Effects of incorporation of nanoparticles of titanium dioxide by spraying/internal mixing methods on the photocatalytic performance and mechanical properties of FA/GGBS-based geopolymers

In this study, titanium dioxide nanoparticles (TDNs) were incorporated into geopolymers containing fly ash and slag using spraying and internal mixing methods to develop photocatalytic geopolymer materials. The influences of the addition method, content and size of TDNs, the initial concentration of nitrogen oxides (nitric oxide and nitrogen dioxide) (CNO), ultraviolet (UV) irradiation intensity and relative humidity (RH) on the photocatalytic performance was systematically investigated. The results indicated that the TDN-doped geopolymers prepared by the spraying method exhibited significantly higher nitrogen oxides degradation efficiency (NDE) than those produced by internal mixing, whereas internal mixing was more beneficial for improving the mechanical properties. The conditions for optimal NDE were an initial CNO of 100 ppm, a UV intensity of 300 μW/cm2 and RH of 50%. Under these conditions, the maximum rates of degradation of nitrogen oxides were 80.74% for the spraying method and 60.03% for the internal mixing method after 60 min. In addition, reducing the size of the TDNs enhanced the NDE. The incorporation of TDNs also increased micropore content while reducing macropores in the geopolymer matrix.