Mechanism On Photocatalytic Treatment Of Environmental Contaminants With TiO₂-Based Nano Hollow Sphere

Water pollution was a global environmental problem that threatened ecosystem function and human health.Human involvement in the degradation of pollutant was a huge challenge.Finding an efficient,low-energy nanocomposite that could deeply oxidize water pollutants has become a major issue for scientists.It was also a frontier in the fields of environmental science and engineering,materials science,etc.This paper was mainly based on the demand for pollutant treatment,and raised the scientific questions of "the rapid recombination of photo-generated electron-hole pairs result the low photon yield of catalys",and we used a new method for the interface structure of nanomaterials("shell-shell composite+precious metal interlayer")was constructed to realize the visible-light absorption and obtain high catalytic activity of the catalyst.And then the low photon yield of catalyst was solved.The structural design and application of nanomaterials were carried out for the purpose of utilizing the photocatalytic synergistic effect of the multi-stage nanocomposites.The diversified functional nanocomposites hollow sphere with double-shell sandwich was applyed to photocatalytic degradation of pollutants,heavy metal treatment and green conversion of benzyl alcohol.At the same time,the synergistic effect of photocatalysis was studied,and a new theoretical concept was proposed from the practical application.The main research results were as follows:1.The cavity sizes in the hollow sphere play a crucial role in determining the photocatalytic reactivity and efficiency.However,the research of the catalytic activity of hollow sphere with controllable size has not been studied.The TiO2 and TiO2@WO3/Au nano hollow sphere with controllable size have been prepared by template method.The feature of the TiO2 and TiO2@WO3/Au hollow sphere with controllable size were investigated by SEM,TEM,XRD,UV-Vis,PL,BET and electrochemical characterization methods.The results showed that the photo-reduction rate of Cr(VI)for 450 nm hollow sphere nanomaterials exhibited an increase compared with 370 nm and 600 nm.The optimal hollow sphere size of TiO2 and TiO2@WO3/Au hollow sphere was 450 nm for the photo-reduction of Cr(?),because the light-harvesting efficiency(the best of absorption edge)and photo-generated electron-hole separation rate(the best of photo-reduction rate)of TiO2 and TiO2@WO3/Au hollow sphere were controlled by its hollow sphere size.2.We explored the importance of controllable location of the Au nanoparticles as cocatalysts of TiO2@CeO2 nanocomposites.And then we proposed that the"double-shelled and sandwiched" nanostructure to solve the instability problem of the noble metals in the photocatalytic process of the catalyst.The photocatalytic properties of TiO2@CeO2 nanocomposites with different Au loading sites were investigated for the photo-degradation of organic pollutant and photo-reduction of Cr(?).The results showed that the catalytic activity and stability of double-shelled and sandwiched TiO2@Au@CeO2 hollow spheres were the highest.The double-shelled and sandwiched TiO2@Au@CeO2 hollow spheres were high catalytic activity for methyl orange and trimesic acid,and also exhibited an improved for the reduction activity of Cr(?).3.In the photocatalytic process of nanomaterials,some catalysts only exhibited a single performance of photo-oxidation or photoreduction,which was not suitable for complex practical environments.In this regard,a bifunctional photocatalyst was designed for photo-reduction of Cr(?)and selective photo-oxidation of benzyl alcohol into benzaldehyde in the presence of water under ambient conditions.The bifunctional TiO2@NMs@ZnO(Au,Pt,Ag,Pd)and TiO2@Pt@CeO2 catalysts were fabricated by using a template method.The feature of the TiO2@NMs@ZnO and TiO2@Pt@CeO2 hollow sphere were investigated by SEM,TEM,XRD,UV-Vis,PL,BET and electrochemistry characterization methods.The results of the photocatalytic oxidation of benzyl alcohol and the photoreduction of Cr(?)confirmed that the TiO2@Ag@ZnO and TiO2@Pt@CeO2 nanocomposites had the better performance of photooxidation of benzyl alcohol and photoreduction of Cr(?).Taking into account the multi-functional combination of precious metals and semiconductor materials,this work could provide new insights for the design of high-performance photocatalysts.4.We also have explored the effect of nanocomposites of inorganic and organic semiconductors on photocatalytic activity of the catalyst.The inorganic and organic TiO2@Pt@C3N4 nanocomposites were fabricated by a simple synthesis method.The feature of the TiO2@Pt@C3N4 was investigated by SEM,TEM,XRD,UV-Vis,PL,BET and electrochemistry characterization methods.The dicyandiamide precursor formed a stable outer layer coating of TiO2@Pt@C3N4 exhibited enhanced catalytic activity than other precursors.The double-shelled structure of hollow spheres and effective noble metals sandwiched into the TiO2@Pt@C3N4 nanocomposites can effectively accelerate photon-induced electron and holes separation and transfer,and thereby improve the efficiency of the photocatalytic process.