Preparation And Photocatalytic Performance Of Porous Magnesium Oxide Nanosheets/Carbon Composites

Magnesium oxide(MgO),as a third-generation wide band-gap semiconductor,can also be inspired to generate photogenerated electron-hole pairs(e^--h⁺)by ultraviolet light(UV light)and perform photocatalytic activity owing to its rich defects and surface active sites.However,the proportion of UV light in the full spectrum is only 4%,far less than 50%of visible light.In order to improve the photocatalytic activity of MgO under visible light,porous MgO nanosheets with rich defects have been prepared.Then,highly active MgO₂ is in-suit growthed on the edge of MgO nanosheets with the synergistic effect of H₂O₂ in the Fenton-like system.Based on this,MgO/graphene nanosheets(MgO/GN)and MgO/carbon quantum dots(MgO/CQDs)composite catalysts have been prepared to furtherly improve the photocatalytic degradation activity of MgO under visible light.Porous MgO nanosheets were prepared by a simple chemical precipitation method.Then a Fenton-like system is considered with H₂O₂ to improve the photocatalytic degradation activity.Firstly,H₂O₂ can generate hydroxyl radicals(·OH)under visible light,which can degrade organic pollutants efficiently and indiscriminately.Secondly,high active MgO₂ is in-suit generated on the edge of MgO nanosheets by reacting with H₂O₂.MgO₂ performs strong oxidation and can release oxygen(O₂)to generate superoxide radical(·O₂^-)with e^-,which can furtherly enhance the photocatalytic oxidation activity.This unique design method,in-suit grow another strong oxidant on the edge of the catalyst,can lead to the synergetic catalysis effect among catalysts and oxidants.The experimental results show that the photocatalytic efficiency of MgO with H₂O₂ under visible light to methylene blue(MB)and rhodamine B(RhB)respectively reaches 98.1%and 85.6%within 60 min,which is 3.2 times without H₂O₂.In addition,the photocatalytic degradation rate of MgO under visible light can reach or exceed that of traditional semiconductor photocatalysts under visible light.Graphene shows excellent electron transport and rich surface defects,which can promote the separation of e^--h⁺pairs and enhance the photocatalytic degradation efficiency.Therefore,the MgO/graphene nanosheets(MgO/GN)composite catalysts have been prepared.In addition,when the mass content of graphene nanosheets is 2%,the MgO/GN-2 composite catalyst performs the best photocatalytic degradation efficiency on MB,reaches 99.4%within 30 min.The wide band-gap MgO can only absorpt and utilize UV light depending on its rich defects and active sites.This is the main reason for the limited photocatalytic efficiency of MgO under visible light.Therefore,combining MgO with CQDs is an effective way to improve the absorption and utilization of visible light.When the mass content of CQDs is 2.5%,the MgO/CQDs-2.5 composite catalyst performs the highest photocatalytic degradation efficiency on MB,reaches 99.4%within 30 min.