Preparation Of Graphitic Carbon Nitride Based Heter-Ojunction Photocatalysts And Investigation Of Their Photocatalytic Performance

The rapid development of industries has been causing drastic environmental pollution and energy scarcity,and semiconductor photocatalysis is regarded as one of the most promising technologies for circumventing these issues.Among various photocatalysts,graphitic carbon nitride(CN)as a visible-light-driven photocatalyst with metal-free nature,environmental friendliness,high chemical stability,and unique physicochemical properties,has received numerous attentions.CN has been widely used in water pollution treatment,CO2 reduction,water splitting,and organic synthesis.Nevertheless,CN suffers from bottlenecks such as poor specific surface area and high recombination of photo-excited charge carriers which thereby,reduces the photocatalytic activity.In this decade,CN-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance.In this thesis,we investigated the synthesis and photocatalytic performance of CN-based hetero junction photo catalysts.Two types of bismuth-based semiconductors,bismuth tungstate(BW)and bismuth vanadate(BV),were used to form heteroj unction photocatalysts with CN,and further studied the catalytic performance and mechanism of benzylamine oxidation under visible light.Furthermore,graphene quantum dots(GQDs)was used to modify the graphitic carbon nitride nanorods(CNNR).The obtained GQDs/CNNR photo catalysts exhibited superior performance for photocatalytic removal of antibiotics.The related work is as follows:1.The heterojunction photo catalysts of graphitic carbon nitride/bismuth tungstate(CN/BW)were fabricated by hydrothermal growth of bismuth tungstate on the surface of graphitic carbon nitride.Characterization results demonstrate that the composites have been well composited and show improved separation ability of photo-generated charge carriers due to the formed type ? band alignment.In comparison to the individual CN and BW,the heterojunctions exhibit apparent enhanced activity for the selective oxidation of amines to imines using O2 as the oxidant under irradiation of visible light.The optimized CN/BW heterojuntion with 75%BW content presents the high conversion(98%)and selectivity(98%)in 3 hours oxidative coupling reaction of benzylamine.Furthermore,this heterojunction photocatalyst also has excellent cycling stability,as well as good catalytic performance for various benzylamine derivatives.On the basis of experimental results,the transfer pathway of photo-excited electrons and holes in the heteroj unction photocatalyst was illustrated and a possible mechanism for the subsequent selective oxidation of amines to imines was proposed2.The two dimensional(2D)/2D CNNS/BV heterostructure was successfully constructed by solvent-thermal method.Compared with individual CNNS and BV,the prepared CNNS/BV heterojunction photocatalysts show significantly enhanced photocatalytic performance for benzylamine oxidation,owing to enhanced charge separation efficiency.Under the optimized reaction conditions,the 50%CNNS/BV sample achieves the high conversion(96%)and selectivity(99%)for benzylamine oxidation,which is 3.8 and 1.9 times higher than pure CNNS and BV,respectively.Additionally,the CNNS/BV possesses excellent reusability and good universality for various benzylamine derivatives.Finally,we proposed a possible photocatalytic mechanism3.The metal-free composite photocatalyst of 0-dimensional(0D)graphene quantum dots(GQDs)decorated graphitic carbon nitride nanorods(CNNR)that was obtained by a hydrothermal treatment.Characterizations of physicochemical properties demonstrate that this GQDs/CNNR photocatalyst has a high crystallization level,enhanced visible light absorption and a staggered band alignment,which can promote the formation,the transportation and the separation of photo-excited electrons and holes.These prominent advantages bring improved photocatalytic activity of the GQDs/CNNR fo r efficient removal of antibiotics.Its photocatalytic reaction rate is 3.4 and 2.0 times higher than those of the pristine CN and the CNNR,respectively.Furthermore,this composite photocatalyst has good application universality for decomposing other antibiotics,and also possesses excellent stability and reusability.We further proved that photo-induced holes and superoxide radicals are main active species in the photocatalytic process.