Synthesis of reusable graphene oxide based nickel-iron superparamagnetic nanoadsorbent from electronic waste for the removal of doxycycline in aqueous media

Graphene oxide-based nickel-iron superparamagnetic nanoadsorbent (GO/Ni-Fe) was synthesized from electronic waste to effectively remove doxycycline (DXC) in aqueous media. The GO/Ni-Fe nanoadsorbent has been characterized using a number of instrumental techniques, including X-ray diffractometer, Zeta potential, Fourier transform infrared spectroscopy, elemental analyzer, vibrating sample magnetometer, transmission electron microscopy, energy dispersive x-ray, and X-ray photoelectron spectroscopy. These techniques showed that nickel-iron (Ni-Fe) nanoparticles with an average size of 4.26 nm were successfully fabricated on GO surfaces. The batch experiments were conducted under different conditions, including contact time, adsorption dosage, pH, concentration, and temperature, to determine the optimal conditions of the adsorption process. The maximum adsorption (90% removal) was established within 20 min, while the adsorbent dose was only 0.1 g/L at pH 5. The adsorption process was best fitted with the pseudo-second-order model, which suggests the interaction of doxycycline with the GO/Ni-Fe nanoadsorbent is mainly controlled by the chemisorption process. This may be due to hydrogen bonding as well as electrostatic interaction and π-π interaction between adsorbates and adsorbents. The isotherm data of the adsorption process was best fitted with Langmuir isotherm model with a maximum adsorption capacity of 13.02 mg g ^{− 1} at 25 °C, indicating that the adsorption is a monolayer adsorption to heterogeneous surfaces with electrostatic interaction. The superparamagnetic properties of GO/Ni-Fe nanoadsorbent can be easily separated by external magnetic field and regenerated with methanol washing. The findings unambiguously demonstrated that magnetically separable GO/Ni-Fe nanoadsorbent could be a good choice to remove DXC from wastewater sources.