N3/Al2O3 composite nanochannels: photoelectric and photoelectric-and-pH cooperatively controlled ion gating

Abstract

Inspired by green chlorophyll pigments in photosynthetic systems that have the inherent ability to harvest solar energy and generate electrons, a photoelectric gated nanochannel system that efficiently converts photon energy into electricity with adjustable ionic conductivity is demonstrated. The nanochannel system is achieved by grafting photoresponsive ruthenium complex molecules (N₃ molecules) onto bullet shaped Al₂O₃ nanochannels forming an organic/inorganic composite. The bullet shaped Al₂O₃ nanochannels working as an asymmetric rigid scaffold allow the composite nanochannels to mimic ionic current rectification (ICR) properties. The deprotonation of free carboxylic acid moieties on the N₃ molecular backbone upon increasing the pH enhanced the surface charge density of the inner walls of the channels, which contributes to pH-tunable ion rectification. Furthermore, the excited state N₃ molecule has a higher value for than that of the ground state pK_a, thus resulting in a better photo-responsive capability of the nanochannels at higher pH values, which are used to develop a photoelectric-and-pH cooperatively controlled ion gating switch with better performance. At pH 7 and the photon-on state, the composite channel is in the ON state, while, at pH 4 and the photon-off state, the ion current is in the OFF state. This facile and environmentally friendly stimulus-responsive system may provide a new strategy to further design and develop future photon harvesting nanochannel systems for mimicking the more comprehensive process of photosynthesis.