The Photoelectrochemical Properties Of Visible Light Catalyst In The Metal Anti-corrosion Protection

The corrosions of metals spread all over the ecnomics in the world.The corrosions not only bring the occurrings of lots of problems,but also result in ecnomical losing that is hard to estimate.It was reported that the losing of all over the world due to the corrosion of metals accounts for 3%～5%of GNP.In our country,the direct losing of metal corrosion exceeded to 28 billion Yuan,while at 2004,it has arrived to 50 billion Yuan,which has exceeded the losing summations of all the natural disasters and accidents.It was proposed that the photoinduced charge-transfer process at the semiconductor photocatalyst interface can be applied to metal corrosion prevention.Theoretically,the semiconductor used is not consumed in the process of cathodic protection,thus it has a long lifetime.In the long run,it can take advantage of the inexhaustible solar energy.However,the photocatalysts so far used for metal corrosion prevention are generally semiconductors with wide band-gap.They can only absorb the ultraviolet radiation,which accounts for a small portion of the solar spectrum.So it is therefore of great significant on how to widen the spectrum response range of the photocatalysts and to take fully use of solar light to protect metals.In this dissertation,visible-light responsive Bi₂MoO₆,MNb₂O₆(M=Ni,Co) photocatalytic materials were synthesized via solid-state reactions,hydrothermal process,and citric complexation method.The characterizations of these materals were conducted by X-ray diffraction(XRD),scanning electron microscope(SEM) and ultraviolet-visible diffuse reflection spectrometer(DRS) techniques.The crystal structures,morphologies and photophysical properties were analyzed and discussed. In addition,the photoelectrochemical conversion and the anticorrosion properties for carbon-steel of these materials were investigated under the illumination of visible-light.First,bulk Bi₂MoO₆ and Bi₂MoO₆ nanoplates were synthesized using the solid-state method and hydrothermal method,respectively.DRS results revealed that samples synthesized using the two methods display good visible light absorption properties.The Bi₂MoO₆ sample with the nanoplate morphology showed a blue shift compared with the bulk sample.In addition,an enhanced photo-to-currrent conversion efficiency was observed over the Bi₂MoO₆ nanoplate photoelectrode. However,the photoelectrochemical anticorrosion properties of the Bi₂MoO₆ product on preoxided carbon steel electrode revealed that the coating can mechanically protect the metal but can not play the effect of cathdic protoprotection effect.This is because the potential of the conduction band of Bi₂MoO₆ is more positive than the electrode potential of carbon-steel,which the photogenerate electrons cannot be transported to the metal and protect the metal.Then,MNb₂O₆(M=Ni,Co) photocatalysts were prepared by citric complexation method.Both materials have been found showing good visible-light absorption and excellent photo-to-current coversion properties.The photoelectrochemical anticorrosion experiments indicated that the MNb₂O₆(M=Ni,Co) can play a role in cathodic photoprotection.