Multifunctional porous spherical polymer networks

Abstract

Introduction of permanent porosity in materials has gathered scientific attention due to their applications in gas capture and selectivity, water treatment, catalysis, adsorption and sensing of environmental pollutants. Porous organic polymers offer tunable structures, chemical stability, inexpensive synthesis route and robustness. These multifunctional network structures are often synthesized using rare catalysts, metal centers through multi-step synthesis. A class of porous polymers, covalent organic polymers (COPs) are usually constructed from readily available monomers and offer an alternative and sustainable way to solve most of the problems that conventional porous materials face.

In this dissertation, a set of covalent organic polymers were built and engineered to meet the chemical interaction demands between target molecules and adsorbent. Permanently porous structures are used for selective capture of gases, metal capture, natural gas sweetening and catalysis. Large scale synthesis were carried out to demonstrate industrial applicability. Sensing units from the polymer structures are used for colorimetric response for easy detection.

Chapter 1 deals with introduction to porous materials and their properties. In Chapter 2, a powerful method of suspension polymerization is used to build highly tunable and porous microspherical polymers where manipulation of the chemical functionalities followed. Microspherical COPs are designed with nitrile functionality and converted to amine groups for post-combustion $CO_2$ capture applications. Effect of porogens, physisorptive and chemisorptive binding, difference in selectivity and binding energies are examined.

Chapter 3 introduces precious metal capture from mixtures such as electronic waste using nitrile and amidoxime units. Successful manipulation of the chemical groups lead to unexpected outcomes for natural gas sweetening as well as e-waste treatment. Amidoxime functionalized polymers showed record high $CO_2$/$CH_4$ selectivity of 24 for methane separation. As nitrile groups are found selective towards gold ions in waste solution, amidoxime units has brought capacity boost more than 20 fold. Polymers are synthesized in 1 kg scale which builds a strong case for scalability in industrial use. Since morphology is obtained right from the beginning, lab scale products could be implemented in industry with ease.

Chapter 4 focuses on a nanoporous network with chiral monomer namely, cinchonine, with microsphere morphology for catalysis applications. Heterogeneous catalysis of Michael addition reactions are studied with covalent organic polymer. Synthesis of polymers with confined pores and chirality made possible with readily available monomers and it is feasible to scale up this material.

Chapter 5 introduces a colorimetric detector for fluoride ions with one-pot synthesis using diaminomaleonitrile units. Color change can be detected with naked eye for concentrations as low as 2 ppm, which is the standard recommendation from World Health Organization, WHO. Selective detection, which is problematic for many sensor systems was tested. High selectivity of $F^-$ ions over $CN^-$ ions present a remarkable and unprecedented selectivity.