Nano-TiO2-based architectural mortar for NO removal and bacteria inactivation: Influence of coating and weathering conditions

In the present study, the photocatalytic activities of TiO2 dip-coated self-compacting glass mortars (SCGMs), in terms of air pollutant removal and bacteria inactivation, were investigated and compared. TiO2 dip-coated glass was used as the control to compare performance. Nitrogen oxide (NO) and Escherichia coli K12 were used as the target air pollutant and bacteria test strain respectively. In addition, the weathering resistance of TiO2-coated samples was evaluated. In the case of NO removal, it is clear that no significant difference between TiO2 dip-coated glass and SCGM was observed, and both exhibited high NO removal efficiency when condition 1 (C1, no weathering) was applied (for EtOH-mortar, up to 14.33 mg m−2 h−1). However, after a period of abrasive weathering, condition 3 (C3, abrasive process), the NO removal ability of the TiO2 dip-coated glass samples almost completely disappeared. In contrast, the NO removal ability of the dip-coated SCGM still remained high (for EtOH-mortar, 8.75 mg m−2 h−1). It appears that the porosity of the dip-coated SCGM surface contributed to favourable TiO2 particles retention after the abrasion action. As for the antibacterial activity, a total inactivation of E. coli was observed on the TiO2 dip-coated glass and SCGM samples within 60 min of UV irradiation. The E. coli inactivation of TiO2 dip-coated glass was nearly negligible after the abrasion process (C3), whereas, the concentration of E. coli remaining on the surface of TiO2 dip-coated SCGM only dropped from about 105 to 103 CFU/mL. The results suggest that the TiO2 retained in the porosity of the dip-coated SCGM can still make a contribution to the E. coli inactivation. Taking all the results into account, it can be concluded that photocatalytic bacteria inactivation is a more complex process and the results for photocatalytic activity of NO removal cannot always be extrapolated to photocatalytic antibacterial activity.