Studies On The Preparation Of Magnetic Chitosan Based Composite Particles And Its Adsorption Properties Toward Two Anionic Dyes

Dyestuff wastewater discharged from textile, dyeing, printing, leather and paper industry is the major source of industrial wastewater pollution. Dye-bearing wastewater, if released into the environment, can damage aquatic life and human beings because it is carcinogenic, teratogenic and mutagenic. Adsorption is considered to be one of the simplest and most attractive methods for dealing with wastewater. A commonly used adsorbent, activated carbon has been widely used for dye adsorption from various effluents. Nevertheless, its application is limited because of its high cost and recalcitrant. Chitosan produced by the partial deacetylation of chitin has attracted particular attention as a functional material because of its rich resources, low price, non-toxicity and adsorption properties. Forming magnetic material with Fe3C>4 can make it easy separated from aqueous solution and provide wide prospect of application.In our work, magnetic Fe3O4/chitosan composite microparticles (MCS) were prepared using a one-step chemical co-precipition method and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The results showed that the particles possessed a honeycomb-like porous structure and had super-paramagnetic properties, with a saturation magnetization of about 36.23 emu/g. The preparation process did not result in Fe3O4 particle phase change. The chitosan on the surface of MCS was successfully cross-linked by the glutaraldehyde. Batch adsorption experiments for Congo Red (CR) and Remazol Turquoise Blue G-133 (RTB G-133) were conducted with varying initial pH, adsorbent dose, initial concentration, contact time, temperature, and ionic strength. The pseudo-second-order kinetic model was more valid for describing this adsorption process. The adsorption behavior of CR onto MCS fitted the Langmuir isotherm model, while the adsorption of RTB G-133 fitted both Langmuir and Freundlich isotherm model. The maximum adsorption capacitys for CR and RTB G-133 were 181.82 mg/g and 270.27 mg/g, respectively at 303 K. The thermodynamic parameters such as Gibbs free energy change (△G0), enthalpy change (△H0) and entropy change (△S0) were calculated using the Van’t Hoff equation. The negative values of △G0 and the positive values of △H0 and △indicatded that the adsorption process was spontaneous and endothermic. High temperature is propitious to the adsorption process.In order to increase the contents of reactive amino groups, magnetic chitosan particles coated with PAMAM (MCS/PAMAM) were prepared by a divergent method using MCS as core. The SEM, FT-IR, XRD and VSM results indicated that the prepared particles still possessed a honeycomb-like porous structure like MCS and had super-paramagnetic properties, with a saturation magnetization of about 33.3 emu/g. The PAMAM was successfully grafted on the surface of MCS without crystal form change. Various influence factors of initial pH, adsorbent dose, initial concentration, contact time, temperature, and ionic strength on CR and RTB G-133 adsorption were investigated. The adsorption process was fitted well with the pseudo-second-order kinetic model. The Langmuir isotherm, compared with the Freundlich isotherm, was more suitable to describe the adsorption of CR and RTB G-133 onto MCS/PAMAM. The maximum adsorption capacities for CR and RTB G-133 were 500.00 mg/g and 555.56 mg/g, respectively at 303 K. The adsorption process is mainly monolayer chemisorption. The thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of the adsorption. A higher temperature could promote the adsorption process.As a novel adsorbent, the prepared MCS and MCS/PAMAM had reusability, magnetic responsivity and excellent adsorption capacity, could be separated easily in the outside magnetic field, which provide wide range of potential applications.