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• Bubble-particle hydrophobic attraction dominates bubble-particle attachment. • Insignificance of electrostatic attraction for bubble-particle attachment. • GO in IL solution achieves maximum hydrophobicity at isoelectric point. • Bubble-GO attachment in IL solution is optimum at GO's isoelectric point. • High carbon chain length IL improves bubble-GO attachment at GO's isoelectric point. This paper presents the synthesis of GO-coated microbubbles which would be useful for environmental remediation and enhanced heat transfer applications. The mechanism of microbubble-GO attachment including electrostatic interactions, hydrophobic attraction, contact angle and Gibb's free energy were determined. Preliminary experiments indicated that water alone is not favourable, which thus necessitated the use of a bridging surfactant. The optimum attachment between microbubbles and GO occurred at the GO's isoelectric point (IEP) in the ionic liquid as surfactant (IL), in which the IL concentration allowed GO to achieve maximum hydrophobicity. Therefore, it is inferred that hydrophobic attraction is the dominant force for microbubble-GO attachment with minor contributions from electrostatic interactions. Further studies showed that the longest carbon chain length IL, i.e. 1-Dodecyl-3-methylimidazolium chloride ([ C 12 mim]Cl) produced the most conducive environment for microbubble-GO attachment at its IEP concentration of 350 ppm. [ABSTRACT FROM AUTHOR]

This research aims to synthesize graphene oxide (GO)-coated microbubbles to enhance polycyclic aromatic hydrocarbon (PAH) removal from aqueous solutions through flotation technology. In this research, 1-Dodecyl-3-methylimidazolium chloride ionic liquid ([C 12 mim]Cl) was used to bridge microbubbles and GO. The attachment between microbubbles and GO in [C 12 mim]Cl solution was successfully observed and quantified using a microscopy visualization technique and UV–VIS Spectrophotometer respectively. The synthesised GO-coated microbubbles were then used to enhance the removal of phenanthrene (PHEN) and pyrene (PYR), a low and high molecular weight PAH respectively, from aqueous solutions via flotation technology. A closed loop laboratory-scale flotation system was developed to compare the PAH removal efficiency by uncoated and GO-coated microbubbles. The PHEN and PYR removal efficiencies increased significantly to 64.77% and 74.01%, respectively for GO-coated microbubbles as compared to uncoated microbubbles of 18.91% and 19.65%, respectively during flotation. Furthermore, the higher removal efficiency of PYR compared to PHEN implied that GO-coated microbubbles were more efficient at removing higher molecular weight PAHs (more hydrophobic) which are more detrimental to the environment [Display omitted] • GO-coated microbubbles enhance PAH removal from aqueous solutions via flotation technology. • GO is coated onto microbubbles with aid of 1-Dodecyl-3-methylimidazolium chloride ionic liquid. • Removal efficiencies of phenanthrene and pyrene are 64.77% and 74.01%, respectively. • Removal of HMW PAH is higher due to increased hydrophobicity and π-π interactions. • GO-coated microbubbles enhances environmental remediation using flotation. [ABSTRACT FROM AUTHOR]

This study presents the feasibility of coating microbubbles with graphene oxide (GO), a transpiring material that has since attracted intensive research in both fundamental science and technology developments. In this study, an imidazolium chloride ionic liquid (IL), namely 1-dodecyl-3-methylimidazolium chloride ([C 12 mim]Cl) at various concentrations from 100 ppm to 8000 ppm was used as the binder surfactant to bridge microbubbles and GO. The mechanism of microbubble-GO attachment studied in this research included microbubble-GO electrostatic interactions, microbubble-GO hydrophobic attraction, microbubble-GO contact angle and Gibb's free energy of a microbubble-GO system. Results showed that the optimum microbubble-GO attachment (highest contact angle and most negative Gibb's free energy) occurred at 350 ppm [C 12 mim]Cl in which GO achieved isoelectric point (IEP – zeta potential (ZP) of GO is at 0 mV). Since GO gained maximum hydrophobicity at IEP, it was inferred that microbubble-GO attachment was dominated by hydrophobic attraction with insignificant electrostatic interactions. Qualitative analysis further confirmed the successful attachment and production of the GO-coated microbubble in 350 ppm[C 12 mim]Cl. Besides that, a single microbubble in 100 ppm[C 12 mim]Cl at which maximum attractive electrostatic forces are anticipated between microbubbles and GO was also analysed qualitatively. Here, GO attachment onto the microbubble was not significantly observable, thus further proving the dominance of hydrophobic attraction. On a different note, the amount of GO attached onto a microbubble in 350 ppm[C 12 mim]Cl was also successfully quantified using UV–Vis method at which GO possessed an absorption peak centered at 233 nm. The outcomes of this study demonstrated the significance of hydrophobic attraction for microbubble-particle attachments particularly for microbubble-GO attachment and successful synthesis of GO-coated microbubbles for various applications. • Graphene-oxide coated microbubbles can be generated at 350 ppm of 1-dodecyl-3-methylimidazolium chloride. • Hydrophobic attraction dominates the electrostatic attraction in the GO-coated microbubbles. • GO-coated microbubbles can be implemented in heat transfer and environmental remediation applications. [ABSTRACT FROM AUTHOR]