Cuprous oxide nanostructures tuned by histidine-containing peptides and their photocatalytic activities

Peptides have been used as modifiers and templates in the fabrication of a variety of inorganic nanostructures including noble metals, silica oxide, and metal oxides. In this work, three peptides, including HGGGHGHGGGHG (HG12), HGGGHG (HG6) and RHTDGLRRIAAR (CN225), were used to tune the morphologies of cuprous oxide (Cu2O) nanoparticles. Unlike the morphologies of modified octahedron with polyvinylpyrrolidone (PVP) and truncated cube with cetyltrimethyl ammonium bromide (CTAB), the Cu2O nanoparticles regulated by peptides showed completely different shapes and size. In the presence of HG12, the nanoparticles still showed octahedral morphology with the edge length of 84 nm, but there were distinct defects on the (1 1 1) facets. The Cu2O nanoparticles were sphere-like with the diameter of ∼86 nm under the regulation of HG6. In the presence of CN225, the Cu2O sample was spherical aggregates of smaller nanoparticles, and the diameter of the aggregates was about 128 nm. The interactions between Cu2+ and peptides have been investigated through UV-Vis spectrometer, circular dichroism spectrometer (CD) and isothermal titration calorimetry (ITC). The different coordinating structures of peptide molecules to Cu2+ ions dominated the nucleation and succedent crystal growth. The cuprous oxide synthesized with CN225 showed the best photocatalytic activity among the synthesized Cu2O particles, and about 67% methyl orange could be removed within 2 h under UV-Vis irradiation. The high photocatalytic activity of Cu2O-CN225 was attributed to the relatively small size and the (1 1 1) crystal planes on the primary particles.