###### Abstract  
We report the synthesis of reduced graphene oxide (rGO)-\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) nanocomposite and its application to remove and recover dissolved oil from a high-salinity oil-water emulsion in batch and column/breakthrough setups. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and nitrogen adsorption characterized the synthesized nanocomposite's structure, morphology, and surface properties. Both batch and continuous breakthrough adsorption studies were investigated. The effect of the adsorption parameters on the adsorption capacity and removal efficiency was analyzed. The rGO-Fe\({}_{2}\)O\({}_{3}\) nanocomposite (rGO-Fe\({}_{2}\)O\({}_{3}\)-NC) demonstrated a superior adsorption capacity, both when measured experimentally (1213 mg/g) and predicted using the Freundlich isotherm (1301 mg/g). The adsorption process followed pseudo-second-order kinetic, and the rGO-Fe\({}_{2}\)O\({}_{3}\)-NC exhibited a very rapid removal, with more than 60% of oil being removed within 10 min. Breakthrough confirmed the exceptional removal capacities with good regeneration and cycling ability under a short contact time. Moreover, the adsorption capacity was enhanced with an emulsion salinity of up to 100,000 ppm, confirming the suitability for high-salinity wastewater. graphene nanocomposites; oil removal; adsorption; high-salinity oil wastewater; breakthrough adsorption +
Footnote †: journal: Applied Sciences  
are promising because of their high surface area and faster adsorption rate [11; 12]. Various studies have confirmed that nanomaterials are effective in wastewater treatment [13; 14; 15; 16]. Nonetheless, pristine graphene has limited application in wastewater treatment. In contrast, the modified graphene or graphene composites incorporating functional moieties or nanoparticles on the graphene surface increase its potential applications. The oxygen groups and defects on the surface of graphene oxide (GO) and reduced graphene oxide (rGO) make them ideal as a support for nanoclusters of metal-based nanoparticles, such as iron oxide [17; 18; 10; 19]. Graphene-based nanomaterials are excellent adsorbents for removing various organic pollutants. The main mechanisms of removing organic contaminants using graphene nanomaterials are anion interaction, cation interaction, \(\pi\)-\(\pi\) interaction, and functional group interaction [20]. [PERSON] et al. [21; 22] synthesized magnetic graphene nanocomposites (G/Fe\({}_{2}\)O\({}_{3}\)) to remove fuchsine dye. The dye sorption was very fast and reached equilibrium within 30 min, with a reported sorption efficiency of 0.0894 g/g. They concluded that G/Fe\({}_{3}\)O was a very effective adsorbent and could be easily regenerated using acidic ethanol. [PERSON] et al. [23] studied the reduction of GO and \(\alpha\)-Fe\({}_{3}\)O\({}_{4}\) for synthesizing G/Fe\({}_{3}\)O\({}_{4}\) hydrogels for the adsorption of oil and heavy metals from wastewater, reporting a removal efficiency of 92% for gasoline removal. Moreover, the G/Fe\({}_{3}\)O\({}_{4}\) hydrogel showed good adsorption capacity towards other oils, e.g., paraffin and vegetable oils, with an adsorption capacity of \(\sim\)27 g/g and very high recyclability. In the adsorption of hydrocarbon oils containing aromatic hydrocarbons, \(\pi\)-\(\pi\) interactions have a primary role in oil removal. Graphene-based nanomaterials were reported to have a higher adsorption capacity than other adsorbents such as activated carbon, organic/inorganic adsorbents, and fly ash [24; 25; 26; 27; 28]. Several functional and nano-adsorbents have been used to remove emulsified oil from wastewater. The performance of such adsorbents is summarized in Table 1. These adsorbents can be classified into three groups: (i) low-performance adsorbents with an adsorption capacity of less than 100 mg/g, (ii) moderate performance adsorbents with an adsorption capacity between 150 and 800 mg/g, and (iii) high-performance adsorbents with an adsorption capacity \(>\)1000 mg/g, including the adsorbent developed in this study.