A Simple, Long-Lasting Treatment for Concrete by Combining Hydrophobic Performance with a Photoinduced Superhydrophilic Surface for Easy Removal of Oil Pollutants

Abstract

Superhydrophobic surfaces present promising applications in the protection of building materials, such as the self-cleaning effect promoted by their high water-repellent properties. However, these surfaces easily lose their properties when exposed to oil contaminants. This is a critical weak point for their application in building facades, which are exposed to environmental pollutants such as hydrocarbons and vandalism (e.g., grafitti). A viable strategy to remove oils is to produce superhydrophilic surfaces, which present underwater superoleophobic behavior. In the case of buildings, the use of this strategy can be considered counterproductive because it promotes their interaction with water, the main vehicle of most decay agents. In this work, we have successfully combined the advantages of a superhydrophilic coating with a hydrophobic impregnation treatment, which prevents water ingress into the porous structure of the substrate. Specifically, a photoinduced superhydrophilic surface was produced on concrete by simple spraying of a starting sol containing TiO 2 NPs, which create a Cassie-Baxter state, a silica oligomer, producing a compatible matrix promoting good adhesion to the substrate and polydimethylsiloxane as a hydrophobic agent. After being exposed to sunlight, the treated surfaces switched from superhydrophobic (SCA 160°) to superhydrophilic (SCA < 10°). These surfaces presented underwater superoleophobicity (SCA 152°with CHCl 3 ) and oil-contaminated dust was easily cleaned without employing detergents. The photoactivation does not alter the protection against water absorption (>85% reduction). The treatment showed suitable adhesion to the substrate and good resistance to rainfall and outdoor exposure due to the presence of the hydrophobic silica matrix in the concrete pore structure.

Photoactive Cements: A Review

“…On the other hand, it prevents water from penetrating into the porous structure of the substrate. Such a solution was proposed by Carrascosa et al [ 38 ] by simply spraying a sol containing titanium nanoparticles, a silica oligomer ensuring good adhesion to the substrate, and a hydrophobic agent—polydimethylsiloxane. Due to the effective penetration of the product into the porous structure of concrete and the formation of a homogeneous and dense coating on the surface, the prepared silica matrix showed long-term resistance to external conditions.…”

Self-Cleaning Coatings and Surfaces of Modern Building Materials for the Removal of Some Air Pollutants

“…Due to their hydrophobic properties, they can be used to protect against compounds such as hydrocarbons or against the unauthorized application of substances such as paints used by the authors of graffiti on the facades. Carrascosa et al [ 46 ] in their work combined the features of a superhydrophilic coating with hydrophobic impregnation in order to prevent water penetration into the porous structure of the substrate. The starting solution, which consisted of TiO 2 -NPs, silica oligomer (to ensure good adhesion to the substrate) and polydimethylsiloxane (as a hydrophobic agent), was sprayed onto concrete.…”

“…These surfaces showed underwater superolophobia, and the oil-contaminated dust was easy to clean without the use of detergents. In addition, they were characterized by adequate adhesion to the substrate and good resistance to precipitation and external exposure [ 46 ].…”

Multifunctional Photothermal Conversion Nanocoatings Toward Highly Efficient and Safe High-Viscosity Oil Cleanup Absorption

“…Classic adsorbents including foam, sponge, and textile have been intensively developed to clean up oil from water. − However, these conventional adsorbents generally focus on the separation of low-viscosity oils or organic solvents. For high-viscosity oils (viscosity >1000 mPa s), it was still difficult to clean up because the high viscosity prevents them from diffusing into the inner pores of adsorbents.…”