Chemistry and Biomedical Sciences
Judith L. Jenkins
As humanity’s energy needs increase, there is a corresponding need for energy sources that are clean, abundant, and sustainable. Solar energy is particularly promising, because the amount of energy in sunlight far exceeds our projected energy needs. Despite the abundance of energy in sunlight, widespread adoption of solar electricity is limited by the varied availability of sunlight. Current research efforts focus on energy storage technologies including solar fuel generation, where the energy is sunlight is used to drive chemical reactions forming small molecules such as hydrogen gas, H2 (g). Converting the energy in sunlight to chemical energy in the form of H2 (g) requires a photocatalyst with conduction band energy sufficiently high to reduce hydrogen ions that also absorbs a significant portion of the solar spectrum. Bulk copper-doped zinc sulfide (Cu-doped ZnS) meets these criteria, but controlled synthesis of this material has not been demonstrated, limiting the material’s impact on energy conversion and storage. This work describes the systematic variation of ZnS nanocrystal (NC) size, shape, and surface chemistry to afford controllable copper doping via cation exchange (CE). During CE, the host NC is exposed to a solution containing the dopant cation. Though CE occurs through multiple simultaneous processes, cation adsorption to the host NC surface is critically important. We hypothesized that cation adsorption will vary with the shape, size, and passivating ligand on the ZnS NC surface, as these factors all influence the relative availability of copper adsorption sites. Results presented here describe any correlations between the ZnS NC surface and CE measured spectroscopically and with electron microscopy. If realized, the ability to controllably copper dope ZnS NCs will enable more detailed studies relating dopant density to photocatalytic activity for H2 (g).