Nigella sativa seed based nanocomposite-MnO2/BC: An antibacterial material for photocatalytic degradation, and adsorptive removal of dye from water

摘要： Antimicrobial Nigella sativa seed-based nanocomposite, MnO2/BC, was synthesized and utilized for water purification through adsorption and photocatalytic degradation. MnO2/BC was prepared by co-precipitation method, and characterized using FT-IR, XRD, SEM, TEM, TGA, and DSC techniques. The composite was investigated for inhibition of bacterial cells growth. FT-IR spectrum indicated the presence of oxygenous groups on the surface; TGA and DSC showed thermal degradation; and XRD, SEM, and TEM investigations indicated amorphous, and porous nature of MnO2/BC having particle size of 190-220 nm. The nanocomposite inhibited the growth of both Gram-positive and Gram-negative bacteria cells in water. The adsorption of Methylene blue (MB) from water was investigated in batch method in terms of amount of MnO2/BC, MB concentration, pH, time, and temperature. 1.0 gL-1 of MnO2/BC removed more than 98% of MB from aqueous solution having concentration of 10 mgL-1 and pH 7.0 at 27°C. The maximum Langmuir adsorption capacity of MnO2/BC was 185.185 mgg-1 at 45°C. The adsorption was an endothermic process which obeyed Freundlich isotherm, and pseudo-second order kinetics. Therefore, the MB binding onto MnO2/BC surface was site-specific partially through weak hydrogen bonding and electrostatic interactions. The photocatalytic activity of MnO2/BC has been investigated by degrading the MB molecules/ions in water under the sunlight and 85% of degradation was achieved during 120 min irradiation. The dye was desorbed at lower pH and regenerated MnO2/BC was used for second cycle of MB adsorption. The results obtained for this study are much better than the previous MB adsorption studies with acid washed Black cumin seeds and MnFe2O4/BC for which the capacities were 73.529 mgg-1 and 10.070 mgg-1 at 27°C, respectively (J. Mol. liq. 2018a, 264, 275-284; J. Clean. Prod. 2018a, 200, 996-1008).