<img itemprop = "contentUrl" src = "http://www.tnh1.com.br/typo3temp/_processed_/csm_size_960_16_9_size_590_energiasolar_6_43d9a08353.jpg" alt = "(Credit: Matt Cardy / Getty Images / Getty Images) being able to synthesize new two-dimensional materials – as they are called materials with the thickness of an atom up to a few nanometers (from the billionth part of the meter).
An international group, with the participation of researchers related to the State University of Campinas (Unicamp), was able to give birth to a new material
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 explored by many mining companies in Brazil.Described in an article published in the journal Nature Nanotechnology. at 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 water into hydrogen and oxygen – and allow the production of electrical energy from hydrogen, for example, in more to have several other applications, "says Douglas Soares Galvão, researcher at CCCB
The new material was extracted from the hematite – mineral that is the main source of iron and the most common, inexpensive and important metals, used in several products, mainly during processing
Unlike carbon and its two-dimensional form (graphene), hematite is a non van der Waals material, as they are called who are held together by an alloy. three-dimensional rather than non-covalent atomic interactions – in which there is no sharing of one or more electron pairs between the atoms involved in the bond – and, comparatively, weaker than the van der Waals materials
. a natural mineral, a non van der Waals material and having large highly oriented crystals, the researchers hypothesized that hematite could act as an excellent precursor for obtaining a new two-dimensional non van der Waals material [19659004] "Most of the two-dimensional materials synthesized to date have been derived from van der Waals solids samples 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. Through 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 – tests have shown that the hematene is ferromagnetic, like a common magnet.
"In ferromagnets, the magnetic moments of the atoms point in the same direction.In the antiferromagnets, the moments in the adjacent atoms alternate," explains Galvão
Photocatalyst effective
The researchers also evaluated the photocatalytic properties – to increase the rate of a photoreaction by the action of a hematene.The results of the badyzes also demonstrated that the photocatalysis of hematene is more effective than that of the Hematite, which was already known to have photocatalytic properties but not enough to be useful.
For a material to be an effective photocatalyst, it is necessary to: absorb the visible part of the light from the sun, for example, generate electrical charges and transport them to the surface of the material in order to perform the desired reaction.
Hematite, for example, absorbs light the sun from the ultraviolet to yellow-orange region, but the charges produced are of very short duration. 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, particularly 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-and.
Source: Examination
