Date of Award
Doctor of Philosophy
Igor I. Slowing
Aaron D. Sadow
This dissertation describes the author’s efforts in developing new heterogeneous catalytic systems. The work is focused on controlling the structure of heterogeneous catalysts at the macroscale (using 3D printing methods) and at the nanoscale (using Mesoporous Silica Nanoparticles). The first chapter consists of a general introduction to 3D printing and its applications in chemistry laboratories and in heterogeneous catalysis.
The second chapter presents the 3D printing process of materials with active functional groups using a commercial stereolithographic 3D printer. Controlling the composition of the 3D printable resin, different organic/inorganic catalytic groups were incorporated into the 3D architectures. The active sites, part of the 3D structure, did not require any post-printing treatment for activation and they can be used directly after printing. The incorporated functionalities were accessible and catalytically active for the Mannich, aldol, and Huisgen cycloaddition reactions. As a proof of concept, custom-made catalysts were printed and used for studying the kinetics of a heterogeneously catalyzed reaction in a conventional solution spectrophotometer. In addition, we used 3D printed millifluidic devices containing catalytic copper(II)acetate sites within the walls to promote the azide-alkyne cycloaddition under flow conditions. We showed that 3D printing allows controlling the morphology of the active materials, resulting in enhancing catalytic activity upon increasing complexity of the 3D architectures.
The third chapter presents a study of the effect of macroscopic catalyst morphology on the performance of batch reactions. A series of catalytically active magnetic stir-bar compartments (SBC) with different architectures were 3D printed and used to promote the hydrolysis of sucrose. Fixing the surface area and the number of accessible catalytic sites of the 3D printed SBC allowed exploring the effect of subtle changes in morphology on the fluid dynamics of the reaction systems, and consequently on the efficiency of the catalytic conversion. Moreover, varying the ratios between acrylic acid (AA) and 1,6- hexandieoldiacrylate (HDDA) in the SBC allowed tuning cooperativity between acidic sites and hydrophobic domains to control the rate of sucrose hydrolysis. This work demonstrates that 3D printing catalytic materials enables optimizing their performance by simultaneously controlling their macroscopic and molecular structures.
The fourth chapter presents a new method for high-throughput screening of 3D printable catalytic resins. While, stereolithography (SLA) is a popular 3D printing technique, large volumes of resins (~150 mL) are required in each printing cycle. Thus, developing materials with different chemical or surface properties can be expensive and time consuming. To address this problem, we designed matrices of compartmentalized resin tanks and adapted them to a commercial 3D printer. The resin tanks with smaller volumes (2 mL) were used for fast and efficient discovery of new library of 3D printable materials, allowing to simultaneously print up to 16 compositions. Using this approach, we screened for resins that can produce 3D objects with different degrees of surface hydrophilicty/hydrophobicity and catalytic activities. The optimized 3D printed catalytic materials with the largest area were used for oxidation of benzyl alcohol into benzaldehyde. The accessibility to screen multiple materials simultaneously allowed us to combine the best observed properties to manufacture an optimized 3D printed geometry (i.e. highest hydrophobicity, highest catalytic activity and highest geometrical surface area)
In chapter five, we studied the functionalization (grafting) kinetics of mesoporous silica nanoparticles (MSN) with organo-substituted trimethoxysilanes (R-TMS). Controlling and understanding the functionalization of MSN is necessary to enable a rational design of hierarchical MSN-based hybrid materials. We observed that the grafting process involves an adsorption/desorption equilibrium of R-TMS with the silica surface prior to its reaction with the surface silanols. Monitoring the changes in 3-aminopropyltrimethoxysilane (AP-TMS) grafting rates as a function of its concentration revealed a substrate-inhibition like behavior. Analysis of methanol production rates showed a significantly higher grafting rate for AP- TMS compared to other R-TMS, due to a catalytic effect of the amino group. This effect was used to control the grafting rates of other R-TMS by adding amines with different pKa values. Solid-state NMR (SSNMR) studies revealed that the amine additives can also control the distribution of the grafted R-TMS on the surface of MSN.
In chapter six, phenyl-functionalized mesoporous silica materials were used to explore the effect of non-covalent interactions on the release of Ibuprofen into simulated body fluid. To this end, phenyl groups with different orientations and conformational mobilities were introduced onto mesoporous silica surfaces. The Ibuprofen release profiles from the materials were analyzed using an adsorption-diffusion model. All phenyl-containing mesoporous materials showed lower initial release rates than the bare silica. Comparing the different orientations of the phenyl groups, we observed that locked phenyl conformations provide stronger interactions with the drug than flexible phenethyl groups. The differences in adsorption interactions were consistent with DFT calculations. These results show how fine- tuning the orientation of groups can result in the control of a drug release profile.
Juan Sebastian Manzano Davila
Manzano Davila, Juan Sebastian, "Customizable heterogeneous catalysts: From 3D printed designs to mesoporous materials" (2018). Graduate Theses and Dissertations. 17260.