Selective removal of copper(II) from aqueous solutions using fine-grained activated carbon functionalized with amine

To develop an effective transition-metal-ion adsorbent material, functionalization of amine (-NH₂) onto fine-grained activated carbon (AC) was performed via the electrophilic aromatic substitution of nitro (-NO₂) groups onto the aromatic backbone of the AC, followed by reduction of -NO₂ to -NH₂. Fourier transform infrared, Brunauer-Emmett-Teller surface area analysis, gravimetric method, and batch metal ion adsorption experiments were performed in parallel on unmodified AC and amine-functionalized AC (NH₂-AC). The competitive adsorption of transition-metal ions (Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺) was measured in batch experiments at pH 2.0-5.8. Metal ions favored the NH₂-AC over the unmodified AC. Based on the distribution coefficients (K_d), the NH₂-AC had an affinity for metal ions in decreasing order of Cu²⁺ ≫ Pb²⁺ > Ni ²⁺ > Cd²⁺. On the NH₂-AC, the copper adsorption equilibrium was reached within 1 min with a saturation loading capacity of 0.86 mmol of Cu/g, 2.5 times greater than that on the unmodified AC. The Langmuir and Redlich-Peterson isotherm models were used successfully to characterize the Cu²⁺ adsorption isotherms. Having K_d values up to 100 000, the NH₂-AC is a useful adsorbent material for removing Cu²⁺ from aqueous wastes.