Liquid‐Repellent Metal Oxide Photocatalysts

Abstract

Metal oxide photocatalysts (MOPCs) decompose organic molecules under illumination. However, the application of MOPCs in industry and research is currently limited by their intrinsic hydrophilicity because MOPCs can be wetted by most liquids. To achieve liquid repellency, the surface needs to possess a low surface energy, but most organic molecules with low surface energy are degraded by photocatalytic activity. Herein, current methods to achieve liquid repellency on MOPCs, while preventing degradation of hydrophobic coatings, are reviewed. Classically, composite materials containing MOPCs and hydrophobic organic compounds possess good liquid repellency. However, composites normally form irregular coatings and are hard to prepare on surfaces such as those that are mesoporous or nanostructured. In addition, the adhesion of composites to substrates is often weak, resulting in delamination. Recent studies have shown that the direct grafting reaction of polydimethylsiloxane (PDMS) from silicone oil (methyl‐terminated PDMS) under illumination results in a stable polymer brush. This easy and simple grafting method allows us to create stable liquid‐repellent surfaces on MOPCs of various types, structures, and sizes. In particular, super‐liquid‐repellent drops with an underlying air layer can be created on PDMS‐grafted nano‐/microstructured MOPCs. Potential applications of surfaces combining liquid repellency and photocatalytic activity are also discussed; thus offering new ways of using MOPCs in a wider range of applications.

One‐Step Fabrication of Universal Slippery Lubricated Surfaces

“…[ 21 ] However, the PALIS can only be prepared on a metal‐oxide photocatalyst under UV light. [ 22,23 ] Most recently, a surface functionalization method to coat flat surfaces with PDMS brushes, followed by silicone oil infusion, was reported. To generate the PDMS brush, the surface was first treated with 1,3,5,7‐tetramethylcyclotetrasiloxane, then immersed into a vinyl‐terminated PDMS solution with a catalyst to graft PDMS by the hydrosilylation reaction.…”

Multimodal Enzyme‐Carrying Suprastructures for Rapid and Sensitive Biocatalytic Cascade Reactions

“…The low contact angle hysteresis (Δ θ = 7 ± 0.3°) and sliding angle ( θ SL = 14 ± 0.7° for 5 µL drop) of water drops confirmed good water repellency with fast depinning of contact line on the PDMS‐grafted surface (Table S1 , Supporting Information). [ 41 , 42 , 43 , 44 , 45 ]…”

“…The low contact angle hysteresis (Δ𝜃 = 7 ± 0.3°) and sliding angle (𝜃 SL = 14 ± 0.7°for 5 μL drop) of water drops confirmed good water repellency with fast depinning of contact line on the PDMS-grafted surface (Table S1, Supporting Information). [41][42][43][44][45] The dispersion drops were prepared by mixing two assynthesized enzymes (GOX or HRP)-carrying NP dispersions. These enzyme-carrying silica NPs were synthesized by a sol-gel reaction in microemulsion with covalently bound enzymes to the silica matrix.…”

Universal Large-Scale and Solvent-Free Surface Modification of Inorganic Particles via Facile Mechanical Grinding

“…Recently, it was shown that the hydrosilylation reaction can be used to graft PSOs onto the surface of oxides. − The siloxane backbone is cleaved in the presence of hydroxyl groups and subsequently grafted to the hydroxyl groups on the surface of oxides, forming a PSO brush of a few nanometers in thickness. The PSO brush grafting reaction has also been applied to modify the surfaces of metal oxides having surface hydroxyl groups, resulting in the formation of various functional surfaces, such as hydrophobic photocatalysts, , stable lubricant impregnated surfaces, ,, and a blood repelling dress . The PSO brush has been used previously on the surfaces of nano/microparticles. , However, the reaction required toxic solvents to mix the particles and PSOs, posing a severe environmental issue and creating a hurdle for mass production.…”