Void engineering to promote the self-cleaning properties of bactericidal zinc oxide nanopillar array coatings

Abstract

Bacterial infections are easily spread by touch, and some bacteria can survive for months on certain surfaces. Current disinfection approaches and self-sanitizing coatings have limitations, which provides the impetus for developing new inexpensive coatings that combine bactericidal activity and self-cleaning properties. One way to achieve this is to mimic natural arrays of nano-pillars, such as those found on insect wings and plant leaves. Accordingly, arrays of zinc oxide nano-pillars display self-sanitizing properties, which are influenced by their dimensions, shape, and spacing. However, a key characteristic of these coatings is their water wettability, which increases the tendency for water-borne contaminants to attach. This wettability is caused by the voids between the nano-pillars that form a network of capillaries. To address this issue, this study introduces modifications to the current hydrothermal production method to adjust the characteristics of these voids, without altering the nano-pillar density in the array. A new hierarchical ‘nano-porcupine’ morphology is also reported. These modifications to the void structure significantly affected the surface chemistry, wettability, and photocatalytic activity of the coatings, improving their self-cleaning properties without compromising their bactericidal activity, as demonstrated by five different tests.