Hierarchical Structured Multifunctional Self‐Cleaning Material with Durable Superhydrophobicity and Photocatalytic Functionalities

Abstract

surface by different behaviors toward the water. Superhydrophilic surfaces, where the water contact angle is less than 5°, can be cleaned by the spreading of water across the surface or a stream of water, like rainfall. [6] In contrast, on superhydrophobic surfaces, water forms spherical droplets that roll across the surface, carrying away contamination particles. [7] This phenomenon is known as the "lotus effect," [8] whose origin is the surface energy and the roughness of the corresponding surface. [9] In comparison, there are more advantages in choosing superhydrophobicity over superhydrophilicity as self-cleaning materials due to the reduction of bacterial and contamination adhesion, [10] and their waterproof and antimist characteristics. [11] To achieve a superhydrophobic surface with a water contact angle of more than 150°, a low surface energy material is necessary, as well as a high roughness of micro-or nanostructured surface architecture. Therefore, hydrophobic polymers, alkyl silanes, or semifluorinated silanes are candidates for the generation of superhydrophobic surfaces. [12] Methods for constructing nano-or microstructure surfaces are important for realizing superhydrophobic surfaces. However, these methods are limited to particular substrates (e.g., silicon wafer or aluminum foil) or by the complexity of processing (e.g., lithography and anodization), which restrict its broader applications. Moreover, surface superhydrophobicity could be damaged by the oily contamination from organic compounds or bacterial biofilm. [13] Thus, a functionality which can maintain the surface superhydrophobicity is of pivotal importance to keep the durability of self-cleaning materials. One of the most convenient and effective ways to achieve that is through compositing photocatalysts.Artificial photocatalytic surfaces have become increasingly popular over the recent decades since their discovery by Fujishima and Honda in 1972. [14] Among photocatalytic materials, TiO 2 has attracted much attention in scientific research as well as commercial applications. TiO 2 is well-known as an efficient photocatalyst in air and water purification, water splitting, and the disinfection of surfaces. [15] It has been demonstrated that including TiO 2 in the composition of a surface coating is a good approach to fabricating self-cleaning materials. [16] Self-cleaning materials, which are inspired and derived from natural phenomena, have gained significant scientific and commercial interest in the past decades as they are energy-and labor-saving and environmentally friendly. Several technologies are developed to obtain self-cleaning materials. The combination of superhydrophobic and photocatalytic properties enables the efficient removal of solid particles and organic contaminations, which could reduce or damage the superhydrophobicity. However, the fragility of the nanoscale roughness of the superhydrophobic surface limits its practical application. Here, a hierarchical structure approach combining micro-and nanoscale architecture...

Heterogeneous Wettability Surfaces: Principle, Construction, and Applications

“…Water droplets can freely roll off this type of surface and remove dust, granting the surface with a self‐cleaning property. [ 6,7 ] By comparison, a water drop placed on a hydrophilic surface forms a liquid puddle, with the solutes in the liquid finally deposited on the surface after drying. This is the fundamental mechanism for various printing and lithography techniques for material deposition.…”

Shape Control of Lotus Leaf Induced by Surface Submillimeter Texture

“…It is well known that the MP and the nano‐rods with wax on their surfaces effectively enhance the surface roughness and lower the surface energy, inducing the surface to be water‐repellent and self‐clean. [ 14–18 ] But all these contributions by micro and nano‐topographies are not enough. Without the slant angle, pollutants easily stored at the center of the leaf and the lotus surface could not drive the pollutants and dirty water off the surface without any external force, resulting in inhibition of photosynthesis and respiration.…”

The Effect of Fiber Type and Yarn Diameter on Superhydrophobicity, Self-Cleaning Property, and Water Spray Resistance

“…Many techniques have been developed to render surface roughness [ 8 , 9 , 10 ] and hydrophobization. To date, the micro/nano hierarchical structures has been fabricated on the surfaces via plasma etching [ 4 , 5 , 7 , 11 , 12 , 13 ] or chemical etching [ 6 , 14 ], and plasma deposition [ 5 , 15 , 16 , 17 ], chemical vapor deposition [ 18 ], or wet coating [ 1 ] has been used to lower the surface energy. Some studies investigated the effect of the number of monofilament [ 19 ] and yarn types (filament and Drawn Textured Yarn, DTY) [ 20 ] on superhydrophobicity.…”