PhD Oral Exam - Victor Felipe Quezada Novoa, Chemistry

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Metal–organic frameworks (MOFs) have been extensively studied in the last few decades for their potential application in gas adsorption, water capture, catalysis, and others. Metals from the d-block on the periodic table are often applied in MOF synthesis, however, rare-earth (RE) metals, which include scandium, yttrium and the series of fifteen lanthanoids, have also been explored due to the intricate structures and specific properties that RE-MOFs can feature. The chemical warfare agent, sulfur mustard (HD), still exists in stockpiles in different countries and can be easily synthesized by nations under armed conflict. RE-MOFs are promising to study for the sustainable detoxification of HD.

This work exposes the synthesis and characterization of four isostructural series of RE-MOFs obtained using a tetratopic pyrene linker (H4TBAPy) and named RE-CU-04, RE-CU-05, RE-CU-06, and RE-CU-10 (RE = Sc(III), Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Yb(III), Tm(III), or Lu(III); CU = Concordia University). The structure of RE-CU-04 and RE-CU-05 are explored by total X-ray scattering, followed by pair distribution function (PDF) analysis to resolve the local structure of the RE node. Electron diffraction data collected from RE-CU-06 microcrystals indicate a structure with rhombohedral channels and RE chains with frl topology. Single crystal X-ray diffraction (SCXRD) of RE-CU-10 reveals a structure comprised of 12-connected RE9-cluster SBUs, with shp topology, featuring 1D triangular channels.

The accessible surface area of these new MOFs and the ability to generate singlet oxygen using the pyrene-based linker under ultra-violet (UV) irradiation, makes RE-CU-04, RE-CU-05, RE-CU-06, and RE-CU-10 good candidates for the selective photooxidation of HD, where the simulant 2-chloroethyl ethyl sulfide (2-CEES) is oxidized to its less toxic sulfoxide, 2-CEESO. RE-CU-10 shows one of the best photooxidation performances for 2-CEES to 2-CEESO among all pyrene-based MOFs reported, achieving 100% conversion within 15 min. RE-CU-05 and RE-CU-06 feature a slower performance, reaching full conversion at 20 min and 30 min, respectively, while the RE-CU-05 series shows a higher chemical stability than RE-CU-06 under the photooxidation conditions. The synthesis, characterization, photophysical properties, chemical stability, and photooxidation performance of these new RE-MOFs will be discussed.