The Construction Of Fenton-Like-Laccase Bifunctional Synergistic Catalytic System And Its Removal Of PNP In Aqueous Solution

P-nitrophenol（PNP）is a common phenolic pollutant with strong toxicity and pollution,China has included PNP in the blacklist of priority pollutants in water.The individual Fenton-like treatment technology is not thorough enough to treat PNP and requires a large amount of oxidant.Although the single laccase technology has a broad spectrum of degradation of phenolic pollutants,it has weak catalytic oxidation ability to PNP,poor enzyme stability and cannot be reused.In view of the problems existing in the above technologies,a bifunctional catalytic system combining Fenton-like technology（Cu/HAP-s BC as catalyst and H₂O₂ as the oxidant）with laccase-inorganic hybrid nanoflower technology was constructed.The system can improve the stability and reusability of the catalyst,and effectively improve the degradation rate of PNP through the multi-party synergistic effect,which is a new direction with industrial application potential.Firstly,the heterogeneous copper-based catalyst material Cu/HAP-s BC was synthesized by using pure hydroxyapatite（n HAP）and pig-bone hydroxyapatite（p HAP）as raw materials,and the way to improve its structural stability and the synthesis mechanism were studied.Secondly,the effects of different factors on the removal of PNP and the reusability of the catalyst under the Fenton-like system with Cu/HAP-s BC as catalyst were explored.Then,lac-IHN was loaded onto Cu/HAP-s BC by adsorption method to synthesize Fenton-like-laccase bifunctional catalyst（lac-IHN@Cu/HAP-s BC）,and its enzyme stability,catalytic activity and reusability were studied.Finally,the synergistic mechanism of Fenton-like-laccase bifunctional synergistic catalytic system with lac-IHN@Cu/HAP-s BC as bifunctional catalyst,as well as the removal mechanism and degradation pathway of PNP were discussed.The conclusions are as follows:（1）The surface of Cu/HAP-s BC has compact particle aggregates,rough morphology,rich pore structure and high specific surface area（up to 271.5 m²/g）.The crystal structure of HAP was completely retained before and after the synthesis.The copper ion leaching and acid etching rate decreased after composite biochar,and the structural stability of the catalyst was enhanced,which was attributed to the protection of the biochar structure on the HAP structure and the adjustment of the p H microenvironment.（2）In the Fenton-like system with Cu/HAP-s BC as catalysts and H₂O₂ as oxidant,the removal rates of PNP corresponding to Cu/n HAP-s BC and Cu/p HAP-s BC were61.46%and 62.99%,respectively.The main intermediate products of PNP degradation by?OH produced in the Fenton-like system are p-nitrocatechol,1,2,4-benzenetriol,4-nitrocyclohexane-2,5-dienone,p-phenol,p-semiquinone,p-benzoquinone,etc.The possible degradation pathways are mainly divided into three routes,and the final degradation products may be CO₂,H₂O and inorganic nitrogen by-products such as NO₃^-and NH₄⁺.（3）The optimum preparation conditions of lac-IHN@Cu/n HAP-s BC were the volume fraction of lac-IHN suspension 60%,p H 6.0,and the reaction time 2 h;the optimum preparation conditions of lac-IHN@Cu/p HAP-s BC were the volume fraction of lac-IHN suspension 80%,p H 6.0,and the reaction time 2 h.Under the optimal preparation conditions,lac-IHN@Cu/HAP-s BC showed better storage,acid-base and thermal stability than free laccase,and was endowed with reusability.Among them,lac-IHN@Cu/p HAP-s BC showed better reusability,and there was still a high relative activity after ten reaction cycles,up to 80.15%.（4）When the reaction conditions were catalyst dosage of 1.0 g/L,H₂O₂ dosage of50 m M,and PNP concentration of 50 mg/L（room temperature,pure water）,the removal rate of PNP by the Fenton-like-laccase bifunctional synergistic catalytic system could reach 85.33%,which was higher than the sum of single Fenton-like system and single laccase system,proving that there was a synergistic effect between the two systems.Under suitable p H and high temperature reaction conditions,the removal rate of PNP by Fenton-like-laccase bifunctional synergistic catalytic system with lac-IHN@Cu/p HAP-s BC as catalyst and H₂O₂ as oxidant was up to 98.44%,and the reaction rate fitted by reaction kinetics was 0.070 min^-1.After 5 and 10 reaction cycles,86.79%and 61.25%reusability were retained,respectively.The construction of bifunctional catalytic system improved the activity and reusability of the catalyst.（5）The synergistic mechanism of Fenton-like-laccase bifunctional catalytic system is as follows:H₂O₂ is first catalyzed by lac-IHN@Cu/p HAP-s BC to decompose into?OH.Some phenolic intermediates（such as p-aminophenol and hydroquinone）produced by?OH attacking PNP structure have good affinity with laccase system,which provides more binding sites for laccase,thus enhancing the activity of laccase system.The laccase system is involved in the catalytic degradation of phenolic intermediates,so that more?OH in the system can be used to destroy the PNP structure and promote the forward reaction of the Fenton-like system.There are four degradation pathways of PNP in the Fenton-like-laccase bifunctional synergistic catalytic system.In addition to the three pathways of PNP degradation in the Fenton-like system,the main intermediate products of PNP degradation in the laccase system are p-nitrophenol radicals,PNP dimers and their free radicals,and even trimers and polymers.