Preparation and Photocatalytic Wettability Conversion of TiO₂-Based Superhydrophobic Surfaces

Abstract

We present here a facile method for the preparation of TiO2-based superhydrophobic surfaces. It consists of two steps: (1) roughening of the TiO2 surface with a rf (radio frequency) plasma with CF4 as an etchant and (2) modification of the roughened TiO2 surface with an octadodecylphosphonic acid (ODP) monolayer. Plasma etching caused the thinning of the TiO2 film but at the same time enhanced its surface roughness. A discontinuous wedgelike surface microtexture was formed after etching for 30 s, which, after modification with a monolayer of ODP, showed Cassie-type water super-repellency with a contact angle (CA) hysteresis smaller than 2 degrees . The state of water super-repellency (water CA >165 degrees) could be converted to the state of superhydrophilicity (water CA approximately 0 degrees) by means of ultraviolet (UV) illumination as a result of the photocatalytic decomposition of the ODP monolayer by TiO2. Readsorption of ODP molecules leads directly to the recovery of water super-repellency.

Condensation heat transfer on superhydrophobic surfaces

“…Recently, researchers have proposed metal oxides to fabricate more scalable superhydrophobic nanostructured surfaces 47,85,86,[92][93][94][95][96] . The nanoscale oxide can 1) better satisfy the requirement for the structure density to be larger than the nucleation density in order to avoid flooding 55 , and 2) reduce the structure length scale beneath the droplet in order to minimize the structure thermal resistance 67 .…”

Fabrication and superhydrophobicity of fluorinated titanium dioxide nanocoatings

“…More recently, superhydrophobic titanium dioxide surfaces have gradually received attention because they exhibit extraordinary wettability conversion from superhydrophobicity to superhydrophilicity under UV irradiation [5,6]. There are various approaches to preparing TiO 2 films on different solid substrates, including sol-gel technique [7], sputtering [8], liquid-phase deposition [9], chemical vapor deposition [5,6,10], and electrochemical anodizing of Ti sheets [11]. Despite these advanced approaches, there are few reports that focus on (i) development of efficient fabrication for superhydrophobic TiO 2 surfaces and (ii) influence of surface topography on hydrophobicity.…”

Stably superhydrophobic (IL/TiO2) hybrid films: Intelligent self-cleaning materials

“…Obviously, the photocatalytic stability of imidazolium-based ILs can render (IL/TiO 2 ) n layers to be stably photoresponsive smart films. The photoresponsive wetting properties of TiO 2 -based films with different coatings, such as FAS, ODP and oleic acid (C 17 H 33 CO 2 H or OLAC) are compared with each other for some key parameters (Table 1) [34] Resulting in the photocatalytic decomposition of FAS monolayer [34] 165-0 o [34] ODP-modified TiO 2 film 1 hr [35] Resulting in the photocatalytic decomposition of ODP monolayer. [35,36] Readsorption of ODP molecules leading to the recovery of the superhydrophobic state [36] 165-0 o [35] OLAC-modified TiO 2 film 2 hrs [39] 65 days for the hydrophobicity recovery [39] 100-20 o [39] ( …”

“…No signal of Br element proved that the replacement-like reaction was undergone in the LBL process and the counteranions were replaced by negative TiO 2 NPs.3.3. Photoresponsive activity of ([C 12 mim]Br/TiO 2 ) nInitially, the fabrication of superhydrophilic TiO 2 -based surface is usually achieved by coating with alkyl, perfluoroalkyl and silicon-based compounds, such as fluoroalkylsilane (FAS),[34] octadodecylphosphonic acid (ODP) monolayer [35,36]. However, there are two challenges to form stable TiO 2 superhydrophobic surfaces: the photocatalytic property of TiO 2 can result in the photocatalytic oxidation of the…”