Role of Gallic Acid in the Synthesis of Carbon-Encapsulated\nIron Nanoparticles by Hydrothermal Carbonization: Selecting Iron Oxide\nComposition

Abstract

In this work, the\nrole of phenolic compounds in the hydrothermal\nsynthesis of carbon-encapsulated iron nanoparticles (CEINs) was studied.\nTo model phenolic compounds, gallic acid (GA) was selected, with glucose\nas the carbon source. Iron was found as α-Fe₂O₃, γ-Fe₂O₃, Fe₃O₄, and zero-valent iron (ZVI) depending on the synthesis pH\nand GA/Fe molar ratio. For GA/Fe = 1, the CEINs’ yield increased\nsignificantly. In the samples with phenolics, increasing the initial\npH increased the amount of γ-Fe₂O₃ and\nFe₃O₄ and enhanced the iron oxide encapsulation\ndue to enhanced chelating ability. Reducing the GA/Fe ratio to 0.2\nresulted in CEINs with stronger magnetization due to the presence\nof Fe₃O₄. Ash weight, HCl digestion, and Raman\nspectroscopy were used in conjunction to characterize the composition\nof the CEINs. The magnetization of the samples was compared using\na simple magnetic weight setup. A scheme for the reactions occurring\nduring the hydrothermal carbonization of GA–Fe complexes was\nproposed.