Multi-functional biomimetic graphene induced transformation of Fe3O4 to ε-Fe2O3 at room temperature. Issue 109 (21st October 2015)

• Record Type: Journal Article
• Authors: Bhattacharya, Soumya; Roychowdhury, Anirban; Das, Dipankar; Nayar, Suprabha
• Is Part Of: RSC advances. Volume 5:Issue 109(2015)
• Page Start: 89488
• Page End: 89497
• Publication Date: 2015-10-21
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c5ra17247k
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : A schematic showing the formation of nanosized ε-Fe2 O3 in protein–polymer functionalized graphene; the templated IONPs literally coat the graphene nanoflakes. G–IONP colloidal fluid, TEM and MFM micrographs provide visual evidence of the same. Abstract : Epsilon-iron oxide (ε-Fe2 O3 ) has been synthesized in large yields (≈73.7%) in a colloidal form at ambient conditions. Being embedded in biomimetic graphene, the synthesized thermodynamically unstable monoclinic phase is prevented from transforming to other phases. We have used the same protein–polymer mixture both for exfoliating natural graphite and as templating agents for iron oxide nanoparticles. X-ray diffraction of the composites confirms the formation of the ε-Fe2 O3 phase with minor quantities (≈26.3%) of cubic magnetite (Fe3 O4 ). The particle size and distribution was studied using high resolution transmission electron microscopy which clearly shows self-assembled dense nanoparticles on graphene sheets. This exercises strain on graphene; evident from the highly broadened D and G bands of Raman measurements and the blue shifting of the G band. X-ray photoelectron spectra shows signatures of iron oxide, graphene and protein in the sample; deconvoluted C1s, O1s and N1s core level peaks confirm both the attachment of the nanoparticles with the substrate and Fe2p core level peaks reveal the high spin oxidation state of Fe 3+ ions. Magnetic measurements confirm the superparamagnetic nature of the composites; the lack of coercivity unexpected of this polymorph may be explained by the low magnetocrystalline anisotropy of the randomly oriented graphene sheets. We suspect that graphene attracts the maximum ferric (Fe 3+ ) ions of the mixed ferrous/ferric ions in the system resulting in ferrous (Fe 2+ ) cation substitution which also results in the reduction of coercivity. Exchange bias was also observed at low temperature in this antiferro–ferrimagnetic hybrid film.