Date of Award

Spring 2025

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Christine A. Caputo

Second Advisor

Roy Planalp

Third Advisor

Anyin Li

Abstract

To prevent further anthropogenic carbonization of our atmosphere and combat climate change, we must shift away from carbon-based fuels and seek abundant, clean, storable, and energy dense fuels. One of the most promising alternatives to fossil fuels is the solar-driven production of H2 using molecular catalysts coupled to light-absorbing species in hybrid photocatalytic/electrocatalytic systems. However, such systems (especially those that are covalently-bound) often suffer from catalyst degradation and significant back-electron transfer under the conditions employed. In this dissertation, we present the design, preparation, and characterization of several supramolecular photo- and electro-catalytic systems towards the efficient reduction of protons to H2 in neutral water.

Using cyclic voltammetry, we quantify the impact of host-guest threading on the redox properties of methyl viologen using per-carboxypillar[5]arene (CAP[5]), or its water-soluble ammonium salt (WP[5]) as host. We discovered that in organic solvent, there was an observed 58 mV cathodic shift in Epc for the MV2+/MV+● reduction, while a 20 mV anodic shift for the same transition was observed under aqueous buffered conditions. It is well-known that host-guest binding affinity can be tuned by controlling the solvent conditions. However, being able to switch the stability trend by changing solvents is a unique and very exciting finding that opens the door for more complex switches and signaling systems that use these highly modifiable pillararene hosts. It also means that much care must be taken when working with redox active guests, like viologens, that may switch their binding character depending on the solvent condition and oxidation state.

We extend this investigation by exploiting the non-covalent interactions of a host-guest system to co-immobilize molecular catalysts and photosensitizers on the surface of semiconductor nanoparticles for electrocatalysis and photocatalysis, respectively. We have successfully modified both a well-known visible light photosensitizer (PS), [Ru(bpy)3]2+, and hydrogen evolution catalyst (HEC), Co(dmgH)2PyCl, with several guest moieties that are capable of threading into modified pillar[5]arene hosts anchored on TiO2 nanoparticles. Additionally, our choice of guest strategies allows for great flexibility in this system. In particular, we modify pyridines (py) and bipyridines (bpy) with guest moieties prior to complexation with a metal center that allows us to guest-functionalize any PS or HEC containing a py or bpy functionality (a great many!). Future directions for this work include coupling the reduction activity of an HEC or CO2 reduction catalyst with a water oxidation catalyst co-immobilized on the surface of a semiconductor for light−driven water splitting.

Finally, we demonstrate the use of cheapinexpensive, sustainable, Earth−abundant feedstocks to prepare histidine-functionalized carbon dots (HisCD). We show that these semiconductor-like HisCD can complex with [Co(dmgH)2Cl]+ to form a hybrid electrocatalytic material capable of rapid proton shuttling using the myriad basic functionalities on the carbon dot surface. This material shows excellent promise as a sustainable electrocatalyst surpassing the previous record for TOF in neutral water (250,000 s−1), achieving an impressive rate of 330,000 s−1 for H2 evolution at a modest overpotential of 0.38 eV.

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Available for download on Thursday, November 19, 2026

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