Composite Catalyst Of Modified Metal Sulfide And MOFs For Photocatalytic Oxidation Of Benzoyl Amine

Using solar energy as energy source to catalyze some organic oxidation reactions can not only make conditions milder,but also save the energy and effectively avoid the environmental damage caused by the traditional organic chemical industry.Imine,the product of oxidative coupling of benzylamine,is widely used in the synthesis of fine chemicals,organic intermediates,drugs and so on.Metal sulfides have stand out among numerous photocatalytic materials and become the first choice for visible light catalysts due to their strong visible light absorption capacity,good charge transfer performance and suitable and adjustable band structure.However,single metal sulfide catalysts still have some defects in photocatalytic organic reactions,such as easy recombination of photogenerated electron-hole pairs,short carrier lifetime,and poor light absorption capacity.Therefore,the development of new and efficient metal sulfide visible light catalysts has received increasing attention in recent years.The emergence of metal-organic frameworks（MOFs）provides new choice for the development and application of new photocatalytic materials.MOFs materials have strong designability,adjustable band structure and promising stabilities,and are one of the ideal candidates for preparing composite semiconductor photocatalysts.In view of this,this paper designed and synthesized modified metal sulfides,and made them composited with MOFs or orderly composited with another semiconductor catalyst to prepare three types of S-containing semiconductor metal catalysts,which were used in the oxidative coupling reaction of benzylamine.The effects of the properties and structure of the composites on their photocatalytic performance were studied in detail.The main research contents of this paper are as follows:.（1）CdZnS/UiO-66-NH₂ composites were prepared by loading ternary metal sulfide nanoparticles of CdZnS on UiO-66-NH₂ through a simple hydrothermal method,and the prepared composites were applied to the oxidative coupling reaction of benzylamine and its derivatives.The experimental results show that CdZnS/UiO-66-NH₂ has higher photocatalytic activity than any of the pristine CdZnS and UiO-66-NH₂.Under air atmosphere.After 6 hours’illumination,the conversion of benzylamine reaches 98%and the selectivity of the product imine is greater than 99%.The main reason is that the introduction of CdZnS nanoparticles can improve the visible light absorption range of UiO-66-NH₂ photocatalysts,and therefore,effectively facilitate the separation of the collective carriers.Moreover,the photocatalytic activity is almost well maintained and the structure of the catalyst is not destroyed after the photocatalyst had been recycled four times.Finally,the active species capture experiments prove that h⁺is the main active species,and·O₂^-is the secondary active species.They act synergistically have promoted the oxidative coupling of benzylamine.（2）A novel hybrid photocatalyst CdS@MIL-88A（Fe）was prepared by a facile and environmentally friendly method,which simplified the catalyst preparation process and shortened the reaction time.The structure characterization results reveal that there is an effective interface between CdS and MIL-88A（Fe）,which means the formation of a Z-type heterojunction and subsequently improves the separation efficiency of photogenerated carriers.With the as-prepared CdS@MIL-88A（Fe）as photocatalyst,the conversion of benzylamine reaches 97%after 5 hours of irradiation under air conditions,indicating that the catalytic performance of the composite was significantly improved.Eventually,the possible reaction mechanism for the oxidative coupling of benzylamine with this photocatalytic system is proposed through active species trapping experiments.（3）The 2D-2D Ni₂SP/Cd_0.9Zn_0.1S nanocomposite photocatalyst with low loading（3-9wt%）was successfully prepared by oriented loading of Ni₂SP nanosheets onto Cd_0.9Zn_0.1S nanosheets through recombination of the two semiconductors,and then it was employed as visible light responsive catalysts for the oxidative coupling of benzylamine and its derivatives.The results show that the 2D-2D Ni₂SP/Cd_0.9Zn_0.1S nanocomposite photocatalyst can efficiently oxidize benzylamine within 4 hours and exhibits good recyclability in the reaction.The major reasons for the improvement of the photocatalytic activity of the 2D-2D Ni₂SP/Cd_0.9Zn_0.1S composites is mainly attributed to the oriented composition between the simple two semiconductors,which increases the contact tightness of the interface,thereby achieving a better separation of the interface photoinduced charges.