Synthesis of Nanoporous Carbon for Fast Uptake of Cr(VI) and Ni(II) from Aqueous Solution.

  Nanoporous carbon (NPC), based on organic xerogel compounds, was prepared at 650 °C pyrolysis temperature by sol-gel method from pyrogallol and formaldehyde (PF-650) mixtures in water using picric acid as a catalyst. The performance of NPC was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and nitrogen porosimetry. The metal uptake characteristics were explored using effective parameters including pH, contact time, initial metal ion concentration, and temperature. Better adsorption of Cr(VI) and Ni(II) was observed at pH 2 and 4, respectively. The Langmuir model gave the better fit for Cr(VI), whereas for Ni(II), the Freundlich model is better than the other models. The kinetic studies revealed that the adsorption is fast and its data are well fitted by the pseudo-second-order kinetic model. The thermodynamic properties, i.e., ΔG°, and ΔS°, showed that adsorption of Cr(VI) and Ni(II) onto NPC was endothermic, spontaneous and feasible in the temperature range of 300 to 328 K.