TiO2 Nanotube Heterostructure Modified with a Metal-Organic Framework Showing Robust Stability for Photocathodic Protection

TiO2 p-n heterojunctions modified with zeolitic imidazolate framework-67 (ZIF-67), a metal-organic framework, were successfully fabricated by a solution self-assembly method, and their photoelectrochemical and photocathodic performance was investigated. The presence of the organic ligands in ZIF-67 enabled ZIF-67-TiO2 photoanodes to exhibit excellent stable cathodic protection performance under simulated sunlight illumination compared with traditional organic or inorganic cocatalysts. ZIF-67-TiO2 photoanodes could provide 12 h of effective and stable photocathodic protection for 304 stainless steel (304SS) in 3.5 wt% NaCl solution. Experimental results revealed that the morphology of ZIF-67 cocatalysts affected the photoelectrochemical performance of ZIF-67-TiO2 photoanodes. Compared with large (∼900 nm) ZIF-67-modified TiO2, small (∼115 nm) ZIF-67-modified TiO2 demonstrated an upwardly shifted conduction band (CB) and faster separation and migration of photogenerated carriers. Furthermore, a photoanode made from small ZIF-67-modified TiO2 exhibited a lower photogenerated potential (−0.37 V) than the photoanodes made from large ZIF-67-modified TiO2 and TiO2, this photoanode could provide more effective photocathodic protection for 304SS.