Synthesis of magnetite / modified magnetite nano-particles and removal of Cr(VI) from aqueous medias

In this three-staged study, nano sized magnetite is synthesized by chemical co-precipitation method, and nano sized magnetite particles are coated with silica, and then modified magnetite is attained by surface modification of silica coated magnetite nano-particles with amine at first. Secondly, attained nano sized products are characterized by FTIR, XRD, TEM, BET, VSM, Zeta-Meter devices/methods. At last, detailed adsorption experiments are performed to remove hexavalent chrome in aqueous media by magnetite and modified magnetite nano-particles. In addition, adsorption mechanism and thermodynamic parameters [adsorption enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS)] are examined with the attained data. Some of the results can be arranged as following: (i) mean size of synthesized nano magnetite is about 12 nm and its specific surface area is around 89.5 m2/g. (ii) The best result to remove Cr (VI) from aqua among used nano adsorbents (magnetite, silica covered magnetite and modified silica covered magnetite) is attained by magnetite and it is determined that adsorption capacity of the other two adsorbents is too low. (iii) Optimum conditions for Cr(VI) adsorption by nano magnetite are: pH; 3, temperature; 55 oC, contact time; 90 min, adsorbent concentration; 0.5 g/L and 10 mg/L for Cr(VI) initial concentration. Under this circumstances, quantity and efficiency of Cr(VI) adsorption are 33.45 mg/g and %88 respectively. (iv) Thermodynamic parameters are calculated for Cr (VI) adsorption on magnetite nano-particles, and it is found that Cr(VI) adsorption process is endothermic. Relevance of experimental data to Langmuir and Freundlich isotherms is investigated and it is observed that the data is relevant to Langmuir isotherm. (v) Adsorption kinetics investigation showed that the process is correlationn with Pseudo second degree kinetic model.