Research On The Photocathodic Protection Performance Of TiO₂ NTAs Enhanced By Metal Sulfide

With a long coastline,China has witnessed the rapid development of Marine economy in recent years.The construction volume of coastal engineering,wharf and sea-crossing bridge expands rapidly,and a large number of steel materials are applied.However,Marine corrosion is one of the major threats to the development of Marine economy.Therefore,marine environment corrosion and corrosion control have been paid much attention by domestic and foreign scholars.Photocathodic protection can effectively take advantages of the abundant solar energy and high salinity of Marine environment to protect steel materials.TiO2 nanomaterials are commonly used semiconductor materials in the field of photocathodic protection.However,TiO2 also has some defects,which hinder the application of TiO2 nanomaterials.For example,the large bandgap width of TiO2 nanomaterials limits its visible light absorption performance,resulting in the waste of most of the energy in the solar spectrum.The recombination rate of photoinduced carriers in the TiO2 nanomaterials is too high to effectively utilize photoinduced electrons and provide sufficient photoinduced electrons for the protected steel.In this paper,TiO2 nanotube arrays(TiO2 NTAs)were modified by sulfide to broaden its light absorption range and accelerate the separation of photoinduced carriers.Specific research contents are as follows:(1)TiO2 NTAs with uniform diameter,independent and highly ordered were prepared by two-step anodic oxidation method.And the morphology and composition of the samples were characterized by scanning electron microscope and X-ray diffraction(2)The Q235 carbon steel is a common steel used in Marine engineering.For the corrosion of Q235 carbon steel in Marine environment,TiO2 was modified by hydrothermal method with on the surface of TiO2 NTAs supported by.As a narrow band gap(2.1 eV)semiconductor material,CdIn2S4 is an ideal material for improving the visible light response of semiconductor composites.The conduction band(-0.76 eV)of CdIn2S4 is more negative than that of TiO2(-0.29 V),which could cause the negative shift of the Fermi level of TiO2.As a ternary semiconductor,CdIn2S4 is much more stable due to the presence of In3+ along with Cd2+.In addition,similar to TiO2,CdIn2S4 is an n-type semiconductor.The recombination of photoinduced carriers could be inhibited due to the construction of an n-n type heterogeneous betwewn CdIn2S4 and TiO2.Therefore,the loading of CdIn2S4 on the surface of TiO2 could improve the photocathodic protection properties of TiO2.Under visible light illumination,CdIn2S4/TiO2 nanocomposites can provide a photoinduced current density of approximately 50 μA/cm2 and potential drop of approximately 400 mV.(3)The 304 stainless steel is another common steel used in Marine engineering.For the corrosion of 304 stainless steel in Marine environment,TiO2 was modified by hydrothermal method on the surface of TiO2 NTAs supported by MoS2 nanospheres.As a metal sulfide,MoS2 is of a smaller band gap and a wider light absorption range than TiO2,which is conducive to widening the light absorption range of sensitized TiO2.MoS2 is a p-type semiconductor,which can form p-n heterojunction at MoS2/TiO2 interface after composite with TiO2 NTAs.Hence MoS2 could accelerate the separation of photoinduced carriers.In addition,MoS2 is a layered semiconductor from the 2D transition metal dichalcogenide family with high conductivity,which further accelerates the separation of photoinduced carriers.Therefore,compared with TiO2 NTAs,MoS2/TiO2 nanocomposites have better photocathodic protection performance.Under visible light illumination,it can provide a photoinduced current density of approximately 45 μA/cm2 and potential drop of approximately 500 mV.(4)In order to further improve the separation efficiency of photo induced carriers,TiO2 was modified by the deposition of In2S3 and Ag nanoparticles on the surface of TiO2 NTAs by successive ionic layer adsorption and reaction(SILAR)and photoreductions.The narrow band gap of In2S3 can effectively improve the absorption performance of TiO2 in the visible light region.The Localized Surface Plasmon Resonance of Ag nanoparticles can inhibit the recombination rate of In2S3 and TiO2.They can effectively improve the photocathodic protection performance of TiO2 NTAs.Under visible light illumination,In2S3/Ag/TiO2 nanocomposites can provide a photoinduced current density of approximately 45 μA/cm2 and potential drop of approximately 530 mV.(5)TiO2 was modified by grafting 4NBT onto TiO2 NTAs by hydrothermal method.The formation of Ti-S bond improves the valence band structure of TiO2 NTAs,reduces the band gap width and increases the visible light absorption range of 4NB-TiO2 nanocomposite.The presence of benzene ring in 4NBT accelerates the separation of photoinduced carriers.Therefore,compared with TiO2 NTAs,4NB-TiO2 nanocomposite have better photocathodic protection performance.Under visible light illumination,it can provide a photoinduced current density of approximately 20μA/cm2 and potential drop of approximately 320 mV.In summary,the research in this article not only improves the photocathodic protection performance of TiO2 NTAs,but also has a deep discussion on the mechanism of photocathodic protection.It provides a lot of references for the modification of TiO2 NTAs for photocathodic protection in the future.