Enhancement of photocatalytic activity of CaTiO3 through HNO3 acidification

• Enhancement of HNO3 acidification led to the increase of substitutional N.
• Acidified CaTiO3 at pH 2 has the best photocatalytic activity among samples.
• The kobs and |1 − NO–Ti–N/NTi–O–N+Ti–N–O| shows a negatively linear relationship.

CaTiO3 synthesized by the hydrothermal method was treated to improve its photocatalytic activity using the HNO3 acidification. Changes of morphology, structure, and composition of the acidified CaTiO3 were investigated through various means such as XRD, SEM, BET, FTIR, Raman spectra, XPS, and UV–vis DRS. The results show that the enhancement of HNO3 acidification led to the increase of substitutional N (O–Ti–N) compared to interstitial N (Ti–O–N and Ti–N–O) in the CaTiO3 lattice. The apparent first-order reaction constant (kobs) of methylene blue over the acidified CaTiO3 at pH 2 was the largest and increased by 1.0 times than that over the not-acidified CaTiO3, indicating that the acidified CaTiO3 at pH 2 has the best photocatalytic performance among as-prepared samples. A negatively linear relationship between kobs and |1 − NO–Ti–N/NTi–O–N+Ti–N–O| suggests that the improvement of photocatalytic activity of CaTiO3 by HNO3 acidification depends on synergistic effects of substitutional and interstitial N in CaTiO3 lattice.