TiO2 coatings synthesized by liquid flame spray and low temperature sol–gel technologies on autoclaved aerated concrete for air-purifying purposes

• Novel TiO2 synthesis-coatings on concrete for air-purifying purposes
• Air pollutant (toluene) elimination rates in the order of mg·m− 2·h− 1
• Detailed coating characterization from nano- to macro-scale

This article reports for the first time in literature the successful application of two TiO2 synthesis-coating technologies, i.e. low temperature sol–gel (LTS) and liquid flame spraying (LFS), to develop autoclaved aerated concrete with air-purifying properties. Significant differences in crystal and agglomerate sizes, specific surface areas and crystal phase compositions have been observed in the synthesized photocatalytic coatings. These were, however, not reflected in their respective air purification performance as indicated by toluene removal efficiencies around 60% (TOL inlet concentration of 14 ppmv, 23 °C, 50% relative humidity and 3 min gas residence time) for both coating types. The different nano-scale characteristic effects indicate to compensate each other so that the overall photocatalytic activities as observed in our test set-up and conditions do no differ for both synthesis-coating technologies. The toluene elimination rates reported here (approx. 40 mg TOL·m− 2·h− 1) are significantly higher than that reported in previous research using high temperature sol–gel techniques or commercial TiO2 embedded in a cementitious matrix. Moreover, LTS and LFS technologies cannot only be easily applied on precast materials during manufacturing, they can also be applied on existing buildings. Based on these promising results and application potential, further research that systematically investigates the photocatalytic effect of different synthesis-coating parameters is highly encouraged to further improve the knowledge about these technologies.