Photocathodic Protection Performance Of Metal Complexes Of TiO₂ For 304 Stainless Steel

Nowadays,corrosion is a common problem which facing all countries in the world.The marine environment is complex,especially dueing to the effect by the chloride ions(Cl-),the passivation film of low carbon steel,stainless steel and other metals used in the oceanographic engineering tends to be destroyed in marine environments,accelerating corrosion.At present,several methods have been proposed to slow down the corrosion rate of marine metal materials,such as anticorrosion coating,corrosion inhibitor,cathodic protection and so on.Photocathodic protection is a new protective measure for marine metals.And the materials commonly studied are TiO2 semiconductor and its composites.TiO2 is a kind of economic,safe,environmentally friendly semiconductor.It has wide applications in antibacterial,water treatment,antifouling,solar cells and so on.It also has a considerable application prospect in photocathodic protection for marine metals.However,TiO2 is a semiconductor with wide band gap(3.2 eV),the sunlight utilization rate and photogenerated carrier separation rate are low,so it can not take an effective protective for metals in photocathodic protection,so we devoted to studying the application of high efficiency metal complexes of TiO2 in stainless steel anticorrosion.In this paper,we synthesized TiO2 nanotubes on titanium substrate by an electrochemical anodization method,and then modified TiO2 by Ag2S,ZnFeAl-LDHs and ZnPc nanomaterials,respectively.The morphologies,crystal structures,elemental compositions and light absorption capabilities of the TiO2 and its metal complexes were characterized by optical microscope(OM),scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),attenuated total reflectance-fourier transform infrared spectroscopy(ATR-FTIR)and ultraviolet-visible diffuse reflectance spectroscopy(UV-vis DRS)analyses.The performances of photocathodic protection for 304SS were evaluated by the electro-chemical methods including open-circuit potential,photocurrent density and Tafel polarization curves.The main contents are summarized as follows:In this paper,Ag2S-TiO2 composites were prepared by hydrothermal method.The photocathodic protection performances of Ag2S-TiO2 composites synthesized by different sulfur sources-sodium sulfide(Na2S),sodium thiosulfate(Na2S2O3),thioacetamide(CH3CSNH2)were examined.The results showed that Ag2S-TiO2 composites were successfully synthesized by hydrothermal method,and the composites exhibited good photocathodic protection performance due to the enhanced visible-light absorption under light irradiation and increased separation and transport efficiencies of the photocarriers.The photocathodic protection abilities of Ag2S-TiO2 were influenced by sulfur sources.The Ag2S-TiO2 composite all exhibited good visible light absorption and photoelectric conversion compared with pure TiO2.The Ag2S-TiO2 composite with Na2S as sulfur source exhibited the optimal photocathodic protection performance,the protective potential can reach-840 mV under vislble light illumination,which is much lower than the self corrosion potential of 304 stainless steel(304SS),and the maximum current density can reach 30μA/cm2.In this paper,ZnFeAl-LDHs/TiO2 composites with various concentrations of ZnFeAl-LDHs were synthesized by hydrothermal method.The results showed that all the composites exhibit better photocathodic protection performances for 304SS than pure TiO2 which is attributed to the synergistic mechanism of their unique structure and visible-light response property.The composite with a concentration of 80 mmol/L of ZnFeAl-LDHs exhibits the best performance,and the protection potential can reach-760 mV under visible light illumination,and is lower than the corrosion potential of 304SS in the dark.Moreover,the composites have good stability and durability,this work provides a probable approach for effective and stable photocathodic protection of marine metal.In this paper,ZnPc was successfully prepared by solid phase synthesis method,then ZnPc-TiO2 was successfully synthesized by simple coating method.The results show that the visible light absorption of ZnPc-TiO2 composite material is obviously improved compared with pure TiO2,the visible absorption peak of visible light appears in 550 nm.And all the composites exhibit better photocathodic protection performances for 304SS than pure TiO2.The composite with an amount of 100 μL of ZnPc exhibits the best photocathodic protection performance,and the protection potential can reach-700 mV under visible light illumination,and the maximum current density can reach 90 μA/cm2.These three metal complexes of TiO2 have good visible light absorption properties,and exhibit good photocathodic protection performance for 304 stainless steel.