Construction Of Z-scheme Heterojunction By Encapsulation Of TiO₂ Into NH₂-UiO-66 And Their Photocatalytic Performance For Degradation Of VOCs

Volatile Organic Compounds as typical air pollutants are harmful to hunman health and ecological environment.Therefore,how to control the increasing VOCs pollution economically and efficiently has become a hot topic for researchers.The photocatalytic oxidation technology is expected to use solar energy to stimulate semiconductor to produce active species such as·OH and·O₂^-at room temperature,and the VOCs were oxidized into non-toxic CO₂ and H₂O,which makes it have a broad application potentiality in the field of VOCs degradation.Nevertheless,Ti O₂ as the most widely studied traditional semiconductor photocatalyst,due to its small specific surface area,narrow photoresponse range and low separation efficiency of photogenerated electron-hole pairs,leads to low photocatalytic degradation activity of VOCs under visible light,which greatly limits its practical application in photocatalytic degradation.Metal-Organic Frameworks（MOFs）with large specific surface area,uniform pore structure and semiconductor-like propertiesmight have raised attention in the field of VOCs degradation.NH₂-Ui O-66 is a typical class of MOFs materials with large specific surface area,visible light response,excellent thermal and chemical stability,and has the band structure that matches the Ti O₂.Therefore,this paper takes the typical industrial gases ethyl acetate as the research object,introduced the Ti O₂ into the NH₂-Ui O-66 through the"bottle around ship"method that constructed a Z-scheme heterojunction photocatalyst which is beneficial to the separation of photogenerated carriers.Au nanoclusters with excellent electron transport and light absorption ability were further introduced into the heterojunction composite photocatalysis.The relationship between the surface physical and chemical properties like specific surface area,pore structure,interface contact,interfacial charge transfer and the structure of the photocatalyst and the photocatalytic degradation of ethyl acetate were investigated.Finally,the mechanism of efficiency degradation of ethyl acetate by composite photocatalyst was also investigated.The main research of this paper are as follows:1)Firstly,Au³⁺were adsorbed on the PVP modified Ti O₂.Then the Au³⁺/Ti O₂ was reduced to Au-Ti O₂ and encapsulated in the MOF during the growth process of NH₂-Ui O-66due to the reducibility of DMF and H₂and received small Au nanocluster bridging NH₂-Ui O-66 encapulsed Ti O₂ composites（Au-Ti O₂@NH₂-Ui O-66）.The characterization results show that the Au-Ti O₂ can be uniformly encapsulated inside the NH₂-Ui O-66 without destroying the MOF crystal structure.And the the absorption of the composites in the visible region is advanced owing to the LSPR effect of Au particles.2)The photocatalytic degradation activities on ethyl acetate of Ti O₂,NH₂-Ui O-66,Ti O₂@NH₂-Ui O-66 and Au-Ti O₂@NH₂-Ui O-66 were systematically investigated.The results showed that compared with Ti O₂,NH₂-Ui O-66 and Ti O₂@NH₂-Ui O-66,the photocatalytic degradation effience of Au-Ti O₂@NH₂-Ui O-66 was strongly enhanced.The removal rate and mineralization rate of ethyl acetate on Au-Ti O₂@NH₂-Ui O-66 were as high as 94.6%and 85%during 360 min xenon lighting and has well stability.3)The photogenerated electron transport rate,the separation ability of photogenerated electrons and the generation of oxidized species were further studied by X electron spectroscopy,photoluminescence spectroscopy,photoelectrochemical test,infrared thermal imaging and EPR tests,and the mechanism of photocatalytic degradation of ethyl acetate was investigated by combining with photocatalytic degradation performance.The result shows that the Z heterojunction were constructed in Au-Ti O₂@NH₂-Ui O-66 composites,which makes it have strong redox ability because the higher valence band and lower conduction band position in the two components are retained.The small Au nanoclusters bridging Ti O₂ and NH₂-Ui O-66 improved the transfer of ophotogenergated electron and visible light absorption of composites.Eventually the Au-Ti O₂@NH₂-Ui O-66 produces a large number of strongly oxidized species such as photogenerated holes,·OH and·O2-free radicals,which can degrade ethyl acetate efficiently.