ZnO Quantum Photoinitiators as an All-in-One Solution for Multifunctional Photopolymer Nanocomposites.

Nanocomposites are constructed from a matrix material combined with dispersed nanosized filler particles. Such a combination yields a powerful ability to tailor the desired mechanical, optical, electrical, thermodynamic, and antimicrobial material properties. Colloidal semiconductor nanocrystals (SCNCs) are exciting potential fillers, as they display size-, shape-, and composition-controlled properties and are easily embedded in diverse matrices. Here we present their role as quantum photoinitiators (QPIs) in acrylate-based polymer, where they act as a catalytic radical initiator and endow the system with mechanical, photocatalytic, and antimicrobial properties. By utilizing ZnO nanorods (NRs) as QPIs, we were able to increase the tensile strength and elongation at break of poly(ethylene glycol) diacrylate (PEGDA) hydrogels by up to 85%, unlike the use of the same ZnO NRs acting merely as fillers. Simultaneously, we endowed the PEGDA hydrogels with post-polymerization photocatalytic and antimicrobial activities and showed their ability to decompose methylene blue and significantly eradicate antibiotic-resistant bacteria and viral pathogens. Moreover, we demonstrate two fabrication showcase methods, traditional molding and digital light processing printing, that can yield hydrogels with complex architectures. These results position SCNC-based systems as promising candidates to act as all-in-one photoinitiators and fillers in nanocomposites for diverse biomedical applications, where specific and purpose-oriented characteristics are required.

Morphology effect on zinc oxide quantum photoinitiators for radical polymerization.

Semiconductor nanocrystal based photoinitiators, quantum PIs, are a viable alternative to organic photoinitiators demonstrating unique advantages, including a broad and tunable excitation window, limited migration, and more. Aiming towards efficient quantum PIs with tunable properties, a deeper understanding of the relationships between the nanoparticle properties and their efficiency is required. Herein, we studied the morphological effect on ZnO nanocrystals functioning as photoinitiators in both water-based and solvent-free formulations by comparing rod and pyramidal shaped particles of similar volumes and nearly identical surface area. Superior polymerization performances are measured for the nanorods. Photocatalytic characterization including oxygen consumption and reactive oxygen species formation as well as dyes reduction and oxidation, also showed enhanced activities for the nanorods. The different performances were attributed to the anisotropic nanorod morphology which is beneficial for charge separation as well as to the presence of a reactive [0001] facet in the nanorods, which is known to increase the adsorption of molecular oxygen and anionic molecules, thus affecting the catalytic activity. These observations, along with the higher photoinitiation efficiency of the ZnO nanorods, bring them closer to functionality as photoinitiators in numerous photopolymerization applications.