The Study On The Heterogeneous Photocatalytic Selective Oxidation/Dehydrogenation Coupling Reation Of Aromatic Amines

Nowadays,along with the increasing exhaustion of fossil energy sources and the serious environmental pollution problems,the development and utilization of new and clean renewable energy source has become one of the most significant researches.Solar energy,as a kind of renewable energy source with the largest reserve,the cleanest and a sustainable use on the earth,has received extensive attentions of the scientists around the world.In the field of the chemistry and chemical engineering,photocatalysis can use solar energy to initiate and accelerate chemical reactions.On the other hand,the selective coupling of amines to form imines is a key reaction step for the synthesis of fine chemicals and pharmaceuticals,and has been paid great attention in catalytic research.Therefore,the design and development of heterogeneous photocatalytic systems for the efficient coupling reaction of aromatic amines have important scientific value and application prospects.The work of this thesis mainly focuses on the photocatalytic coupling of aromatic amines toprepare imines.The"Oxygen-Bi₂O₂CO₃"system,the"Water-Pt@Ti O₂"system,and the"Nitrogen-Pt@C₃N₄"system have been developed and the efficient conversion of aromatic amines to produce imines under mild conditions was realized.Firstly,in the"Oxygen-Bi₂O₂CO₃"system,a series of bismuth-based photocatalysts were synthesized using different preparation methods and used for the selective transformation of benzylamine to N-benzylidenebenzylamine under visible light conditions,where the semiconductor Bi₂O₂CO₃exhibits a very high photocatalytic activity;meanwhile,its catalytic activity can be adjusted by changing the catalyst morphology relied on the different preparation methods.Among of these Bi₂O₂CO₃materials,it is found that the flower-like Bi₂O₂CO₃material shows the best photocatalytic activity and high stability at room temperature.Under the light irradiation for 6 h,the conversion of benzylamine and the selectivity of the target product N-benzylidenebenzylamine reached 100%and more than 99.0%,respectively.In addition,the flower-like Bi₂O₂CO₃catalyst also shows high catalytic activities on the oxidative coupling processes of other aromatic amines and aliphatic amines.Based on the characterization of the catalytic materials,it was found that the excellent catalytic performance of the catalyst can be attributed to the specific flower-like morphology,thin nanopetals,low band gap energy and large specific surface area.This approach provides a green,cheap and environmentally friendly heterogeneous photocatalytic process for the synthesis of imines under the oxygen atmosphere.Secondly,in the"Water-Pt@Ti O₂"system,a new photocatalytic technology is developed to achieve the coupling reaction of aromatic amines using water as the mediate oxidant.In this photocatalytic system,a 1%Pt@Ti O₂-500 catalyst was used to combine oxidative coupling of aromatic amine with the photocatalyticwater splitting,in which the amines were selectively transformed to corresponding imines and the hydrogen was simultaneously released on this catalytic system.To the activity of this photocatalyst,the experimental results showed that the introduction of nano Pt resulted in the occurrence of the"hydrogen overflow"phenomenon during the reduction treatment of Ti O₂,which caused to generate a large amount of oxygen holes on the surface of Ti O₂material and further improved the catalytic activity of the catalyst.For the oxidative coupling of benzylamine,a nearly 100%conversion of benzylamine and 92.5%selectivity of N-benzylidenebenzylamine could be obtained using 1%Pt@Ti O₂-500 as the heterogeneous photocatalyst under light irradiation for16 h at room temperature,.Furthermore,highly efficient and selective conversion of other aromatic amines and aliphatic amines were also successfully carried out using1%Pt@Ti O₂-500 as the photocatalyst and pure water as the oxidant.On the other hand,catalyst recycling experiment results showed that the 1%Pt@Ti O₂-500 catalyst still keeps a high catalytic activity even after being reused for five times.Finally,in the"Nitrogen-Pt@C₃N₄"system,a novel photocatalytic acceptorless dehydrogenation strategy was devised to realize the conversion of aromatic amines to produce the imines with the synergy effect of metal Pt and C₃N₄material.During the dehydrogenation coupling reaction of benzylamine,using 2%Pt@g-C₃N₄as a catalyst,the conversion of benzylamine and selectivity of main product N-benzylidenebenzylamine arrived at 100%and 99.0%after 15 h light irradiation at room temperature,respectively.Based on the characterization results of catalyst,it was found that the modification of g-C₃N₄with Pt can effectively reduce the band gap energy of the g-C₃N₄catalyst,thereby improving its catalytic activity.Moreover,the results of control experiments indicated that the holes play the key role on the photocatalytic processes.Of course,this photocatalytic system also has high activities and good selectivity of imines for the dehydrogenation coupling reaction of other aromatic amines and aliphatic amines.Compared to the traditional thermal method that needs employing the composite noble metal catalysts to realize the acceptorless dehydrogenation coupling process at high temperature,the direct photocatalytic acceptorless dehydrogenation coupling of aromatic amines provides a green,promising and environmentally friendlyway to form C=N bond under relatively mild conditions.