(569b) Composite Photocatalyst Design through Supramolecular Assembly

Low quantum efficiencies are a major challenge in photocatalysis that must be addressed to realize the potential of solar-mediated processes in practice. One approach to address this challenge focuses on leveraging electric fields at the interface between a conductive support (e.g., graphene) and deposited active site (e.g., metal nanoparticle), which can facilitate electron-hole separation and improve charge carrier lifetimes. Unfortunately, studies that aim to understand the effect of photocatalyst structure on these properties are limited by the structural heterogeneities that accompany many composite photocatalysts. This work aims to improve uniformity and control over the active site-support interface by leveraging supramolecular assembly during catalyst synthesis.

In particular, we functionalize melamine cyanurate (MCA), a two-dimensional hydrogen-bonded network, with metallic nanoparticles (e.g., Au⁰) using nanoparticle ligands that mimic monomers involved during the assembly process, i.e., bifunctional monomer-ligands. We probe this hypothesis by varying the amount (5 to 50 mol%) and incorporation method (during supramolecular assembly vs. post-synthetically) of these bifunctional monomer-ligands in the MCA supramolecular structure. The evolution of catalyst structure as well as physicochemical and optoelectronic structures due to synthetic variations is characterized using a variety of techniques including x-ray diffraction (XRD), diffuse reflectance UV-Vis spectroscopy (DR UV-vis), photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS).

We see that we can tailor the density and distribution of active sites within the supramolecular structure, resulting in unique electronic interfaces and improved order. We demonstrate that these ordered composite catalysts give rise to improved turnover numbers in a probe photocatalytic reaction, Rhodamine B dye degradation. This work establishes a new synthetic protocol that may be generalized to other hydrogen-bonded assemblies and active site types, which can be applied to different photocatalytic applications (water splitting, CO₂ reduction) and catalyst design more broadly.