Study On Barium Salt Regulating The Energy Band Structure Of Graphitic Carbon Nitride And Photocatalytic Degradation Performance Of Organic Wastewater

The rapid economic development has led to a rapid decline in environmental carrying capacity,and the problem of water pollution has become increasingly serious.The discharge of organic wastewater has greatly increased,which not only destroys our living environment,but also threatens human health.Traditional sewage treatment including biological,physical,chemical and other technologies,which often consume a lot of energy and usually require a combination of several treatment methods to meet discharge standards.Photocatalytic technology is widely recognized as an ideal technology for the degradation of organic wastewater due to its simple operation process,environmental friendliness,and only using sunlight as energy.However,the biggest challenge to realize the practical application of photocatalytic technology is to develop an effective and low-cost photocatalyst.Graphitic carbon nitride（g-C₃N₄）,as an organic semiconductor photocatalyst,has the characteristics of suitable band gap（～2.7 e V）,good chemical and thermal stability,and abundant raw material sources,so it is widely used for photolysis of water to produce hydrogen,NOx elimination,CO₂ reduction,and industrial wastewater treatment.Sadly,g-C₃N₄ has weak absorption of visible light and fast carrier recombination,which limits its application and development.Optimizing the energy band structure of g-C₃N₄ by reasonable modification methods and improving its carrier separation efficiency can make g-C₃N₄ have higher photocatalytic activity,which can realize the efficient degradation of organic wastewater,which has great research value.In this paper,three kinds of barium salts were used to modify g-C₃N₄,and the structure and properties of the catalyst were deeply analyzed by combining various characterization methods.The synthetically prepared composite materials are used to efficiently degrade organic pollutants.The energy band structure of barium salt modified g-C₃N₄ with different properties,the mechanism of promoting carrier separation,and the degradation mechanism of high-efficiency treatment of organic wastewater were explored.It mainly includes the following tasks:Firstly,the hexagonal Ba?（PO?）?was prepared by solvothermal method,and then it was mixed and calcined with melamine（C₃H₆N₆）to successfully prepare Ba?（PO?）?/g-C₃N₄.Through XRD,FT-IR,XPS,UV-vis DRS,VB-XPS,PL and other characterizations,the structure of Ba?（PO?）?/g-C₃N₄ was analyzed in depth.The results show that Ba?（PO?）?narrows the band gap of g-C₃N₄,regulates the position of the valence band,and accelerates carrier migration.Compared with g-C₃N₄,Ba?（PO?）?/g-C₃N₄ exhibits stronger visible light absorption capacity,more positive valence band position and faster electron-hole separation efficiency,so that it has stronger oxidation ability and higher catalytic activity.Under visible light irradiation,Ba?（PO?）?/g-C₃N₄ contains more reactive oxygen species.The photocatalytic degradation efficiency of 20 mg/L tetracycline hydrochloride（TC）within 120 minutes is 2.06 times and 5.44 times that of g-C₃N₄ and Ba?（PO?）?,respectively.Secondly,an anion/cation co-modified graphite carbon nitride BaCO₃/g-C₃N₄ was synthesized by direct calcination of BaCO₃ and C₃H₆N₆,and it was used to remove crystal violet（CV）and TC in wastewater under visible irradiation.From the perspective of co-modification of anion and cation,the mechanism of BaCO₃ enhancing the photocatalytic activity of g-C₃N₄ has been deeply studied.The presence of BaCO₃ improves the electronic structure of g-C₃N₄ and extends the charge transport channel,improves the light absorption capacity,and accelerates the charge separation efficiency.Finally,BaCO₃/g-C₃N₄ photocatalysis showed excellent photodegradation activity and stability for CV and TC wastewater.The photocatalytic degradation of 20 mg/L CV and TC by BaCO₃/g-C₃N₄ was 3.5 times and 2.5 times that of g-C₃N₄.HPLC-MS technology dynamically monitors the intermediate products of photodegradation of CV.Finally,the Ba²⁺doped and cyano group（?C≡N）defect co-modified g-C₃N₄ catalyst Ba CN-C₃N₄ was constructed by the soluble barium chloride assisted method.Ba²⁺and cyano groups can narrow the band gap structure and efficiently separate photogenerated electron-hole pairs.Specifically,Ba²⁺captured by ion-dipole interaction changes the electronic structure of g-C₃N₄ and narrows its band gap,and acts as an electron donor to accelerate the separation of electron-hole pairs.In addition,Ba²⁺also affects the polycondensation process of g-C₃N₄,causing some heptaazine ring openings to produce cyano defects,which further regulates the energy structure of g-C₃N₄,and cyano groups also act as electron acceptors to accelerate the effectiveness of carriers.The noval Ba CN-C₃N₄ catalyst is used for photocatalytic degradation of TC,photolysis of water to produce hydrogen,and photocatalysis of TC wastewater to produce hydrogen to achieve simultaneous water environmental purification and new energy development.The intermediates of photodegradation of TC were dynamically monitored by HPLC-MS technology.