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Abstract
TiO2 powders with varying Ag (3.125-12.500 mol% metal basis; single cation doping and codoping) and N (0.2-0.6 mL into 20 mL precursor solution; single anion doping and codoping) were fabricated by modified sol-gel method, followed by drying at room temperature for 12 h and then calcinated at 450°C for 5 h. The mineralogical, chemical, nanostructural, electronic and photocatalytic properties under both UV and visible irradiation of the thin films were determined. Anatase was the only phase in essentially all the samples. XRD and XPS data revealed that, in Ag-doped TiO2 samples, Ag+ ions were likely to occupy one and both of two interstices at low-level and high-level doping, respectively. N3- ions were likely to substitute lattice O2- in N-doped TiO2 samples. However, Ag/N-doped TiO2 samples exhibited the coexistence of interstitial Ag+ and substitutional/interstitial N3- doping. XPS data indicated that both Ag doping, N doping, Ag/N codoping facilitated the formation of oxygen vacancies V_O^(••), while Ag doping and N doping could facilitate the formation of Ti3+. Further, XPS indicated the presence of Ag0 at high-doping levels, leading to the presence of Ag0/TiO2 heterojunction and the generation of Ag0/TiO2 heterojunction can be enhanced by the incorporation of N doping, which was confirmed by TEM images. SEM showed that the Ag doping was likely to suppress the agglomeration at high doping level while N doping and Ag/N codoping were likely to enhance the agglomeration. TEM suggested that N doping and Ag/N codoping caused expansion on TiO2 grains associated with the decreased surface area. Although Ag doping slightly affected grain size, the surface area of Ag-doped TiO2 samples increased and decreased with the increased doping level owing to the reduced porosity and densified agglomerates. PL spectra showed that both Ag and N doping could facilitate the photoexcitation. The photocatalytic performance test indicated that Ag doping generally enhanced the photocatalysis while only low-level nitrogen doping enhanced the photocatalysis under visible light. General trend discussion of photocatalysis in Ag/N-codoped TiO2 samples suggested that surface area and axial ratio were the predominant factors for the photocatalysis under UV and visible light respectively