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 (TiO 2 ) nanowire as core and NTU-9 as shell are synthesized via a surfactant-free approach based on the favorable bonding of linkers with TiO 2 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 TiO 2 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 TiO 2 /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 TiO 2 /NTU-9 core–shell nanowire array exhibits an augmented and selective PEC response for small size molecules ( e.g., H 2 O 2 ${\mathrm{H}}_2{\mathrm{O}}_2$ ) at a very low potential (–0.25 V vs Ag/AgCl), outperforming the pure TiO 2 nanowire array and the counterpart with a grain-boundary-rich NTU-9 shell that is prepared by pretreatment of the TiO 2 nanowires with PVP functionalization.