Fig c presents the photocatalytic activities of N ndash
Fig. 6(f) shows PL spectra of Na2Ti3O7, TTO-6, and N–TTO-6-2 with an excitation wavelength of 325 nm. The main emission peak for Na2Ti3O7 is centered at ∼467 nm, which can be ascribed to the band gap recombination of electron–hole pairs . The peak positions in TTO-6 and N–TTO-6-2 are similar to those in pure Na2Ti3O7.