Mesoporous (2-50 nm pore size) materials are widely used in numerous applications from catalysis to drug delivery to energy storage and generation. In most of these cases, the connectivity and size of these pores are critical to their performance. Templated synthetic methods provide one route to control both of these properties. The typical direct synthesis scheme for these materials involves the assembly of block copolymers or surfactants with functional precursors such as sol gel nanoparticles (NPs) or crystalline NPs. The efficient fabrication of these materials remains challenging in many cases, especially with regards to complex transition metal oxides. Even for the synthesis of a common silicate, SBA-15, the standard process involves 48 hours of hydrothermal synthesis and calcination at 550 °C for 5 hours (with an additional 3 hours for heating and cooling). These lengthy fabrication processes and energy intensive calcination processes are significant limitations to material diversity and commercial innovations. Using microwave reactors can reduce the synthesis time for mesoporous silicates from days to hours. With the advances in microwave technology for controlling power output, the full synthesis of ordered mesoporous silicas, including template degradation, can be performed in a single step in a few hours instead of days. But there is limited information on how to rationally select precursors and templates for use in microwave reactions that enable the direct fabrication of highly functional ordered mesoporous materials in a single step. Here the PI aims to investigate the utility of microwave methods for the synthesis of a diverse class of mesoporous materials including metal carbonates and oxides.
Intellectual Merit This project will elucidate how the morphology of self-assembled ordered mesoporous materials is impacted by the template and precursor selection and show how microwave processing enables the formation of mixed metal oxide nanoparticles that are not possible using conventional methods. The PI hypothesizes that (1) the thermal stability of the block copolymer template is critical to the final structure of the mesoporous material, (2) high throughput screening will enable identification of compositions where ordered mesoporous structure can(not) be obtained, (3) microwave processing will enable synthesis of compositions not accessible by conventional paths, and (4) roll-to-roll processing provides a continuous route to the rapid and scalable fabrication of these materials. To test these hypotheses, the PI will utilize a systematic series of block copolymers and metal nitrate-citrate (Fe, Co, Ni, and Mn) chemistry for precursors to the metal oxides. The conversion of the metal nitrate to metal oxide and the degradation of the polymer template will be examined using Fourier transform infrared spectroscopy (FTIR) and ellipsometry. The reaction kinetics will be examined as a function of microwave power and contrasted against conventional thermal methods. The chemical transformations will be correlated with the structure as elucidated by small angle x-ray scattering, atomic force microscopy, and x-ray diffraction to provide information on both the atomic crystal structure and the self-assembled nanostructure. Finally the electrochemical properties of these materials will be examined to understand how the structure impacts performance for batteries and supercapacitors based on these self-assembled materials.
Broader Impact Sustainable, cheap energy is a significant challenge. Energy generation (solar cells) and storage (batteries and supercapacitors) properties can be significantly enhanced by exercising control over morphology, porosity, and interfacial modifications. The understanding garnered through this project could provide guidelines for improving the properties of these materials that could be utilized in these applications, which could help the US toward energy independence. The broader educational impact will involve participation of underrepresented undergraduate students. Partnerships with the Akron Global Polymer Academy and St. Vincent St. Mary's high school will include teachers and high school students in both research and dissemination to a broad audience of K-12 students, whereby high school students involved in the research will disseminate to other K-12 students and parents through participation in Science Fair competitions. The outreach efforts will include graduate students who will thus have an opportunity to present at less technical levels necessary for improving overall science literacy.
