Abstract:
In this study, three novel hexadecylamine graphene quantum dots (hexadecyl-GQDs) with varying moieties
on the surface were synthesised and characterised to examine the effect of surface functionalisation on
their adsorption efficiency. Introducing hydrophobic moieties via in situ generation of an amide bond by
coupling hydrophilic carboxylic acid-functionalised GQDs with hexadecylamine improved the adsorption
capacity of GQDs. The AFM and Raman spectroscopy results revealed the formation of multilayered
GQDs with an average diameter of 10.0, 9.8, and 7.0 nm for C16-GQDs, C16-NGQDs and C16-SNGQDs,
respectively. According to the sum of squared error (SSE) values obtained from fitting phenanthrene
adsorption experimental data to two- and three-parameter models, the Sips hybrid isotherm model best
described the adsorption of sorbate to the doped hexadecyl-GQDs (0.55 $ SSE # 0.72), with R2 values
>0.9. Furthermore, doping of the GQDs favoured a multilayer adsorption mechanism over monolayer
adsorption, enhancing adsorption capacities (KF & Kd). Hexadecylamine sulphur and nitrogen co-doped
GQDs (C16-SNGQDs) gave the highest maximum adsorption capacity (qm) of 1377 mg g 1. Pristine
GQDs interact with phenanthrene endothermically, while the adsorption of phenanthrene onto modified
GQDs is spontaneously exothermic. The adsorption of phenanthrene is most affected by the presence of
sulfate and phosphate anions and is best at ambient temperature and acidic pH. Co-doping with
nitrogen and sulphur groups and modification of hydrophilic to hydrophobic form enhanced the
physicochemical and adsorption performance of C16-SNGQDs, making them potentially suitable as
materials for the extraction of hydrophobic organic pollutants from water.
