Removal of Cr(VI) from Aqueous Solution Using Magnetic Activated Carbon Prepared from Waste Shell of <i>Marigold Flower Straw:</i> Kinetics, Isotherm and Mechanism Studies

When Cr(VI) was released from industrial waste into water bodies harms aquatic ecosystems and poses risks to human well-being. To reduce risks, it's crucial to lower Cr(VI) levels through the sustainable process. In order to extract Cr(VI) from a liquid, the magnetic activated carbon adsorbent was created for the current investigation. H3PO4 was utilised as an activating agent in the thermal procedure to prepare activated carbon from marigold flower straw for the first time. The marigold flower straw activated carbon (MFSAC) was further decorated with Fe3O4 nanoparticles (Fe3O4/MFSAC) in the reflux process. The complete analysis of the MFSAC and Fe3O4/MFSAC nanocomposite properties was carried out utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET (Brunauer-Emmett-Teller) and zero-point charge (pHIEP) to get information about the morphology, functional group, crystallinity, surface area, and surface charge respectively. At an initial concentration of 20 mg/L, a pH of 3, a contract time of 40 minutes, and an adsorbent dose of 2 g, around 99% of Cr(VI) was eliminated. The Langmuir isotherm showed that the Fe3O4/MFSAC nanocomposite could adsorb 8.76 mg/g. The pseudo-second-order kinetic model had the best-fitting R2 values, which were 0.99. On the surface of the Fe3O4/MFSAC nanocomposite, electrostatic attraction and porosity adsorption were the main mechanisms for Cr(VI) adsorption. Therefore, in wastewater treatment, the Fe3O4/MFSAC nanocomposite functions as a possible adsorbent.