Facile synthesis of reduced graphene oxide/Fe3O4 nanocomposite for preconcentration and trace determination of tetracyclines and rare earth elements in water / Ungku Amirul Arif Ungku Abdullah

A green magnetic adsorbent, reduced graphene oxide/Fe3O4 nanocomposite, was
synthesized via one-pot reaction method and characterized via X-Ray Diffraction, Field
Emission Scanning Electron Microscope, Fourier-transform infrared spectroscopy,
Energy Dispersive X-ray spectroscopy, Point of Zero Charge and Vibrating-sample
magnetometer. The adsorbent was used to develop magnetic solid-phase extraction
(MSPE) technique for tetracycline antibiotics (TCAs) and rare earth elements (REEs)
from water samples. The MSPE procedure for TCAs was optimised with respect to the
necessary parameters; pH 4 for sample solution, 10 mg of adsorbent, 8 mL of sample,
5 min of extraction time, ethanol as the eluent and 2 min of desorption time. Under the
optimised MSPE conditions, good linearity was achieved for the selected TCAs at
concentrations ranging 0.05–1.0 mg L-1. The limit of detection and limit of
quantification were 0.006–0.011 mg L-1 and 0.019–0.036 mg L-1, respectively. The
intra-day and inter-day precisions were less than 3.38% and 5.59%, respectively.
Satisfactory recoveries were obtained from real sample analysis ranging from 89.77–
106.33%. Meanwhile, the MSPE procedure for REEs was optimised with respect to the
necessary parameters; sample solution at pH 4, 20 mg of adsorbent, 100 mL of sample,
5 min of extraction time, 0.5 M of HNO3 as the eluent and 3 min of desorption time.
The method also revealed good linearity for the selected REEs, ranging from 10–1000
μg L-1. The limit of detection and limit of quantification were obtained in the range of
0.044–0.115 μg L-1 and 0.147–0.389 μg L-1, respectively. The intra-day and inter-day
precisions were less than 3.87% and 4.21%, respectively. Satisfactory recoveries were
obtained from real sample analysis ranging from 90.19–102.43%. Both analytes obeyed
Langmuir adsorption isotherm model with adsorption capacity up to 52.64 and 53.56
mg g-1, respectively. The adsorbent can be reused up to 10 cycles without a significant
loss of performance.