Abstract
Abstract : Water pollution by heavy metals is a serious problem in South Africa due to mining activities, electroplating industries, weathering of minerals and soils and coal combustion. Most river systems have been exposed to heavy metals contamination due to effluent disposal and this directly affects communities that use these sources for domestic purposes. For example, Umtata River which is exposed to Cd(II) is used for various purposes by a large population of the Transkei, most of which is rural - domestic (cooking, drinking and washing), agricultural (that is, livestock watering and irrigation), and recreational purposes (swimming). Water pollution by heavy metals such as, Cd(II) in particular is unavoidable and it causes undesirable health effects, such as hypertension and kidney failure. Thus, it is very important to find new ways to efficiently remove these metals from water. Nanostructured membranes are amongst other water treatment methods that have shown the ability to efficiently remove heavy metals from water. Therefore, this study seeks to provide a facile and effective method to remove heavy metals such as cadmium(II) from synthetic solutions and industrial water effluents. This was achieved by embedding carbon nanodots (CNDs) on a polyethersulfone (PES) membrane as support via phase inversion. The synthesized CNDs and fabricated membranes were characterized using Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscope (SEM), Atomic Force Microscope (AFM), contact angle and pure water flux assessment. TEM analysis confirmed that the synthesized CNDs were well dispersed with uniform shape and size (6.7±2.8 nm). Raman analysis illustrated that the CNDs were embedded on the PES and that after blending the PES with CNDs the ID/IG ratio slightly increased after modification of the membranes with CNDs showing that the membranes maintained good structural integrity. The CNDs/PES membranes showed improved hydrophilicity compared to the pristine PES. vi At constant pressure of 300 kPa the flux of pristine PES, 0.01% CNDs/PES, 0.05% CNDs/PES and CNDs/PES was 60.00 L.m-2.h-1, 96.93 L.m-2.h-1, 142.16 L.m-2.h-1 and 196.62 L.m-2.h-1 respectively. The performance of the membrane was optimised using batch adsorption experiments. The analysis revealed that 95.71, 96.32, 97.69 and 99.78% Cd2+ was removed by PES, 0.01% CNDs/PES, 0.05% CNDs/PES and 0.5% CNDs/PES, respectively at optimum conditions: 30 minutes contact time, at pH 5 and 0.5 ppm Cd(II) solution. The membrane, which contained 0.5% CNDs/PES, showed the highest percentage removal. This was due to the –OH and enhanced -COO- on the membrane composite, which could be attributed to the increase in the presence of CNDs within the membrane.
M.Sc. (Chemistry)