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Iridium hydroxide (Ir(OH)3) nanoparticles exhibiting high catalytic activity for water oxidation were immobilized inside mesospaces of a silica-nanoparticles assembly (SiO2NPA) to suppress catalytic deactivation due to agglomeration. The Ir(OH)3 nanoparticles immobilized in SiO2NPA (Ir(OH)3/SiO2NPA) catalyzed water oxidation by visible light irradiation of a solution containing persulfate ion (S2O82−) and tris(2,2′-bipyridine)ruthenium(II) ion ([RuII(bpy)3]2+) as a sacrificial electron acceptor and a photosensitizer, respectively. The yield of oxygen (O2) based on the used amount of S2O82− was maintained over 80% for four repetitive runs using Ir(OH)3/SiO2NPA prepared by the co-accumulation method, although the yield decreased for the reaction system using Ir(OH)3/SiO2NPA prepared by the equilibrium adsorption method or Ir(OH)3 nanoparticles without SiO2NPA support under the same reaction conditions. Immobilization of Ir(OH)3 nanoparticles in Al3+-doped SiO2NPA (Al-SiO2NPA) results in further enhancement of the catalytic stability with the yield of more than 95% at the fourth run of the repetitive experiments.

π-Conjugated molecules have been utilized to functionalize inorganic surfaces to form organic–inorganic hybrid materials. However, the intrinsically strong π–π interaction results in undesirable aggregations on the inorganic surface, thereby disturbing the charge transfer through the organic–inorganic interface. In this study, a new strategy was developed using insulated π-conjugated molecules bearing a [1]rotaxane structure, where the π-conjugation was covered with covalently linked permethylated α-cyclodextrins. Aggregation-free immobilization was achieved on an inorganic surface by using insulated molecules to suppress intermolecular interaction. In the presence of these insulated molecules, the hybrid interface displayed excellent interfacial electrical properties. Moreover, the functionalized hybrid surface was utilized as an electrocatalyst to produce hydrogen peroxide using a Co(II)–chlorin complex, wherein the catalytic efficiency was improved dramatically by utilizing insulated molecules as bridging moieties at the interface. These results demonstrate that the insulation of π-conjugated molecules is a powerful strategy for modifying inorganic surfaces.