Chemically assembled heterojunctions of SnO2nanorods with TiO2nanoparticlesvia “click” chemistry

Abstract

SnO₂ is a promising material for photovoltaic and photocatalytic applications because it exhibits high electron mobility, its conduction band lies at a convenient energy to act as an electron acceptor, and it can be easily grown in a variety of different nanostructures including nanoparticles, nanorods, and nanosheets. However, strategies for surface functionalization of SnO₂ are much less well developed than alternative oxides. Here, we demonstrate the growth and subsequent chemical functionalization of SnO₂ nanorods to enable the chemically directed assembly of SnO₂ nanorod–TiO₂ nanoparticle heterojunctions, and we characterize the charge-transfer properties using time-resolved surface photovoltage measurements. Vertically aligned SnO₂ nanorods were grown via a high-pressure chemical synthesis method. The SnO₂ nanorods were square in cross-section, exposing sidewalls consisting of {110}-type crystal planes. Functionalization via photochemical grafting with butenol yielded nanorods terminated with a high density of –OH groups that were converted to azide groups. The azide groups were linked with alkyne-modified TiO₂ nanoparticles via the Cu(I)-catalyzed Azide–Alkyne Cycloaddition (CuAAC) reaction, a form of “click” chemistry, thereby covalently grafting the TiO₂ nanoparticles to the SnO₂ nanorods. Time-resolved surface photovoltage measurements of the resulting adducts showed that the covalent bonding of TiO₂ nanoparticles to the SnO₂ nanorods enhances the interfacial charge transfer compared to the unmodified SnO₂ nanorods, leading to an increased accumulation of holes at the surface.