ZINC SULFIDE (ZNS): STRUCTURE, PROPERTIES AND USES - CHEMISTRY - 2025

The zinc sulfide is an inorganic compound of the formula Z _n S formed by cations Zn ²⁺ and anions S ^2-. It is found in nature mainly as two minerals: wurtzite and sphalerite (or zinc blende), the latter being its main form.

Sphalerite is naturally black in color due to its impurities. In its pure form it presents white crystals, while wurtzite has grayish-white crystals.

Source: By Killerlimpet, from Wikimedia Commons

Zinc sulfide is insoluble in water. It can cause environmental damage, since it penetrates the ground and contaminates groundwater and its currents.

Zinc sulfide can be produced, among other reactions, by corrosion and by neutralization.

By corrosion:

Zn + H ₂ S => ZnS + H ₂

By neutralization:

H ₂ S + Zn (OH) ₂ => ZnS + 2H ₂ O

Zinc sulfide is a phosphorescent salt, which gives it the capacity for multiple uses and applications. Also, it is a semiconductor and a photocatalyst.

Structure

Zinc sulfide adopts crystalline structures governed by electrostatic attractions between the Zn ²⁺ cation and the S ^2- anion. These are two: sphalerite or zinc blende, and wurzite. In both, the ions minimize repulsions between ions of equal charges.

The zinc blende is the most stable in terrestrial conditions of pressure and temperature; and wurzite, which is less dense, results from crystalline rearrangement due to increased temperature.

The two structures can coexist in the same ZnS solid at the same time although, very slowly, the wurzite will end up dominating.

Zinc blende

Source: By Solid State, from Wikimedia Commons

The upper image shows the cubic unit cell centered on the faces of the zinc blende structure. The yellow spheres correspond to the S ^2- anions, and the gray spheres to the Zn ²⁺ cations, located in the corners and in the centers of the cube faces.

Note the tetrahedral geometries around the ions. The zinc blende can also be represented by these tetrahedra, whose holes inside the crystal have the same geometry (tetrahedral holes).

Likewise, within the unit cells the ZnS proportion is fulfilled; that is, a 1: 1 ratio. Thus, for each Zn ²⁺ cation there is an S ^2- anion. In the image it may seem that gray spheres are abundant, but in reality, since they are in the corners and center of the cube's faces, they are shared by other cells.

For example, if you take the four yellow spheres that are inside the box, the “pieces” of all the gray spheres around it should equal (and do) four. Thus, in the cubic unit cell there are four Zn ²⁺ and four S ^2-, the stoichiometric ratio ZnS being fulfilled.

It is also important to emphasize that there are tetrahedral holes in front of and behind the yellow spheres (the space that separates them from one another).

Wurzita

Source: By Solid State, from Wikimedia Commons

Unlike the structure of zinc blende, wurzite adopts a hexagonal crystal system (top image). This is less compact, so the solid has a lower density. The ions in wurzite also have tetrahedral surroundings and a 1: 1 ratio that agrees with the formula ZnS.

Properties

Color

It can be presented in three ways:

-Wurtzite, with white and hexagonal crystals.

-The sphalerite, with greyish-white crystals and cubic crystals.

-As a white to grayish-white or yellowish powder, and cubic yellowish crystals.

Melting point

1700º C.

Water solubility

Practically insoluble (0.00069 g / 100 ml at 18 ° C).

Solubility

Insoluble in alkalis, soluble in dilute mineral acids.

Density

Sphalerite 4.04 g / cm ³ and wurtzite 4.09 g / cm ³.

Hardness

It has a hardness of 3 to 4 on the Mohs scale.

Stability

When it contains water, it slowly oxidizes to sulfate. In a dry environment it is stable.

Decomposition

When heated to high temperatures it emits toxic vapors of zinc and sulfur oxides.

Nomenclature

The electron configuration of Zn is 3d ¹⁰ 4s ². By losing the two electrons of the 4s orbital it remains as the Zn ²⁺ cation with its d orbitals filled. Therefore, since Zn ²⁺ is electronically much more stable than Zn ⁺, it only has a valence of +2.

Hence, for the stock nomenclature, adding its valence enclosed in parentheses and with Roman numerals is omitted: zinc (II) sulfide.

Systematic and traditional nomenclatures

But there are other ways to call the ZnS besides the one already mentioned. In systematics, the number of atoms of each element is specified with the Greek numerators; with the only exception of the element to the right when it is only one. Thus, the ZnS is named as: zinc mono sulfide (and not monozinc monosulfide).

With respect to the traditional nomenclature, zinc having a single valence of +2 is added by adding the suffix –ico. Consequently, its traditional name is: zinc sulphide ico.

Applications

As pigments or coatings

-Sachtolith is a white pigment made with zinc sulfide. It is used in caulks, mastics, sealants, undercoats, latex paints, and signage.

Its use in combination with ultraviolet light absorbing pigments, such as micro titanium or transparent iron oxide pigments, is necessary in weather resistant pigments.

-When ZnS is applied to latex or textured paints it has a prolonged microbicidal action.

-Due to its great hardness and resistance to breakage, erosion, rain or dust, it makes it suitable for exterior infrared windows or in aircraft frames.

-ZnS is used in the coating of rotors used in the transport of compounds, to reduce wear. It is also used in the production of printing inks, insulating compounds, thermoplastic pigmentation, flame resistant plastics and electroluminescent lamps.

-Zinc sulfide can be transparent and can be used as a window for visible optics and infrared optics. It is used in night vision devices, television screens, radar screens, and fluorescent coatings.

-The doping of ZnS with Cu is used in the production of electroluminescence panels. Also, it is used in rocket propulsion and gravimetry.

For its phosphorescence

-Its phosphorescence is used to tint the clock hands and thus display the time in the dark; also in paint for toys, in emergency signs and traffic warnings.

Phosphorescence allows a use of zinc sulfide in cathode ray tubes and X-ray screens to glow in dark spots. The color of the phosphorescence depends on the activator used.

Semiconductor, Photocatalyst and Catalyst

-Sphalerite and wurtzite are broadband slit semiconductors. Sphalerite has a band gap of 3.54 eV, whereas wurtzite has a band gap of 3.91 eV.

-ZnS is used in the preparation of a photocatalyst composed of CdS - ZnS / zirconium - titanium phosphate used for the production of hydrogen under visible light.

-It intervenes as a catalyst for the degradation of organic pollutants. It is used in the preparation of a color synchronizer in LED lamps.

-Its nanocrystals are used for the ultrasensitive detection of proteins. For example, by emitting light from quantum dots of ZnS. It is used in the preparation of a combined photocatalyst (CdS / ZnS) -TiO2 for electrical production via photoelectrocatalysis.

References

1. PubChem. (2018). Zinc sulfide. Taken from: pubchem.ncbi.nlm.nih.gov
2. QuimiNet. (2015, January 16). White Pigment based on Zinc Sulfide. Recovered from: quiminet.com
3. Wikipedia. (2018). Zinc sulfide. Taken from: en.wikipedia.org
4. II-VI UK. (2015). Zinc Sulfide (ZnS). Taken from: ii-vi.es
5. Rob Toreki. (March 30, 2015). The Zincblende (ZnS) Structure. Taken from: ilpi.com
6. Chemistry LibreTexts. (January 22, 2017). Structure-Zinc Blende (ZnS). Taken from: chem.libretexts.org
7. Reade. (2018). Zinc Sulfide / Zinc Sulphide (ZnS). Taken from: reade.com