The selective removal of Congo red using dumbbell-shaped hierarchically porous Ca-Mg mixed oxide

Hierarchically porous Ca-Mg mixed oxide (Hr-CaO.MgO) has been synthesized using the co-precipitation method using gelatin as a template and glycerol/water as the solvent system. XRD, SEM, FTIR, EDX and N2adsorption-desorption isotherms have been used to characterize the prepared samples. As-synthesized Hr-CaO.MgO exhibits a dumbbell morphology and possesses a surface area of 44.5 m2g−1with hierarchical porosity. The adsorption efficiency of Hr-CaO.MgO has been investigated using four dyes, Congo red (CR), Methyl orange (MO), Rhodamine B (RhB) and Methylene blue (MB). The adsorbent exhibits highly selective adsorption of CR individually and in binary dye mixtures. Batch adsorption studies have been performed to understand the effect of the adsorption parameters on the adsorption of CR in detail. CR adsorption on Hr-CaO.MgO is well-described by the Langmuir isotherm model and obeys the pseudo second order kinetic model. A maximum adsorption capacity of 357.14 mg g−1was exhibited by Hr-CaO.MgO for CR. Electrostatic attraction and hydrogen bonding have been found to be the two dominant interactions responsible for the selective adsorption of CR on Hr-CaO.MgO. Thus, Hr-CaO.MgO has been found to be a potential candidate for the selective adsorption of CR from wastewaters.