Synthesis and characterisation of magnetic graphene-nanoparticle composites for water purification.

Abstract

The synthesis of reduced graphene oxide is investigated in this work, with a focus on water purification. The work stems from the interest gained from the discovery of graphene and its high surface area. The study focused on the synthesis of reduced graphene oxide. This afforded the synthesis of reduced graphene oxide nanoparticles composites and doped reduced graphene oxide. The composites were produced with magnetic nickel, cobalt and cobalt ferrite nanoparticles. The doped reduced graphene oxide was synthesized using nitrogen and boron as dopants. The prepared samples were rGO, N-rGO, B-rGO, Co-rGO, Ni-rGO and FeCo-rGO. All the samples were characterized using Transmission Electron Microscopy (TEM), Fourier Transform Infra-red (FTIR) spectroscopy, Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Raman Spectroscopy and X-ray Diffraction (XRD). All the samples were found to have magnetic properties. The composites have superparamagnetic properties and FeCo-rGO had the highest magnetization at 12.54 emu.g-1. The conductivity results showed that the doped samples and composites had better conductivity than rGO with the Ni-rGO having the highest conductivity of 62695.82 S.m-1. All samples had conductivity which were similar to semiconductors. The prepared samples have high surface area and a large number adsorption sites and thus were used in applications of water purification in the removal of Cr(VI) ions from solution. The Co-rGO was found to have the ability to adsorb the Cr(VI) in form of CrO42- while other samples catalysed reduction of Cr(VI) to Cr(III). Thus Co-rGO was used in the removal of Cr(VI) ions from solution. The adsorption of Cr(VI) ions occurs through electrostatic interaction between CrO42- and Co-rGO. The optimum conditions for the removal of chromium ions were experimentally determined. The conditions, were a dosage of 300 mg.L-1, a pH of 8, contact time 90 minutes and temperature was 298 K. The removal efficiency was affected by the concentration of chromium ions and there was 90 % removal efficiency for the concentration of 20 mg.L-1