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. (19659003) After the isolation of graphene in 2004, a race was launched to synthesize new two-dimensional materials – as they are called materials with a thickness of an atom up to a few nanometers billionth of a meter ).
An international group, with the participation of researchers related to the University of Campinas State ( UNICAMP ), has achieved a high degree of success in the field of nanotechnology and nanotechnology.
Scientists were able to extract a material called hematene, which has three atoms of thickness and unusual photocatalytic properties, from an ordinary iron ore such as those mined by many miners in Brazil [19659004] The new material was described in an article published in Nature Nanotechnology . The research was conducted at the Center for Engineering and Computational Sciences (CECC) – one of the Centers for Research, Innovation and Dissemination (CEPID) supported by FAPESP – and in a research internship abroad, also with a FAPESP purse
"The material we synthesize can act as a photocatalyst – to divide the water into hydrogen and oxygen – and allow the production of energy from the hydrogen, for example, in addition to having several other applications, "Douglas said. The new material was extracted from hematite – mineral which is the main source of iron and the most common, cheap and important metals, used in many
Unlike carbon and its two-dimensional form (graphene) , hematite is a non-van der Waals material, as they are called those which are held together by three-dimensional link networks instead of non-covalent atomic interactions – in which there is no no sharing of one or more electron pairs between atoms involved in binding – and, comparatively, weaker than van der Waals materials
Being a natural mineral, being a non-organic material van der Waals and having large highly oriented crystals, the researchers hypothesized that hematite could act as an excellent precursor to obtain a new two-dimensional non-van der Waals material.
"Most of the two-dimensional materials synthesized to date have been derived from van der Waals solids samples, and two-dimensional non-van der Waals materials with highly ordered and coarse atomic layers are still rare" explains Galvão.
To obtain hematite a material with such characteristics – the hematene – the researchers used this technique. liquid exfoliation in an organic solvent, N-dimethylformamide (DMF). Through transmission electron microscopy, they were able to confirm the exfoliation and haematin formation in the loose leaves of three iron and oxygen atoms (monolayer) and randomly stacked leaves (bilayer ).
With tests and mathematical calculations the magnetic properties of hematene have been studied. By means of these calculations and tests, the researchers discovered that the magnetic properties of hematoma differ from those of hematite.
– – (Unicamp / Agência Fapesp / Divulgação)
While hematite is typically antiferromagnetic – its magnetic dipoles are arranged antiparallel – the tests have shown that the hematene is ferromagnetic, like a common magnet.
"In ferromagnets, the magnetic moments of the atoms s point in the same direction.
Photocatalyst effective
The researchers also evaluated the photocatalytic properties – to increase the speed of a photoreaction by the action of a hematene catalyst.The results of the badyzes also demonstrated that the photocatalysis of hematene is more effective than that of hematite, of which it was already known that. it had photocatalytic properties but not enough to be useful.
For a material to be an effective photocatalyst, one must: absorb the visible part of the sunlight, for example, generate electrical charges and transport them on the surface of the material in order to effect the desired reaction.
Hematite, for example, absorbs sunlight from the ultraviolet to yellow-orange region, but the charges produced are As a result, they are extinguished before reaching the surface.
The photocatalysis of hematene is more efficient, since photons generate negative and positive charges in a few atoms of the surface, compared the researchers. And by pairing new materials with matrices of titanium dioxide nanotubes – which provide an easy path for electrons to leave the hematene – they found that they could allow more visible light to emerge. to be absorbed.
"Hematene can be an effective photocatalyst, especially for splitting water into hydrogen and oxygen, but can also serve as an ultra-thin magnetic material for spintronic-based devices [ou magnetoeletrônica]" said Galvão.
The group studied other non van der Waals potential materials to give birth to other two-dimensional materials with exotic properties. "There are a number of other iron oxides and their derivatives that are likely to give rise to new two-dimensional materials," said Galvão
The article Exfoliation of a non vanous material der Waals from iron ore hematite (doi: 10.1038 / s41565-018-0134-y), by Pulickel M. Ajayan et al., can be read in the journal Nature Nanotechnology at www.nature.com/articles/s41565 -018-0134-y
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