The rapid development of the textile industry in Indonesia has increased the need for dyes. Meanwhile, magnetite nanoparticles are widely used due to their large adsorption capacity, nano-sized with a wider surface area, non-toxic, biodegradable, and easily separated due to their magnetic properties. Therefore, this study aims to examine the preparation and characterization of fulvic acid-coated magnetite nanoparticles (MnP-FA) and their application for methylene blue (MB) adsorption with variations in pH, contact time, and concentration. The extraction of FA from peat soil in Samboja, East Kalimantan under alkaline conditions and then coated with MnP using the coprecipitation method. FTIR characteristics result of MnP-FA was shown the interaction of the carboxyl group on FA with the Fe-O surface on MnP, loss of C-H deformation at 1404 cm-1, and a shift in the C-H carboxylate group at 1126 cm-1. MnP-FA diffractogram did not change the crystal structure compared to MnP, and SEM image MnP-FA showed that the morphology is a smooth surface with non-uniform size attached to the spherical MnP. The magnetic property decreased after the addition of FA but is still attracted by an external magnet. Adsorption of methylene blue using MnP-FA was optimum at pH 7 with a contact time of 30 minutes, adsorption capacity (Qa) of 2.20 mg/g, and adsorption percentage of 56.%. The results showed that the capacity of MnP-FA was almost the same as that of MnP but the contact time was more effective for methylene blue adsorption. The results showed that the adsorption capacity of MnP-FA was greater than MnP and contact time was faster for methylene blue adsorption.
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