Graphene oxide-iron oxide nanocomposites for dye contaminated wastewater remediation

Abstract

The development of active and stable heterogeneous Fenton-like catalysts have emerged as an alternative to overcome the practical limitations related to the homogeneous Fenton catalyst, where various iron species and/or iron oxides are immobilised within the structure of different catalyst supports. Clay, alumina, zeolite and carbonaceous materials such as activated carbon and carbon nanotubes have been used as catalyst supports of choice by the scientific community. However, there is a knowledge gap associated with using high aspect ratio 2D (dimension) graphene oxide (GO) as an alternative catalyst support. Of particular interest, it is postulated that the structure and functionalities of GO as a support confers to the resultant catalyst overall catalytic activity beyond the conventional Fenton catalysts. In this thesis, the structural and physicochemical properties of resultant catalyst with their corresponding catalytic activity were systematically investigated. To this end, the synergistic interaction between GO and immobilised iron oxide nanoparticles (Fe3O4 NPs) was proposed for an oxidative degradation of synthetic dye acid orange 7 (AO7), which is a major water pollutant from textile production.The GO-Fe3O4 nanocomposites were initially synthesised through a facile one-pot method by coprecipitating irons salts onto GO sheets in a basic solution. The formation of GO-Fe3O4 was postulated as follows: (i) Fe 3+ / Fe 2+ ions are adsorbed and coordinated by the carboxyl groups (C=O) of GO sheets, (ii) hydrolysed ions form nanoclusters on GO sheets when NaOH is introduced, (iii) followed by condensation of the nanoclusters to form Fe3O4 nuclei, and (iv) further nucleation and growth of Fe3O4 crystallites on GO sheets were due to the redox reaction as the pH is increased to 10. The incorporation of GO led to an enhancement on the catalytic activity of the nanocomposites with 76% AO7 removal over the control catalysts of Fe3O4 NPs and GO sheets, which corresponds to 48 and 22%, respectively.Further improvements on the catalytic activity of GO-Fe3O4 were performed by modifying the synthesis through pre-hydrolysing iron salts prior to GO addition at pH 4 with various GO loadings.The key finding of this new method is the formation of two sets of different mesoporous structure.At low GO loadings 10 wt%, GO-Fe3O4 nanocomposites resulted in high surface area up to 409 m 2 g -1 , in tandem with high 92-98% degradation of AO7. By contrast, GO loadings 10 wt% led to reduced surface area and lower GO-Fe3O4 activity (60%). The presence of strong interfacial interactions (Fe-O-C bonds) in the nanocomposites contributed to the superior degradation of AO7, in tandem with structural-morphological features.iiiThe operational conditions of heterogeneous Fenton-like reaction were evaluated and modelled as a function of nanocomposites dosage, pH, temperature, oxidant and dye concentrations. Best results showed a fast 80% degradation in ~20 min, whilst ~98% of AO7 was successfully removed after 180 min of reaction time. O...