Study On The Photogenerated Cathodic Protection Of TiO₂ Nanocomposites For Metals

This study pays attention to the photocathode protection,a newly developed corrosion protection methods for metals,and discusses the photocathode protection performance of several nanocomposites under visible light.TiO₂ has attracted wide attention in the field of photocathode protection due to the advantages of low cost,non-toxic,chemical stability,excellent photoelectric performance as well as simple preparation.However,because of a large band gap,TiO₂ possesses a narrow light response range,which can only absorb ultraviolet light.Besides,the photovoltaic properties of TiO₂ are also affected immensely by its high recombination rate of photogenerated carriers.In response to these shortages,narrow gap semiconductors were combined with TiO₂ to enhance the photocathode protection performance of composites.Firstly,the TiO₂ nanotube arrays were prepared on the titanium substrate by two-step anodization.Subsequently,Fe₂O₃,Bi₂Ti₂O₇ and In₂S₃ nanoparticles were modified on the TiO₂ nanotube arrays by successive ionic layer adsorption and reaction?SILAR?method,chemical bath and hydrothermal method.The morphology,crystal structure and element state of the composites were observed by scanning electron microscope?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The photocathodic protection properties of composite materials for metal were discussed by electrochemical method.?1?Fe₂O₃ nanoparticles were decorated on the surface of TiO₂ nanotube by chemical bath method.The amount of Fe₂O₃ nanoparticles was changed by changing the concentration of iron source?Fe?NO₃?₃?in the preparation process.The results declared that when the concentration of Fe?NO₃?₃ solution was 0.05 mol/L,the open circuit potential decreased to 500 mV and the photoinduced current density was 40?A/cm²,which was the best one for the photocathodic protection for 304 stainless steel.Due to the charge accumulation,the contact interface between Fe₂O₃ and TiO₂will form an effective heterojunction,which changes the relative position of the guide band,promotes the electronic transmission and improves the photocathode protection performance.?2?The octahedral Bi₂Ti₂O₇ nanoparticles were successfully prepared on the TiO₂ nanotube by hydrothermal method.Then the photocathode protection properties of Bi₂Ti₂O₇/TiO₂ nanocomposites for 304 stainless steel and Q235 carbon steel were analyzed by electrochemical method.Under the intermittent visible light,the coupling potential of Bi₂Ti₂O₇/TiO₂ composite and 304 stainless steel decreased to670 mV,and the photoinduced current density was 45?A/cm²,while the coupling potential of Bi₂Ti₂O₇/TiO₂ composite and Q235 carbon steel decreased to 330 mV,and the photoinduced current density was 30?A/cm².It turned out that Bi₂Ti₂O₇/TiO₂nanocomposite owned an outstanding photocathode protection for 304 stainless steel and Q235 carbon steel.?3?In₂S₃ nanoparticles were loaded on TiO₂ nanotube by successive ionic layer adsorption and reaction method.The photoinduced cathodic protection properties of In₂S₃/TiO₂ nanocomposites for 304 stainless steel without hole trapping agent was researched.It illustrated that In₂S₃/TiO₂ nanocomposites owned narrow band gap and excellent light response,enhanced photoresponse performance and superior photocathodic protection performance for 304 stainless steel.When the number of In₂S₃ deposition was 35 times,the photocathode protection on 304 stainless steel under visible light in 3.5%NaCl solution was optimal.