- Structure of copper sulfide
- Links
- Coordinations in la covelita
- Alternative formula
- Other crystals
- Properties
- General
- Covelite
- Molar mass
- Density
- Melting point
- Water solubility
- Applications
- Nanoparticles in medicine
- Nanoscience
- References
The copper sulphide is a family of inorganic compounds whose general formula is Cu chemistry x S and. If x is larger than y it means that said sulfide is richer in copper than in sulfur; and if, on the contrary, x is smaller than y, then the sulfur is richer in sulfur than in copper.
In nature, numerous minerals predominate that represent 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 Cu x S; here x can even take fractional values, indicative of a non-stoichiometric solid (Cu 1.75 S, for example).
A sample of covellite mineral, one of the many natural sources of copper sulfide. Source: James St. John
Although sulfur is yellow in its elemental state, its derived compounds have dark colors; This is also the case with copper sulfide. 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.
Structure of copper sulfide
Links
This compound has the appearance of being crystalline, so it can be immediately thought of as being composed of ions Cu + (monovalent copper), Cu 2+ (divalent copper), S 2- and, inclusive, S 2 - and S 2 2 - (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 crystal 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 rather that in the middle of their attractions (cation-anion) there is a slight overlap of their external orbitals (electron sharing).
Coordinations in la covelita
Crystal structure of covellite. Source: Benjah-bmm27.
Having said the above, the crystal 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 join 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 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 the second type of carbon, tetrahedral, is in turn.
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, we are faced with the disulfide anion, which can be seen below and within the same structure of the covelite:
Tetrahedral coordination of the disulfide anion in covellite. Source: Benjah-bmm27.
Alternative formula
There are then ions Cu 2+, Cu +, S 2- and S 2 2-. 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 (S 2−) (S 2) -.
Note that the Cu: S ratio for the above formula remains 1, and furthermore the charges cancel.
Other crystals
A copper sulfide can adopt orthorhombic crystals, as in the polymorph, γ-Cu 2 S, of chalcocite; cubic, as in another polymorph of chalcocite, α-Cu 2 S; tetragonal, in the mineral anilite, Cu 1.75 S; monoclinics, in djurleite, Cu 1.96 S, among others.
For each defined crystal there is a mineral, and in turn, each mineral has its own characteristics and properties.
Properties
General
The properties of copper sulfide are subject to the Cu: S ratio of its solids. For example, those that present S 2 2- anions have hexagonal structures, and can be either semiconductors or metallic conductors.
If, on the other hand, the sulfur content consists merely of S 2- anions, the sulfides behave as semiconductors, and also present ionic conductivities at high temperatures. This is because its ions begin to vibrate and move within the crystals, thus carrying 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 x S y nanoparticles.
Covelite
Each mineral or copper sulfide has unique properties. However, of all of them, 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.
Molar mass
95.611 g / mol.
Density
4.76 g / mL.
Melting point
500 ° C; but it breaks down.
Water solubility
3.3 · 10 -5 g / 100 mL at 18 ° C.
Applications
Nanoparticles in medicine
Not only does the size of the particles vary until they reach nanometric dimensions, but also their morphologies can fluctuate 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.
Nanoscience
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.
References
- Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
- Wikipedia. (2019). Copper sulfide. Recovered from: en.wikipedia.org
- Ivan Grozdanov and Metodija Najdoski. (nineteen ninety five). Optical and Electrical Properties of Copper Sulfide Films of Variable Composition. Journal of Solid State Chemistry Volume 114, Issue 2, 1 February 1995, Pages 469-475. doi.org/10.1006/jssc.1995.1070
- National Center for Biotechnology Information. (2019). Copper sulfide (CuS). PubChem Database. CID = 14831. Recovered from: pubchem.ncbi.nlm.nih.gov
- Peter A. Ajibade and Nandipha L. Botha. (2017). Synthesis, Optical and Structural Properties
- of Copper Sulfide Nanocrystals from Single Molecule Precursors. Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa. Nanomaterials, 7, 32.
- Collaboration: Authors and editors of the volumes III / 17E-17F-41C (nd). Copper sulfides (Cu2S, Cu (2-x) S) crystal structure, lattice parameters. In: Madelung O., Rössler U., Schulz M. (eds) Non-Tetrahedrally Bonded Elements and Binary Compounds I. Landolt-Börnstein- Group III Condensed Matter (Numerical Data and Functional Relationships in Science and Technology), vol 41C. Springer, Berlin, Heidelberg.
- Momtazan, F., Vafaei, A., Ghaedi, M. et al. Korean J. Chem. Eng. (2018). Application of copper sulfide nanoparticles loaded activated carbon for simultaneous adsorption of ternary dyes: Response surface methodology. 35: 1108. doi.org/10.1007/s11814-018-0012-1
- Goel, S., Chen, F., & Cai, W. (2014). Synthesis and biomedical applications of copper sulfide nanoparticles: from sensors to theranostics. Small (Weinheim an der Bergstrasse, Germany), 10 (4), 631–645. doi: 10.1002 / smll.201301174