Hydrophobic interactions of bisphenol A with organically modified magnetite nanoparticles

Magnetic nanoparticles were synthesized, purified, characterized, and functionalized with sodium oleate and sodium cholate to enhance their adsorption capacity for bisphenol A from aqueous solutions. The effect of varying oleate and cholate load on the adsorption was studied in the presence of sodium chloride and calcium chloride. The initial concentration of bisphenol A in the solutions ranged from 0.05 to 5 mg/L. High-sensitivity quantification of bisphenol A was performed using ultraperformance liquid chromatography-tandem mass spectrometry. Oleate-modified magnetite nanoparticles exhibited a substantial increase in bisphenol A adsorption efficiency compared to bare magnetite, achieving a maximum of 77.50 ± 0.81% at an oleate coverage of 0.6 mmol/g in the presence of 10 mmol/L calcium chloride. Adsorption efficiency improved with higher oleate coverage (1.2 mmol/g) in the presence of calcium chloride compared to sodium chloride, shifting the isoelectric point and promoting stronger hydrophobic interactions. In contrast, cholate-modified magnetite nanoparticles showed a lower adsorption efficiency of 56.35 ± 1.15% at 0.8 mmol/g optimum coverage, with no significant effect observed upon calcium chloride addition. The highest theoretical adsorption capacity, based on Langmuir fitting, was found for oleate-modified magnetite in the presence of calcium chloride, with a q max value of 3.59 mg/g. These results reveal that oleate-coated magnetite nanoparticles show significant potential for the removal of bisphenol A from aqueous solutions, particularly in the presence of specific electrolytes, and offer promising potential for environmental remediation applications. • Hydrophobic coated magnetite NPs were prepared to enhance BPA adsorption. • Increased adsorption efficiency compared to the highly polar bare magnetite was observed. • The adsorption of BPA on hydrophobized MNPs can be described as physisorption, mainly driven by partitioning mechanism. • Oleate coverage seemed more effective for BPA removal compared to cholate coating. • Indifferent/specific electrolytes had a prominent effect on the adsorption.