Fabrication Of Array Nano Semiconductor Composites And Their Photocathodic Protection Effects

The photocathodic protection,a newly technique combined with the traditional cathodic protection technology and semiconductor optoelectronic technology,has been highly concerned by the corrosion researchers.The basic principle of the photocathodic protection technology is to inhibit metal corrosion through making the metal enter cathodic polarization region utilizing the photoelectrons generated in the semiconductor material under illumination.It is a corrosion protection method with good application prospects benefited from its superiorities of non-toxic,energy-saving,environmentally-friendly,sustainable and easy maintenance.At present,photocathodic protection researches mainly focus on the design and develop of photoanodes.TiO2-based semiconductor is the earliest and most studied photoanode material.The advantages of TiO2 semiconductor materials are obvious,and the defects cannot be ignored neither.TiO2 is green,non-toxic,low cost,easy preparation,has high chemical stability,high catalytic activity,and its morphology can be controlled precisely.However,TiO2 has a wide bandgap(3.0-3.2 eV)without visible light absorption,and the photogenerated electrons and holes trend to recombined,showing a low photoelectric conversion efficiency.Moreover,TiO2 cannot store photoelectrons,resulting in that the photocathodic protection will disappear once the light supply is cut off.These all shortages are the technical barriers to obstruct the industrial application of TiO2 based photocathodic protection technique.How to overcome these technical problems is the research focus of the corrosion researchers.In order to overcome these technical problems,in this work,various TiO2-based photoanodes were developed by surface modifications.At the same time,a new type of photoanode based on WO3 was designed and synthetized.In this paper,the morphology controls,photoelectrochemical properties,photoelectric conversion mechanisms and photocathodic protection effects of the obtained photoanodes were studied in depth through various modern characterization techniques.The main research contents and research progress are as follows:(1)A two-step method including anodization and pulse current electrodeposition was developed to fabricate a ?-Bi2O3/TiO2 composite photoanode with high photoelectrochemical performance.Due to the p-n heterojunction at ?-Bi2O3 and TiO2 interface,the charge separation and transfer efficiency was significantly improved.Its photocurrent was 80 ?A/cm2,which is four times that of the pure TiO2.When 403SS was coupled with the ?-Bi2O3/TiO2 photoanode,its potential can be negatively shifted by 450 mV,showing an obvious photocathodic protection effect.(2)A new Ag/g-C3N4/TiO2 ternary composite photoanode was brought via anodization,chemical vapor deposition(CVD)and chemical bath deposition(CBD)techniques.Due to the heterojunction structure between g-C3N4 and TiO2,and the synergistic effect of Ag SPR effect,the photoelectrochemical performance of the photoanode was significantly enhanced.The light absorption range was extended to visible light region,the separation efficiency of photogenerated carriers was improved,and the photocurrent density reached 135 ?A/cm2,which was 11 times that of TiO2.Under white light,the composite film can reduce the 403SS potential by about 530 mV,which was much better than of the TiO2 photoanode(?270 mV).(3)A new process containing hydrothermal and CVD was proposed to construct a g-C3N4/SrTiO3/TiO2 composite photoanode.In this composite,g-C3N4 has visible light response,and the highest the conduction band position,and TiO2 has the lowest conduction band position.Such an energy band arrangement greatly promoted the separation of electrons and holes,and significantly enhanced the photoelectrochemical performance with a photocurrent density of 180 ?A/cm2.In the photocathodic protection application,the 403SS coupled with the g-C3N4/SrTiO3/TiO2 composite can be polarized to about-580 mV(vs.SCE),and the photocathodic protection effect was remarkable.(4)A WO3-based photoanode(ZnS-Bi2S3/TiO2/WO3)was designed and prepared through a three-step process.In this photoanode,WO3 is the matrix and electron storage material,TiO2 is the transition layer for electron transport,Bi2S3 is the photosensitive material,and ZnS is the protective layer.The synergistic effect of the four materials makes the composite have good optical storage properties,visible light response,high charge separation efficiency and stability.Under white light,the composite film can provide a cathodic protection of?540 mV for 403SS,and the cathodic protection can be maintained for at least 20 h after the light supply was stopped.