Photocatalytic Self-Fenton Degradation Of Antibiotics By Two-Dimensional Porous Self-Assembly Materials

In recent years,antibiotic pollution has become one of the water pollution problems facing all mankind.The antibiotics were discharged into the water,soil and other external environment,then remain and spread in the environment due to abuse and improper treatment,which poses a potential threat to natural ecology and human health.Typical antibiotic molecules,such as sulfamethoxazole,cannot be completely mineralized by traditional physical and biological methods due to their largeπ-electron conjugated system.If its decomposition is not complete,it may form more toxic intermediate products and cause greater harm to the ecological environment.Therefore,it is an urgent need to develop a low-cost and efficient method to remove antibiotics from the water environment,which is of great strategic significance for promoting the improvement of energy efficiency of new sewage treatment facilities and accelerating the establishment of a sound green,low-carbon and circular development economic system.As all know,Fenton technology can efficiently degrade antibiotics in water,showing great advantages in the treatment of new pollutants and collaborative control.However,the traditional Fenton technology causes resource waste and environmental harm due to adding a large amount of H₂O₂ and producing large iron sludge.Therefore,focusing on reducing or even avoiding additional H₂O₂ and realizing in-situ,continuous and stable self-production of H₂O₂,this article innovatively puts forward the strategy of utilizing the green and environmentally friendly photocatalytic self-Fenton technology and efficiently regulating the two control factors of photocatalytic self-Fenton technology,"oxygen and electron"cycle and utilization efficiency.The photocatalytic self-production of H₂O₂ can be greatly improved and the pollution of iron sludge can be reduced,so as to accelerate the process of deep mineralization of typical refractory antibiotics,and finally achieve the goal of completely purifying the new pollutants represented by antibiotics in the water environment.Firstly,oxygen as one of the most important reactants in the photocatalytic self-Fenton process,not only provides the source of singlet oxygen generation in the non-free radical path,but also acts as the oxygen species of self-producing H₂O₂ to decompose hydroxyl radicals in the free radical path,ultimately determining the mineralization rate.Therefore,from the point of view of increasing the circulation and utilization rate of molecular oxygen,we prepared a new kind of two-dimensional porous self-assembled micellar Bi OCl nano-flower by using saponin powder with low-cost and high surface activity as the surfactant,in order to enhance the adsorption and reduction rate of O₂,increasing the active site of its reaction with electrons to improve the productivity of H₂O₂.The DFT results showed that the hydrophobic group（-CH₂-）on the micelle could increase the O₂ adsorption site on the surface of Bi OCl,thus expanding the O₂ adsorption capacity.The enhancement of the peak intensity of O 1s in the XPS spectrum fully confirmed the increase of oxygen species sources that can interact with electrons on the surface,which provided the molecular structure basis for the improvement of H₂O₂ yield.At the same time,the accumulation charge on the micellar surface can accelerate the reduction of molecular oxygen to·O₂^-,even in pure water,H₂O₂ production can reach 108.6μM h^-1 g^-1,which is 7.99 times higher than the bulk Bi OCl.Compared with Bi OCl,the degradation efficiency of SA-Bi OCl for sulfamethoxazole was increased by 16.8 times.In the above work,micellar two-dimensional porous self-assembled inorganic materials were effectively obtained from the perspective of improving the O₂ utilization rate,and higher antibiotic mineralization efficiency was obtained by improving the reduction and transfer efficiency of O₂ inside and outside the layer.However,the separation,migration and conversion efficiency of the electron,another key factor restricting the self-Fenton technology,still becomes the key factor affecting the improvement of the final H₂O₂ generation yield.Therefore,how to design a material system with high electron delocalization and gradient periodic conversion performance in a wider range of molecular systems is still a key issue worthy of further research.Focusing on improving the recycling and utilization efficiency of electrons,we further designed and synthesized a two-dimensional porous self-assembled organic material system,namely a light-driven covalent organic framework material system,covalent organic framework material system,covalent organic framework material system,and used it to efficiently generate H₂O₂ and deep mineralization antibiotics through photocatalysis.Due to the excellent electron donor and abundant surface hydroxyl functional groups of the two-dimensional porous self-assembled organic material system,the COF-TAPT/DHA material showed excellent self-production capacity of H₂O₂,even without the presence of electron sacrificial agents,with a yield of 1629μM h^-1 g^-1.It is better than COF-TAPT/PDA(446μM h^-1 g^-1)without hydroxyl functional group on the surface.By introducing surface hydroxyl groups,D-A system（triazine-hydroxyl）can be constructed in COFs,which is conducive to the dual electron pathway of ORR,thus accelerating the separation,migration and conversion efficiency of electrons,and increasing the photocatalytic self-produced H₂O₂ yield.At the same time,the surface hydroxyl group can also provide adsorption sites for O₂,so that·O₂^-can be transformed into H₂O₂ at the valence band of COFs.The cyclic test further confirmed that the triazine-hydroxyl D-A COFs material has good reusability,and can still maintain 87.6%after four cycles,showing high H₂O₂ production activity.In addition,under visible light irradiation,the degradation rates of COF-TAPT/DHA with D-A structure to sulfamethoxazole and ciprofloxacin were 63.2%and 56.4%,respectively.The above results systematically reveal the strong activity of COFs materials in sustainable water treatment,which can provide a reference for the design of future photocatalytic H₂O₂ production systems from Fenton.Aiming at the Angle of photocatalytic two-electron oxygen reduction and protonation efficiency improvement,in the above work,we found that slow charge dynamics restricted the occurrence of two-electron ORR process,so we constructed a series of COFs photocatalytic materials based on the quinoline bond by using a multi-component reaction mode.By grafting strongly polar oxygen-containing functional groups（hydroxyl,carboxyl）onto the surface of COFs,charge separation,migration and conversion efficiency were significantly improved from multiple dimensions,and proton transfer was significantly enhanced.The photocatalytic yield of H₂O₂ was significantly increased to 1547μM h^-1 g^-1 by the functionalized COFs（Q-COF-TAPT/DHA）containing oxygen-containing functional groups without sacrificial agents or cocatalysts.The yield of COFs（Q-COF-TAPT/PDA）was 1.51 times higher than that of COFs(1028μM h^-1 g^-1)with only carboxyl group on the surface.Mechanistic studies have shown that the improved photocatalytic performance is attributable to significantly enhanced two-electron oxygen reduction through the formation of·O₂^-at the triazine unit and holes at the site of oxygen-containing functional groups.In addition,under visible light irradiation,the degradation rates of SMX and CIP were 71.7%and 67.2%,respectively.These findings provide a powerful new method of charge regulation mediated by strongly polar oxygen-containing functional groups for the development of highly efficient two-dimensional porous self-assembled organic photocatalytic materials.In summary,we mainly start from the perspective of improving the two key factors that restrict photocatalytic self-Fenton,O₂ and the efficiency of electron cycling and utilization.Through the comprehensive design of inorganic and organic two-dimensional porous self-assembly material systems with each advantage,we solve the key scientific problems of O₂reduction and electron utilization respectively from multiple dimensions.Thus,the photocatalytic self-produced H₂O₂ yield is greatly improved,and finally the deep mineralization of the typical new pollutants represented by antibiotics is realized.