In-situ preparation of magnetic chitosan nanoparticles and its adsorption properties for Ag(I)

The magnetic chitosan nanoparticles (MCN) are in-situ prepared by adding the NaOH solution precipitant into a W/O microemulsion system, which is composed of chitosan and Fe²⁺/Fe³⁺ salts solution as water phase, cyclohexane/n-hexyl alcohol as oil phase, and Triton X-100 as emulsifier. The influences of different parameters such as pH, initial Ag (I) concentration and temperature on Ag (I) adsorption by MCN are investigated. The results show that MCN are monodispersed and have a particle size of 15-40 nm and a saturation magnetization of 25.6 emu/-g. The optimum pH value for Ag(l) adsorption is pH 6.0. The Ag(l) adsorption capacity decreased with increasing the temperature. The adsorption kinetic is fitted well with the second-order model and the adsorption process is spontaneous and exothermic. Langmuir, Freundlich and D-R models are used for fitting the equilibrium data, and the results show very good fits with the Langmuir isotherm equation for the monolayer adsorption process, and the maximum adsorption capacity is 2.06 mmol/g. The E values (E=8.94-9.10 kJ/mol) indicated that the adsorption is predominant on the chemisorption. (authors)