Dissertations, Theses, and Capstone Projects

Date of Degree

6-2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Chemistry

Advisor

Alan M. Lyons

Committee Members

Alexandar Greer

Sharon Loverde

Subject Categories

Chemistry | Materials Chemistry | Polymer Chemistry

Keywords

Superhydrophobic surfaces, Singlet oxygen, Water treatment, Photoreactors, Fluorinated porphyrins and phthalocyanines, Photosensitizer immobilization

Abstract

Photosensitized singlet oxygen (1O2) generation often achieved using homogenous photosensitizer (PS) systems due to their higher yields compared to the heterogenous systems. However, these systems pose practical limitations, including challenges in PS recovery, increased operational costs, and potential contamination due to PS leaching. Immobilizing PSs on solid supports like polymer membranes offers a promising alternative; yet, in most cases, PSs are embedded within the substrate to prevent leaching, which significantly reduces 1O2 yields. To address these challenges, our group has been utilizing superhydrophobic (SH) surfaces for PS immobilization as a better alternative to conventional polymer supports. In SH system, PSs are anchored on the outer surface of the polymer substrate which enhances the diffusion of 1O2 to the targeted substrates. Moreover, the presence of plastron layer would serve as an oxygen reservoir enhancing the 1O2 generation even in hypoxia, and SH surface prevents PS leaching, thereby increasing the reusability of the system.  Despite these advantages, the 1O2 yields from these SH systems remain lower than the homogenous systems. To enhance the efficacy of 1O2 production in such heterogenous systems-not limited to SH surfaces-it is essential to understand the parameters that directly influence 1O2 generation. These include the effect of incident light, PS aggregation state, surface texture, PS wetting, solvent evaporation rates and surface roughness. Accordingly, the central focus of this thesis is to improve 1O2 generation efficiency from immobilized photosensitizer systems.

In my first introductory chapter, I presented a detailed overview of superhydrophobic surfaces and the mechanisms underlying photosensitized 1O2 generation. The second chapter, I focused on fabrication and potential application of SH surfaces as a pH sensor using different morphologies of CaCO3. Here, I studied the dissolution rates of CaCO3 as a function of pH and the amount of surfactant present on CaCO3 surface which was measured by sessile droplet transition from Cassie state to Wenzel state.

In chapter 3, I explored SH surfaces as potential solid support for 1O2 generation.  Here, I studied the effect of PS coating and incident light on 1O2 generation for PS immobilized SH support coated with the photosensitizer 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin (TFPP).  This study addresses the challenges of a heterogeneous system by using a support that exhibits low 1O2 physical quenching rates, a fluorinated PS that is chemically resistant to photooxidation, and a superhydrophobic surface that entraps a layer of air called “plastron”. The arrangement of PS, TFPP was found to be unaggregated on SH PDMS surface which is a favorable characteristic for a heterogenous PS system. This study further demonstrated that the 1O2 generation from heterogenous PSs comply with Kasha’s rule, while the amount of 1O2 generated is correlated with the absorption coefficient of the PS.

In chapter 4, I studied the effect of PS self-assembly on 1O2 generation in terms of their morphology and aggregation state on solid polymer substrates using commonly used polymer supports such as polyethylene terephthalate and polydimethylsiloxane. The effect of polymer wetting properties and surface roughness on PS precipitation and 1O2yields was also explored. Contrary to the expectation, PS aggregate state and higher PS loadings were not found to be strongly correlated with 1O2 yields.  Instead, 1O2 yields increased with rapid solvent evaporation, film-wise wetting of the polymer surface, and superhydrophobic topography.  The PS aggregation state was characterized by the UV/Vis and fluorescence emission spectroscopy while PS morphologies on solid supports were obtained by scanning electron microscopy.

Finally, in Chapter 5, I explored a novel singlet oxygen photoreactor comprise of PMMA lightguides. Two hydrophobic fluorinated PSs, TFPP and Zinc 1,2,3,4,8,9,10,11,15, 16,17,18, 22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine (ZnF16PC) were immobilized on the sidewalls of roughened lightguides and comparatively studied the efficacy of 1O2generation from these two PSs. When coupled with LED illumination, the roughened lightguides scattered over ~90% of the incident light through their sidewalls, in stark contrast to the ~5% scattering observed from smooth lightguides. This higher light scattering of the roughened surface would significantly improve the light reaching to the immobilized PSs, thereby increases the 1O2 yield. The system’s effectiveness was further demonstrated by the degradation of a series of active pharmaceutical compounds (APCs), showing the potential of immobilized PSs in industrial applications. The APCs degradation rates were studied as a function of PS where TFPP showed significantly higher efficiency compared to ZnF16PC.

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