Photoactive and hydrophobic nano-ZnO/poly(alkyl siloxane) coating for the protection of sandstone

[Display omitted] •Poly(alkyl siloxane) coating on sandstone was enriched with ZnO NPs (0.5 wt%).•The addition of ZnO NPs did not change the appearance of the sandstone.•Contact angle of water on the enriched coating is 128° (±2°).•The enriched coating led to >50% reduction in water absorption for ∼8 h.•Self-cleaning ability of the enriched coating under UV irradiation was observed. Poly(alkyl siloxane) containing photoactive nano-ZnO (0.5 wt%) has been studied as a protective coating of glauconitic sandstone. Effect on visual appearance, hydrophobicity, porosity, water absorption/evaporation, and self-cleaning ability of the sandstone was measured. The results were evaluated in comparison with uncoated and poly(alkyl siloxane)-coated sandstone. Static contact angle of water reached 89° ± 3° and 128° ± 2° for poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coating, respectively. Poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coatings led to increased reduction in water absorption (>50%) for ∼18 h and ∼8 h, respectively, compared to the uncoated sandstone. The shorter time is compensated by self-cleaning ability: photodegradation of methylene blue on the nano-ZnO/poly(alkyl siloxane) coating after 5 h of UV irradiation was observed. This coating is a promising candidate for practical use in sandstone monuments protection.