Synthesis And Photocatalytic Properties Of 3D Carbon Nitride-Cellulose Composite

Graphitic carbon nitride?g-C₃N₄?is a metal-free n-type semiconductor,have excellent electric,optical and physiochemical properties,demonstrating promising applications in photocatalytic water splitting,pollutant degradation and CO₂ reduction.However,g-C₃N₄generally exhibited the low photocatalytic activity,due to its insufficient visible absorption and high carriers recombiadation.The nanostructural g-C₃N₄ not only suffered from the random aggregation in the water,but also leaded to a complicated recovery step,setting a hurdle for the practical application.In order to improve the photocatalytic activity and cycle performance of g-C₃N₄,this thesis prepared 3D g-C₃N₄-cellulose composite by compositing the cellulose with g-C₃N₄ or Br-doped g-C₃N₄?Br-C₃N₄?which was obtained by thermal condensation of melamine.The effect of g-C₃N₄ addition on the morphology,chemical structure,thermal stability and mechanical strength was investigated.The photocatalytic activities of two kind of g-C₃N₄-cellulose composites were been determined toward the degradation of methylene blue?MB?and rhodamine B?Rh B?,and their photocatalytic mechanism were also discussed.The results were showed as follows:?1?The synthesis and characterization of 3D g-C₃N₄-cellulose composite:3D g-C₃N₄-cellulose composite was prepared with different amounts of g-C₃N₄ by mixing the g-C₃N₄ with cellulose.The obtained composites exhibited 3D interconnected porous structure with the porosity higher than 92%.When the content of g-C₃N₄ was 3%and the strain was 60%,compressive stress of 3D g-C₃N₄-cellulose composite reached 1.1MPa in dry condition and 0.2MPa in wet condition,showing excellent mechanical strength.?2?The photocatalytic property of 3D g-C₃N₄-cellulose composite:The DRS result showed that the 3D g-C₃N₄-cellulose composite was a visible light photocatalyst with the band gap of2.77 eV.When the content of g-C₃N₄ was 3%,the 3D g-C₃N₄-cellulose composite had the best photocatalytic performance,and the degradation of MB reached 99.8%after 80 min visible light irradiation,and the photodegradation efficiency can still reach 95.5%after four cycles.The results of PL and EIS showed that the 3D g-C₃N₄-cellulose composite exhibited faster carrier transport efficiency and lower photogenerated electron-hole recombination rate than g-C₃N₄,showing higher photocatalytic activity.During the photocatalytic process,superoxide radical?·O₂^-?,hydroxyl radical?·OH?and h⁺all played a role,but the superoxide radical?·O₂^-?was the main active specie.?3?The synthesis and photocatalytic performance of Br-C₃N₄-cellulose composite:the Br-doped g-C₃N₄?Br-C₃N₄?were obtained by heating the mixture of melamine,urea and ammonium bromide precursors with different mass ratios.The stuctural characterization and photocatalytic performance confirmed that the but the doping of Br can optimize the optical and photocatalytic property of g-C₃N₄.Then the Br-C₃N₄-cellulose composite was prepared by compounding Br-C₃N₄ with cellulose,showing enhanced photocatalytic activity,its photodegradation effeciency of MB reached 99.5%after 120 min light irradiation,and the photocatalytic degradation rate of RhB was 95%.In this thesis,two kind of carbon nitride-cellulose composites with 3D interconnected porous structure were prepared.Compared with pure g-C₃N₄,it not only had high adsorption and enrichment capacity,but also exhibited faster carrier transport efficiency.These carbon nitride-cellulose composites showed enhanced photocatalytic activity,and could separate from solution and reuse quickly,demonstrating excellent potential applications in the large-scale water pollution treatment.