The Analytical and Surface Chemistry (ASC) Program of the Division of Chemistry supports the research program of Prof. Maryanne Collinson of Virginia Commonwealth University. Prof. Collinson and her students will design and fabricate three new classes of high surface area materials using a multifaceted approach that merges key features of sol-gel chemistry, templating, lithography, electrodeposition, and thin film preparation. At the heart of this proposal is the use of recessed electrodes as nanoscale flower pots to electrochemically grow 3D arrays of vertically aligned silica pillars using newly developed electrodeposition techniques. From an analytical perspective, such high surface area, three-dimensional supports provide a means to significantly improve response times, recovery rates, and throughput by enabling reagents encapsulated in the porous network to be more accessible to a diffusing substrate, a task that is necessary to improve their performance in chemical analysis. The study will provide excellent training opportunities for undergraduate and graduate students in a highly inter-disciplinary area at the interface between chemistry and material science and engineering. In addition to their research, Prof. Collinson and her students will promote chemistry to a broader audience through the development of an outreach activity specifically designed for K-5 children.
Intellectual and Broader Impact Merit. High surface area, porous materials have many important roles in science and engineering. They serve as a means to deliver therapeutic agents into the human body, store large quantities of gas for energy storage applications, help separate trace components from gases and solutions, and serve as a platform for chemical and biochemical sensors designed to sense and detect minute concentrations of a species in an ever-complex environment. In applications related to chemical sensing and analysis, in particular, performance relies on four material related characteristics: response time, recovery rate, sensitivity, and detection limit. Ultimately, these four characteristics (or attributes) are strongly influenced by the accessibility of external agents to internal sites, which often constitutes the rate-limiting step in a chemical sensor. Materials with wide open structures, high surface areas and interconnected pores are needed to improve mass transport and accessibility. The intellectual merit of this project focused on the design, fabrication and characterization of new classes of high surface area silica materials with a well-defined, interconnected pore architecture on more than one length scale (e.g., hierarchical) for applications related to chemical sensing. The broader impact merit was to promote teaching, training, and learning to undergraduate, graduate, and postdoctoral students in science and engineering through hands-on research and educational activities. Project Outcomes. Through the course of this research, we have constructed what we have termed a ‘hierarchical’ template, defined specifically as a template with well-defined morphology on multiple length scales. This template is ideal for making hierarchical materials, or materials that have well-defined pores on more than one length scale. This new class of materials provides a means to overcome issues related to accessibility. Any application (e.g., chemical sensing, catalysis, drug delivery) that relies on the transport of a reagent/analyte into a porous network would benefit from having a material with a hierarchical framework. A large pore, for example, will facilitate transport to the smaller pores, which act to increase the surface area. We have used these hierarchical templates to prepare (1) multi-modal porous silica powders, (2) hollow porous silica capsules with well-defined windows, and (3) bi-modal porous gold films with a well-defined bimodal architecture. The advantages that this approach provides are simplicity and versatility: (a) the template is size-tailorable; (b) only one template made completely out of polystyrene is needed; (c) both 2D (films) or 3D (monoliths, powders, capsules) can be made, and (d) the materials produced have well-defined, interconnected pores. In other related work, we have also demonstrated the power of electroassisted deposition of silica, particularly when coupled with lithography, which spatially confines the metal oxide to pre-selected locations, to form thick film-like porous materials with an open framework. Equally important, this research has served as an important interdisciplinary training ground for students in chemistry, material science, analytical science, and nanoscience. Scientific education goes beyond that which takes place in the traditional classroom setting. A total of four undergraduate students, two chemistry graduate students, and two postdoctoral research associates have worked on various aspects of this work. Project participants have received valuable training in the areas of chemical safety, hypothesis driven research, experimental design and testing, silane chemistry, thin film preparation (dip coating, spin coating, electrodeposition) and characterization using microscopic methods of analysis such as atomic force microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, and electrochemical methods. These skills are particularly important given the strong national interest in nano- and material science and the growing need to fully characterize the microscopic properties of materials. This research has resulted in 2 PhD theses and both graduate students are currently employed (one in industry and another as a research associate) as are the postdoctoral research associates.
