Preparation And Piezo-Photocatalytic Performance Of BiFeO₃/g-C₃N₄ Composite

Photocatalytic technology has significant advantages in degrading organic dyes in sewage,and is one of the advanced green water treatment technologies that has developed rapidly in recent years.At present,there are some problems in the application of this technology,for example,most photocatalysts only respond in the ultraviolet light region,the lifetime of photogenerated carriers is short,and the catalyst cost is high.To solve these problems,bismuth ferrite（BiFeO₃）and graphitic carbon nitride（g-C₃N₄）with good response to visible light,and BiFeO₃/g-C₃N₄ composite materials have been synthesized."Piezo-photo synergistic catalytic system"were constructed by coupling piezocatalysis and photocatalysis to improve catalytic degradation performance.The specific research results are as follows:（1）Three morphological BiFeO₃ were synthesized by different methods:particle（NP）,sheet（NS）and bulk（Bulk）.The materials were characterized by X-ray diffraction（XRD）,field emission scanning electron microscope（FESEM）,transmission electron microscope（TEM）and other analytical methods.The degradation rate of Rhodamine B（RhB）solution under ultrasonic conditions was the evaluation index of piezoelectric catalytic performance.The results show that the three morphological materials have good crystallinity,hexagonal crystal system,regular morphology,uniform pore size distribution and well visible light absorption performance.Among them,the piezoelectric catalytic degradation efficiency of sheet BiFeO₃ is the highest.The degradation rate of 10 mg L^-1RhB within 60 min is 37.62%,which is higher than that of particle catalyst and bulk catalyst,20.35%and 32.57%,respectively.（2）In order to construct a"2D-2D piezoelectric-photosynthetic catalysis"system,BiFeO₃/g-C₃N₄ composites with different mass ratios were prepared by a two-step hydrothermal-calcination method.The test and analysis results of XRD,FESEM,TEM,photoluminescence（PL）and photocurrent show that the BiFeO₃/g-C₃N₄ composite has good crystallinity,no impurity formation,overlapping lamellar structure.Compared with BiFeO₃,the ratio of electron-hole recombination decreases and the photocurrent density increases.15%of the samples posses the best catalytic performance,with degradation rate of 43.25%for RhB under visible illumination,and 98.27%under the synergistic effect of ultrasound and illumination.（3）The products in the degradation process of RhB were analyzed by high performance liquid chromatography-mass spectrometry（HPLC-MS）,and the results showed that the degradation of RhB involved:N-deethylation,decarboxylation,largeπbond breaking,ring opening,mineralization and other processes.The final small molecules are mainly benzoic acid,malonate,phthalimidoethyl and glycerol,etc.（4）Through the radical trapping experiment and electron spin resonance（ESR）,it shows that the main active substances in the piezoelectric photocatalytic degradation of BiFeO₃/g-C₃N₄ system were·O^2-and·OH.According to the experiment,the piezo-photocatalytic mechanism of Z-type heterojunction BiFeO₃/g-C₃N₄composite was proposed.