Design of nanomaterials for a reduced toxicological impact and development of nanomaterials for utilization of CO2 by oxidation-reduction chemistry

This work is comprised of two distinct objectives: to study the nanotoxicity of complex nanomaterials and to develop nanomaterials for a process called chemical looping dry reforming (CLDR). For the first objective, nickel-containing nanomaterials (hollow Ni@SiO2, non-hollow hNi@SiO2, and Ni-SiO2) were assessed as environmental contaminants. We hypothesized that incorporation of a silica support would stabilize the nickel nanoparticle and hence mitigate its toxicity. An initial assessment of agglomeration and dissolution indicated that nhNi@SiO2 has smaller agglomerates, while Ni-SiO2 allows for greater nickel ion shedding into solution. A toxicity screening was also done by 5-day nanomaterial exposures with zebrafish embryos. High survival of the zebrafish suggested a low toxic potential for silica-structured nanomaterials. However, nhNi@SiO2 and Ni-SiO2 materials stood out as having either slightly higher deformations or altered motility trends at high doses, respectively. Finally, elevated uptake of nickel following particle exposure suggested the possibility of internalization of the nanoparticle agglomerates. While the toxic potential of complex nanomaterials was probed above, the potential value of such materials was also of interest. Hence, the efficacy of nanomaterials in a specific application was assessed as well. CLDR is a process in which CO2 reacts with a metal oxide to form CO. The metal oxide is regenerated back to a metal by reduction with a fuel (e.g., methane). The result is a cyclic process, which allows utilization of CO2 (a greenhouse gas) by conversion to CO. Fe-based materials were selected as the most suitable for the process and core-shell, Design of Nanomaterials for a Reduced Toxicological Impact and Development of Nanomaterials for Utilization of CO2 by Oxidation-Reduction Chemistry Michelle Najera, PhD University of Pittsburgh, 2013 v composite, and surface deposited nanomaterials were developed. According to comparison in thermogravimetric analysis (TGA), iron utilization of the nanomaterials was in the order of Fe@CeO2 > Fe-CeO2 > Fe-Barium hexa-aluminate > hollow Fe@SiO2 > Fe@SiO2. Among these, only the ceria-supported materials underwent an adequate extent of reduction with methane to complete the cyclic process. The ceria-supported materials also had superior oxidation capacity. Lastly, performance of the surface deposited Fe-CeO2 in a fixed bed reactor was comparable that of the Fe@CeO2 material, leading us to conclude that there was no observable benefit to the use of complex and costly core-shell structures for the CLDR process.