Preparation And Performance Of A Novel Chitosan/Nickel-Iron Layered Double Hydroxides Composites

Phenolic compounds are a kind of widely used chemical raw materials.The phenolic industrial wastewater has a wide range of pollution and seriously endangers for human health and water ecological environment.Therefore,it is of great significance to study new composite materials in the field of water pollution prevention and control.In this study,a novel chitosan/nickel-iron layered double hydrotalcites composite(CS/NiFe-LDHs)and nickel-iron layered double hydrotalcites(NiFe-LDHs)were prepared by low saturation coprecipitation method for the special properties and layered structure of hydrotalcite,and the two materials synthesized were characterized by TEM,XRD,FTIR and SEM.With CS/NiFe-LDHs and NiFe-LDHs as adsorbents,the adsorption effects of two materials on phenolic compounds(2,4-DCP,BPA and phenol)were studied by single factor method.In order to further investigate the adsorption properties of CS/NiFe-LDHs and NiFe-LDHs,the adsorption kinetics was studied and its quasi-first-order kinetics and quasi-second-order kinetics were fitted.At the same time,the adsorption isotherm curve was fitted.The TG-DTG analysis of the composites was carried out to investigate the structural properties of the composites,ande the oxidation properties of CS/NiFe-LDHs composites on phenolic compounds were investigated.In order to investigate the catalytic performance of CS/NiFe-LDHs,as a catalyst for heterogeneous Fenton oxidation system,the catalytic oxidation effect of phenolic oxides and its influencing factors were studied.The reutilization performance of composite materials in Fenton-like catalytic systems was investigated.The comparative effects of phenolic compounds removal in different systems were compared.The results show:(1)Preparation and characterization of CS/NiFe-LDHs and NiFe-LDHs.When amodified chitosan molecule is introduced into the hydrotalcite structure,the formed composite still retains its layered structure,but its crystallinity decreases.In the Fourier infrared spectrum of the material,chitosan is clearly shown.The characteristic infrared absorption peak indicates that the modified chitosan molecule and hydrotalcite combine to form CS/NiFe-LDHs.The successful preparation of CS/NiFe-LDHs was further confirmed by XRD and TEM.(2)Study on adsorption properties of CS/NiFe-LDHs and NiFe-LDHs.The optimal conditions for adsorption were obtained by single factor analysis.Under the optimal conditions,the removal rates of phenolic compounds(BPA,2,4-DCP and phenol,100mg·L-1)by CS/NiFe-LDHs were: 40.4% and 38.4% and 17.9%,respectively;NiFe-LDHs versus phenol The removal rates of the compounds(BPA,2,4-DCP and phenol,100mg·L-1)were: 30.2% and 28.4% and 11.5%,respectively.and NiFe-LDHs was studied by the method of quasi-first-order kinetics and quasi-secondary kinetics.The results show that CS/NiFe-LDHs composites have phenolic compounds.The removal effect is obviously better than that of NiFe-LDHs,and the adsorption curves of the two materials are in accordance with the quasi-secondary kinetic model.The adsorption behavior of phenolic compounds is mainly the chemical adsorption process.The adsorption isotherms of CS/NiFe-LDHs and NiFe-LDHs were also studied by the Langmuir isotherm model and the Freundlich isotherm model.The results show that the adsorption isotherms of CS/NiFe-LDHs and NiFe-LDHs The fit to both models is high.The maximum adsorption capacities of CS/NiFe-LDHs for phenolic compounds(BPA,2,4-DCP and phenol)were 3.829 mg·g-1,3.335 mg·g-1 and 1.443 mg·g-1,respectively;NiFe-LDHs for phenolic compounds(BPA,The maximum adsorption amounts of 2,4-DCP and phenol were 2.523 mg·g-1,2.221 mg·g-1 and 1.023 mg·g-1,respectively.The adsorption capacity of CS/NiFe-LDHs is larger than that of NiFe-LDHs.The n value can be used to determine the adsorption of phenolic compounds(BPA,2,4-DCP and phenol)by two materials.Under the optimal conditions,the adsorption capacity of CS/CFLDHs to 2,4-DCP was 1.9456 mg·g-1.In the comparative study,the adsorption capacity of the new CS/NiFe-LDHs composites was greater than CS/CFLDHs,indicating CS./NiFe-LDHs has better adsorption performance for phenolic compoundsthan CS/CFLDHs.(3)Study on Oxidation Properties of phenolic compounds by CS/NiFe-LDHs composites.The TG-DTG analysis of the pyrolysis characteristics of CS/NiFe-LDHs showed that the introduction of modified chitosan molecules did not change the layered structure of hydrotalcite.The main structure of the composite material was hydrotalcite.The structure between the plies is composed of two metal ions,Ni2+ and Fe3+,which have good oxidation properties.Under the optimum conditions,CS/NiFe-LDHs are compatible with phenolic compounds(BPA,2,4-DCP and phenol).The removal rates were 62.25%,70.02%,and 42.13%,respectively.(4)Catalytic Performance of CS/NiFe-LDHs Composites in Fenton-like Fenton Oxidation Systems.The degradation rate of phenolic compounds(BPA,2,4-DCP and phenol)by CS/NiFe-LDHs was 94.8%,93.71% and 98.98%,respectively,under heterogeneous Fenton oxidation system.The removal rates of COD were 31%,43% and28%,respectively.At the same time,compared with the homogeneous Fenton system of traditional Fenton oxidation technology and the system without adding composite materials,the results show that CS/NiFe-LDHs composites have good catalytic performance and stability,and can be reused many times.Comprehensive comparison of CS/NiFe-LDHs composites on the removal of phenolic compounds,its oxidation performance is better than adsorption performance,and no sludge is produced in the Fenton-like reaction,and the pH range is increased,which has a good development and application.prospect.