Facile controllable hydrothermal route for a porous CoMn2O4 nanostructure: synthesis, characterization, and textile dye removal from aqueous media

We herein report the synthesis of a pure sphere-like spinel CoMn2O4 nanostructure using a facile and surfactant-free hydrothermal approach followed by a thermal decomposition of the as-prepared CoCO3/MnCO3 composite precursor. Various factors affecting the hydrothermal reaction of cobalt chloride, manganese chloride, and ammonium hydrogen carbonate have been investigated to synthesize a pure CoCO3/MnCO3 composite precursor. Calcination of the CoCO3/MnCO3 composite (synthesized using 0.4Co(2+) : 0.6Mn(2+) molar ratio) at 550 degrees C for 1 h gave the pure sphere-like spinel CoMn2O4 nanostructure product (similar to 16 nm), but the other carbonate composites (synthesized using other molar ratios) did not generate pure spinel CoMn2O4 on calcination. The as-prepared products were identified employing XRD, FT-IR, TEM, EDS, FE-SEM, zeta potential, TG, and BET analyses. The as-prepared spinel CoMn2O4 product showed high adsorption capacity (132 mg g(-1)) for the removal of Reactive Black 5 (RB5) dye from aqueous media. The pseudo-second-order kinetics and Langmuir isotherm models described well the experimental adsorption results. The adsorption of RB5 dye on the as-prepared adsorbent is an endothermic, spontaneous, and physisorption process according to the calculated thermodynamic constants: Delta H-0 (22.144 kJ mol(-1)), Delta G(0) (from -4.321 to -6.990 kJ mol(-1)), and E-a (20.916 kJ mol(-1)), respectively. The as-prepared spinel CoMn2O4 adsorbent showed high stability, reusability, and high adsorption capacity implying its efficiency in removing the RB5 textile dye from aqueous media.