Controlled Growth of a Highly Energetic, Less Electron-Dense Tetrahedral Fe³⁺ Phase on the Surface of α-Fe₂O₃ Nanoparticles toward Enhanced Optical, Magnetic, and Supercapacitive Performance

Abstract

Nanoplate to pseudocubic-shaped hematite (α-Fe 2 O 3 ) nanoparticles along with the gradual engravement of tetrahedral Fe 3+ has been synthesized by controlling the precursor (FeCl 3 •6H 2 O) concentration from 0.005 M (A 1 ) to 0.2 M (A 4 ). The role of the surfactant polyvinylpyrrolidone on the preferential plane ([110] to [012]) growth and highly energetic tetrahedral Fe 3+ phase (increases 2.7 times for A 4 than A 1 ) nucleation over the hematite surface has been elucidated from the HRTEM images, XPS, and Raman spectroscopy. This tetrahedral phase and the morphology variation facilitate the Fe−Fe interaction significantly, which improves the saturation magnetization from 0.13 emu/g (A 1 ) to 0.37 emu/g (A 4 ). Stronger magnetic d−d coupling in the A 4 sample promotes dominant photoluminance (PL) spectra. It also exhibits linear dependence with the excitation wavelength (300−380 nm) that can be exploited in the design of a UV detector. The supercapacitive performance of ethylene glycol supported PEDOT-PSS-α-Fe 2 O 3 composite films as negative electrode materials, in the voltage window of −1.3 to −0.5 V, suggests this material to be a promising candidate for the next-generation charge storage devices. The sample engraved with the richest Fe 3+ ions shows the highest specific capacitance of 705.7 F/g in 2 M SO 3 2− electrolytes, and its cyclic stability increases to 111% over 1500 cycles.

Solid-State Reaction of Ferrocene Controlled by Co-Precursor and Reaction Atmosphere Leading to Hematite and Cohenite Nanomaterials: A Reaction Kinetic Study

“…Synthesis and characterization of iron oxide nanoparticles have become an exciting area of research as these materials possess many outstanding characteristics like low-energy band gap, high sensitivity, tunable optical and magnetic properties, superparamagnetism, biodegradability, biocompatibility, and high stability. − Among the different iron oxides known so far, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), and hematite (α-Fe 2 O 3 ) are the most commonly found in nature, whereas hematite is the most stable iron oxide at ambient atmosphere, and thus, hematite nanoparticles are paving newer avenues of applications. − Though hematite nanoparticles are available in different morphologies and synthesized using different physical and chemical methods, thermal synthesis of hematite nanoparticles from iron-organic solid precursors at comparatively low temperatures has become a significantly convenient synthetic method . This technique has a number of benefits, apart from the synthesis at comparatively low temperatures, such as quick reaction time, control by reaction environment, and use of a variety of iron-organic compounds as precursors …”