Studies On The Synthesis Of TiO₂ Heterojunction And The Photocatalytic Performance

With the rapid increase of the global population,economic development and social progress,people's requirements for the living environment and quality of life are also getting higher and higher.At the same time,industrial wastewater,agricultural sewage,domestic sewage,domestic waste,air pollution and the like,not only affect our physical and mental health,but also threaten to future generations.Photocatalysis is a hot research topic in recent years,of which TiO₂ is a kind of two element transition metal oxide.It has many advantages,such as nontoxicity,good chemical stability,simple synthesis method and so on.But there are unavoidable drawbacks,which is a wide band gap,limiting the use of solar light.This paper successfully prepared anatase/rutile heterojunction material?TiAR?,anatase/brookite heterojunction material?TiAB?and mesoporous CdS/TiO₂ heterojunction material?CdS/TiO₂?,studyed the effect of H₂ reduction and H₂O₂ oxidation process on the surface properties of anatase/rutile heterojunction material?TiAR?and anatase/brookite heterojunction material?TiAB?and the relationship between the surface chemistry and photocatalytic properties,also discussed the optimal doping ratio of cadmium sulfide in TiO₂.In addition,SEM,BET,TEM,XRD,Raman,Uv-Vis,XPS,EPR and Zeta potential were used to characterize the crystal type,texture characteristics,morphology,crystal structure and surface chemical state of materials.The photocatalytic properties were tested by photocatalytic degradation experiment and light current experiment.The concrete research content are as follows:?1?Anatase/rutile heterojunction material?TiAR?was prepared by hydrothermal method,and the TiAR were respectively reduced in H₂ and oxidized in H₂O₂ solution to study the effects of reduction and oxidation treatment on the properties of anatase/rutile heterojunction?TiAR?.The results showed that TiAR was consisted of nanoparticles?anatase?and nanobricks?rutile?,with nanoparticles patched on nanobricks.Whether H₂ reduction treatment or H₂O₂ oxidation treatment,TiAR retained its morphology,crystalline phase and particle size,only the phase ratio and band gap changed slightly.H₂-reduced TiAR demonstrated lower activity in methylene orange?MO?degradation.On the contrary,the activity of H₂O₂-oxidized TiAR was higher than that of untreated TiAR,among which,TiAR?H₂O₂160?showed the highest activity.?2?Anatase/brookite heterojunction material?TiAB?was prepared by hydrothermal method,and the TiAB were respectively reduced in H₂ and oxidized in H₂O₂ solution to study the effects of reduction and oxidation treatment on the properties of anatase/ brookite heterojunction?Ti AB?.The results showed that TiAB was consisted of nanoparticles?anatase?and nanorods?brookite?,and the nanorods had a dominant position.Whether H₂ reduction treatment or H₂O₂ oxidation treatment,TiAB retained its morphology,crystalline phase and particle size,only the phase ratio and band gap changed slightly.Untreated TiAB demonstrated the highest activity in methylene orange?MO?degradation,mainly because the surface Ti3+ and oxygen vacancies could enhance the charge separation.Both reduction and oxidation treatment could lead to the decrease of TiAB activity,and the decrease of TiAB?H₂O₂?activity also depended on the reaction temperature.?3?Mesoporous TiO₂ and a series of mesoporous CdS/TiO₂ heterojunction material?CdS/TiO₂?with different molar ratios were prepared by sol gel method,and the photocatalytic activity of TiO₂ was improved by adjusting the proportion of CdS.The results showed that UV-vis spectra of heterostructure had an obvious red shift when the molar ratio of CdS and TiO₂ was 0.12.Its photocatalytic performance was better than pure mesoporous TiO₂ and pure CdS,activity and stability were still good even after five cycle of degradation of methyl orange solution,indicating that the amount of CdS is the most suitable for suppressing the recombination of electrons and holes,which can increase the charge separation of CdS/TiO₂ composites.In addition,degradation for methylene blue,bisphenol A?BPA?,rhodamine B and malachite green further showed that the catalyst was provided with the most significant performance when the molar ratio of CdS to TiO₂ was 0.12.