Adsorption of Congo red and methylene blue from aqueous solution by magnetic cobalt nanoparticles embedded in hierarchical porous carbon prepared via a one-pot approach

Abstract

In this work, magnetic cobalt nanoparticles embedded in hierarchical porous carbon (Co-PC) are successfully prepared via a one-pot approach. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET). The adsorption properties of anionic dye Congo red (CR) and cationic dye methylene blue (MB) onto the Co-PC are systematically studied by controlling the contact time, original concentration, adsorbent dosage, temperature, pH, and Na+ intensity. The results showed that Co-PC with a special hierarchical structure and high specific surface area exhibited obvious selective adsorption toward anionic dye CR, and the adsorption rate of CR at 5 min was 3.66 times that of MB for organic dyes at 120 mg L−1. Meanwhile, the adsorption kinetics and isotherms and adsorption thermodynamics were systematically investigated and found the adsorption of both dyes to be well fitted with pseudo-second-order kinetic and Langmuir isotherm model, in which the maximum adsorption amount of CR obtained by Langmuir isotherm model was 3.75 times that of MB, at the same time, the adsorption process was proved to be a spontaneous endothermic reaction. Furthermore, the stability of the materials is tested and it can be found that Co-PC is stable even after 5 cycles with the removal rate of CR and MB above 80%. Therefore, this work provides a simple strategy for designing recyclable materials with highly efficient, low cost, easy separation under magnetic field and selective adsorption of anionic organic dyes in water.