Removal of Mercury and Arsenic Metal Pollutants from Water Using Iron Oxide Nanoparticles Synthesized from Lichen Sinensis Ramalina Extract

Background & objectives: The import of heavy metals into various sources of drinking water supply is one of the major problems of water quality, especially in industrial areas. The aim of this study was to investigate the ability of mercury and arsenic metal pollutants to be removed from aqueous solutions using green oxide nanoparticles synthesized by green method. For this purpose, the extract from an indigenous lichen sample of Ardabil province was used as a sorbent for synthesis of iron oxide nanoparticles. Methods: For the preparation of magnetized iron oxide nanoparticles, a fast and common method called co-adsorption was used. In this method, a mixture of bivalent and trivalent iron salts with a specified stoichiometric ratio is added to a certain volume of the extract obtained from Sinensis Ramalina (SR). Due to the use of lichen in the process of synthesis of iron oxide nanoparticles, the method used in the present study is also referred to as the green synthesis method. UV-Vis spectrophotometry, XRD, FT-IR, SEM and EDX elemental analysis were used to confirm the synthesized iron oxide nanoparticles. Results: In the spectrophotometer spectrum, the peak appearing at 574±5 cm-1 indicates the transfer of oxygen electrons to the iron synthesized from SR lichens. The XRD spectrum also confirms the purity of the iron oxide nanoparticles, as the diffraction pattern was correctly obtained at 2θ=30.40, 35.75, 43.60, 57.90, 63.60. The uniform spherical nature of the iron oxide (III) nanoparticles with a size between 31.74 to 53.91 nm can be seen using SEM images. EDX analysis was also used to show the elemental structure of the synthesized iron oxide nanoparticles. Elemental analysis revealed that the synthesized nanoparticles contained 19.68% by weight of iron and 51.49% by weight of oxygen. Conclusion: Studies showed that mercury follows the Langmuir adsorption isotherm model (R2=0.998) and arsenic follows the Freundlich adsorption isotherm model (R2=0.968) and the removal process in both metals is spontaneous and exothermic. The data obtained from the kinetic studies of removal of both metals from aqueous solutions were fitted to the pseudo-second-order kinetic model with an appropriate correlation coefficient above 0.99. The ability to remove arsenic and mercury by magnetic iron oxide nanoparticles synthesized by SR plant extract was 71.02% and 72.84% at pH=4 and initial concentration of 50 mg/l, respectively.