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

Abstract

In this work, the role of phenolic compounds in the hydrothermal synthesis of carbon-encapsulated iron nanoparticles (CEINs) was studied. To model phenolic compounds, gallic acid (GA) was selected, with glucose as the carbon source. Iron was found as α-Fe₂O₃, γ-Fe₂O₃, Fe₃O₄, and zero-valent iron (ZVI) depending on the synthesis pH and GA/Fe molar ratio. For GA/Fe = 1, the CEINs' yield increased significantly. In the samples with phenolics, increasing the initial pH increased the amount of γ-Fe₂O₃ and Fe₃O₄ and enhanced the iron oxide encapsulation due to enhanced chelating ability. Reducing the GA/Fe ratio to 0.2 resulted in CEINs with stronger magnetization due to the presence of Fe₃O₄. Ash weight, HCl digestion, and Raman spectroscopy were used in conjunction to characterize the composition of the CEINs. The magnetization of the samples was compared using a simple magnetic weight setup. A scheme for the reactions occurring during the hydrothermal carbonization of GA-Fe complexes was proposed.