Study On Preparation And Properties Of A Novel Chitosan-based Co-Ni-Fe Hydrotalcite Composites

With the continuous advancement of social industrialization,the problem of organic wastewater pollution has aroused widespread concern.Chlorophenols compounds are a class of widely used compounds and are often used in the production of pesticides.Chlorophenols compounds are extremely toxic,and a low concentration can have serious toxic effects on organisms.Due to its special structure,hydrotalcite-like materials have a certain effect on the removal of chlorophenol pollutants.Therefore,the study of new hydrotalcite composite materials has certain environmental benefits for the removal of chlorophenols.In this study,based on the special structure of hydrotalcite,Co-Ni-Fe hydrotalcite(Co-Ni-Fe-LDH_S)and chitosan-based Co-Ni-Fe hydrotalcite composites(C/Co-Ni-Fe-LDH_S)were prepared by low saturation co-precipitation method.Co-Ni-Fe layered oxides(Co-Ni-Fe-LDO)and chitosan-sacrificial Co-Ni-Fe layered oxides(C/Co-Ni-Fe-LDO)were prepared by low saturation co-precipitation and calcination.The four materials were characterized by FTIR,XRD,SEM,BET and other characterization methods,and the morphology and structural characteristics of the materials were explored.The above four materials were used as adsorbents to adsorb 2,4-dichlorophenol(2,4-DCP)in simulated wastewater,and the influence of different adsorption conditions on the adsorption effect were also explored.The adsorption kinetic model and the adsorption isotherm fitting model were used to analyze the adsorption process at the basic level.By changing the reaction conditions,the oxidation removal performance of the above four materials on the 2,4-DCP in the simulated wastewater was comparatively studied,and the influence of the oxidation system conditions on the oxidation performance of the materials was also explored.In the heterogeneous Fenton-like oxidation system containing H₂O₂,the four materials prepared were used as the catalyst of the system.The factors affecting the degradation of 2,4-DCP in the heterogeneous Fenton-like oxidation system were explored and the degradation conditions were improved to improve the degradation effect and exert the catalytic performance of the material.The reusability of the material was investigated through multiple cycle tests.The results of this study are as follows:(1)Preparation and characterization of four materials.The Co-Ni-Fe-LDHs material with good crystallinity was prepared by the low saturation co-precipitation method,which has the layered structure of traditional hydrotalcite materials.After the modified chitosan molecules were introduced into the hydrotalcite-like material,the XRD pattern shows that the crystallinity of the formed composite material is reduced,and the SEM pattern shows that the material still has a layered structure.In the FTIR spectrum,the characteristic absorption peaks of chitosan molecules appear clearly.The characterization results show that the specific surface area of the material increases after sintering,and the layered structure is partially destroyed.(2)Comparative study on the adsorption performance of the four materials.The single factor method was used to optimize the reaction conditions of the adsorption system.By comparing the adsorption capacity of the materials to 2,4-DCP,the adsorption performance of the four materials was compared.Under the optimal conditions,the removal rates of Co-Ni-Fe-LDHs and Co-Ni-Fe-LDO on 2,4-DCP(20mg·L^-1)were 18.93%and 35.45%,respectively.The removal rates of C/Co-Ni-Fe-LDHs and C/Co-Ni-Fe-LDO for 2,4-DCP(100 mg·L^-1)were 25.72%and 36.45%,respectively.The adsorption capacity of Co-Ni-Fe-LDHs,Co-Ni-Fe-LDO,C/Co-Ni-Fe-LDHs and C/Co-Ni-Fe-LDO to 2,4-DCP could reach 0.9465 mg·g^-1,1.7725 mg·g^-1,2.572 mg·g^-1 and 3.6452 mg·g^-1,indicating that the introduction of chitosan and roasting improved the adsorption performance of the material.The adsorption kinetics equation was used to fit the adsorption process of the four materials for 2,4-DCP.The results show that the adsorption fitting curves of the four materials are better matched with the quasi-second-order kinetics model,indicating that the adsorption behavior of the four materials is dominated by chemisorption.Langmuir and Freundlich adsorption isotherm models were used to fit the adsorption processes of the four materials for 2,4-DCP.The results show that the isotherm adsorption fittings of the four materials are better matched with the Langmuir adsorption isotherm model,indicating that the adsorption process of the four materials for 2,4-DCP is an effective monolith chemisorption.The fitted data shows that the saturated adsorption capacity of C/Co-Ni-Fe-LDO(Qmax=3.9481 mg·g^-1)is better than the other three materials,and the saturated adsorption capacity of C/Co-Ni-Fe-LDHs(Qmax=3.0972 mg·g^-1)is better than Co-Ni-Fe-LDHs,further indicating that the adsorption performance of the modified material is better than that of the material before modification.(3)Comparison of the oxidative degradation performance of four materials on 2,4-DCP.The main layer structure of hydrotalcite is composed of oxides of the transition metals cobalt,nickel,and iron.The transition metal Fe³⁺has good catalytic oxidation performance.By modifying materials and changing reaction conditions,the oxidative degradation effect of Fe³⁺can be fully utilized.Under the optimal conditions,the oxidation removal efficiency of Co-Ni-Fe-LDHS,Co-Ni-Fe-LDO,C/Co-Ni-Fe-LDHS and C/Co-Ni-Fe-LDO for 2,4-DCP(100 mg·g^-1)were 72.88%,71.88%,83.20%and79.45%,respectively.(4)Comparison of the catalytic oxidative degradation performance of four materials on 2,4-DCP.The four materials with transition metal oxide as the main structure have good catalytic oxidation performance.By introducing H₂O₂ and improving the reaction conditions,the material's catalytic oxidation performance can be fully utilized.In the Fenton-like oxidation system with 2,4-DCP as the substrate,the degradation efficiency of 2,4-DCP(100 mg·g^-1)by Co-Ni-Fe-LDHS,Co-Ni-Fe-LDO,C/Co-Ni-Fe-LDHS and C/Co-Ni-Fe-LDO could reach 99.14%,74.32%,97.17%and71.77%,respectively,under the optimal reaction conditions.The results of 5 cycles show that the material as a catalyst has strong reusability and good stability.In this paper,the removal performance of 2,4-DCP was compared comprehensively.The results show that C/Co-Ni-Fe-LDHS has the best adsorption performance for 2,4-DCP.Co-Ni-Fe-LDO has the best oxidation degradation effect on 2,4-DCP.Co-Ni-Fe-LDHs and C/Co-Ni-Fe-LDHs,as catalysts for Fenton like reactions,have a wide range of p H adaptability and great potential for development and utilization.