Enhanced photoelectron transfer from light-harvesting antenna of phycocyanin to Fe3O4 hierarchical structure

Highlights: • Effectively promoting photoelectron transfer from Phycocyanin Antenna to interface. • Visible light excited photocurrent was enhanced by 5.4 times. • Electron transfer path from phycocyanin to the interface was elucidated. • Conformational change is a key to promote electron transfer from phycocyanin to Fe₃O₄. Phycocyanin, which contains proteins and chromophore, is a natural light capturer for the photosynthesis process of cyanobacteria, while its artificial application as light antenna for sensitizing semiconductors is highly restricted due to low charge transfer efficiency at the interface. In this work, we show how to improve the transfer efficiency of photo-electrons from a new point of view. It is found that the conformation change of proteins is a key to promote photoelectrons transfer from phycocyanin antenna to the surface of hierarchical Fe₃O₄ microsphers. Conformation change was induced by electrostatic interaction between the carboxyl groups on Fe₃O₄ micropheres and the amino groups of proteins' backbone. During the process of conformation change, hydrogen bonds formed between proteins and the surface of Fe₃O₄ microspheres played a role in stabilizing proteins' structure to achieve polymeric steric stabilization. Due to this strategy, photocurrent density was enhanced by 5.4 times, photovoltage increased by 2 fold, and majority carriers in the space charge region were improved by 35%. Electron transfer path from phycocyanin to the interface was elucidated based on photoelectronic and photoluminescent studies. Meanwhile, we noticed IPCE increased at 650–700 nm, which might be related to the allosteric effect of protein or electron tunneling.