Liquid Phase Deposition of Nickel Oxide as a Hole Transport Layer for TEMPO-Mediated Oxidation

Favor Igwilo, Texas Christian University, Class of 2026
Laboratory of Dr. Benjamin Sherman, PhD;
Department of Chemistry and Biochemistry

Efficient positive charge (hole) transport is essential in photoelectrochemical systems for driving oxidation reactions. In our target process, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), a stable free radical mediator, drives the redox reaction of benzyl alcohol to benzaldehyde, a reaction with significant applications in industrial processes and synthetic chemistry. TEMPO-mediated oxidation offers a sustainable alternative to conventional oxidation methods that generate hazardous waste, highlighting the need to enhance its viability in photoelectrochemical applications. Nickel oxide (NiO), a p-type semiconductor, is suited for this role due to its hole transport ability, abundance and cost-effectiveness compared to conventional alternatives such as TiO₂. To integrate NiO as a hole transport layer in TEMPO-mediated oxidation, we developed a liquid phase deposition (LPD) protocol for fabricating uniform NiO films on fluorine-doped tin oxide (FTO) glass. These films were incorporated into FTO|WO3-BiVO4 photoanodes to improve charge separation and hole extraction under light conditions.

Our experiments indicates that the uniformity and quality of NiO films are affected by deposition parameters, including the pH of the boric acid (H₃BO₃) solution, the type of base employed for pH adjustment (NH₄OH vs. NaOH)), and the temperature of nickel(II) fluoride tetrahydrate (NiF₂·4H₂O) to H₃BO₃ precursors. Characterization by profilometry reveals that maintaining a pH between 7.5 and 8 consistently produces uniform films with thicknesses in the range of 100–200 nm. UV–Vis spectroscopic analysis confirms the expected optical absorption of NiO in the near-ultraviolet region, while further electrochemical characterizations via cyclic voltammetry and chronoamperometry will further assess hole transport efficiency. This work establishes a scalable approach for NiO film fabrication that will enhance the performance of WO₃–BiVO₄ photoanodes in TEMPO-mediated oxidation processes, advancing sustainable, solar-driven alcohol oxidation with reduced environmental impact.

Emma Kulla, ¹Emily Rathke, ¹Braden Chadwick, Shauna M McGillivray, and Jean-Luc Montchamp*

¹Contributed equally

"Synthesis of Penicillin G Prodrugs and Assessment of Antibiotic Activity"

ABSTRACT
The goal of our project is to synthesize and evaluate prodrugs for phosphorus-containing antibiotics. To begin, we evaluated common prodrug moieties. This is because the preparation of phosphorus prodrugs is significantly more complex than that of carboxylic acids. In an attempt at determining the best prodrug moieties or at least establish if there are significant differences among the various bacterial strains, a series of compounds was synthesized. Penicillin G (potassium salt) was chosen as the model compound since it is a well-established antibiotic, and since there is only a carboxylate group needing derivatization. The potassium salt of penicillin G (PenCOOK) was esterified directly to PenCOOR by alkylation in DMF. The following R groups have been prepared: CH₂OC(O)t-Bu, CH₂C₆H₄(4-OAc), CH₂C₆H₄(4-NO₂), and CH₂C₆H₅. The former two compounds should be triggered by bacterial esterases, whereas the nitrobenzyl ester should be triggered by bacterial nitrogenases. The benzyl ester provides a control for the para-substituted benzyl derivatives. These compounds were then tested against the gram-positive pathogen, Bacillus anthracis Sterne. We find that the minimum inhibitor concentration (MIC) of the control (non-derivatized) penicillin-G was 120 μM (approximately 40 μg/ml), which is consistent with our previous studies. The addition of the prodrug moieties substantially increased the effectiveness of penicillin for all 4 pro-drugs. This result was most striking with EK31 (R = CH₂OC(O)t-Bu), which lowered the MIC to 3.75 μM (1.25 μg/ml). These results may be confounded by the lack of solubility of these prodrugs in aqueous media as EK31 also had the best solubility of the prodrugs tested. Future experiments will be needed to address this challenge and optimize the prodrugs, but our results indicate this is an effective approach.

Oxidative stress through the production of reactive oxygen species (ROS) has been shown to damage molecules in the brain and lead to the neuronal damage characteristic of AD. Additionally, metal ions like iron, copper, and zinc have been shown to not only bind to amyloid beta proteins and induce their aggregation, one hallmark of AD, but these metals also stimulate the production of ROS. To effectively fight AD, therapeutics should not only be able to chelate these metals and reduce oxidative stress but also prevent the aggregation of amyloid beta proteins. The Green Lab has produced ligands that both effectively chelate metals and reduce oxidative stress through interacting with ROS, but these ligands simply prevent the progression of the disease without affecting amyloid-beta protein aggregation directly. In this presentation, a synthetic scheme is proposed for the creation of a Green Lab ligand with the KLVFF peptide attached. The KLVFF peptide in the past has been shown to prevent amyloid-beta plaques from aggregating in vitro. Additionally, research has also been done showing that KLVFF, when attached to nanoparticles, can pass through RAGE receptors that are produced in the brains of AD patients. Through the addition of this peptide to the ligand, a small molecule that can chelate transition metals, reduce the effects of ROS, and prevent amyloid-beta aggregation will have been synthesized, providing a potential new therapeutic solution for Alzheimer's Disease treatment.

Salt-induced diffusiophoresis is the migration of a charged nanoparticle in water, induced by an imposed directional gradient of salt concentration. This transport phenomenon has emerged as a valuable tool for particle manipulation inside porous materials and microfluidics. Micelles represent a common example of nanoparticles with the crucial ability of hosting small guest molecules. Thus, micelle diffusiophoresis is important in the manipulation of small molecules. Micelle diffusiophoresis depends on micelle Brownian mobility or diffusion coefficient. This transport parameter describes the intrinsic ability of a micelle to randomly move (diffuse) in water. The poster reports diffusion-coefficient measurements carried out on aqueous solutions of the surfactant, hexadecylpyridinium chloride (CPC), in the presence of aqueous NaCl by dynamic light scattering. The effect of surfactant and salt concentrations on the diffusion coefficient of CPC micelles is discussed. These data are used to characterize salt-induced diffusiophoresis of charged micelles.

In this work, a single-layer tungsten oxide (WO₃) film on fluorine-doped tin oxide (FTO) coated glass was successfully prepared by the dip-coating method, followed by thermal treatment at 450°C. The structure and electrochemical properties of the WO₃ film were then determined via UV-Vis spectroscopy, IR absorption, surface profilometry, and XRD analysis. The result suggests that the films have consistent thickness and uniformity, with future investigations needed to explore how they interact with the addition of a nickel oxide layer and bismuth vanadate layer determined by electrochemical measurements such as cyclic voltammetry, chronoamperometry under light and dark conditions. WO₃ electrode can be used as the base layer to make FTO-WO₃-Bismuth Van(BiVO₄)-Nickel Oxide (NiO) electrode ,which has the potential to improve the photochemical performance in photoelectrochemical cells.