Study On Chitosan Modified Materials Preparation And Their Adsorption Performance And Mechanism Of Heavy Metal Ions In Aqueous Solution

In recent years,the amount of wastewater containing heavy metals has been increasing.The problem of heavy metal pollution has attracted more attention from public.The toxicity of heavy metal ions from wastewater reside has long residence in organism.The toxicity is big and difficult to be biodegraded which has a detrimental effect on large aquatic organisms and human health.Chitosan is a natural polymer and a kind of polymer from chitin deacetylation.The molecular chain of chitosan contains abundant hydroxyl,carboxyl and amino functional groups,thus it can have axial coordination with a variety of heavy metal ion to formulate coordination compounds.It can significantly improve the adsorption capacity and effect.Meanwhile,chitosan is widely applied in the field of efficient treatment of heavy metal wastewater because of its advantages of convenience,low cost,no toxicity and no two pollution.However,because chitosan is easy to be lost in acid environment,difficult to recycle and its chemical stability and mechanical strength are low,its application in the field of heavy metal wastewater treatment is limited to some extent.In order to overcome the defects of chitosan,this paper focuses on the new application method of chitosan in the treatment of water heavy metal pollutants.The heavy metal Cu?II?,Cr?VI?and Pb?II?in aqueous solution are the target pollutant.Through crosslinking,fastening and synthetizing method,chitosan were modified to prepare four kinds of modified chitosan adsorbent which can be applied in the treatment of copper,chromium,lead wastewater.Through Transmission Electron Microscopy?TEM?,Scanning Electron Microscopy?SEM?,Fourier Transform Infrared?FTIR?,X Ray diffraction?XRD?,X Ray Photoelectron Spectroscopy?XPS?,specific surface area and pore size analysis methods,four kinds of modified chitosan adsorbents were characterized and analyzed.The adsorption effects of four adsorbents were evaluated in terms of preparation methods,single reaction conditions,adsorption kinetics,adsorption thermodynamics and adsorption isotherms.The impact of various adsorption conditions,e.g.the initial pH value,heavy metal ion solution initial concentration,reaction time,reaction temperature,Zeta potential,electrolyte,on adsorption effect.The optimum adsorption conditions of different adsorbents were determined and the adsorption mechanism of these adsorbents in the treatment of Cu?II?,Cr?VI?and Pb?II?wastewater were studied in this paper.The concrete research contents and achievements are mainly four aspects as follows:?1?Based on the advantages of adsorption and nano material,nano magnetic particles?Fe₃O₄?chitosan-coated magnetic nanoparticles?CCM?and immobilizing Saccharomyces cerevisiae on the surface of chitosan-coated magnetic nanoparticles?SICCM?were prepared.The adsorption materials were characterized by TEM,FTIR and XRD.The results show that the particle size of SICCM is about 100nm.The prepared SICCM was further applied in the adsorption experiments of copper ions in aqueous solution.The effect of single factor on the adsorption effect and adsorption mechanism was investigated.In a certain range,the adsorption of SICCM on Cu?II?can be improved by increasing pH,initial concentration and temperature.When the pH value was 4.5,the adsorption capacity reached a maximum value of 96.2 mg/g.The adsorption kinetics showed that the adsorption efficiency of SICCM on Cu?II?was remarkable which was close to the maximum adsorption capacity of 98%after 15min and achieved stability of adsorption efficiency after 1h.The adsorption process agrees with the quasi two order kinetic equation.The study of adsorption isotherms and adsorption thermodynamics further showed that the adsorption process accords with Langmuir adsorption model.Through fitting the Langmuir isotherm equation calculation in the temperature 28?,38 ? and 48 ?,the maximum adsorption capacity of Cu???through SICCM were 148.94,161.73 and 176.35 mg/g.The adsorption process is a spontaneous endothermic process and the adsorption efficiency is fast which is accompanied by a certain degree of intraparticle diffusion.?2?Water hyacinth biomass was used as raw material to be soaked in the ferric chloride solution and calcined to prepare a magnetic water hyacinth biochar?MB?.It was convenient to be separated from aqueous solution after adsorption.Chitosan magnetic,Eichhornia,crassipes,biochar was prepared by modification of magnetic biochar with chitosan.The structure characteristics and properties of CMMB were characterized by various monitoring methods.CMMB was used to remove Cr???in aqueous solution.The magnetic properties of MB and CMMB before and after modification of chitosan were analyzed.It was found that the saturation magnetization?Ms?was not changed.Zeta potential analysis showed that the pHzpc of CMMB was 6.27.The MB and CMMB were applied to the adsorption comparison of Cr???in aqueous solution and the study of the adsorption mechanism.Compared with MB,the adsorption effect of CMMB on Cr???is more remarkable.The influence of initial pH value and solution background electrolyte on the amount of adsorption was evaluated.When the initial pH value is higher,the adsorption capacity of CMMB to Cr?VI?is weak,and the adsorption effect is the best when the pH is 2.The electrostatic attraction is beneficial to the adsorption of Cr?VI?.Through fitting the adsorption kinetics,adsorption isotherms and adsorption thermodynamic models,it proves that the experimental data agree with the quasi two order kinetic model and Langmuir model,and the adsorption of monolayer is dominant.The maximum adsorption capacity of adsorbents in 20?,30 ? and 40 ? are 154.14,159.27,170.54 mg/g,respectively.CMMB adsorption of Cr?VI?in aqueous solution is a spontaneous endothermic reaction.?3?The abundant cellulose contained in Pleurotus ostreatus is a kind of natural macromolecule polymer.The natural absorbent of Pleurotus ostrealus is used as main raw material and modified with tartaric acid to prepare modified Pleurotus ostreatus powder?POP?.Chitosan,P.ostreatus hydrogel beads?CPHB?was prepared by chitosan immobilization.The mechanical strength of the new adsorbent was improved by cross-linking,which was used to remove Cr?VI?in aqueous solution.CPHB were characterized by TEM,FTIR,XPS and Zeta Potential analysis,respectively.The modified CPHB improves its stability in acid media and mechanical strength.The surface had a regular spherical shape and pore structure was more developed.It provides the adsorption process with a larger surface area and it is beneficial to improve the adsorption capacity of the adsorbent.After adsorption,the internal structure of CPHB-Cr?VI?is reticular,and the structure is more dense.These favorable factors have greatly increased the adsorption capacity of adsorbent to Cr?VI?.The effects of pH,adsorption time and initial Cr?VI?concentration on the adsorption efficiency were investigated.It is found that the amount of adsorption decreases with the increase of the pH value of the solution.The adsorption capacity is very small when the initial pH value is greater than 8.The optimum pH was 2 when the maximum adsorption capacity reached 81.21 mg/g.The adsorption equilibrium time of adsorbent for Cr?VI?is 6 hours.The amount of adsorption increases with the initial concentration of Cr?VI?.When the initial concentration is larger than 600 mg/L,the adsorption amount reaches saturation state.The adsorption kinetics accorded with the quasi two order kinetic model.The experimental data were fitted by the isothermal adsorption model of Langmuir and Freundlich.It was found that the maximum adsorption capacity was 196.83 mg/g,which was more in line with the Freundlich isotherm model.Thermodynamic experiments show that the adsorption process of Cr?VI?by CPHB is a spontaneous endothermic reaction.?4?Amino modified porous chitosan hydrogel beads?AMCHB?were prepared for the adsorption of lead ion Pb?II?in aqueous solution.The surface morphology and internal structure of the adsorbent were observed before and after adsorption by SEM.The infrared spectra were measured by FTIR and the change of surface group of adsorbent was analyzed.The elemental composition and chemical composition of AMCHB before and after adsorption were analyzed by XPS.The characterization results show that the stability of AMCHB is greatly improved.Amino groups play a major role in the adsorption of Pb?II?on APCHB.Amino protection-release and amino grafting can effectively increase the number of amino groups and improve the adsorption capacity of adsorbent.The properties and change rules of surface charge were studied by Zeta potential analysis.The average moisture content of AMCHB was determined to be 94.2%.In the batch experiments,the effects of initial pH,ionic strength,reaction temperature,and amount of porogen on the adsorption of Pb?II?were investigated.The kinetic,thermodynamic and isotherm models of AMCHB adsorption on Pb?II?were fitted,and the adsorption mechanism was discussed.The experimental data agree with the quasi two order kinetic model and the Langmuir isothermal model,and it proves the monolayer adsorption is dominant.The maximum adsorption capacity of APCHB to Pb?II?was 295.60,307.64 and 312.31 mg/g at 15?,30 ? and 45 ?,respectively.Thermodynamic studies have proved that adsorption is a spontaneous endothermic process,and the increase of temperature is beneficial to the adsorption reaction.