POM/g-C₃N₄ Electrostatic Complexes For Photocatalytic Oxidation Of Benzylamine

In recent years,with the emergence of global warming,environmental pollution,and the abuse of fossil energy,it is urgent to find sustainable development strategies to deal with these crises.Therefore,making full use of solar energy,a renewable resource,has attracted extensive attention.Among them,photocatalysis,using sunlight as the driving force for chemical reactions,has become one of the most promising technologies due to its advantages of low energy consumption and mild conditions.Carbon nitride（g-C₃N₄）,as a semiconductor photocatalyst with abundant storage capacity and excellent performance,has many advantages in photocatalysis that have received attention,such as high visible light activity,and strong chemical stability in catalysis,low cost,and easy synthesis of materials in preparation,etc.However,pure g-C₃N₄ has problems such as low carrier separation efficiency after light irradiation and limited absorption range of sunlight,which lead to unsatisfactory photocatalysis.To overcome these shortcomings,some studies on the modification of g-C₃N₄ have been reported,among which,one of the most effective methods is to use electron acceptors to separate photogenerated carriers.Polyoxometalate（POM）,as a class of precise nanoscale small molecule anionic metal oxygen clusters,have rich chemical and physical properties,including acid-base and redox characteristics;high-valence metals can also make them good electron acceptors,and the characteristics of gaining and losing electron cluster structures that remain unchanged have shown great potential in the field of catalysis.Therefore,in this thesis,g-C₃N₄is combined with POM through electrostatic interaction,and POM is used to accept the photogenerated electrons generated by g-C₃N₄,which weakens the recombination of g-C₃N₄photogenerated electrons and holes.As g-C₃N₄ is used as a photocatalytic semiconductor carrier to load POM,the advantage of the two complement each other to improve the photocatalytic efficiency.Based on the above background,the research work carried out in this paper is as follows:（1）The synthesized g-C₃N₄ was protonated with hydrochloric acid to obtain the positively charged protonated g-C₃N₄,which was used as a semiconductor and combined with POM as an anion cluster to form a photocatalyst through electrostatic interaction.The catalyst was used for the photocatalytic oxidation of the small organic molecule benzylamine,and the photocatalytic performance of the catalyst was explored.The results show that the oxidation reaction of benzylamine can be carried out rapidly in a short time,and has a high conversion rate and selectivity.However,during the photocatalytic oxidation of benzylamine,the prepared catalysts have obvious color changes after the reaction.According to the EPR results,the valence state of POM after the reaction has been changed was irreversible.Therefore,the photocatalyst formed by loading POM on g-C₃N₄ is reduced after receiving electrons as an electron trap after light irradiation,which is not conducive to the reuse of the catalyst.（2）Through the first part of the experimental analysis,cocatalyst graphene oxide（GO）carbon material is introduced to improve the cycle stability of the catalyst.The introduction of GO not only contributes to efficient charge separation and transport,improves the valence band of the catalyst,and further stores electrons in the co-catalyst to achieve recycling of the catalyst,but also broadens the light absorption range of the material to improve the use of the solar spectrum.The precursor of g-C₃N₄ was calcined with graphene oxide to prepare GO-CN,and then combined with POM through electrostatic interaction to prepare the photocatalyst POM@GO-CN.The catalyst is used to catalyze the oxidation reaction of benzylamine,and the photocatalytic performance is explored.The reaction can be carried out under mild conditions and has a considerable conversion rate and selectivity.The catalyst was recycled and reused,and the results show that the catalyst still has a high conversion rate and selectivity after five cycles,and good cycle stability is still maintained,realizing the recycling and reuse of the catalyst.In this thesis,g-C₃N₄ is used as a photosensitizer semiconductor and a carrier to load POM,and POM as an electron acceptor can weaken the rapid recombination of photogenerated carriers of g-C₃N₄,and GO can further store electrons and broaden the light absorption range of the material.After combining these materials,the multi-phase composite photocatalyst prepared can effectively improve the photocatalytic efficiency by taking advantage of the complementary advantages of the materials.Therefore,we hope to obtain a new scientific understanding of the improvement of photocatalytic efficiency through the research of this thesis,and also provide an alternative approach for the subsequent simple preparation of heterogeneous composite polyoxometalate-based photocatalysts.