- Gold nanostars could help increase solar energy use and combat climate change.
- When coated with a semiconductor, they produce hydrogen from water 4 times more efficiently than previous demonstrations.
Colloidal gold nanoparticles have been used for decades due to their vibrant color producing capabilities after being introduced to visible light. These unique optoelectronic characteristics are now being studied and utilized in other applications as well, such as sensory probes, therapeutic agents, and organic photovoltaics.
Since optical and electronic properties of gold can be easily changed by altering its shape, size, state and surface chemistry, it opens a door to wider utilization of advanced materials.
Recently, researchers at Rutgers University found that star-shaped gold nanoparticle could help increase solar energy use and combat climate change. When coated with a semiconductor, gold nanostars can generate hydrogen from water 4 times more efficiently compared to other techniques.
How Did They Do This?
This study focuses on photocatalysis, i.e. harnessing sunlight to make cheaper and faster reactions. Titanium dioxide exposed to ultraviolet (UV) light can be utilized as a catalyst, but UV light isn’t much efficient.
Rather than using UV light, researchers leveraged the energy of infrared and visible light to excite gold nanoparticle’s electrons. These electrons can be transmitted more efficiently to the semiconductor that catalyzes the chemical reaction.
In order to coat these gold nanoparticles with crystalline titanium, the researchers used low-temperature synthesis. They coated gold nanostars with titanium dioxide and exposed it to infrared, visible and UV light.
Nanostars are the most temperature-sensitive gold nanoparticles, and also the most promising particles for generating hot electrons. They are synthesized in the absence of surfactant, enabling titanium oxide shell to be grown directly onto the surface of the gold. One can configure their morphology to change dimensions and spike numbers.
These nanostars can produce intense localized electromagnetic fields around their spikes, which causes a concentration of hot electrons right at the interface between titanium oxide and metal.
What are hot electrons, you asked? Well, they are electrons that absorb enough energy from the excited plasmons to reach above Fermi level from gold valance band to the titanium oxide conduction band across the interfacial Schottky barrier (a potential barrier for electrons formed at the junction of a metal and a semiconductor).
After investigating how electrons transfer from gold to the semiconductor, they concluded that these electrons produce hydrogen from water 4 times more efficiently than previous demonstrations. Hydrogen can be stored and used as fuel to produce electricity or power vehicles when no sunlight is available.
The technique can be further enhanced to increase the ways we leverage sunlight. Researchers believe that this type of materials can have a wide range of applications, for instance, chemical or solar industries or it could convert carbon dioxide into something that we can utilize.