Adsorption of copper on tri-amino-functionalized mesoporous delta manganese dioxide from aqueous solution

A novel adsorbent, named tri-amino-functionalized mesoporous delta manganese dioxide (NNN-MnO₂), was synthesized by bonding trimethoxysilyl propyl diethylenetriamine onto the surface of delta manganese dioxide (δ-MnO₂) and used as a Cu(II) adsorbent in aqueous solution. The graft of silane coupling agent onto δ-MnO₂was verified by Fourier transform infrared spectroscopy. The crystalline structure of the adsorbents was indicated by an X-ray powder diffractometer. The specific surface area, pore volume, and Barrett-Joyner-Halenda pore diameter of the NNN-MnO₂were 93.50 m² g(-1), 0.31 cm⁻¹ g⁻¹, and 13.12 nm, respectively. The Elovich equation described well the Cu(II) adsorbing process and the negative values of ΔG and the positive values of ΔH and ΔS indicated a spontaneous and endothermic process. The Langmuir equation fitted well the adsorption isotherm at 298 K and the maximum adsorption capacity of NNN-MnO₂for Cu(II) at pH 4 was 87.72 mg g⁻¹, which was higher than that of the un-functionalized δ-MnO₂(66.67 mg g⁻¹). The graft of tri-amino-functional groups enhanced the uptake of Cu(II), and NNN-MnO₂was a promising candidate for Cu(II) removal from aqueous solution.