Switchable Wettability in SnO2 Nanowires and SnO2@SnO2 Heterostructures

We present here the synthesis of SnO2 nanowires SnO2@SnO2 and SnO2@SnO2@SiOx heterostructures via the chemical vapor deposition (CVD) method. Surface wettability could be modulated from superhydrophilic to superhydrophobic by changing both chemical composition and the geometrical architecture of nanoheterostructures. The random SnO2 nanowires with a contact angle of 3 degrees presented a superhydrophilic property. The contact angle of SnO2@SnO2 heterostructures synthesized by a two-step CVD process increased to 133 degrees. The corresponding contact angle of SnO2@SnO2@SiOx heterostructures was 155.8 degrees. Switchable surface wettability of the SnO2@SnO2@SiOx heterostructure was observed by alternation of UV irradiation, dark storage, and O-2 annealing, indicating that geometric microstructure was the major determinant in the switchable wettability from superhydrophilic to superhydrophobic. The switchable surface wettability of SnO2 nanostructures may develop the significant potential for industrial coating and self-cleaning system.