Preparation Of Carbon Materials Modified TiO₂ Composite Visible Light Photocatalyst And Study On The Mechanism Of Photoinduced Interfacial Charge Transfer

With the development of economy,not only the balance of natural environment but also human health was affected because industrial waste and waste water processing technology was not mature enough.So it was urgent to develop a new waste treatment with the worsening of environment pollution.For this reason,the photocatalysis based on semiconductors gradually came into people's eyes.Photocatalysis was a promising photochemical technology,which has been widely studied since the 1970s due to its energy saving,environmental friendliness and sustainability.Among these semiconductors,TiO₂ was widely used for photocatalytic degradation of organic pollutants due to its high photocatalytic activity and good chemical stability.However,TiO₂ also had many inherent shortcomings:?1?wide bandgap and low light absorption capacity,?2?rapid recombination of photoinduced hole-electron pairs and low quantum efficiency,?3?difficult to recycle and low using efficiency.These issues restricted the further development and practical application of TiO₂ photocatalytic technology.This theses focused on the above-mentioned issues and tended to modify the interface of TiO₂ materials by using different carbon materials,like graphene oxide,C₃N₄ and conjugated mesoporous polymers,aiming at improving the photocatalytic activity of TiO₂ under visible light irradiation.Meanwhile,the reduction behavior of electrons on different carbon materials was explored,and the influence of the reduction behavior on the photocatalytic activity was also investigated,which provided theoretical and experimental basis for the design and application of new photocatalytic materials.The specific research contents were as follows:?1?Using TiCl₃ as a titanium source,a visible-light-driven Ti³⁺-TiO₂-r GO composite photocatalyst with high photocatalytic activity was prepared by the microemulsion method.The content of Ti?III?in the lattice was effectively controlled by the amount of GO added,and the effect of different Ti?III?content on the photocatalytic activity was also explored.It was revealed from the experimental results that GO could serve as the aggregation center and oxidant of Ti-containing compounds due to the negative charge on the surface,so more Ti?III?could be introduced into the Ti³⁺-TiO₂-r GO composite by hydrolysis.Among the self-doped samples,the larger the GO content added,the more the Ti?III?content in the crystal lattice,and the higher the peak intensity of the ESR spectra obtained.The introduced GO could act as an oxidant to regulate the content of Ti?III?in the crystal lattice and promote the separation of photoinduced hole-electrons pairs,resulting in higher photocatalytic activity.When the addition amount of GO was 0.2 m L,the photocatalytic activity of Ti³⁺-TiO₂-r GO was the highest,and the removal rate of methyl orange reached 80.3%under visible light irradiation for 90 min,which was 1.76 times that of pure Ti³⁺-TiO₂.?2?Using tetrabutyl titanate as a titanium source,TiO₂ microspheres were prepared by solvothermal method.In addition,Fe?III?clusters were grafted onto the surface of TiO₂microspheres by a simple deposition method to trigger interfacial charge transfer?IFCT?,which resulted in the red shift of TiO₂ photoresponse.The TiO₂-Fe-C₃N₄ composite was prepared by introducing C₃N₄ to further improve the separation efficiency of photoinduced hole-electrons pairs of TiO₂-Fe.The experimental results showed that the Fe?III?clusters on the surface of TiO₂ microspheres could trigger the IFCT effect,and act as a electronic bridge that transferred photoinduced electrons from TiO₂-Fe to the valence band of C₃N₄,leaving the photoinduced holes in the valence band of TiO₂ and photoinduced electrons in the conduction band of C₃N₄for the degradation of organic pollutants,improving the photocatalytic activity of the composite greatly.In addition,due to the introduction of C₃N₄,the amount of photoinduced holes in the valence band of TiO₂ in the TiO₂-Fe-C₃N₄ composite was significantly higher than that of TiO₂-Fe,which indicated that the IFCT effect was greatly improved.When the loading of C₃N₄ was10wt%,the photocatalytic activity of TiO₂-Fe-C₃N₄composite photocatalyst was the highest.Under visible light irradiation for 60 min,the removal rate of methyl orange reached 86.9%,which was 25.17 times higher than that of TiO₂-C₃N₄ composite.?3?For the first time,copper porphyrin?CuP?as a monomer was polymerized on the surface of TiO₂ microspheres obtained by a solvothermal method to construct a TiO₂-Cu CMP photocatalyst with high photocatalytic activity under visible light irradiation.It has been found that Cu?II?on copper porphyrin could trigger the IFCT effect and shift the photoresponse of TiO₂ to the visible light region.After absorbing visible light,the electrons in the valence band of TiO₂ could be transferred to the copper porphyrin,leaving holes in the valence band of TiO₂for the degradation of organic pollutants.At the same time,due to the excellent conjugated structure of the conjugated polymer,the electrons transitioning to the copper porphyrin could perform multi-electron reduction,greatly improving the photocatalytic activity of the TiO₂-Cu CMP composite under visible light irradiation.The experimental results confirmed that the IFCT effect was the main reason for improving the photocatalytic activity of the composite.Under visible light irradiation,the photocatalytic performance of TiO₂-Cu CMP for the degradation of methyl orange was significantly better than that of pure TiO₂-CMP and TiO₂-Cu,which was probably ascribed to the synergy effect between TiO₂-CMP and TiO₂-Cu.The amount of photoinduced holes in the valence band of TiO₂ in the TiO₂-Cu CMP composite was significantly higher than that of TiO₂-Cu,which indicated that the IFCT effect was greatly improved due to the introduction of the excellent conjugated structure.?4?Using iron porphyrin and TiO₂ microspheres as raw materials,a complex of conjugated mesoporous polymers with iron porphyrin as monomers was constructed on the surface of TiO₂microspheres to prepare TiO₂-Fe CMP composite.The analysis of ESR confirmed that the presence of Fe ions in the polymer could trigger the IFCT effect,and the holes in the valence band of TiO₂ microspheres could be excited under visible light irradiation.By comparing the photocatalytic MO degradation of TiO₂-Fe CMP composite with the corresponding free-radical trapping agents,it was found that photoinduced holes in the valence band of TiO₂ played a major role during the degradation process.In addition,oxygen reduction reaction?ORR?was found in the TiO₂-Fe CMP composite through CV scanning.It was found that the transferred electron number of TiO₂-Fe CMP at reaction times of 0 h,6 h,12 h,and 18 h were 1.83,2.36,3.32,and 2.07,respectively,and their photocatalytic activity was quite different.It was revealed from ESR analysis that TiO₂-Fe CMP series composites had different numbers of photoinduced holes,which had a corresponding relationship with the photocatalytic performance.Based on the previously interfacial electron migration mechanism,the mechanism of multi-electron reduction were analyzed.It was confirmed that the four-electron oxygen reduction reaction was more favorable for the generation of holes in the IFCT process than the two-electron oxygen reduction reaction.More holes could be used for the degradation of pollutants,and a better photocatalytic degradation effect was achieved.