Engineering tannic acid-polyethyleneimine multilayer-decorated melamine sponge for highly efficient Pb(II) adsorption

Melamine sponge (MS) with open three-dimensional porous structure is regarded to be an ideal substrate to prepare monolithic adsorbents for heavy metal ions removal. However, most of the existing surface modification strategies of MS are still difficult to achieve a satisfactory adsorption ability for Pb(II). In this study, tannic acid (TA) and polyethyleneimine (PEI) were alternatively deposited on the framework of MS via layer-by-layer covalent assembly between polyphenols of TA and amine groups of PEI. The morphology, molecular structure, and overall properties of the obtained multilayer-decorated MS materials (PEI-TA)n-MS were characterized using SEM, XPS, FT-IR, and TGA. (PEI-TA)2-MS was demonstrated to be extremely stable and exhibited excellent adsorption behavior for Pb(II). The maximum Pb(II) adsorption capacity reached 257.4 mg/g at pH value of 5.0 and initial Pb(II) concentration of 200 mg/L. It is better than those of previous reported PEI-based adsorbents under similar conditions. The kinetic and isotherm data revealed that such process is exothermic, and well fits the Langmuir isotherm and the pseudo-second-order kinetic models. The present PEI-TA-based layer-by-layer assembly strategy may offer new prospects for the versatile design of other monolithic adsorbent materials.