Study On Construction And Performance Of Multi-composite Photocatalytic Material System

Photocathodic protection(PCP)is a metal corrosion protection technology that perfectly combined the utilization of light energy and cathodic protection,which has gradually developed into a research hotspot in recent years.However,the PCP technology still has technical problems such as narrow absorption spectrum,low photoelectric conversion efficiency,large electronic transmission loss,and poor dark-state protection performance.The root cause of the above problems is that the currently used photocatalytic materials are relatively single and lack composite functional design and performance integration optimization.Therefore,it is urgent to carry out the research and construction of the composite material system,starting from the production,separation,transfer,storage and other links of the photoelectron to carry out the functional design and performance control of the material.This thesis has carried out a systematic study on the four scientific issues of photocatalytic materials:spectral absorption,carrier separation,photoelectron transfer,and photoelectron storage.Using quantum dots(QDs)sensitization,heterostructure construction,oxygen vacancy introduction,conductivity enhancement,energy storage design and other technical solutions,four kinds of photocatalytic composite materials were prepared.A composite photocatalytic material system was constructed,and its synergy mechanism has been studied.The main research contents and results were as follows:1.The sensitization strategy was used to prepare the TiO2@CdSe binary composite material,which successfully solved the problem of the limited light absorption range of TiO2.First,CdSe QDs with a wide spectral absorption range,good dispersibility and small particle size were prepared in a typical high internal phase emulsion(HIPE)system.The influence of growth space size and raw material ratio on the dispersion and light absorption properties of QDs was studied.HRTEM,XPS,UV-vis absorption spectroscopy test results showd that the TiO2@CdSe composite has a nano-sheet morphology and close interface contact,the absorption edge was red-shifted by 134nm,showing a significantly broadened visible light absorption characteristic.Under simulated sunlight irradiation,the self-corrosion potential of 304 stainless steel(304SS)coupled with TiO2@CdSe photoelectrode dropped to-675mV,showing excellent PCP effect.In addition,the degradation efficiency of TiO2@CdSe composite material for sewage containing methylene blue has been increased from 41.5%(pure TiO2)to 90.5%.From the perspective of other applications,the prepared binary composite material has good visible light absorption characteristics and photoelectric conversion performance.2.The pyramid-BiVO4 with abundant oxygen vacancies was successfully synthesized by the low-temperature solvothermal method,and the BiVO4/CdSe heterojunction system was constructed with CdSe QDs,which effectively improved the carrier separation efficiency of the BiVO4 photocatalytic material.SEM,XPS,and ESR test results showed that adjusting the pH and adding sodium dodecyl benzene sulfonate(SDBS)surfactant has a greater impact on the morphology and oxygen vacancy concentration of the BiVO4,and it was found that the pyramid-BiVO4 has the largest concentration of oxygen vacancies.Simultaneously,the construction of BiVO4/CdSe heterojunction system by introduced CdSe QDs,which further promotes the solar energy harvest and the carriers separation.The photoelectrochemical performance test results showd that after 304SS coupled with 8BiVO4/CdSe(8V-BC)photoelectrode,the photocurrent density(608 ?A·cm-2)and the corrosion potential drop(708mV)were 5.06 times and 2.10 times that of the original BiVO4,respectively,showing a significantly enhanced cathodic protection effect.In addition,the 8V-BC photoelectrode reduced the self-corrosion potential of 65Mn carbon steel from-593mV to-920mV,which also showed a good cathodic protection effect.3.In order to solve the problem of low transfer efficiency of photoelectrons to metal substrates,Ti3C2 was introduced as a photoelectron transfer agent into the field of PCP for the first time.A thin-layer Ti3C2 was prepared by etching-stripping strategy,and the effect of etching time and temperature on its layered structure,conductivity and hydrophilicity were investigated.Further research found that when the ratio of BiVO4 to Ti3C2 was 1:2,it can self-assemble into BiVO4/Ti3C2 microspheres due to the electrostatic adsorption effect of the functional groups on the Ti3C2 surface.The results showd that the self-corrosion potential of 304SS negatively shifted to-921 mV under simulated sunlight irradiation,which was 800mV lower than that of self-corrosion potential,showing excellent cathodic protection performance.The excellent PCP performance of BiVO4/Ti3C2 microspheres can be attributed to the following aspects:The conductivity of Ti3C2 promotes the transfer efficiency of photoelectrons to metal and inhibits the recombination of photoelectron-hole pairs on the surface of BiVO4;The hydrophilicity of Ti3C2 enables the interface contact between the composite microsphere and the electrolyte more sufficient;The BiVO4/Ti3C2 composite intercalation structure could prevent Ti3C2 from stacking and collapse,which was beneficial to maintain the stability of the microspheres.4.This thesis designed and prepared TiO2/CdSe/polyaniline(PANI)/graphene(TCPG)quaternary composite material with energy storage performance,which has made a technological breakthrough in solving the dark state protection in the field of PCP.At the same time,in order to solve the problems of complex structure and low electron conduction efficiency of existing PCP devices.A PCP coating(ETCPG)was developed with TCPG as the core material to realize in-situ protection of the metal under the coating.The performance test results showd that under simulated sunlight irradiation,the photocurrent density of 304SS coated with ETCPG coating reached 340?A·cm-2,and the self-corrosion potential dropped from-408mV to-844mV,showing an excellent cathodic protection effect.More importantly,the double conversion structure of PANI endows the ETCPG coating with charging/discharging functions,resulting in a certain energy storage effect,so that the PCP effect can last for 4 hours in the dark state.The 15-day seawater immersion corrosion test results showd that the anticorrosion shielding performance and PCP effect of the ETCPG coating have not changed significantly,indicating that the coating has good chemical stability and functional continuity.