Lead sorption from aqueous solutions on chitosan nanoparticles

Chitosan nanoparticles with different mean size ranging from 40 to 100 nm, which are well dispersed and stable in aqueous solution, have been prepared by ionic gelation of chitosan and tripolyphosphate (CS-TPP). The physicochemical properties of nanoparticles were characterized by size and zeta-potential analyzer, atomic force microscopy, FTIR spectra, and X-ray powder diffraction. Its sorption capacity and sorption isotherms for lead ions were studied. Factors such as initial concentration of lead ions, sorbent amount, temperature, sorbent size, agitation period, and pH value of solution that influence sorption capacity were investigated. It is found that chitosan nanoparticles could sorb lead ions effectively, the sorption rate was affected significantly by initial concentrations of solutions, sorbent amount, size, agitation speed, and pH value of solution. The maximum capacity of lead sorption deduced from the use of Langmuir isotherm equation was 398 mg/g. The experimental data of lead ions sorption equilibrium correlated well with the Langmuir isotherm equation. New sorption sites were provided by introducing phosphoric groups, and the freeze-drying procedure led to the low crystallinity of chitosan nanoparticles; as a result, the sorption capacity was improved greatly.