Production of Fe nanoparticles from γ-Fe2O3 by high-pressure hydrogen reduction.

I Dirba,O Gutfleisch,P Komissinskiy,C A Schwöbel,A Zintler,L Molina-Luna

doi:10.1039/d0na00635a

Abstract

In this work, the reduction of iron oxide γ-Fe2O3 nanoparticles by hydrogen at high pressures is studied. Increasing the hydrogen pressure enables reduction of γ-Fe2O3 to α-Fe at significantly lower temperatures. At low pressures, a temperature of 390 °C is necessary whereas at 530 bar complete reduction can be realized at temperatures as low as 210 °C. This leads to significant improvement in the final particle morphology, maintaining high surface-to-volume ratio of the nanoparticles with an average size of 47 ± 5 nm which is close to that of the precursor γ-Fe2O3. Neck formation, coalescence and growth during reduction can be significantly suppressed. Investigations of magnetic properties show that saturation magnetization of the reduced α-Fe nanoparticles decreases with particle size from 209 A m2 kg−1 at 390 °C reduction temperature to 204 A m2 kg−1 at 210 °C. Coercivity for the fine iron particles reaches 0.076 T which exceeds the theoretical anisotropy field. This is attributed to nano-scale surface effects.

Highlights

Iron nanoparticles have important applications due to their unique chemical and magnetic properties.[1]
Similar catalytic activity to platinum-based materials for chemical hydrogen storage applications has been reported for amorphous Fe nanoparticles.[3]
Synthesis of nanoparticles with controlled particle size, morphology and surface modi cations can be achieved by solution chemistry techniques.[12,13,14]

Summary

Introduction

Synthesis of nanoparticles with controlled particle size, morphology and surface modi cations can be achieved by solution chemistry techniques.[12,13,14] This approach is well suited for biomedical applications where minimizing reactivity and agglomeration is important. Reduction of iron oxides to a-Fe with hydrogen is typically conducted at temperatures of at least 390 C– 500 C.16–18 This choice of temperature is supported by hygrometry measurements, where the maximum rate of H2O production was from 389 C to 522 C 19,20 depending on the heating rate. In this work, we attempt to achieve complete reduction of Fe2O3 at signi cantly lower temperatures by using high hydrogen pressures. This approach should result in improved morphology of the produced nanoparticles since the detrimental coarsening during the reduction step is suppressed

Experimental

Results and discussion

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Summary