Manganese oxide incorporated ferric oxide nanocomposites (MIFN): A novel adsorbent for effective removal of Cr(VI) from contaminated water

Manganese oxide incorporated ferric oxide nanocomposite (MIFN), a novel adsorbent has been synthesized, characterized and explored for the removal of Cr(VI) from contaminated water. Surface elemental composition of semi-crystalline adsorbent was analyzed by SEM-EDX spectroscopy and was found to contain Fe (42.5%), Mn (8.1%) and O (49.4%), confirming Fe/Mn mole ratio of 5.0. BET surface area, particle diameter, pore size and total pore volume of the adsorbent were estimated as 186.28 m2g−1, 5–7 nm, 81.2 A0 and 0.31 cm3 g−1 respectively. The adsorption of Cr(VI) was highly pH sensitive, and maximum adsorption was achieved within pH 2.0–3.0. Adsorption kinetics were described well by pseudo 2nd order model and were followed by both film diffusion as well as intra-particle pore diffusion mechanism. Langmuir isotherm was recognized to be the best fit model and maximum monolayer adsorption capacity was estimated as 47.84 mg g−1 for Cr(VI) at pH 3.0 at 303 K. Thermodynamic analysis revealed that the adsorption was highly favorable, spontaneous and endothermic in nature. Adsorption of Cr(VI) was strongly inhibited by phosphate and sulphate, whereas fluoride, carbonate, bicarbonate and silicate have no significant interference. Adsorption efficiency of the spent adsorbent (MIFN) could be rejuvenated around 78–80% by 1.0 M NaOH and subsequently be reused. The present study revealed that MIFN could be an efficient adsorbent for scavenging Cr(VI) from contaminated water because of its high adsorption capacity and reusability.