Preparation And Photocatalytic Activity Of Graphite-phase Nitrided Carbon?g-C₃N₄?

Global energy shortage and environmental pollution have become the major obstacles hindering the development of human society,which has prompted scientists to explore new clean and sustainable energies that may replace fossil fuels.As a green technology with important application prospect in the field of environment,photocatalyst has enormous potential for development in energy and environmental protection.graphite phase carbon nitride?g-C₃N₄?,as a semiconductor-structured photocatalyst,has attracted extensive attention in the field of photocatalysis because of its low cost,safety and non-toxicity,and stable chemical properties.however,its inherent disadvantages,such as high recombination rate of photogenerated carriers,small optical absorption range and narrow band gap?2.82 e V?,have limited its application.In this paper,through the chemical reaction of carboxyl group and amino group,the aromatic ring was introduced into the g-C₃N₄lamellar structure for molecular modification,and the heterojunction composites were constructed by combining g-C₃N₄ with CdS quantum dots and MoO₃ with different mass ratios,which effectively improved the photocatalytic properties of g-C₃N₄.The main results are as follows:The free amino group is present at the edge of the g-C₃N₄ lamellar structure,and the photocatalytic performance of the carbon nitride is limited.After the g-C₃N₄ and p-nitrobenzoic acid?PNA?were mixed with different mass ratios,the mixed powder was calcined at 360?for 5 h,so that the aromatic ring could be successfully grafting into the lamellar structure of g-C₃N₄ by the complete reaction of amino group and carboxy group.The proper addition of PNA can effectively increase the photodegradation rate of rhodamine B?Rh B?,but the excess PNA can destroy the lamellar edge structure,resulting in lower photodegradation performance.When the addition of PNA is 1wt%,the photodegradation rate of the modified g-C₃N₄ is the fastest,the efficiency is the highest,and 85%is achieved in 25 min.The cyclic experiments show that the modified g-C₃N₄ has stable structure and photodegradation property after four cycles.The results of free radical capture and ESR show that the?O₂^-plays a decisive role in the photodegradation of Rh B.Cadmium sulfide quantum dots?CdS QDs?were loaded on g-C₃N₄ lamellar structure by hydrothermal synthesis,and CdS/g-C₃N₄ composites with different mass ratios were successfully prepared.The morphology analysis shows that the nanocomposites are mainly composed of g-C₃N₄ lamellar structure,and CdS is loaded in g-C₃N₄ lamellar structure in the form of quantum dots?10nm?.The photocatalytic activity of the composite was evaluated by degradation of ofloxacin?OFLX?.The experimental results show that the mass ratio of CdS QDs/g-C₃N₄ is 1:2 to reach the maximum photocatalytic performance,and the degradation rate of ofloxacin can reach 74.45%after 25 min light.The cyclic experiments show that the composite maintains high photocatalytic performance after four cycles,indicating that CdS QDs/g-C₃N₄ has good stability.The capture experiments show that?OH and?O₂^-are the effective free radicals of OFLX.MoO₃/g-C₃N₄ composites with different mass ratios were constructed by oil bath heating.Morphology analysis showed that h-MoO₃ and g-C₃N₄ heterostructures were successfully synthesized.The photocatalytic performance of the composite was evaluated by degradation of methylene blue?MB?.The results showed that when the mass ratio of MoO₃/g-C₃N₄ was 1:1,the photodegradation performance was the best,and the degradation rate was 71.84%when the light intensity was 40 min.The cyclic experiments show that the photocatalytic performance of MoO₃/g-C₃N₄ composites does not decrease obviously after four cycles,indicating that MoO₃/g-C₃N₄ composites have good repeatability.The experimental results show that both?OH,h⁺and?O₂^-can play a certain role in the degradation of methylene blue.