Zinc phosphide

Zinc phosphide (Zn3P2) is an inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black. It is used as a rodenticide.[2] Zn3P2 is a semiconductor with a direct band gap of 1.5 eV[3] and may have applications in photovoltaic cells.[4] A second zinc phosphide is known, with the stoichiometry ZnP2.

Zinc phosphide[1]
Names
Other names
trizinc diphosphide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.859
EC Number
  • 234-867-3
UNII
Properties
Zn3P2
Molar mass 258.12 g/mol
Appearance gray tetragonal crystals
Density 4.55 g/cm3
Melting point 1,160 °C (2,120 °F; 1,430 K)
reacts
Solubility insoluble in ethanol, soluble in benzene, reacts with acids
Structure
Tetragonal, tP40
P42/nmc, No. 137
Hazards
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H260, H300
P223, P231+232, P264, P270, P280, P301+310, P321, P330, P335+334, P370+378, P402+404, P405, P501
NFPA 704 (fire diamond)
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 4: Very short exposure could cause death or major residual injury. E.g. VX gasReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
3
4
1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Synthesis and reactions

Zinc phosphide can be prepared by the reaction of zinc with phosphorus; however, for critical applications, additional processing to remove arsenic compounds may be needed.[5]

3 Zn + 2 P → Zn3P2

Another method of preparation include reacting tri-n-octylphosphine with dimethylzinc.[6]

Zinc phosphide reacts with water to produce phosphine (PH3) and zinc hydroxide (Zn(OH)2):

Zn3P2 + 6 H2O → 2 PH3 + 3 Zn(OH)2

Structure

Zn3P2 has a room-temperature tetragonal form that converts to a cubic form at around 845 °C.[7] In the room-temperature form there are discrete P atoms, zinc atoms are tetrahedrally coordinated and phosphorus six coordinate, with zinc atoms at 6 of the vertices of a distorted cube.[8] ZnP2 also has two forms, a lower-temperature red tetragonal form and a black monoclinic form.[7] In both of these there are chains of P atoms, helical in the tetragonal, semi-spiral in the monoclinic.[9]

Thin film photovoltaic applications

Zinc phosphide is an ideal candidate for thin film photovoltaic applications, for it has strong optical absorption and an almost ideal band gap (1.5eV). In addition to this, both zinc and phosphorus are found abundantly in the earth’s crust, meaning that material extraction cost is low compared with that of other thin film photovoltaics. Both zinc and phosphorus are also nontoxic, which is not the case for other common commercial thin film photovoltaics, like cadmium telluride.[10]

Researchers at the University of Alberta were the first to successfully synthesize colloidal zinc phosphide. Before this, researchers were able to create efficient solar cells from bulk zinc phosphide, but their fabrication required temperatures greater than 850°C or complicated vacuum deposition methods. By contrast, colloidal zinc phosphide nanoparticles, contained in a zinc phosphide “ink”, allows for inexpensive, easy large-scale production, by means of slot-die coating or spray coating.[11]

The testing and development of these zinc phosphide thin films is still in its early stages, but early results have been positive. Prototype heterojunction devices fabricated from zinc phosphide nanoparticle ink exhibited a rectification ratio of 600 and photosensitivity with an on/off ratio near 100. These are both acceptable suitability benchmarks for solar cells. Development still needs to be made on optimizing the nanoparticle ink formation and device architecture before commercialization is possible, but commercial spray-on zinc phosphide solar cells may be possible within ten years.[12]

Rodenticide

Metal phosphides have been used as rodenticides. A mixture of food and zinc phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate toxic phosphine gas. This method of vermin control has possible use in places where rodents are immune to other common poisons. Other pesticides similar to zinc phosphide are aluminium phosphide and calcium phosphide.

Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. Such baits have a strong, pungent garlic-like odor characteristic of phosphine liberated by hydrolysis. The odor attracts rodents, but has a repulsive effect on other animals; However, birds, notably wild turkeys, are not sensitive to the smell. The baits have to contain sufficient amount of zinc phosphide in sufficiently attractive food in order to kill rodents in a single serving; a sublethal dose may cause aversion towards zinc phosphide baits encountered by surviving rodents in the future.

Rodenticide-grade zinc phosphide usually comes as a black powder containing 75% of zinc phosphide and 25% of antimony potassium tartrate, an emetic to cause vomiting if the material is accidentally ingested by humans or domestic animals. However, it is still effective against rats, mice, guinea pigs and rabbits, none of which have a vomiting reflex.[13]

Zinc phosphide use in New Zealand

The New Zealand Environmental Protection Authority has approved the import and manufacture of Microencapsulated Zinc Phosphide (MZP Paste) for the ground control of possums. The application was made by Pest Tech Limited, with support from Connovation Ltd, Lincoln University and the Animal Health Board. It will be used as an additional vertebrate poison in certain situations. Unlike 1080 poison, it cannot be used for aerial application.[14]

Safety

Zinc phosphide is highly toxic. In Indian certification markings, it is marked as 'Highly Dangerous', which means that 1–50 mg of the substance ingested orally can be lethal.[15]

References
  1. Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 4–100. ISBN 0-8493-0594-2.
  2. Bettermann, G.; Krause, W.; Riess, G.; Hofmann, T. (2002). "Phosphorus Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_527. ISBN 3527306730.
  3. Kimball, Gregory M.; Müller, Astrid M.; Lewis, Nathan S.; Atwater, Harry A. (2009). "Photoluminescence-based measurements of the energy gap and diffusion length of Zn[sub 3]P[sub 2]" (PDF). Applied Physics Letters. 95 (11): 112103. doi:10.1063/1.3225151. ISSN 0003-6951.
  4. Specialist Periodical Reports, Photochemistry, 1981, Royal Society of Chemistry, ISBN 9780851860954
  5. F. Wagenknecht and R. Juza "Zinc Phosphides" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1080-1.
  6. Luber, Erik J.; Mobarok, Md Hosnay; Buriak, Jillian M. (2013). "Solution-Processed Zinc Phosphide (α-Zn3P2) Colloidal Semiconducting Nanocrystals for Thin Film Photovoltaic Applications". ACS Nano. 7 (9): 8136–8146. doi:10.1021/nn4034234. ISSN 1936-0851.
  7. Evgeniĭ I︠U︡rʹevich Tonkov, 1992, High Pressure Phase Transformations: A Handbook, Vol 2, Gordon and Breach Science Publishers, ISBN 9782881247590
  8. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  9. Hans Georg von Schnering and Wolfgang Hönle, 1994, Phosphides: Solid State Chemistry, Encyclopedia of Inorganic chemistry, Ed. R Bruce King, John Wiley and Sons, ISBN 0-471-93620-0
  10. Luber, Erik J. (2013). "Solution-Processed Zinc Phosphide (α-Zn 3 P 2 ) Colloidal Semiconducting Nanocrystals for Thin Film Photovoltaic Applications". ACS Nano. 7 (9): 8136–8146. doi:10.1021/nn4034234.
  11. http://nanotechweb.org/cws/article/tech/54627
  12. http://www.solarnovus.com/zinc-phosphide-nonocrystals-for-spray-on-solar-thin-films_N7005.html
  13. "Why rats can't vomit". Ratbehavior.org. Retrieved 2013-08-17.
  14. Environment Risk Management Authority New Zealand. "Zinc phosphide pest poison approved with controls". Retrieved 2011-08-14.
  15. Toxicity label
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