Engineering sp2-Conjugated Covalent Organic Frameworks for Photocatalytic Degradation of Bisphenol A in Water at Trace Level

Abstract

This thesis presents an innovative investigation into using sp2-conjugated covalent organic frameworks (sp2c-COFs) for photocatalytic degradation of Bisphenol A (BPA) microplastic commonly encountered in water. sp2c-COFs are a specific class of COFs that possess complete conjugation via interconnected conjugated frameworks formed by sp2 carbon-carbon bonds. In contrast to conventional COFs, sp2c-COFs demonstrate exceptional stability and semiconductor characteristics, making them extremely well-suited for a wide range of applications, including photocatalysis. Methodologically, the study involves the synthesis of pristine sp2c-COF and modifying the functionality of the framework by introducing -OH and NH2 hydrophilic groups, followed by a comprehensive characterization of the materials using advanced spectroscopy and microscopy techniques and their application in the photocatalytic degradation of BPA. The research aims to optimize the photocatalytic reaction conditions, evaluate the efficiency of the catalyst, and assess its recyclability in the degradation of BPA. Herein, we report a two-step synthesis as the amidoxime group is likely to react with the monomers and inhibit the formation of COF. The cyano-based COF was obtained through the Knoevenagel condensation reaction between 1,3,6,8-tetrakis (4-formyl phenyl) pyrene (Py) and 4,4’-(benzothiadiazole-4,7-diyl) acetonitrile (BSZ) building units under solvothermal conditions to yield PyBSZ COF. The yielded COF was then treated with hydroxylamine and ethanol forming amidoxime-functionalized COF (PyBSZ-AO).

The characterization results obtained from the PXRD analysis display two distinct and sharp peaks, indicating the crystallinity of the sample and strongly correlating to the formation of a COF. In addition, the porosity of sp2c-PyBSZ-COF was investigated using the N2 adsorption isotherm at standard temperature and pressure (STP). The analysis revealed a BET surface area of 380 m2g–1 for the synthesized COF. Furthermore, employing nonlinear density functional theory (NLDFT), the approximate pore size of sp2c-PyBSZ-COF was determined to be 1.14 nm. We engineered a versatile two-dimensional (2D) semiconductor COF through reticular chemistry to enhance the hydrophilicity, dispersibility in water, and mass diffusion without altering the pore channels and topology of the COF. The amidoxime groups within the pores of the COF enhanced the hydrophilicity of the framework and the mass transfer of pollutants within the pores, thereby enhancing the performance of the modified PyBSZ-AO COF compared to the pristine PyBSZ COF. PyBSZ-AO degraded 100% of 200 ppb BPA in 15 minutes for 3 consecutive cycles across all pH ranges from 3 to 11. According to the scavenging experiment, the photocatalytic degradation mechanism is most likely facilitated by the superoxide radicals (•O2-) and photogenerated holes (h+) to a smaller extent.

Date of Award	12 Dec 2024
Original language	American English
Supervisor	Dinesh Shetty (Supervisor)