Chemical Modification And Arsenic Adsorption Properties Of Chitosan And Its Derivatives

With the rapid development of industry,arsenic pollution in water has become one of the problems to be solved.Adsorption is considered as a simple and efficient method to remove heavy metal arsenic from water.Chitosan is one of the most widely used biological materials because of its good biodegradability,non-toxicity and regeneration.However,chitosan still has a disadvantage of limited adsorption capacity.Thus,it is generally necessary to improve the adsorption properties of chitosan by physical or chemical modification.Based on the pollution characteristics of arsenic in water,a variety of new materials with arsenic adsorption function was developed by chemical modification of chitosan using different methods in this study.Their adsorption behavior and mechanism of arsenic in water were studied,which could realize the effective removal of arsenic from water.The maincontents researched in this dissertation are as follows:（1）Fe（III）and CTAB modified chitosan composites（Fe（III）?CS and Fe（III）?CS?CTAB）were prepared using an ionotropic gelation method,aiming to effectively remove As（V）.Various techniques were used to characterize the morphology,structure and properties of the adsorbents,including SEM-EDS,FT-IR,XRD,XPS and zeta potential.The addition amount of Fe Cl₃ and CTAB and the p H of the adsorption environment were optimized during the preparation process.Taking As（V）as the target,the influencing factors such as p H,adsorption time and initial adsorption concentration were studied.Compared with Fe（III）?CS,Fe（III）?CS?CTAB was more effective for As（V）adsorption at a wide range of p H（3–8）.The kinetic results showed that Fe（III）?CS and Fe（III）?CS?CTAB reached equilibrium at 25 min and 50 min,respectively.The adsorption kinetics could be described by the pseudo-second-order model（R²=0.998and 0.992）,whereas the adsorption isotherms could be fitted by the Freundlich model（R²=0.963 and 0.987）.The maximum adsorption capacities of the Fe（III）?CS and Fe（III）?CS?CTAB were 33.85 and 31.69mg g^-1 at 25°C,respectively.The presence of Mg²⁺,Ca²⁺,NO₃^-,SO₄^2-and HA in the environment had little effect on the adsorption of As（V）by the two adsorbents.Fe（III）?CS?CTAB adsorbent with 0.8 g L^-1 could reduce the As（V）concentration of tap water,lake water and river water with initial As（V）concentration lower than 1.0 mg L^-1 to less than 0.01 mg L^-1.1%w/v Na OH solution was determined to be the most suitable desorption agent（96.3%and 96.1%,respectively）.Fe（III）?CS and Fe（III）?CS?CTAB still maintained their initial adsorption capacities after five adsorption-desorption cycles.The adsorption mechanism of Fe（III）?CS and Fe（III）?CS?CTAB on As（V）in water were mainly electrostatic interaction and inner sphere complexation.In addition,Fe?OH、C?OH、?NH₃⁺and?N⁺（CH₃）₃ functional groups were the key active site.The results show that Fe（III）?CS and Fe（III）?CS?CTAB can effectively remove As（V）in water,which has great application prospect.（2）A new type of Fe（III）and amino functionalized adsorption material（Fe?ACMC）was prepared by one-pot method in order to obtain a better material for arsenic adsorption.Various techniques were used to characterize the morphology,structure and properties of the adsorbents,including SEM-EDS,FT-IR,XRD,XPS and zeta potential.The addition amount of APTES and p H of adsorption environment in the process of material preparation were optimized.Taking As（V）as the target,the influencing factors such as p H,adsorption time and initial adsorption concentration were studied.Fe?ACMC showed high As（V）adsorption capacity(84.18 mg g^-1),and the removal rate was over 99%at p H 3?9.The adsorption rate of Fe?ACMC was fast,which reached equilibrium in25 min.The adsorption kinetics could be described by the pseudo-second-order model,whereas the adsorption isotherms could be fitted by the Freundlich model（R²=0.979）.The presence of Mg²⁺,Ca²⁺,SO₃^2-、NO₃^-、CO₃^2-、SO₄^2-and HA in the environment has little effect on As（V）adsorption.When the adsorbent concentration was 0.8 g L^-1,the removal of As（V）from tap water,lake water and river water by Fe?ACMC was 99.7%,99.6%and 99.6%,respectively.The desorption rate of As（V）in 0.2 M HCl solution reached 94.5%,but the adsorption capacity decreased significantly from 31.72 mg g^-1 to 18.13 mg g^-1 after 5cycles.The adsorption mechanism of Fe?ACMC for As（V）in water was confirmed to be electrostatic attraction and complexation of As（V）with inner spheres on the adsorbent surface(?NH₂…Fe³⁺).The prepared adsorbent is a promising adsorbent for the efficient removal of As（V）from water.（3）The fixed-bed column adsorption experiment was carried out with Fe?ACMC as the packing material,aiming to provide important reference value for the design of fixed-bed reactor.The adsorption property of fixed-bed column was evaluated by flow rate,initial As（V）concentration and bed height.The lower influent velocity,the lower initial As（V）concentration and the higher bed height required and the adsorption saturation time would be long.The highest removal rate（93.4%on average）was achieved with the flow rate of 3 m L min^-1,the initial concentration of As（V）60 mg L^-1 and the bed height 0.6 cm.The dynamic adsorption capacity was 47.04 mg g^-1.The Thomas model could describe the adsorption behavior of Fe?ACMC bed column well.The dynamic adsorption capacity remained at a high level after 8 cycles.These results showed that Fe?ACMC has a high adsorption capacity and a fast adsorption speed.Thus,it can be widely used in fixed-bed reactors to remove inorganic arsenic from water with good ecological and economic benefits.36 Figures,13 Table and 168 References...