Preparation Of Chitosan Derivative Supported Fe/Pd Bimetallic Catalyst And Its Degradation Performance On 2,4-dichlorophenol

2,4-dichlorophenol（2,4-DCP） is an important intermediate in the production process of pesticides,organic chemicals,pharmaceuticals,etc.And it is also one of the main components of the adsorbable organic halogen（AOX）in pulp and paper making wastewater.Due to the failure of traditional secondary biodegradation to remove chlorophenols,some chlorophenols were transferred to physicochemical sludge or even biochemical sludge,which further affected the high value utilization of sludge.2,4-DCP is biologically toxic,carcinogenic,teratogenic,and mutagenic to organisms,which is extremely harmful to the natural environment and human health.Due to the benzene ring in the molecular structure of 2,4-DCP,its chemical properties are very stable,and it is difficult to degrade under natural conditions.Therefore,it is of great practical significance to develop effective degradation methods of2,4-DCP.Iron-palladium bimetallic catalyst（Fe/Pd）has the advantages of small particle size,large specific surface area and strong reaction activity.It is often used for dechlorination of chlorinated organic compounds to reduce their toxicity.However,due to the small particle size of Fe/Pd,the particles tend to agglomerate,resulting in larger particle size.In addition,Fe/Pd has a strong reducibility and is easy to oxidize in air,which will reduce the catalytic activity of Fe/Pd.In order to solve these problems,carboxymethyl chitosan（CMCS）and phosphorylated chitosan（RPBCS）were used as stabilizers to surface modification of Fe/Pd to obtain the modified Fe/Pd catalyst,and the degradation effect of 2,4-DCP was studied.In this paper,a carboxymethyl chitosan supported ironpalladium bimetallic catalyst（CMCS@Fe/Pd）was prepared by the liquid phase reduction method.The material has good dispersion and oxidation resistance.The structure of the material was characterized by SEM and TEM,and the results showed that compared with Fe/Pd,the particle size of CMCS@Fe/Pd was smaller and the dispersion was more uniform.The FT-IR results showed that the CMCS molecule and Fe/Pd in the CMCS@Fe/Pd material were combined by carboxylic monodentate coordination and hydrogen bond between hydroxyl molecules,which proved that Fe/Pd was successfully loaded onto the carboxymethyl chitosan.The analysis results of XRD and XPS showed that the Fe/Pd particles were oxidized inside,while CMCS@Fe/Pdonly oxidized on the surface,indicating that the addition of carboxymethyl chitosan inhibited the oxidation of the bimetallic catalyst to a certain extent.CMCS@Fe/Pd was used as a catalyst to degrade 2,4-DCP in this paper.The results of HPLC analysis showed that the intermediate product of degradation was 2-CP and the final product was phenol.In addition,the effects of initial concentration of 2,4-DCP,dosage of CMCS@Fe/Pd catalyst,Pd loading in catalyst,initial p H of solution,reaction temperature,content of amino group,carboxyl group and molecular weight in CMCS on the dechlorination efficiency of 2,4-DCP were also studied.The experimental results showed that the higher the initial concentration of 2,4-DCP,the greater the removal rate of 2,4-DCP.The greater the dosage of CMCS@Fe/Pd catalyst,the higher the Pd loading in CMCS@Fe/Pd catalyst,the greater the removal rate of 2,4-DCP and the reaction rate constant.The initial p H of the solution was weakly acidic,and the effect was best.The removal rate and reaction rate of2,4-DCP increase with the increase of reaction temperature,and the activation energy was55.37k J mol^-1.Surface adsorption and degradation was the decisive steps of the reaction.The larger the molecular weight of CMCS,the higher the content of carboxyl group and amino group,and the greater the reaction rate constant of 2,4-DCP.Compared with some dechlorination technologies reported in the literature,CMCS@Fe/Pd has a higher reaction rate constant for 2,4-DCP,indicating that the material has a good application prospects.In this paper,phosphorylated chitosan（RPBCS）was prepared by dehydration,esterification and reduction using 1,2,4-tricarboxylic butane phosphate（PBTCA）and chitosan as raw materials.LC-MS results showed that the intermediate phosphoric anhydride was successfully synthesized.FT-IR results showed that the characteristic peak of P=O bond of RPBCS appeared at 1066 cm^-1,indicating the successful synthesis of RPBCS;XRD results showed that the intensity of characteristic diffraction peak of RPBCS decreased after esterification,which means that the crystallinity of RPBCS decreased and the crystal structure disappeared.The phosphorus content of the phosphorylated chitosan prepared in this paper is5.36%.Phosphorylated chitosan supported Fe/Pd bimetallic catalyst（RPBCS@Fe/Pd）was prepared by using RPBCS as a stabilizer for the removal of 2,4-DCP.The results showed that RPBCS@Fe/Pd had an excellent effect on the removal of 2,4-DCP.In summary,the chitosan from marine waste was modified by carboxylation and phosphorylation,and carboxyl and phosphoric groups were introduced to improve the loading capacity of metal ions and further improve the catalytic activity of Fe/Pd nanoparticles on2,4-DCP.The results of this paper showed that the two chitosan-based derivatives supported metal catalysts showed good removal effect on 2,4-DCP,which provided an effective idea for the non-toxic degradation of chlorinated organic compounds.