Removal, preconcentration and determination of methyl red in water samples using silica coated magnetic nanoparticles

A method was developed for removal, preconcentration and spectrophotometric determination of trace amounts of methyl red based on SiO2-coated Fe3O4magnetic nanoparticles. The influence of pH, dosage of adsorbent and contact time on the adsorption of dye was explored by central composite design. The kinetic data were analyzed based on the Langmuir and Freundlich adsorption isotherms. The Langmuir model was fitted well to data and the maximum monolayer capacity q max of 49.50 mg g−1 was calculated. The results showed that desorption efficiencies of higher than 99% can be achieved in a short contact time of 3 min and in one step elution using 2.0 mL of 0.1 mol L−1 NaOH. The magnetic nanoparticles were washed with deionized water and reused for two successive removal processes with removal efficiencies more than 90%. Then desorbed dye was determined spectrophotometrically. The calibration curve was linear in the range of 0.025–0.250 mg L−1 of dye with a correlation coefficient of 0.9922. The relative standard deviations obtained upon application of the method to the real samples were lower than 0.7%. A preconcentration factor of the method was 50.