Author: Jonathan Batey | Major: Chemistry | Semester: Fall 2024

Measuring copper concentration using an atomic absorption spectrometer.

While pursing my chemistry degree during the fall 2024 semester, I have been collaborating with my mentor, Dr. Jingyi Chen of the Department of Chemistry and Biochemistry, to establish an efficient and effective method for coating gold and copper nanoparticles with mesoporous silica. We are interested in the effect of the silica coating on the nanoparticles’ catalytic ability and stability. Transition metal nanoparticles, like gold and copper, have been of great interest because of their catalytic ability. However, many transition metals are not stable and react readily with air such as copper, which reacts with oxygen in the air leading to oxidation of copper nanoparticles. Despite copper’s instability, copper nanoparticles are of great interest because of copper’s high earthly abundance. Copper, compared to heavier transition metals like gold and platinum, is more abundant and cost-effective. So, a coating that could improve copper’s stability is important for developing cost effective catalysts. Of course, an ideal coating would not only improve the stability of the particles, but also allow them to retain or improve their catalytic properties. This means that the coating needs to allow for surface utilization of the particle. The development of such a coating is what Dr. Chen and I decided would be my research project.

Because of the copper’s tendency to oxidize I first set out to establish a coating method with a more stable nanoparticle, gold nanocages, that I would then apply to copper nanoparticles. To start, I researched previous silica coatings already established in literature and Dr. Chen suggested several research papers to read. After reading many papers, I planned a synthesis that involved three parts: surface functionalization of gold nanocages, coating gold nanocages with silica, and etching the silica coating to make mesoporous channels. After implementing my plan and going through the synthesis Deborah, a senior graduate assistant in the Chen group, took transmission electron microscope (TEM) images of the gold nanocages so I could evaluate my success. Despite my high hopes, very little of the gold nanocages were coated and they did not possess mesoporous channels. Dr. Chen explained that failing was quite common in the development of a new synthesis and although the end goal was not met, failures provide valuable information for future trials. It took many trials and consulting more research papers until I settled on a two-step synthesis involving surface functionalization of the gold nanocages and a one-step silica coating and etching step. After receiving the TEM images from Deborah I was able to see silica coated gold nanocages with mesoporous channels and it was time to apply the coating to copper nanoparticles.

Upon planning for the coating of copper one large problem presented itself, water was used as a catalyst in the previously established method. The use of water in the synthesis would cause the oxidation of the copper nanoparticles, the very thing the coating was aimed at preventing. Upon discussing this problem with Dr. Chen, we decided that I would go ahead with the synthesis using the established method. The solvent used in the coating procedure was not pure water and the particles could be redispersed in ethanol after the synthesis, so we hoped that copper oxide would not have a large presence in the solution. After synthesizing the copper nanoparticles, I applied the silica coating procedure and obtained TEM images from Deborah. The coating was somewhat successful. The particles were indeed coated with mesoporous silica however the particles had agglomerated which could negatively affect their catalytic ability.

To move forward, I have begun to learn a phase transfer procedure. By applying this transfer technique, I can put the copper nanoparticles into an aqueous phase instead of the organic phase that the nanoparticles are synthesized in. By transferring the particles to an aqueous phase, we hope that the agglomeration will decrease in the synthesis of the mesoporous silica coated nanoparticles. After I obtain mesoporous silica coated copper nanoparticles, I will test their catalytic ability using a model reaction, a nitrophenol reduction, to ensure that the coating did not have a negative effect on the catalytic ability of the nanoparticles.