Preparation Of Magnetic G-C₃N₄ Composite And Their Application In Catalytic Degradation Of Dye Wastewater

With the economic and social development of mankind,water shortages and pollution problems have become increasingly prominent.The printing and dyeing industry is one of the major industries causing water pollution.The dye wastewater is large quantity,large chroma,complex composition,and hard to degrade,which seriously threatens the survival and health of humans and other organisms.In recent years,using advanced oxidative methods such as heterogeneous Fenton,photocatalysis,and photo-Fenton to degrade dye wastewater has become an emerging research area.Compared with traditional methods,it can completely degrade dyes into carbon dioxide,water and inorganic ions.This is of great significance to protect water resources and ecological environment and realize the sustainable development of human society.However,these methods still suffer from severe reaction conditions,such as high processing costs,low visible light utilization,and slow degradation rates.Therefore,synthesis environmentally friendly,easily recyclable,reusable catalysts using inexpensive materials by simple method to treat dye wastewater is a very important research.This thesis uses Orange ? dye,a typical anionic azo dye that widely used in the industries of papermaking,printing,food,cosmetics,textiles,and leather,as a simulated dye wastewater treatment target.Fabricating Iron oxide nanoparticles,graphene-like carbon-nitrogen compounds?g-C₃N₄?and their composites?g-C₃N₄/?-Fe₂O₃/Fe₃O₄?using inexpensive and readily available raw materials by simple methods.The degradation behavior and mechanism in Orange ? dye solution was studied by Fe₃O₄ as heterogeneous Fenton catalyst,g-C₃N₄ as photocatalysis and g-C₃N₄/?-Fe₂O₃/Fe₃O4 as photo-Fenton catalysts,respectively.This thesis focuses on experimental research and the reaction mechanism analysis.The main research results are as follows:1.Co-precipitation,thermal decomposition and solvothermal method were used to successfully prepare Fe₃O₄ particles with different morphology and size.In the solvothermal method,ferric chloride was used as a precursor,and the size and morphology of the Fe₃O₄nanoparticles were controlled mainly by changing the proportions of the solvents ethylene glycol?EG?and diethylene glycol?DEG?.The results showed that the viscosity of the solution plays a decisive role in the formation process of Fe₃O₄ nanoparticles.When the solvent had a higher viscous DEG,the product shape was flake-like;when the solvent had a lower viscous EG,the product was a walnut shape.The morphology of Fe₃O₄,from sheet,globular,to walnut-like and the size could be controlled by changing the mixing ratio of EG to DEG.Fe₃O₄ nanoparticles were used as heterogeneous Fenton catalysts to degrade dye wastewater,and the effects of catalytic degradation of Orange ? on size,morphology,temperature,pH,and H₂O₂ dosage were studied in detail.The catalytic degradation mechanism studies showed that the hydroxyl radical?·OH?was the main active material for the degradation of Orange ? dye.2.Tetracyanoethylene?TCNE?,a compound containing only C and N elements,was used as a copolymer and urea as precursor to prepare a novel TCNE modified g-C₃N₄?CN/TCNE-x?by a simple one-pot thermal copolymerization method in the muffle furnace at 550°C.The measurements of structure,morphology,energy spectrum and chemical composition showed that CN/TCNE was a carbon-rich g-C₃N₄.The reason for carbon enrichment was due to formation of nitrogen deficiency.The TCNE modification could increase the specific surface area and pore volume of the material,shift the absorption threshold boundary towards the long wave direction,narrow the bandgap,facilitate the absorption of visible light,and promote the separation of photoelectron-hole pairs.The test of photocatalytic degradation of Orange ? dyes showed that the CN/TCNE-40?40 mg TCNE in 30g Urea?had the highest catalytic degradation effeciency;the pseudo-first-order rate constant of CN/TCNE-40 was4.88 times as large as that of pristine g-C₃N₄.The Orange ? dye could be effectively degraded at different pH values.Repeated catalytic degradation experiments showed that CN/TCNE-40could still achieve very good degradation effect after 5 times,indicating it had good stability.The results of trapping experiments showed that the superoxide?·O₂^-?was the main active substance to degrade orange ? dye.3.A novel type of magnetic composite,g-C₃N₄/?-Fe₂O₃/Fe₃O₄,was prepared by a simple hydrothermal method using TCNE-modified g-C₃N₄ with semiconductor material?-Fe₂O₃and magnetic material Fe₃O₄.It was showed that the diamond-shaped?-Fe₂O₃ and spherical Fe₃O4 were coated by the flake-shaped g-C₃N₄ very well.The composite had a higher specific surface area and pore volume,which could promote the charge separation in the composite system.The absorption threshold boundary of the composite material moved toward the long wave region with the increase of the amount of Fe₃O₄,which narrowing of the bandgap and facilitating the absorption of visible light.The photogenerated carriers of the composite had high intensity and long lifetime,which was beneficial to make more electrons and holes participating in the photo-Fenton reaction.Magnetic tests show that the composite material had higher saturation magnetization and could easily be separated and recoveried from the dye solution.Photo-Fenton catalytic degradation of Orange ? dye showed that the appropriate amount of Fe₃O₄ was beneficial to improve the photocatalytic efficiency of the composite.When the Fe₃O₄ amount is 30%,the catalytic degradation effeciency is best,which was almost 4.01 times higher than?-Fe₂O₃ and 2.65 times higher than g-C₃N₄/?-Fe₂O₃ under the same conditions.Free radical capture test and·OH generation verification experiments showed that the composites had significantly enhanced photocatalytic activity,·OH,·O₂^-and holes were generated in the system to rapid degrade Orange ? under visible light and neutral solution.