Photocatalytic TiO2-Based Coatings for Mortars on Facades: A Review of Efficiency, Durability, and Sustainability

Abstract

Due to the urgent need for a more sustainable built environment and actions against climate change, this paper presents a literature review about photocatalytic TiO2-based thin layers to be applied on mortars in facades. Photocatalysis may be a potential strategy against current environmental and climate challenges by transforming or eliminating hazardous greenhouse gases from the atmosphere. The main subjects researched were the coatings’ efficiency (which encompassed their self-cleaning ability, depolluting effect, and antimicrobial properties), durability, and sustainability. The method was based on the systematic literature review approach. Self-cleaning ability was the most recurrent topic retrieved from published studies, followed by depolluting effect and durability. There are few investigations about antimicrobial properties considering TiO2-coated mortars in facades. However, sustainability studies through Life Cycle Assessment and Life Cycle Costing represented the most significant gap, even requiring broader surveys. The photocatalytic activity of the coatings is well-proven in the literature, although specific evaluations may be needed for each coating composition and testing condition to understand their performance. The type of contamination agents, TiO2 dispersion and characteristics, dopants, nanocomposites, and substrate are among the principal agents influencing the results; therefore, caution must be taken when comparing research. Mainly, adhesion and photocatalytic efficiency after ageing were studied on durability. More field exposures may be recommended. Regarding the trade-offs concerning the environmental impacts of TiO2-based coatings, it is urgent to clarify whether their overall outcome is indeed advantageous and to investigate their resilience regarding climate change scenarios.