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Exfoliation of a non-van der Waals material from iron ore hematite

ABSTRACT

With the advent of graphene, the most studied of all two-dimensional materials, many inorganic analogues have been synthesized and are being exploited for novel applications. Several approaches have been used to obtain large-grain, high-quality materials. Naturally occurring ores, for example, are the best precursors for obtaining highly ordered and large-grain atomic layers by exfoliation. Here, we demonstrate a new two-dimensional material ‘hematene’ obtained from natural iron ore hematite (α-Fe2O3), which is isolated by means of liquid exfoliation. The two-dimensional morphology of hematene is confirmed by transmission electron microscopy. Magnetic measurements together with density functional theory calculations confirm the ferromagnetic order in hematene while its parent form exhibits antiferromagnetic order. When loaded on titania nanotube arrays, hematene exhibits enhanced visible light photocatalytic activity. Our study indicates that photogenerated electrons can be transferred from hematene to titania despite a band alignment unfavourable for charge transfer.

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Acknowledgements

A.P.B. acknowledges University Grants Commission, Government of India for Basic Scientific Research (BSR) Fellowship (Grant No. No.F.25-1/2013-14 (BSR)/5-22/2007(BSR) dated 30/05/2014). A.P.B., S.R., C.S.T, A.A., V.K. and P.M.A. acknowledge the US Army Research Office MURI grant W911NF-11-1-0362 for financial assistance. A.P.B., P.M.A. and R.V. acknowledge support from the Airforce Office of Scientific Research (AFOSR) through Grant No. FA9550-14-1-0268. C.F.W. thanks the São Paulo Research Foundation (FAPESP) Grant No. 2016/12340-9 for financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID Grant No. 2013/08293-7 is acknowledged. L.D and C.-W.C. thank the US Air Force Office of Scientific Research Grant FA9550-15-1-0236, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston for financial support. O.K.V. thanks Shell International Exploration and Production Inc. Game Changer and New Energies Research and Technology group for financial support. A.M.R. acknowledges India based neutrino observatory (INO) for the travel grant and University Grants Commission (UGC), India for awarding UGC-BSR Faculty Fellowship.

Author information

A.P.B., S.R., C.S.T., A.A., V.K., A.R.H., A.M.R., R.V. and P.M.A planned and conducted experiments. C.F.W. and D.S.G. performed the theoretical simulations. S.K.S. and P.A.v.A performed the microscopy experiments. L.D. and C.-W.C performed the magnetic measurements. B.M.R., M.P., R.N. and O.K.V. conducted the photocatalytic experiments and analysis. G.C. collected the natural sample and performed the characterizations on the parent crystal. C.d.l.R. and A.A.M. performed the optical measurements. All the authors contributed to the analysis of data and writing the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to Chandra Sekhar Tiwary or Anantharaman Malie Madom Ramaswamy Iyer or Pulickel M. Ajayan.

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Further reading

Fig. 1: Liquid-phase exfoliation of hematite to hematene.
Fig. 2: Two-dimensional morphology of hematene.
Fig. 3: Characterization of hematene
Fig. 4: Magnetism of hematene.
Fig. 5: Photocatalysis.