Oxygen-Generating Gel Systems Induced by Visible Light and Application to Artificial Photosynthesis
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Oxygen-Generating Gel Systems Induced by Visible Light and Application to Artificial Photosynthesis Kosuke Okeyoshi 1, 2 and Ryo Yoshida 2 1
RIKEN Advanced Science Institute
2
Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo
ABSTRACT Toward complete artificial photosynthesis systems to generate hydrogen and oxygen using visible light and water, we firstly design and fabricate oxygen-generating gel systems using the electrostatic interactions of ionic functional groups and steric effects of a polymer network. By using a graft polymer chain with Ru(bpy)32+ units as sensitizers to closely arrange RuO2 nanoparticles as catalyst, the functional groups transmit multiple electrons cooperatively to generate oxygen. In this study, a novel strategy is shown to design a hierarchical network structure using colloidal nanoparticles and macromonomers.
INTRODUCTION Electronic transmission circuits to generate oxygen induced by visible light have been designed by several strategies using supramolecules.[1-6] The circuit is composed of the O2-generating catalyst, the sensitizer, and the oxidant. But the higher-order structures are necessary for the complete artificial photosynthesis. Here, we firstly constructed oxygen generating gel systems that contained RuO2 as a catalyst, and Ru(bpy)32+ units as a sensitizer (Fig. 1). The gel is an open material system capable of the transformation or transmission of energy or information. By utilizing such a material, we could arrange the functional groups to cooperate with each other. In fact, many kinds of functional gels have been developed by devising the inner network structure to respond to the chemical and physical signals from the exterior.[7, 8] The photo-excited reaction needs four electrons simultaneously to generate one O2 molecule; (1). Therefore, it is necessary for RuO2 and Ru(bpy)33+ to interact smoothly. To accomplish the reaction, the gel systems were constructed by using the electrostatic interactions of ionic molecules and steric effects. Firstly, for the RuO2 nanoparticles (NPs) and Ru(bpy)32+ units to coexist in the gel, the RuO2 NPs dispersed by the anionic surfactant sodium dodecyl sulfate (SDS-RuO2 NPs) were mixed with poly(NIPAAm-co-Ru(bpy)3). The SDS-RuO2 NPs and cationic Ru(bpy)32+ units are arranged closely by electrostatic interactions. Simultaneously, the polymer chain physically restricts the aggregation among the same functional groups; each RuO2 NP and each Ru(bpy)32+ unit. Secondly, by grafting poly(NIPAAm-co-Ru(bpy)3) to a crosslinked PNIPAAm network, a gel that contained RuO2 NPs and the
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Ru(bpy)32+ units was fabricated. This hierarchical arrangement of a polymer network allows the different functional groups (RuO2 NPs and Ru(bpy)32+) to coexist closely by electrostatic interactions and the same functional groups to exist separately by physical restriction. Thus, by introducing the functional groups hierarchically, oxygen-generating gel systems were achieved to operate the multi-electronic transmitting cir
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