Green synthesis of Ag 2 O nanoparticles using Punica granatum leaf extract for sulfamethoxazole antibiotic adsorption: characterization, experimental study, modeling, and DFT calculation.

Silver oxide (Ag 2 O) nanoparticles (NPs) were generated by synthesizing green leaf extract of Punica granatum, and afterwards they were used as adsorbent to remove the antibiotic additive sulfamethoxazole (SMX) from aqueous solutions. Prior of their use as adsorbent, the Ag 2 O NPs were characterized by various methods such as X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), scanning electron microscopy/energy-dispersive X-ray (SEM-EDX), and transmission electron microscopy (TEM). The Ag 2 O NPs were found to be spherically shaped and stabilized by the constituents of the extract. Further, at SMX antibiotic concentration of 100 mg L -1 , the Ag 2 O NPs achieved almost complete removal of 98.93% within 90 min, and by using 0.8 g L -1 of adsorbent dose at pH=4 and temperature T=308 K. In addition, the experimental data were well fitted with the theoretical Langmuir model indicating homogeneous adsorbed layer of the SMX antibiotic on the Ag 2 O NPs surface. The maximum uptake capacity was 277.85 mg g -1 . A good agreement was also found between the kinetic adsorption data and the theoretical pseudo-second-order model. Regarding the thermodynamic adsorption aspects, the data revealed an endothermic nature and confirmed the feasibility and the spontaneity of the adsorption reaction. Furthermore, the regeneration study has shown that the Ag 2 O NPs could be efficiently reused for up to five cycles. The geometric structures have been optimized and quantum chemical parameters were calculated for the SMX unprotonated (SMX +/- ) and protonated (SMX + ) using density functional theory (DFT) calculation. The DFT results indicated that the unprotonated SMX +/- reacts more favorably on the Ag 2 O surface, as compared to the protonated SMX + . The SMX binding mechanism was predominantly controlled by the electrostatic attraction, hydrogen bond, hydrophobic, and π-π interactions. The overall data suggest that the Ag 2 O NPs have promising potential for antibiotic removal from wastewater.