Nigella sativa seed based nanohybrid composite-FeO-SnO/BC: A novel material for enhanced adsorptive removal of methylene blue from water.

In this work, an advance approach is reported for the water treatment technology using nanohybrid composite FeO-SnO/BC prepared by incorporation of iron-tin binary oxide into the cellulosic framework of medicinally active Nigella sativa (Black cumin) seed powder. The co-precipitation method was followed to prepare the nanohybrid composite which was subjected to investigate its physiochemical properties using spectroscopic and microscopic techniques. Fourier-transform infrared spectroscopy analysis confirmed the formation of highly functionalized nanocomposite through the hydrogen and electrostatic interactions between the functional groups of seeds and FeO-SnO. X-ray and selected area electron diffraction pattern revealed the presence of cubic phase of γ-FeO and tetragonal phase of SnO in the composite. The scanning electron microscopic images suggested the porous and relatively smooth surface of the composite, and transmittance electron microscopic images showed the trapping of nano-cubes of FeO-SnO, having particles size in the range 95-185 nm, into the organic framework of Black cumin seeds, whose zero point charge was found at pH 7.2. The composite was investigated for adsorption of Methylene blue dye from water for which the results revealed that 2.0 gL amount of FeO-SnO/BC was sufficient to remove more than 95% dye, within 15 min, at 6-9 pH, from its 10 mgL concentration. The thermodynamic studies established spontaneity, feasibility, and endothermic nature of the adsorption process. The adsorption data was satisfactorily described by the Freundlich isotherm which indicated inhomogeneous surface of the composite. Application of Temkin isotherm revealed the same extent of bonding probability and heat of adsorption at 27, 35, and 45 °C. The free energy change calculated from Dubinin-Radushkevich isotherm suggested weak interaction between Methylene blue and FeO-SnO/BC. The process satisfactorily followed the pseudo-second order kinetics that was controlled by the film diffusion step which indicated interaction of Methylene blue with functional sites of the FeO-SnO/BC. The Fourier-transform infrared spectroscopy analysis gave the confirmatory evidence for interaction of Methylene blue to FeO-SnO/BC. The maximum Langmuir adsorption capacity of the FeO-SnO/BC was found to be 58.82 mgg at 27 °C which is higher than the previously reported adsorbents, MnFeO/BC [J. Clean. Prod. 2018. 200, 996-1008], and FeO-ZrO/BC [J. Clean. Prod. 2019. 223, 849-868]. Therefore, the study showed excellent results for water treatment and can be useful to develop advance water treatment technology.