Effect of gaseous atmosphere on photoinduced water wetting of ZnO nanowires

ZnO nanowires were synthesized by using chemical vapor deposition system at 1000°C temperature. The as synthesized ZnO nanowires show superhydrophilic nature with water contact angle value of 0°. After dark storage for about 50 days, the nanowires show superhydrophobic nature with contact angle value of about 155°. When these nanowires were exposed to ultraviolet light in air atmosphere, the nanowires becomes superhydrophilic. It was found that the rate of change of contact angle depends on the gases atmosphere during UV light illumination. The rate of change of contact angle with UV light illumination is higher in presence of oxygen gas whereas it is very slow in presence of hydrogen gas. Possible mechanism for the dependence of photo induced water wetting on ZnO nanowires in gaseous atmosphere is discussed.