The Study On Refractory Organic Pollutants Degradation By Photocatalytic Activated Peroxymonosulfate Using Graphite Phase Carbon Nitride-based Material

Traditional sewage treatment is difficult to remove Refractory organic wastewater because of the such pollutants poor biodegradability,which is easy to enter the external environment with tail water.Over time,it will damage the ecological environment and pose a threat to the growth of animals and plants as well as human health.Advance Oxidation Processes（AOPs）have the characteristics of fast treatment efficiency,high degradation degree and wide application range,and have good application prospects in the field of refractory organic wastewater treatment.Therefore,the advanced oxidation technology based on sulfate radical can effectively remove all kinds of refractory organic pollutants.Photocatalytic activation of persulfate by graphite-phase carbon nitride based materials was used to remove various simulated organic pollutants in this paper.Additional energy and the addition of homogeneous or heterogeneous materials can activate peroxymonosulfate（PMS）to produce active substances with strong oxidability to further remove refractory organic wastewater.However,these activation methods have some problems such as high energy consumption,unstable activation effect and secondary pollution caused by the dissolution of metal ions.It is still a great challenge to develop efficient,stable and environmentally friendly catalytic activation materials.The visible light-driven non-metal material graphite-phase carbon nitride（g-C₃N₄）can not only activate PMS as a catalyst independently,but also its unique layered structure can be used as a carrier material of metal.More importantly,g-C₃N₄and metal can play a synergistic effect to improve the activation effect of oversulfate.Therefore,a series of g-C₃N₄based materials were prepared and used to activate PMS to degrade organic pollutants by adjusting the morphology and structure to increase the specific surface area of the material,and doping metal elements to adjust the electronic structure of g-C₃N₄.,and the mechanism and efficiency of each reaction system are systematically studied.The main contents include the following aspects:（1）Three pure graphite-phase carbon nitride materials g-C₃N₄,SRCN and CN are prepared by simple high-temperature thermal polycondensation using melamine,hydrothermal treated melamine and supramolecular materials with melamine-cyanic acid as precursors,respectively,which was used to activate PMS to degrade rhodamine B（Rh B）.After characterization analysis,it is found that the CN sample with supramolecular structure as the precursor contains porous structure,with larger specific surface area and higher photogenic electron-hole separation efficiency,which made the CN sample has better photocatalytic activation effect.The CN/PMS reaction system can degrade 96%of Rh B（25mg/L）in 40 min,about twice that of the other two samples of the same conditions.Free radical capture experiments showed that free radical active substances such as SO₄^·-,·O₂^-,·OH co-existed with non-free radical singlet oxygen（¹O₂）and holes in Rh B degradation system.（2）Based on the above study,it was found that specific surface area could significantly affect the photocatalytic activation performance of the material.Then,Ti O₂/g-C₃N₄composite catalyst（TCN）was constructed by simple ammonium salt-assisted hydrothermal calcination method.Free radical trapping experiments showed that z-type heterojunction was formed between Ti O₂and g-C₃N₄,which could effectively promote the separation of photoelectron-hole pairs.After illumination for 60min,the degradation rate of Rh B in TCN1/PMS system was 92.3%,but only 59.8%and 63.2%in the g-C₃N₄/PMS and Ti O₂/PMS systems.The TCN1-4 sample prepared by adding ammonium sulfate into the precursor of composite material has higher specific surface area（116.44 m²/g,3.3 times and 14.5 times of TCN1 and g-C₃N₄,respectively）,the corresponding photocatalytic activation of PMS is better.The degradation rate of Rh B in TCN1-4/PMS system reached 93.9%after 30min,compared with TCN1/PMS,the reaction time was reduced by half and the degradation rate was doubled under the same conditions,which further proved that increasing the specific surface area of the material could improve its photocatalytic activation performance.In addition,the active species capture experiment showed that there were free radical(·OH,SO₄^·-,·O₂^-),non-free radical（¹O₂）active substances and holes in the TCN1-4/PMS reaction system.（3）The structure of g-C₃N₄contains abundant surface functional groups,which is conducive to doping transition metal.After metal doping modification,the electronic structure of the material can be adjusted and its photocatalytic activation performance can be improved.In chapter 5,the co-doped g-C₃N₄composite photocatalytic activator（Co CN）was prepared by using organic framework material（MOFs）ZIF-47 as cobalt source and supramolecular material with higher specific surface area as carbon nitride precursor.After doping with metal cobalt,the specific surface area increase of composite Co CN10 is limited,only 1.2 times of monomer CN samples.However,after 60 min of reaction,the degradation rate of OFX in Co CN10/PMS reaction system can reach 85%,while CN/PMS reaction system is only 24.3%,indicating that Co elements may be the active point in the composite material,there is synergistic interaction between cobalt and carbon nitride.For the Co CN10/PMS reaction system,the main factor that significantly affects the photocatalytic activation performance of Co CN10 is the cobalt doped in the composite rather than the specific surface area of the material.The Co CN/PMS reaction system is dominated by free radicals,and the main active material is SO₄^·-.（4）The high cost of cobalt metal is not conducive to large-scale production and application,Chapter 6 use cheap and readily available iron instead of cobalt.A Fe（Ⅲ）-doped g-C₃N₄composite photocatalytic material（Fe CNx）was prepared by a simple"one-pot"method,using MOFs（MIL-53）as the iron source.The photocatalytic activation experiments show that Fe element is the active point in the composite,and there is a synergistic effect between Fe and carbon nitride.In active species capture,ethanol and tert-butanol could not effectively inhibit the degradation of Rh B in Fe CN/PMS system,and the reaction system had almost no catalytic degradation to benzoic acid,indicating that·OH and SO₄^·-are not active substances in this reaction system.The degradation of Rh B is inhibited by the addition of L-histidine,which indicated that there was singlet oxygen（¹O₂）in the system.After adding the strong reductive inorganic Na NO₂with the same concentration of L-histidine,Rh B degradation inhibition is more significant,indicating that there are other oxidizing substances in the reaction system except ¹O₂,The fixed Fe（Ⅲ）in Fe CN6 is converted to Fe ^IV=O by electron transfer and involved in Rh B degradation.Thus,the Fe CN/PMS reaction system is dominated by non-free radicals,and the main active species within the reaction system are Fe ^IV=O,¹O₂,and h⁺.