Photocatalytic Properties Of Carbon-modified TiO₂ Composites With Different Crystal Planes

In recent years,with the emergence of environmental pollution and energy shortage problems,semiconductor materials have attracted more and more attention dut to their huge application potential in photocatalytic degradation of pollutants and photocatalytic hydrogen production.TiO₂ is one of the most popular semiconductor materials with advantages of non-toxic,low cost and high catalytic activity.However,the development of TiO₂ in the field of photocatalysis is limited by the defects of low solar light utilization and high electron hole recombination.Carbon materials can expand the response spectrum of TiO₂ to visible light and reduce the recombination efficiency of its electron hole pairs.Therefore,the composite of carbon and TiO₂ has been one of the hot spots in photocatalytic research.At the same time,the exposed crystal surface also has a great influence on the catalytic activity.It is of great significance to study the process of TiO₂ with different exposed crystal planes to degrade organic pollutants for understanding the photocatalytic principle of nanomaterials and improving its catalytic activity.However,as far as anatase TiO₂ is concerned,there is no uniform conclusion about the catalytic activity of the two exposed crystal planes {101} and {001}.Based on these results,this paper mainly did the following two aspects of research:（1）The composite of carbon quantum dots（CQDs）with good luminescent properties,CQDs and TiO₂ with different crystal surface exposure ratios（TiO₂（001）/CQDs,TiO₂（101）/CQDs）were synthesized by hydrothermal method.Fluorescence spectroscopy shows that the fluorescence peaks of CQDs exhibit very different response characteristics under short-wavelength and long-wavelength excitation,which may be due to the different emission centers of oxygen-containing groups on the surface of CQDs.The fluorescence lifetime results show that there is an obvious electron transfer between CQDs and TiO₂,and the direction is from CQDs to the conduction band of TiO₂,indicating that CQDs can effectively sensitize TiO₂.Compared wtih TiO₂（001）,CQDs is able to sensitize TiO₂（101）more efficiently,resulting in higher catalytic activity of TiO₂（101）/CQDs under visible light.This may be due to the introduction of F ions during the preparation of TiO₂/CQDs,which weakens the sensitization effect of CQDs and TiO₂（001）,thereby reducing its catalytic activity.（2）The composites of amorphous carbon and TiO₂ with different crystal plane exposure ratios（TiO₂（101）/C,TiO₂（001）/C）were synthesized by hydrothermal method,and their morphology,structure and visible light catalytic performance were characterized.The results show that although the time difference between TiO₂（001）/C and TiO₂（101）/C for complete degradation of Rh B is not significant,the formation rate of intermediate product（Rh-110）is faster in TiO₂（001）/C/Rh B system,which indicates that {001} surface is more favorable for the deethylation reaction of Rh B at the early stage of reaction.Based on these results,this paper proposes a possible explanation that the synergistic effect of TiO₂ and carbonaceous materials on its surface can degrade Rh B under visible light,and the difference of facet properties and energy band structure leads to the degradation process of Rh B showing the characteristics related to crystal surface.Our findings provide the evidence for revealing the relationship between the photocatalytic activity of TiO₂ nanoparticles and the exposed crystal plane.In this paper,two kinds of catalysts,TiO₂/CQDs and TiO₂/C,were synthesized for the low utilization of TiO₂ to sunlight under visible light.The optical properties of the composites were analyzed,and the catalytic properties of the two composite materials under visible light were studied with Rh B as degradation object.The results show that the addition of two kinds of carbon materials can effectively improve the catalytic activity of TiO₂ under visible light,and the electron transfer process between CQDs and TiO₂ and the degradation process of Rh B have a certain dependence on the exposed crystal surface of TiO₂.The research results in this paper are of great significance for improving the catalytic activity of TiO₂ under visible light,in-depth understanding of the dependence of the catalytic activity of TiO₂ on the crystal plane and the exploration of other new semiconductor catalytic materials.