Monovalent sulfur oxoanions enable millimeter-long single-crystallineh-WO3nanowire synthesis

Here, we discuss a misunderstanding regarding chemical capping, which has intrinsically hindered the extension of the length of hexagonal (h)-WO(3)nanowires in previous studies. Although divalent sulfate ions (SO42-) have been strongly believed to be efficient capping ions for directing anisotropich-WO(3)nanowire growth, we have found that the presence of SO(4)(2-)is highly detrimental to the anisotropic crystal growth of theh-WO(3)nanowires, and a monovalent sulfur oxoanion (HSO4-) rather than SO(4)(2-)only substantially promotes the anisotropich-WO(3)nanowire growth.Ab initioelectronic structure simulations revealed that the monovalent sulfur oxoanions were preferentially able to cap the sidewall plane (100) of theh-WO(3)nanowires due to the lower hydration energy when compared with SO42-. Based on this capping strategy, using the monovalent sulfur oxoanion (CH3SO3-), which cannot generate divalent sulfur oxoanions, we have successfully fabricated ultra-longh-WO(3)nanowires up to the millimeter range (1.2 mm) for a wider range of precursor concentrations. We have demonstrated the feasibility of these millimeter-longh-WO(3)nanowires for the electrical sensing of molecules (lung cancer biomarker: nonanal) on flexible substrates, which can be operated at room temperature with mechanical flexibility with bending cycles up to 10(4)times due to the enhanced textile effect.