CTAB mediated Mg-doped nano Fe2O3: synthesis, characterization, and fluoride adsorption behavior

Abstract

Magnesium-doped nano ranged hematite was prepared following surfactant (cationic surfactant cetyltrimethyl ammonium bromide, [CTAB]) mediation-precipitation technique. The chemical composition of the synthesized sample was: Fe 63.8% and Mg 1.35%. Presence of crystalline hematite phase was confirmed from the X-ray diffraction pattern. The transmission electron microscopy (TEM) image showed spherical particles varying in the range of 40-200 nm. Fluoride adsorption studies were carried out in batch mode under different experimental conditions, which included time, pH, and amount of adsorbent and adsorbate. The contact time data were fitted to a number of rate equations. The fluoride adsorption reached a maximum at a pH of 7.0 and then, decreased with further increase of pH. The equilibrium data followed both the Langmuir and Freundlich models. Delta G degrees values were estimated to be -6.695, -5.399, -3.819, -3.568, and -2.740 kJ/mole at 293, 303, 308, 313, and 323 K, respectively. Delta D degrees and Delta S degrees were -47.12 kJ/mole and -138.58 J/mole/deg, respectively. The negative Delta H degrees value confirmed the adsorption process to be exothermic in nature, while the negative Delta S degrees indicated decreased randomness at the solid solution interface during adsorption. The fluoride loaded sample was characterized using TEM, selected area electron diffraction, and energy dispersive analysis of x. The present results show that the nano structured Mg-doped hematite synthesized by the present procedure can be regarded as a potential adsorbent for fluoride removal from aqueous solutions, as it can be effectively used at pH values of 5.75 and 7.0 which are applicable to the treatment of actual fluoride contaminated water. Fluoride containing water sample collected from nearby location was tested for defluoridation to establish real time use of adsorbent.