A Study On The Fabrication And Adsorption Efficiency Of The Advanced Magnetic Chitosan-based Adsorbents

The chitosan-based adsorbent was fabricated through the facile in-situ coprecipitation technique.This natural biomass composite was selected as the environmental functional material for the removal of heavy metal ions and dyes from wastewater.The physicochemical characteristics was fully investigated,and the batch adsorption experiments were conducted to study the adsorption capacity,optimize the adsorption condition,understand the adsorption behavior and mechanism.The main results were as follows:1)The magnetic chitosan gel bead was prepared via an in-situ coprecipitation procedure,and the as-prepared composite was characterized using LEXT,SEM,TEM,EDS,FT-IR,VSM etc.The magnetic gel beads showed a multi-layered porous honeycomb-like structure.The crosslinker sodium citrate enhanced the acid resistance of the chitosan,and functional groups of the material,which were-NH₃,-OH,-COOH,was hardly affected by the introduction of Fe₃O₄.The Fe₃O₄ nanoparticles with diameter of 5±2 nm dispersed uniformly within the chitosan gel,which enable the adsorbent with the superparamagnetism,and the saturation magnetization was approximately 25 emu/g.2)The magnetic chitosan gel beads were used for the removal of Pb²⁺from wastewater,and the effect of pH,initial concentration and the contact time on the adsorbent capacity was investigated.The adsorption kinetic models and the isotherm equations was used to study the adsorption behavior and mechanism.The results showed that the magnetic chitosan gel beads reached its highest removal efficiency at pH 6,and the adsorption equilibrium was achieved within 3h.The adsorption capacity of the adsorbent increased with the initial concentration,yet the removal efficiency for the solution showed an adverse trend.The 5 cycling experiments showed a less than 20%of the removal efficiency decrease after desorption with 0.01 M of Na₂EDTA solution.The XPS results showed that the adsorption between magnetic chitosan beads and Pb²⁺was dominated by the functional group of-NH₃,and the data fit the pseudo-second-order equation and Langmuir model best,indicating that the adsorption process was controlled by the monolayer chemical adsorption.The maximum adsorption capacity for Pb²⁺was 84.02 mg/g.3)The magnetic chitosan fluid was fabricated through an in-situ coprecipitation method,and the physicochemical property was analyzed by SEM,TEM,BET,FT-IR,VSM etc.The magnetic chitosan fluid showed an loose morphology with specific area of 274.7 m²/g.The crystal structure of the composite showed that the magnetic chitosan fluid was well performed,and the Fe₃O₄ nanoparticles with diameter of17.8±0.3 nm dispersed uniformly within the chitosan.The functional groups of the adsorbent remained as-NH₃ and-OH.This superparamagnetic fluid possessed the saturation magnetization of 25 emu/g.4)A batch of adsorption experiments was conducted by utilizing magnetic chitosan fluid as an adsorbent for the removal of Pb²⁺from wastewater.The experimental condition such as pH,initial concentration and contact time was studied,and different type of adsorption kinetic model and isotherm equation was used for the better understanding of adsorption process.The optimal pH for the adsorption was pH6,and the adsorption equilibrium could be achieved within 1h.The adsorption capacity increased with the initial concentration while the removal efficiency decreased.The 0.01 M of Na₂EDTA solution was used for the regeneration of the adsorbent,and the adsorption capacity of the magnetic fluid was renewed for more than 80%after 5 cycles.The pseudo-second-order equation and Langmuir model describe the adsorption process better than other models,suggesting that the adsorption was limited by the monolayer chemical adsorption.The maximum adsorption capacity for Pb²⁺was 113.38 mg/g.5)The magnetic chitosan fluid was used for the adsorption of congo red from wastewater,and the experimental condition of pH,initial concentration and contact time was optimized and studied.The data was also fitted with adsorption kinetic and isotherm equation to describe the adsorption behavior.The adsorption capacity for congo red fluctuated slightly between pH 7-10,and the adsorption equilibrium was achieved within 5 min indicated the fast kinetic of the adsorbent regardless of the congo red concentration.The removal amount increased with the initial concentration while the adsorption rate decreased.The 1.25 M of NaOH was used as desorption solution for the magnetic chitosan fluid,and the adsorption capacity dropped less than10%after 5 cycles.The best fitted models pseudo-second-order equation and Langmuir model showed that the adsorption of congo red on magnetic chitosan fluid based on the monolayer chemical adsorption,and the maximum adsorption capacity was 1724 mg/g.