Chromophore amphiphile–polyelectrolyte hybrid hydrogels for photocatalytic hydrogen production

Abstract

Hybrid systems based on covalent polymers and supramolecular assemblies offer unique opportunities for functional materials based on the pathway-dependent dynamic structures of supramolecular assemblies and the mechanical stability of covalent polymers. We report here on the synthesis of functional hybrid hydrogels containing self-assembling chromophore amphiphiles and polyelectrolytes. Chromophore amphiphiles were introduced into non-aqueous solvent swollen polymer matrices and self-assembly of the chromophore amphiphiles into crystalline nanostructures was triggered in the confined environment of the covalent network upon solvent exchange for water. Opposite charges in the covalent polyelectrolyte and the chromophore amphiphiles and sterics entrap the supramolecular assemblies within the mechanically stable network. However, molecular components necessary for catalysis, byproducts from photocatalysis, and the hydrogen produced are able to diffuse in or out of the covalent network to create a reusable robust host for photocatalysis. By varying the monomer and crosslinker composition in the feed, we can tune the porosity of the network as well as the chemical environment in which supramolecular crystallization of the chromophore amphiphiles takes place. This allows optimization of the hydrogel mechanical properties, retention of the chromophore amphiphile assemblies, and the photocatalytic reaction efficiency. Coarse-grained molecular dynamics simulations revealed that the chromophore amphiphile assembly is guided by the polyelectrolyte network via ionic interactions. We also demonstrate successful photocatalytic hydrogen production from catalyst-laden hybrid hydrogels with the turnover frequency approaching that of the supramolecular hydrogel system, and also show that the hybrid hydrogels can be reused over multiple cycles as photosensitizers.