Design And Preparation Of Titanium-based Metal-organic Frameworks And Hydrotalcite Composites And Study Of Their Photocatalytic Properties

Organic synthesis was the most common and indispensable part of modern chemical synthesis,however,the traditional organic synthesis process not only consumed a large amount of fossil energy,but also accompanyed a large amount of pollutant emissions,causing a serious of energy crisis and environmental problems.Therefore,using solar energy as a power source for organic synthesis was one of the most effective ways to solve the above dilemma.Layered double hydroxides（LDHs）,referred to as hydrotalcites,was a class of two-dimensional anionic clay materials consisting of interlayer anions and main laminates with positively charged.It was an emerging photocatalysts with low manufacturing cost and many advantages.For example,its main laminate cations and interlayer anions,was adjustable.However,LDHs synthesized by co-precipitation,hydrothermal or electrodeposition methods was prone to stacking,with few exposed active sites and high mass transfer resistance,which greatly limited the application of hydrotalcite as photocatalysts.In recent years,Metal-organic frameworks（MOFs）had been rapidly developed as a new class of inorganic-organic hybrid materials with a wide range of applications in photocatalysis,and the metal nodes and morphologies of MOFs provides templates and metal sources for the synthesis of LDHs with specific morphologies.Therefore,in this paper,NH₂-MIL-125（Ti）with octahedral morphology was used as the template to construct NH₂-MIL-125（Ti）@LDHs composites using an in-situ growth strategy combined with hydrothermal method,and its application in photocatalytic organic synthesis was explored.The main contents of this paper are listed as follows:1.Construction of NH₂-MIL-125（Ti）@Zn Ti-LDHs hierarchical photocatalysts for dimethyl sulfide oxidation to dimethyl sulfoxide.NH₂-MIL-125（Ti）with octahedral structure was synthesized by hydrothermal method firstly.Then NH₂-MIL-125（Ti）@Zn Ti-LDHs composites was constructed by hydrothermal method and in-situ growth strategy.The morphology and chemical structure of NH₂-MIL-125（Ti）@Zn Ti-LDHs were analyzed by FT-IR,XRD,SEM,TEM and XPS techniques.The results showed that the Zn Ti-LDHs formed after etching NH₂-MIL-125（Ti）,and the interlayer anion of Zn Ti-LDHs was 2-amino terephthalic acid anion.The photoxidation of dimethyl sulfide to synthesis dimethyl sulfoxide was selected as a model to systematically investigate the catalytic performance of NH₂-MIL-125（Ti）@Zn Ti-LDHs.The conversion rate of dimethyl sulfide reached 99.90%and the selectivity of dimethyl sulfoxide could reach 96.47%under the reaction conditions ofλ>320 nm and the light time of 11 h.The photocatalytic activity was significantly better than NH₂-MIL-125（Ti）and Zn Ti-LDHs,which was mainly because the intercalated NH₂-MIL-125（Ti）and Zn Ti-LDHs promote the transfer of electrons and the energy band structure of NH₂-MIL-125（Ti）@Zn Ti-LDHs could generate highly reactive ¹O₂and·O₂^?,thus accelerating reaction proceeding.Finally,NH₂-MIL-125（Ti）@Zn Ti-LDHs showed a great catalytic stability without obvious changes in selectivity and conversion rate after five cycles.2.Design of a NH₂-MIL-125（Ti）@Ni Co-LDHs by in-situ method:highly efficient catalytic photo-oxidation of benzyl alcohol under mild conditions.Based on the previous work,the NH₂-MIL-125（Ti）was etched more severely,which led to the low light absorption capacity of the system.Therefore,we used the MOFs-On-MOFs strategy to address this problem by growing ZIF-67 on the surface of NH₂-MIL-125（Ti）for the purpose to protect the NH₂-MIL-125（Ti）.Then the ZIF-67 was converted into Ni Co-LDHs and the NH₂-MIL-125（Ti）@Ni Co-LDHs composites was obtained.The morphology and chemical structure of NH₂-MIL-125（Ti）@Ni Co-LDHs were analyzed by FT-IR,XRD,SEM,TEM,HRTEM,and XPS techniques.The results showed that the ZIF-67on the surface of NH₂-MIL-125（Ti）was successfully converted to Ni Co-LDHs,and the morphology and structure of NH₂-MIL-125（Ti）remained intact.The oxidative synthesis of benzaldehyde from benzyl alcohol was selected as the model to systematically investigate the catalytic performance of NH₂-MIL-125（Ti）@Ni Co-LDHs.The results showed that the conversion rate of benzyl alcohol reached 51.20%and the selectivity of benzaldehyde reached 99.00%,which was significantly better than Ni Co-LDHs and NH₂-MIL-125（Ti）under the light condition ofλ>400 nm,which was attributed to the synergistic effect between Ni Co-LDHs and NH₂-MIL-125（Ti）to improve the separation efficiency and charge transfer efficiency of photogenerated charge.Besides,the conduction potential of NH₂-MIL-125（Ti）@Ni Co-LDHs was more conducive to produce·O₂^?.NH₂-MIL-125（Ti）@Zn Ti-LDHs showed a good catalytic stability after five cycles of the experiment,the conversion rate of benzyl alcohol and selectivity of benzaldehyde don’t decrease significantly.