Ligand Exchange for Potential Pb-Doping of ZnS Nanocrystals

Presenter Hometown

Williamsburg, KY

Major

BS Chemistry

Department

Chemistry

Degree

Undergraduate

Mentor

Judith L. Jenkins

Mentor Department

Chemistry

Abstract

The global population is expected to increase to eight billion by the year 2025 as reported by the United Nations Population Fund. The Population Reference Bureau has estimated the current world population is 7.4 billion, while the Central Intelligence Agency released information stating energy usage per capita is approximately 2,674 kWh. From these studies it can be deduced that the world will need 1.60x1012 kWh additionally to compensate for this population increase. With this ever-increasing population growth comes a need to provide enough energy in a safe and efficient manner; the overarching idea is to provide a renewable and environmentally safe method of energy production. Solar energy production is a way of solving the necessity for energy, while also following the guidelines listed above. One particular technique is the usage of photocatalysts for water-splitting, a process that yields hydrogen gas to produce a storable and environmentally friendly fuel source. An ideal photocatalyst needs to be able to absorb energy from the sunlight in certain wavelengths for electron excitation, must be a semiconductor, and is preferably composed of relatively cheap and abundant materials. We are developing lead (Pb)-doped zinc sulfide (ZnS) nanocrystals, which are capable of absorbing energy from the sun for photocatalytic water splitting. However, controlled doping of ZnS with Pb is difficult due to the relative size of lead (Radius= 202 pm) compared to zinc (Radius= 139 pm). This size difference makes it difficult to insert a lead atom in place of a zinc atom in fear of destabilizing the structure of the nanocrystal. Our research is currently developing a method for Pb-doping, starting with ligand exchange. We hypothesize that, under the proper conditions, our procedure will exchange the native oleylamine ligands on the surface of our ZnS nanocrystals with glucosamine ligands. Glucosamine, in polymer form, has been shown to facilitate the transfer of lead out of aqueous solutions into ZnS nanocrystals. We suggest the glucosamine monomer may similarly facilitate lead doping of ZnS. This work describes ligand exchange efforts designed to replace the native oleylamine ligands with glucosamine ligands. Oftentimes ligand exchange can prove to be difficult because of the binding affinity of the original ligand, if our native ligand is strongly bound to our nanocrystal it becomes a challenge to remove it while also maintaining the structure of the nanocrystal. Both ligands being used can also be soluble in organic or aqueous solutions, which can make it tough to ensure the new ligand is able to reach the nanocrystal for proper displacement. If successful, these nanocrystals can be used as additional approach of attempting lead-doping, which, in turn, can provide further pathways in photocatalyst development and energy production.

Presentation format

Poster

Poster Number

049

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Ligand Exchange for Potential Pb-Doping of ZnS Nanocrystals

The global population is expected to increase to eight billion by the year 2025 as reported by the United Nations Population Fund. The Population Reference Bureau has estimated the current world population is 7.4 billion, while the Central Intelligence Agency released information stating energy usage per capita is approximately 2,674 kWh. From these studies it can be deduced that the world will need 1.60x1012 kWh additionally to compensate for this population increase. With this ever-increasing population growth comes a need to provide enough energy in a safe and efficient manner; the overarching idea is to provide a renewable and environmentally safe method of energy production. Solar energy production is a way of solving the necessity for energy, while also following the guidelines listed above. One particular technique is the usage of photocatalysts for water-splitting, a process that yields hydrogen gas to produce a storable and environmentally friendly fuel source. An ideal photocatalyst needs to be able to absorb energy from the sunlight in certain wavelengths for electron excitation, must be a semiconductor, and is preferably composed of relatively cheap and abundant materials. We are developing lead (Pb)-doped zinc sulfide (ZnS) nanocrystals, which are capable of absorbing energy from the sun for photocatalytic water splitting. However, controlled doping of ZnS with Pb is difficult due to the relative size of lead (Radius= 202 pm) compared to zinc (Radius= 139 pm). This size difference makes it difficult to insert a lead atom in place of a zinc atom in fear of destabilizing the structure of the nanocrystal. Our research is currently developing a method for Pb-doping, starting with ligand exchange. We hypothesize that, under the proper conditions, our procedure will exchange the native oleylamine ligands on the surface of our ZnS nanocrystals with glucosamine ligands. Glucosamine, in polymer form, has been shown to facilitate the transfer of lead out of aqueous solutions into ZnS nanocrystals. We suggest the glucosamine monomer may similarly facilitate lead doping of ZnS. This work describes ligand exchange efforts designed to replace the native oleylamine ligands with glucosamine ligands. Oftentimes ligand exchange can prove to be difficult because of the binding affinity of the original ligand, if our native ligand is strongly bound to our nanocrystal it becomes a challenge to remove it while also maintaining the structure of the nanocrystal. Both ligands being used can also be soluble in organic or aqueous solutions, which can make it tough to ensure the new ligand is able to reach the nanocrystal for proper displacement. If successful, these nanocrystals can be used as additional approach of attempting lead-doping, which, in turn, can provide further pathways in photocatalyst development and energy production.