“…The XPS results show that the valence states of the composition elements are consistent with the formula K(I)Cu(II)Ta(V) 3 O(II) 9 . By using a Gaussian fitting method, high-resolution K 2p can be fitted and displayed in Figure e, the peaks located at 291.8 and 294.6 eV are attributed to K 2p 3/2 and K 2p 1/2 , respectively. , For Cu 2p XPS spectra (Figure f), two peaks assigned to Cu 2p 3/2 and Cu 2p 1/2 of Cu 2+ species are observed with two shakeup satellites (indicated as “Sat.”) peaks located at higher binding energy, proving that the Cu 2+ state in both the KCTO and KCTO@C-10. , Ta 4f XPS spectra of KCTO and KCTO@C-10 (Figure g) show that there are two peaks at 25.4 and 27.3 eV, which correspond to the binding energies of Ta 4f 7/2 and Ta 4f 5/2 of Ta 5+ species, respectively. , Clearly, no obvious reduced tantalum species (Ta 4+ or Ta 3+ ) can be observed, which is beneficial to improve the photocatalytic activity due to the fact that these reduced tantalum species act as deep trapping sites or recombination centers for the photogenerated electron–hole pairs. − As shown in Figure h, for both the KCTO and KCTO@C-10 samples, the O 1s state involves three overlapping peaks centered at 529.7, 531.1, and 532.5 eV, which are assignable to Ta–O, C–O, and −OH bonds, respectively. , The relatively higher intensity of the C–O bond in KCTO@C-10 indicates the formation of carbon species on the surface of KCTO. The high-resolution C 1s spectra of KCTO and KCTO@C-10 are displayed in Figure i.…”