Adsorption Properties Of Chitosan-based Aerogels On Heavy Metal Ions

Water as the most basic natural resources,its security and scarcity were once valued.What’s more,water pollution has become one of the main causes of poor water quality.The impact of heavy metal pollution on biological systems is well known and poses a serious threat to public health and aquatic life.Adsorption method is generally considered to be the most effective and environmentally friendly method to remove pollutants.It is particularly important to pursue adsorbents with low cost,fast adsorption rate,high adsorption ratio and reusability.Aerogel has a three-dimensional network structure,high specific surface area and a large number of connected pores,which can fix heavy metal ions in the pores in the adsorption process,so it is a good candidate for adsorbent.Chitosan（CS）has a high content of amino and hydroxyl functional groups,which can adsorb by hydrogen bonding and chelation with heavy metal ions in water.However,chitosan has the disadvantages of low porosity,easy loss and instability in acidic media,which limits its application.Therefore,chitosan aerogels with porous network structure with high specific surface area were prepared from chitosan for adsorption of heavy metal ions.The research contents and results of this topic are as follows:Graphene oxide（GO）was prepared.GO and CS with different mass ratios were mixed.The GO/CS aerogel was prepared by freeze-drying with glutaraldehyde as crosslinking agent.The aerogel was characterized by infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）and other techniques,and the adsorption effects of initial concentration,adsorption time and other factors on Cu²⁺were investigated.The experimental results showed that:GO was successfully prepared and the adsorption capacity of GO/CS aerogel on Cu²⁺increased with the increase of GO content.At 300K,the maximum adsorption capacity of GO/CS-25 on Cu²⁺was 42.17 mg/g.The isothermal adsorption curve of GO/CS-25 aerogel on Cu²⁺conforms to the Langmuir model,and the adsorption kinetic curve conforms to the quasi-first-order kinetic model.It takes 140min to reach the adsorption equilibrium.The adsorption of Pb²⁺is best in the seawater environment,followed by Cu²⁺,and the worst is Cd²⁺.The homogeneous aerogel of chitosan was obtained by physical crosslinking method and freeze-drying.E-CS aerogel was obtained by modifying chitosan with ethylenediamine tetraacetic anhydride（EDTAA）.The E-CS aerogel was characterized by FTIR,SEM and other techniques,and the adsorption effects of p H,initial concentration,adsorption time,adsorbent dosage and recycling on Cu²⁺,Pb²⁺and Cd²⁺were investigated.X-ray photoelectron spectroscopy（XPS）was used to study the adsorption of copper,cadmium and lead ions by E-CS aerogel.The experimental results showed that the modification of aerogel was successful.Under the conditions of p H=5 and T=300 K,the adsorption capacities of Cu²⁺,Pb²⁺and Cd²⁺were 112.97 mg/g,154.65 mg/g and 89.62 mg/g,respectively.The isothermal adsorption curves of E-CS aerogel on Cu²⁺,Pb²⁺and Cd²⁺conform to the Langmuir model,and the adsorption kinetics curves conform to the quasi-second-order kinetic model.The adsorption mechanism of E-CS aerogel on Cu²⁺is mainly coordination.The increase of active adsorption sites by modification significantly enhanced the heavy metal ion trapping capacity of E-CS aerogel.Even after three cycles of HCL desorption and regeneration,the removal efficiency of Cu²⁺,Pb²⁺and Cd²⁺by adsorbent can reach 93.7%,94.2%and 92.3%,showing good recycling performance.