Modification of Silica Nanoparticles with Cysteine or Methionine Amino Acids for the Removal of Uranium (VI) from Aqueous Solution

Abstract

Silica nanoparticles (SiO2-NPs), modified silica nanoparticles with cysteine (SiO2-Cys) or methionine (SiO2-Meth) were used for sorption of uranium (VI) ion from aqueous solution. Silica nanoparticles and its modified forms were prepared and characterized by elemental analysis, FTIR, XRD, XRF, TGA, DSC, SEM, TEM, BET and zeta potential. Sorption of uranium(VI) ion using batch technique by silica nanoparticles, SiO2-Cys and SiO2-Meth was studied as a function of initial concentration, sorbent dosage, pH, contact time and temperature. The percent uptakes for silica nanoparticles, SiO2-Cys, SiO2-Meth were 27%, 33%, 30% respectively for U(VI) ion at 25 °C. The kinetic studies show that sorption of U(VI) ion by silica nanoparticles, SiO2-Cys and SiO2-Meth was well described by the pseudo second order equation. Negative values of Gibbs free energy (ΔG°) suggest the spontaneity of the sorption process on silica nanoparticles and its modified forms (SiO2-Cys) and (SiO2-Meth). Positive values of enthalpy (ΔH°) indicate endothermic adsorption process. The sorption isotherm was better fitted by Langmuir model with maximum sorption capacity for silica nanoparticles, SiO2-Cys and SiO2-Meth was found to be 3.6, 4.5, 3.8 mg/g respectively. Desorption studies indicate that the most favorable desorption reagent for uranium(VI) is 0.1 M HNO3 and the highest percent recovery was achieved from silica nanoparticles (~71%) than its modified forms SiO2-Cys and SiO2-Meth.