Within the past decade, much has been learned about the nanoscale properties of metal/metal oxide nanocomposite materials, but much is still left to be discovered regarding the interrelationship between environmental conditions and nanoscale properties and their resulting effects on the nanocomposite's catalytic and/or sensing properties. Specifically, the unique catalytic properties of Au nanoparticles or their clusters are strongly affected by their size, shape (platelets, rods, etc.) and the metal oxide host material. While supported nanoparticles have been shown to be unstable and generally form spheres at elevated temperatures, embedded nanoparticles have been shown to retain their unique shapes at elevated temperatures. Thus they show great promise for enabling unique catalytic reactions at elevated temperatures. In this project, they will systematically study catalytic reactions at the interface of the metal/metal oxide nanocomposite to determine how the size and shape of the metal nanoparticle as well as the ceramic?s chemistry affect the reaction. The project will provide educational opportunities for graduate, undergraduate and high school students through an outreach program which will enable both research and education focused outcomes.
TECHNICAL DETAILS: They will develop an all-optical localized surface plasmon resonance/micro surface enhanced Raman spectroscopy (LSPR/uSERS) analytical method for the study of gold nanoparticle (AuNP)- metal oxide nanocomposite films with precise grain size and shape control. The unique catalytic properties of Au nanoparticles or their clusters are strongly affected by their size, shape (platelets, rods, etc.) and metal oxide host material. However, supported particles are thermally unstable at elevated temperatures and tend to grow and or become spherical and thus their unique catalytic properties are not amenable for a broad range of thermal environments. Embedded particles have been shown to be more stable and will be deposited using electron beam lithography and aerosol-assisted chemical vapor deposition and these will be studied for their thermal stability as well as for their unique optical and catalytic activity. As catalytic reactions typically involve a number of charge transfer events, plasmonic studies will be used to determine the total charge on the catalytically active nanoparticle in parallel with uSERS for probing both the surface chemistry as well as the metal oxide host. This project will enable the development and study of novel catalytically active materials, new plasmonic sensing array paradigms as well as an educational outreach program for graduate, undergraduate and high school students.
The unique catalytic properties of composites containing Au or Ag nanoparticles are strongly affected by their size, shape and the metal oxide material that serves as its host. This NSF program was focused on studying surface chemical reactions of combustion related gases on these composite materials at high temperatures. The need for these studies is based on the development of both high temperature compatible chemical sensors, which can be used to regulate emissions from combustion sources such as power plants, as well as for the development of new catalyst materials. A key demonstration from this project was the temperature stability (up to 800oC) of Au nanorods embedded in yttria-stabilized zirconia (YSZ). Arrays of Au nanorods embedded in YSZ have since been fabricated and were studied for its unique catalytic and chemical sensing properties. Results from these studies have shown that these nanorod samples are sensitive and selective towards the detection of combustion related gases within an air carrier gas and an operation temperature of 500oC. A significant portion of the work within this program has been the development and application of statistical algorithms for the analysis of this chemical sensing array data. The results of which showed that these materials show promise for the sensitive and selective detection of CO and NO2 gases within an air carrier gas at 500oC. As there isn’t a sensor that currently exists that can detect these types of gases under these conditions, this demonstration is a clear indication of the intellectual merit of the work. This research program has also developed a new type of nanocomposite thin film material. This thin film is comprised a silver nanoparticles (AgNP) whose size distribution is bimodal in character. The two average sizes of these AgNPs are 6nm and 160nm. This is a novel result with respect to both the intellectual merit and the broader impacts of this program. First, the intellectual merit is highlighted through the new methods that were used to create this nanocomposite. These methods were adapted from previous work in the literature, which used uniformly co-deposited aluminum with platinum to prevent the subsequent films from undergoing large crystal grain growth during high temperature thermal annealing processes. The adopted method used in this program utilized the deposition of a silver precursor film deposited in the presence of a concentration gradient of aluminum. After deposition the resulting film was annealed to 900oC in 99.999% pure argon with the balance being oxygen. As the aluminum readily oxidizes to form aluminum oxide it served as a barrier towards the growth of large AgNPs. Thus, silver in close proximity to the substrate surface is surrounded by aluminum oxide and which creates the smaller AgNPs. While silver close to the film surface is not encapsulated by aluminum oxide and thus forms the large AgNPs. The resulting film takes advantage of the high chemical reactivity of the small AgNPs as well as the strong light absorption properties of the large AgNPs. This combination has resulted in a new type of material that presents strong photo-induced chemical reactive properties, which will lead to new catalyst materials for industrial and energy applications thus providing a broad impact to the scientific community. Broader impacts of this program also include educational initiatives. As part of the College of Nanoscale Science and Engineering’s (CNSE) educational outreach Nanocareer program, Prof. Carpenter has given 30 minute "Introductory to Nano" lecture to six separate school districts and a total of 120 students each year of the NSF program, for a total of 360 students. The aim of these nanocareer day presentations is to get middle school to high school aged kids excited about the math, science and engineering fields. Prof. Carpenter also developed a laboratory unit for 20 middle school girls in the summer of 2012. This activity was hosted through Girls Inc., with the students primarily from city school districts in the Albany region. The lab activity focused on the material and chemical properties of liquids and solids. The girls finished the activity with the assembly and testing of a battery operated conductivity sensor for a series of unknown liquids. This lab activity was used again during the summer of 2013 and through these activities a total of 40 inner city middle school students participated in this sensor based lab activity. Over the 3 years of this NSF program a research scientist, four graduate students and a total of ten undergraduates have participated in research and educational activities.
