| With the acceleration of industrialization and urbanization,the problem of water pollution has received widespread attention.The heterogeneous Fenton reaction has the advantages of strong oxidation capacity,high mineralization efficiency,and easy separation and recovery of catalysts,and has become one of the research hotspots of water protection and treatment.However,the actual wastewater composition is extremely complex and diverse,and there may be a variety of non-toxic dissolved organic compounds and inorganic salt ions.Their concentrations can be orders of magnitude higher than the target contaminant,resulting in active species being consumed in large quantities or transformed into low-activity groups.Therefore,the study of efficient and selective removal of target pollutants has attracted attention.In recent years,a variety of carbon material Fenton reaction catalysts have been reported,among which two-dimensional sheet Fe doped g-C3N4 can show strong catalytic activity in a wide pH range and stably generate hydroxyl radicals(·OH)with strong oxidizing ability.However,-OH does not have selective oxidation capacity.Singlet oxygen(1O2)and high valence Fe(Ⅳ)selectively oxidize organic contaminants with electron-rich functional groups.However,they have poor oxidation capacity and difficulty in regulating generation.In view of the above problems,a heterogeneous Fenton catalyst with efficient and selective degradation of target pollutants was prepared by modifying Fe doped g-C3N4.At the same time,the morphology,composition and structure of the materials themselves were systematically characterized,and the mechanism and application prospects of selective catalysis in Fenton-like systems were explored.The main research content of this paper is divided into three parts:1.Fe and Na co-doped g-C3N4 were prepared by one-step calcination.The characterization results showed that Fe and Na ions were bound to pyridine nitrogen of g-C3N4 by coordination.Doping of Fe inhibits the polymerization of g-C3N4,resulting in a fragmented distribution of g-C3N4.The doping of alkali metal Na hydroxylates the surface of g-C3N4,which in turn affects the surface Zeta potential of g-C3N4.Subsequent studies have shown that the surface Zeta potential of g-C3N4 varies linearly with the doping amount of alkali metal Na.The experimental results show that Fe/Na-CN shows strong selective adsorption performance against cationic pollutants methylene blue(MB).Under the action of electrostatic gravity,the adsorption equilibrium can be reached within 3 minutes,and the maximum adsorption capacity is 1955.6 mg/g.In multi-mixed solutions,the adsorbent exhibits nearly 100%selective adsorption of MB.The adsorbent showed the best adsorption performance at pH=9.0 and remained stable after five cycles.2.On the basis of the previous chapter,we regulated the adsorption performance of the catalyst by changing the doping amount of alkali metal Na.Fe ions,as Fenton-like activity centers,activate the efficient production of H2O2 and-OH.Firstly,under the action of electrostatic attraction,the selective enrichment of cationic pollutants was realized on the surface of the catalyst,and the selective degradation of cationic organic pollutants was realized with the strong oxidation ability of-OH.The experimental results show that the selective absorption capacity of the catalyst to cationic organic pollutants MB gradually increases with the increase of Na doping amount.However,when the adsorption capacity of the catalyst is too strong,the active site will be embedded,resulting in a decrease in the degradation capacity of the catalyst.Therefore,moderate adsorption is conducive to degradation,and excessive adsorption hinders contact.A variety of inorganic salt ion interference and different water-based experiments show that the system with double sites of adsorption site and degradation site has strong anti-interference ability.At the same time,it maintains efficient degradation performance for MB in the range of pH:4.5～11.5.The removal rate of total organic carbon content(TOC)within 20 minutes of 100 mg/L MB is as high as 86%.The catalytic performance of the catalyst remained stable after five cycles.3.Fe-doped g-C3N4 was first prepared by one-step calcination,and then Fe-CN was chemically etched with hydrochloric acid.Finally,the catalyst x-Fe-CN-NH2 for surface amination was obtained.The characterization results showed that the Fe ions were immobilized in a nitrogen tank.With the increase of hydrochloric acid concentration used for chemical etching,the amino surface of the catalyst intensified,and the surface Zeta potential gradually increased to+49 mV.The experimental results show that x-Fe-CN-NH2 has strong selective adsorption performance against anionic organic pollutants under electrostatic attraction.The active site Fe activates H2O2 and thus efficiently produces ·OH.With the strong oxidation ability of ·OH,the effect of selective degradation of anionic organic pollutants is achieved.Ion interference and different water-based experiments show that the system has strong anti-interference ability.At the same time,according to the toxicity analysis results of degradation intermediates,it is further confirmed that the system has strong detoxification ability.After five cycles,it still maintains good catalytic performance. |
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