Preparation Of G-C₃N₄/g-C₃N₄/MoS₂ Ternary Nano-photocatalyst And Photocatalytic Activity For Degradation Of Antibiotic Under Visible Light

In recent years,environmental antibiotic contamination has attracted worldwide attention.The use of semiconductor photocatalytic for degradation of antibiotics under visible light is a new idea to solve this problem.As a kind of visible-light responsive photocatalyst,polymeric graphitic carbon nitride?g-C₃N₄?has adjustable band gap?2.4-2.8 eV?,good chemical stability and nontoxicity.However,the low utilization of visible light and high recombination rate of photo-generated electron-hole pairs limit the further improvement of the photocatalytic performance of g-C₃N₄.In this study,we have prepared type II g-C₃N₄/g-C₃N₄ isotype heterojunction and the structure was adjusted by changing the types and ratios of precursor.Binary hybrids?g-C₃N₄/MoS₂?and ternary hybrids?g-C₃N₄/g-C₃N₄/MoS₂?were synthesized via a ultrasound and bathing method.The samples were characterized by XRD,XPS,TEM,EDS,UV-Vis and PL methods.In photocatalytic degradation experiments,rhodamine B?RhB?was used as the simulated pollutant and tetracycline hydrochloride?TC?as the practical pollutant.Finally,the photocatalytic mechanism was discussed systematically.The main conclusions are as follows:The formation of g-C₃N₄/g-C₃N₄ isotype heterojunctions and ternary heterojunctions were confirmed by XRD,TEM and XPS methods.UV-vis spectra shows that the loading of MoS₂ enhances visible light absorption of g-C₃N₄,PL spectras shows that the formation of the isotype heterojunction can improve the separation and transfer of photogenerated electron-hole pairs in g-C₃N₄,and the addition of MoS₂ can further accelerate this process.Photocatalytic degradation experiment:In the U-gCN/T-gCN isotype heterojunctions prepared with urea and thiourea as precursor,when the ratio of urea to thiourea was 2:1,the prepared isotype heterojunction exhibited the highest photocatalytic activity and the photodegradation rates for RhB and TC were 99.8%and 95.1%after being visible light irradiated for 1 h and 4 h respectively.After being reused for 5 times,the degradation rate decreases to 98.4%for RhB and to 81.2%for TC.In the U-gCN/D-gCN isotype heterojunctions prepared with dicyandiamide and urea as precursor,when the ratio of dicyandiamide to urea was 1:3,the prepared isotype heterojunction exhibited the highest photocatalytic activity and the photodegradation rates for TC was 89.1%after being visible light irradiated for 4 h.After being reused for 5 times,the degradation rate decreases to 76.1%for TC.For U-gCN/T-gCN/MoS₂ ternary hybrids,when the weight ratio of MoS₂ is 7.5%,the photodegradation rates for TC was 93.9%after being visible light irradiated for 2 h.A photodegradation rate of 85.9%was reached after being reused 5 times.Hence,the ternary hybrid shows pretty good reusable photoactivity for degradation.Photocatalytic mechanism:For isotype heterojunctions,the enhanced photocatalytic performance can be ascribed to the differences in electronic band structures between different kinds of g-C₃N₄ prepared with different precursor,which enhances the separation rate of electrons-hole pairs and prolong the lifetime of charge carriers.For ternary hybrids,the enhanced photocatalytic performance can be ascribed to the effects of well-formed interfaces berween MoS₂ and g-C₃N₄,which enhances the visible light absorption and accelerates the separation and transfer of photogenerated electron-hole pairs.Mechanism experiment demonstrates that·O^2-is the major reactive specie in the ternary hybrid and the h⁺in the isotype heterojunction,which shows that the establishment of ternary system changed the major reactive specie in photocatalytic reaction.The photocatalytic mechanism model established in this paper provides a new way for the design of g-C₃N₄-based photocatalysts.