The copper sulfide is a family of inorganic compounds whose general chemical formula is CuxSY. Yes x It's bigger than Y it means that said sulfide is richer in copper than in sulfur; and if on the contrary, x It is smaller than Y, then sulfur is richer in sulfur than copper.
In nature, numerous minerals predominate, representing natural sources of this compound. Almost all of them are richer in copper than in sulfur, and their composition is expressed and simplified by the formula CuxS; here x can even take fractional values, indicative of a non-stoichiometric solid (Cu1.75S, for example).
Although sulfur is yellow in its elemental state, its derived compounds appear dark in color; this is also the case with copper sulphide. However, the mineral covelite (top image), which is composed primarily of CuS, exhibits metallic luster and bluish iridescence..
They can be prepared from different sources of copper and sulfur, using different techniques and varying the synthesis parameters. Thus, you can obtain CuS nanoparticles with interesting morphologies.
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This compound has the appearance of being crystalline, so it can be immediately thought that it is composed of Cu ions+ (monovalent copper), Cutwo+ (divalent copper), Stwo- and, inclusive, Stwo- and Stwotwo- (disulfide anions), which interact through electrostatic forces or ionic bonding.
However, there is a slight covalent character between Cu and S, and therefore the Cu-S bond cannot be ruled out. From this reasoning, the crystalline structure of CuS (and that of all its derived solids) begins to differ from those found or characterized for other ionic or covalent compounds..
In other words, we cannot speak of pure ions, but in the middle of their attractions (cation-anion) there is a slight overlap of their external orbitals (electron sharing).
Having said the above, the crystalline structure of the covelite is shown in the upper image. It consists of hexagonal crystals (defined by the parameters of their unit cells), where the ions unite and orient themselves in different coordinations; these are, with a varied number of close neighbors.
In the image, copper ions are represented by pink spheres, while sulfur ions are represented by yellow spheres..
Focusing the attention first on the pink spheres, it will be noted that some are surrounded by three yellow spheres (trigonal plane coordination), and others by four (tetrahedral coordination)..
The first type of copper, trigonal, can be identified in the planes perpendicular to the hexagonal faces facing the reader, in which are in turn the second type of carbon, tetrahedral.
Turning now to the yellow spheres, some have five pink spheres as neighbors (trigonal bipyramid coordination), and others three and a yellow sphere (again, tetrahedral coordination); In the latter, the disulfide anion is seen, which can be seen below and within the same structure of the covelite:
There are then Cu ionstwo+, Cu+, Stwo- and Stwotwo-. However, studies carried out with X-ray photoelectron spectroscopy (XPS), indicate that all copper is as Cu cations+; and therefore, the initial formula CuS, is expressed "better" as (Cu+)3(S2−) (Stwo)-.
Note that the Cu: S ratio for the above formula continues to be 1, and furthermore the charges cancel.
A copper sulfide can adopt orthorhombic crystals, as in the polymorph, γ-CutwoS, from chalcocite; cubic, as in another polymorph of chalcocite, α-CutwoS; tetragonal, in the mineral anilite, Cu1.75S; monoclinics, in the djurleita, Cu1.96Yes, among others.
For each defined crystal there is a mineral, and in turn, each mineral has its own characteristics and properties.
The properties of copper sulfide are subject to the Cu: S ratio of its solids. For example, those that have S anionstwotwo- have hexagonal structures, and can be either semiconductors or metallic conductors.
If on the other hand the sulfur content consists merely of anions Stwo-, sulfides behave as semiconductors, and also exhibit ionic conductivities at high temperatures. This is because its ions begin to vibrate and move within the crystals, thus transporting electrical charges..
Optically, although it also depends on their copper and sulfur composition, sulfides may or may not absorb radiation in the infrared region of the electromagnetic spectrum. These optical and electrical properties make it potential materials to be implemented in different ranges of devices..
Another variable to consider, in addition to the Cu: S ratio, is the size of the crystals. It is not only that there are more “sulfur” or “coppery” copper sulphides, but the dimensions of their crystals impart an imprecise effect on their properties; Thus, scientists are eager to study and seek applications for Cu nanoparticles.xSY.
Each mineral or copper sulfide has unique properties. However, of all of them, the covelite is the most interesting from a structural and aesthetic point of view (due to its iridescence and blue tones). Therefore, some of its properties are mentioned below.
95.611 g / mol.
4.76 g / mL.
500 ° C; but it breaks down.
3.3 10-5 g / 100 mL at 18ºC.
Not only does the size of the particles vary until they reach nanometric dimensions, but their morphologies can also vary greatly. Thus, copper sulfide can form nanospheres, rods, plates, thin films, cages, cables or tubes..
These particles and their attractive morphologies acquire individual applications in different fields of medicine..
For example, nanocages or empty spheres can serve as drug carriers within the body. Nanospheres have been used, supported by carbon glass electrodes and carbon nanotubes, to function as glucose detectors; as well as its aggregates are sensitive to the detection of biomolecules such as DNA.
CuS nanotubes outperform nanospheres in detecting glucose. In addition to these biomolecules, immunosensors have been designed from thin CuS films and certain supports for the detection of pathogens..
Nanocrystals and amorphous aggregates of CuS can even cause apoptosis of cancer cells, without causing damage to healthy cells.
In the previous subsection it was said that its nanoparticles have been part of biosensors and electrodes. In addition to such uses, scientists and technicians have also taken advantage of its properties to design solar cells, capacitors, lithium batteries, and catalysts for very specific organic reactions; Indispensable elements in nanoscience.
It is also worth mentioning that when supported on activated carbon, the NpCuS-CA set (CA: Activated Carbon, and Np: Nanoparticles) proved to serve as a remover of dyes harmful to humans and, therefore, works as a purifier of sources of water absorbing unwanted molecules.
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