| The environmental problems caused by organic pollutants are becoming more and more serious,especially the pollution of water resources.Photocatalytic technology uses solar energy to degrade organic wastewater effectively by the conversion of solar energy to chemical energy.It is a green and convenient water treatment technology.In the latest development of visible light-responsive semiconductors,two-dimensional graphite phase carbon nitride（g-C3N4）has been extensively studied due to its metal-free,low cost,easy thermal preparation,non-toxicity and high light stability.However,a single-phase g-C3N4 material has some limitations,such as the easy recombination of photo-generated charge carriers and lower visible light utilization.In order to solve the problems list above,this subject introduce other p-type or n-type semiconductors to construct a g-C3N4 based p-n heterojunction or n-n heterojunction.Metallic silver particles are introduced onto the surface of g-C3N4 by light deposition to improve the separation of charges via the surface plasmon resonance effect（SPR）.Since transition metal sulfides（MSx）generally have a narrow band gap and can improve the utilization of sunlight,different transition metal sulfides（Cu S,Mo S2,Sn S2）were coupled with Ag/g-C3N4to form composites.Rhodamine B（Rh B）was selected as the typical organic waste to test the actual photocatalytic performance of the materials.The main work are as follows:（1）Lamellar graphite phase carbon nitride g-C3N4 was prepared through secondary calcination at 550°C using thiourea as the precursor.The best two-phase composite material of 5%Ag/g-C3N4 could be obtained via light deposition method.Cu S prepared by solvothermal was selected to be composited with the Ag/g-C3N4,and the three-phase composite catalyst Cu S-Ag/g-C3N4（p-n type heterostructure）was successfully prepared by the method of ultrasonic mixing and solvent evaporation The results show that Cu S-Ag/g-C3N4 has a significantly higher effect and higher rate of photocatalytic degradation of Rh B than g-C3N4.,The photocatalytic rate of the compatible catalyst material with the 10%Cu S mass content is 4.3 times that of g-C3N4.It indicates that the specific surface area of the material increases,which significantly improves the material’s utilization rate of visible light and expands the light absorption range.（2）Mo S2 crystals were prepared under different hydrothermal time（4 h,8 h,12 h）at the temperature of 210℃.Mo S2 prepared in 8 h was selected to composite with 5%Ag/g-C3N4.The three-phase composite Mo S2-Ag/g-C3N4 was prepared by ultrasonic and evaporative solvothermal methods,which construct nn-type heheterostructure.A variety of characterization methods were used to analyze the morphology and elemental composition of the composite materials with different Mo S2 ratios.Solid ultraviolet diffuse reflectance spectroscopy proved that the composite materials have an enhanced ability to absorb and utilize light.The photocatalytic degradation of Rh B experiment proved that the photocatalytic effect of the material is the best when the proportion of Mo S2 is 10%,and the degradation rate is 0.02979 min-1,which is 3.4 times that of g-C3N4.The experiment of the material cyclic degradation of Rh B shows that the consistent photocatalytic material has a stable photocatalytic ability,and the degradation rate can still reach to 87.2%after four cycles.The main active substances in the photocatalysis process are superoxide radicals and holes which were proved by trapping agent experiment,and we also propose the mechanism of photocatalysis.（3）Sn S2 crystals were prepared hydrothermally at 180℃for 8 hours with different amounts of PEG-6000 dispersant,and Sn S2 prepared with a dispersant dosage of 0.3 g was selected to participate in the subsequent composite materials.Sn S2-Ag/g-C3N4 was prepared by ultrasonic mixing and solvent evaporation,and the nn-type heterostructure was constructed.The three-phase composite materials with different Sn S2 ratios were characterized,which proved that Sn S2-Ag/g-C3N4 improved the specific surface area and light absorption capacity of g-C3N4.The photocatalytic ability of Sn S2-Ag/g-C3N4composite for Rh B is significantly better than single-phase g-C3N4,and the best photocatalytic degradation efficiency is 95.6%with 10%Sn S2 mass content.The degradation efficiency is 0.03092 min-1,which is about 3.5 times that of g-C3N4.The stability of the composite material is proved by the cyclic experiment.At the same time,it is explored that the composite catalyst material has a better catalytic effect under acidic conditions.Finally,the trapping agent experiment proves that the main active substances in the photocatalysis process are superoxide radicals and holes,and the possible mechanism of photocatalysis is proposed. |
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