Molecular sieving of semiconductive NTU-9 coatings on titanium dioxide nanowire arrays: Augmented yet selective photoelectrochemical response enabled by boosting charge separation and transfer in confined space

Radial heterostructures with titanium dioxide (TiO2) nanowire as core and NTU-9 as shell are synthesized via a surfactant-free approach based on the favorable bonding of linkers with TiO2 nanowire. Relative to the traditional growth strategy of surface modification, the thin NTU-9 shell with ordered arrangement of two-dimensional networks is uniformly formed on the sidewalls of TiO2 nanowire through the orientational growth process. Using the core-shell nanowire arrays as photoanodes, wide-range light absorption and high charge carrier separation efficiency are achieved due to the conjugation of NTU-9, leading to enhanced water oxidation performance in photoelectrochemical (PEC) water splitting. Under appropriately low applied potentials, the photogenerated holes are preferable to accumulate at TiO2/NTU-9/electrolyte three-phase interface and thus the long-range ordered NTU-9 shell can also serve as a size-exclusion filter to improve selectivity toward molecules of different sizes. Consequently, the TiO2/NTU-9 core-shell nanowire array exhibits an augmented and selective PEC response for small size molecules (e.g.,H2O2) at a very low potential (-0.25 V vs Ag/AgCl), outperforming the pure TiO2 nanowire array and the counterpart with a grain-boundary-rich NTU-9 shell that is prepared by pretreatment of the TiO2 nanowires with PVP functionalization.