Green synthesis of Ag/MgO nanoparticle modified nanohydroxyapatite and its potential for defluoridation and pathogen removal in groundwater

The paper presents a facile green method of synthesizing a multi-functional 3-layered Ag-MgO/nanohydroxyapatite (Ag-MgOnHaP) composite via a combined microwave and ultrasonically modified methods with emphasis on simultaneous pathogens and fluoride removal in groundwater. The reduction of Ag and MgO ions by aqueous Citrus paradisi peel extracts was utilized for the impregnation Ag-MgO nanoparticles on the adsorbent surface. Ag-MgOnHaP composite morphological structures were characterized by UV-Visible spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive-X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analysis. Batch sorption studies using the nanocomposite under different experimental parameters were investigated to determine its adsorption capacity. The antibacterial activity of the adsorbent against Escherichia coli and Klebsiella pneumonia in water was also evaluated. The results showed the successful synthesis of the core-shell Ag-MgOnHaP composite with the presence of an optical intense absorption band at 290 nm together with a blue-shifted broad band of 378 nm typical of MgO and Ag nanoparticles. Ultrasound irradiation in synthesis resulted in the improved production of spherically smaller particle sizes of 16.44 nm. The optimum adsorption capacity of 2.146 mg/g at 298 K was recorded with more than 90% fluoride removal at 0.3g dosage. Maximum adsorption was achieved at pH 6. The sorption process fitted well to the Freundlich isotherm model and follows the pseudo-second-order kinetics at room temperature. The overall results showed not only the potential ability of the nanocomposite toward fluoride removal but also recorded strong antibacterial activity against E. coli and K. pneumonia.