Stable Hydrophobic Metal‐Oxide Photocatalysts via Grafting Polydimethylsiloxane Brush

Abstract

Polydimethylsiloxane (PDMS) can be grafted to metal-oxide photocatalysts such as titanium oxide by simple UV irradiation in solution or melt. The PDMS graft metal oxides are still photocatalytically active. They are hydrophobic, liquid repellent, self-cleaning, prevent biofouling and are long-term stable even in UV light.

Liquid‐Repellent Metal Oxide Photocatalysts

“…The direct surface modification of MOPCs is the best way to produce different liquid‐repellent MOPCs. To graft PDMS to the surface of MOPCs with no organic linking groups, a simple direct grafting method of a PDMS brush to the surface of the MOPCs was recently developed . The PDMS brush can be formed from silicone oil (methyl‐terminated PDMS melt) on the surface of MOPCs by inducing photocatalytic activity.…”

“…Similarly, silicone oil, methyl‐terminated PDMS, can be activated through photocatalytic activity in the presence of MOPCs and produces a PDMS brush of 3–10 nm on the surface (Figure a). Therefore, both advancing and receding CAs of water drops on MOPCs increase upon PDMS grafting and are saturated at about 109 and 100°, respectively, after UV illumination for 30 min . The PDMS brush is covalently attached (Metal−O−Si bond) with a high dissociation energy (e.g., the dissociation energy of Ti−O bond is ≈662 kJ mol −1 ) on the surface of MOPCs without any additional organic linking groups, resulting in a stable brush resistant to photocatalytic activity.…”

“…In addition, this long‐term hydrophobic stability of PDMS‐grafted TiO 2 was confirmed by outdoor exposure tests. Samples mounted horizontally in an outdoor open space (November 2015 in Mainz, Germany) retained hydrophobicity, with a static water CA of 103° after 15 days …”

“…Given these results, the PDMS brush can be grafted onto various MOPC structures, types, and sizes. Figure shows the PDMS‐grafted (≈5 nm) mesoporous TiO 2 with pores of about 10 nm, ZnO nanorods, micropillar structured mesoporous TiO 2 , and TiO 2 ‐coated etched aluminum . Due to the surface roughness of these structures after grafting, water drops show even higher CAs on the surfaces than that on the flat surface.…”

One‐Step Direct Synthesis of SiO2–TiO2 Composite Nanoparticle Assemblies with Hollow Spherical Morphology

“…However, surface hydrophobicity (lipophilicity) is necessary in some applications such as reinforcing agents in polymeric composites, [34,35] hydrophobic organic pollutant treatment, [5,36] corrosion protection of metals, [37,38] anti-biofouling, self-cleaning materials, [39] and oilwater separation. [40,41] Thus, controlling the hydrophilic-lipophilic balance (HLB) is one of the most important surface factors in a number of applications.…”