Preparation Of Graphite Carbon Nitride And Phosphorus-based Composites And Study On Photocatalytic Degradation Of Rhodamine

As one of the harmful substances in industrial wastewater,Rhodamine B（RhB）is difficult to degrade in nature,which seriously threatens the ecological environment and human health.Photocatalytic technology has the characteristics of mild reaction conditions and green environmental protection,and has attracted much attention in dye wastewater treatment technology.As an inorganic non-metallic material,graphitic carbon nitride（g-C₃N₄）has been widely used in the degradation of organic pollutants due to its superior physical and chemical properties.However,the photocatalytic efficiency of g-C₃N₄ is low due to its low utilization of visible light and high recombination rate of photogenerated electron-hole pairs in photocatalytic reaction.In the current proposed modification strategy for g-C₃N₄,forming heterojunction with other semiconductors is an effective way to overcome the above shortcomings.In the previous study of the research group,it was found that the adding of inorganic non-metallic material silica（SiO₂）into g-C₃N₄ can increase the specific surface area and enhance the catalytic effect.Red phosphorus（RP）has high conductivity and stability,and black phosphorus（BP）can be generated in situ under certain conditions.The construction of BP/RP heterojunction can achieve close interface contact between different semiconductors and effectively promote the separation of photogenerated carriers.In this paper,g-C₃N₄/SiO₂,RP-g-C₃N₄/SiO₂ and BP/RP-g-C₃N₄/SiO₂ series of photocatalytic materials were designed using ultrasonic method and ball milling method and prepared to solve the problems of low visible light utilization rate and high photogenerated charge recombination rate of g-C₃N₄.The microstructure,physicochemical properties and degradation mechanism of the series of composite photocatalytic materials were investigated.The efficient degradation of organic pollutants by g-C₃N₄ composite catalytic system under light conditions was realized.The main research results of this paper are as follows:（1）The g-C₃N₄/SiO₂ binary composite photocatalyst was prepared by using urea and SiO₂ as raw materials.The degradation of RhB by g-C₃N₄/SiO₂ binary composite photocatalyst under simulated sunlight was studied.The degradation efficiency of g-C₃N₄/SiO₂ for 20 mg/L RhB reached 68%within 26min,which was 1.39 times higher than that of pure g-C₃N₄.The characterization showed that the introduction of SiO₂ did not change the crystal structure of g-C₃N₄,but significantly improved the specific surface area of g-C₃N₄,weakened the interlayer stacking of g-C₃N₄,and improved the photogenerated carrier fraction efficiency of g-C₃N₄.（2）Commercial red phosphorus（RP）and crystalline red phosphorus（cRP）were ultrasonically combined with g-C₃N₄/SiO₂materials to obtain RP-g-C₃N₄/SiO₂ and cRP-g-C₃N₄/SiO₂ ternary photocatalytic materials.The degradation of 20 mg/L RhB by RP-g-C₃N₄/SiO₂ containing 10%RP reached 93%in 26min under ultrasonic time of 1h.The degradation of 20 mg/L RhB by cRP-g-C₃N₄/SiO₂ with 10%cRP reached 86.9%in 26min.The active substances of RP-g-C₃N₄/SiO₂ and cRP-g-C₃N₄/SiO₂ were detected.It was found that the active substances of the two catalysts were superoxide radicals（·O₂^-）and holes（h⁺）.（3）Due to the high energy generated during ball milling,RP is converted into BP/RP and forms a close heterostructure with g-C₃N₄/SiO₂.The photocatalytic effect of BP/RP-g-C₃N₄/SiO₂ was 1.16 and 1.76 times higher than that of BP/RP and g-C₃N₄/SiO₂,respectively.Raman spectroscopy,X-ray photoelectron spectroscopy（XPS）,solid-state nuclear magnetic resonance（NMR）and other characterizations confirmed the presence of BP in BP/RP-g-C₃N₄/SiO₂ and the formation of P-C bonds,which is conducive to the effective separation of electrons and holes.The stability of the catalyst was studied,and it was found that the degradation effect of RhB decreased within 5%after four cycles.Raman spectroscopy was performed on the samples after the cycle,and no other characteristic peaks were found,indicating that BP/RP-g-C₃N₄/SiO₂had good stability.