The Significance of Organometallic Complexes in the Photochemical Reduction of Cu2+ Onto Semiconductor Scaffolds

Abstract

Metal-metal oxide nanoparticles (MMO-NP) show promise as an alternative to diffusive topical antibiotics as they are capable of slowly releasing metal ions upon contact-activated oxidation which promotes toxicity to prokaryotes. Modification of semiconducting nanoparticles with metals also has great relevance in terms of increasing the photocatalytic activity of the particles, which are inherently limited in practicality due to their large band gap energies. The use of semiconductor nanoparticles for the reduction of metal ions has been widely explored, however, more work needs to be done to make the reduction of metal ions like Cu2+ more facile. This work will focus on the mechanism and efficacy of incorporating Cu2+ into organometallic complexes for the photoreduction of Cu2+ on the surface of TiO2 and ZnO. The mechanistic contribution of bidentate complexes of Cu2+ in the complete reduction of Cu2+ will be explored. The implementation of L-serine (SER), L-arginine (ARG), and glucono-delta-lactone (GDL) as ligands will be observed. Initial results show that the coordination of Cu2+ into an organometallic complex provides an effective medium for the delivery of Cu2+ to the surface of TiO2. Spectroscopic analysis will be used to determine if the ligands contribute to the two-electron reduction via ligand to metal charge transfer (LMCT) or via non-covalent interactions that increase the effective concentration of Cu2+ at the nanoparticle surface. The surface modification of TiO2 will be observed post-reaction with scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and atomic absorption spectroscopy (AAS) to measure copper content on the surface. Antimicrobial effectiveness will be characterized via Kirby Bauer testing as well as single cell optical imaging, with E. coli being the model microbe. Photocatalytic activity will be observed via the degradation kinetics of model pollutants. Preliminary results indicate that the addition of ligands greatly increased the yield of reduced copper at low pH and that there is some extent of control over the copper ion leaching as Kirby Bauer tests showed no zones of inhibition.