CaIn2S4 nanosheets and SnO2 nanoflowers co-sensitized TiO2 nanotubes photoanode for continuous and efficient photocathodic protection of Q235 carbon steel

To solve the problem of poor photocathodic protection (PCP) effect of pure TiO2 nanotubes (NTs) on Q235 carbon steel (CS), CaIn2S4 nanosheets (NSs) and SnO2 nanoflowers (NFs) co-sensitized TiO2 NTs were prepared by anodization, hydrothermal and solvothermal method. Results showed that the absorption edge of CaIn2S4/SnO2/TiO2 NTs extended to 540 nm, indicating the utilization efficiency of visible light was greatly improved. Under light, the CaIn2S4/SnO2/TiO2 NTs exhibited an open circuit potential drop of 530 mV vs. SCE and a photocurrent density of 624 μA cm−2, which was 23 and 48 times that of TiO2 NTs, respectively. The PCP properties of CaIn2S4/SnO2/TiO2 NTs were better than that of TiO2 NTs because the separation and transfer efficiency of electrons and holes were promoted due to the heterojunction structure formed between TiO2, SnO2 and CaIn2S4. Furthermore, the CaIn2S4/SnO2/TiO2 NTs could also provide time-delay protection up to 10 h in the dark state. Obviously, CaIn2S4/SnO2/TiO2 NTs have excellent electron storage capacity and could provide efficient and continuous protection, which may be due to the presence of SnO2 NFs. This work provides an effective strategy of designing more efficient photoanodes for PCP of metals.