prepared by reaction of GO with L-cysteine and evaluated for removal of Hg(II) ions. Phosphate functionalised GO (GO-PO4) for removal of U(VI) ions were prepared via the Arbuzov reaction. Plain GO nanosheets and their functionalised derivatives were characterised for structure, elemental composition and functionalisation by TEM, XRD, FTIR and CHNS and the removal efficiencies of Hg(II) and U(VI) were determined in batch experiments. TFN membranes were fabricated by in-situ interfacial polymerization and characterised for elemental composition, surface morphology, interlayer spacing and water permeability using SEM-EDX, CHNS, AFM, FTIR and Contact angle. Hg(II) and U(VI) removal efficiencies were quantified using a dead-end filtration system. GO nanosheets in TEM ranged in size from 1 μm to 200 nm and X-ray diffraction revealed that while phosphate functionalisation increased GO inter-sheet spacing from 0.48 to 1.24 nm, thiolation using L-cysteine decreased inter-sheet spacing to 0.38 nm. Further, thiolation using L-cysteine reduced GO, resulting in thiol-functionalised reduced graphene oxide (rGO-SH). Optimal removal of Hg(II) by rGO-SH nanosheets was 0.0436 mg g-1(~95% efficiency) and U(VI) removal by GO-PO4nanosheets was 0.062mg g-1(~100% efficiency), the capacities were achieved at pH 4. In TFN membranes ,the presence of functionalised GO nanosheets in the polyamide (PA) layer resulted in a decrease in membrane surface roughness and contact angle, and an increase in water flux and fouling resistance. Water flux increased from 38.6 Lm-2h-1 in membranes with unfunctionalized GO, to 50.9 Lm-2h-1 and 51.8 Lm-2h-1 in membranes containing rGO-SH and GO-PO4, respectively. In comparison to membranes with unfunctionalized GO, membranes with rGO-SH and GO-PO4 displayed higher Hg(II) and U(VI) rejection (~100%) compared to those with unfunctionalized GO (~90%). Similar results were seen when membranes were tested on field samples of mine-drainage contaminated water (pH 2.78). The presence of GO in TFN membranes increased rejection of U(VI) by up to 100% and these membranes were also found to be suitable for rejection of other ions present in AMD including As, Cu,Pb, Cr, etc. indicating that the membrane is not selective towards the ions in study. While GO nanosheets are a good adsorbent for cationic pollutants, the results of studies reported here show that functionalisation increases contaminant removal considerably. Further, when used in membranes for practical application, cysteine and phosphate functionalisation of GO also increases the flux and fouling resistance of membranes. Together, these results suggest that functionalisation of GO nanosheets by cysteine and phosphate are simple and green approaches that can improve the performance of membranes used for treatment of AMD-contaminated waterenThesis