Embedding molecular light-driven catalysts in soft matter
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Abstract
Sustainable energy conversion of solar radiation into productive chemical reactivity can be implemented by heterogeneous light-driven catalysis. Here we report progress in the development of two separate hierarchically structured soft matter composites consisting of porous polymeric supports, electrostatically embedded with molecular thiomolybdate or polyoxometalate (POMs) catalysts and model molecular photosensitizers. We demonstrate the use of these composites for the light-driven hydrogen evolution reaction (HER) and water oxidation catalysis (WOC), respectively.
First, we discuss recent advances in thiomolybdate chemistry, emphasizing that any newly developed multifunctional material must be critically assessed, as the identification of active sites and HER mechanisms is highly dependent on heterogenization and precise reaction conditions. Deposition strategies for thiomolybdates and their pioneering and emergent applications, particularly in electro- and photocatalysis, are further outlined.
We then highlight the challenges and benefits of complementary and valuable analytical tools in evaluating the structural integrity, stability and reactivity of POMs embedded in soft matter matrices. In addition, we provide a synopsis of the key principles of soft matter chemistry, their hybridization strategies with POMs and their potential applications.
Next, we present the visible light-driven water oxidation activity of novel nanoporous block copolymer membranes. Multimodal in situ, operando and ex situ analyses of the so-called “WOCbranes” showed a uniform and stable distribution of photosensitizer and catalyst on the micro- and macroscale. However, variations in the O2 evolution rates were also observed, indicating inhomogeneities in the pore size distribution within the matrix.
We also recite the preparation, optimization and functionalization of stimuli-responsive polyampholytic hydrogels for light-driven HER and WOC. Despite the difficulties in maintaining the mechanical integrity of the hydrogel scaffold under oxidative conditions, we unveil a positive effect of the polymer environment on photoactivity and stability of the molecular building blocks under optimized catalytic conditions and infer an attractive approach for self-repair of the dye mediated by reversible electrostatic interactions.
Finally, a comprehensive outlook delineates prospective research directions, focusing on the challenges that arise when ruthenium polypyridyl-based chromophores are used in organic and aqueous solvent mixtures to drive photocatalysis.