Adsorption performance and removal mechanism of Cd(II) in water by magnesium modified carbon foam

This study displayed a preparation method of efficient and environmentally friendly adsorbent for the removal of Cd(II) from water. By directly mixing the modifier Mg(NO3)(2) with the precursor resin derived from enzymatic hydrolysis lignin liquefied product resin (LP resin), followed by microwave-foaming and carbonization, a magnesium-modified carbon foam (Mg/CF) was successfully fabricated. The surface functional groups and phase composition of Mg/CF composite adsorbent material were analyzed using an infrared spectrum, X-ray polycrystalline diffractometer, X-ray photoelectron spectroscopy, and other characterization methods. The results revealed that the loaded MgO was evenly distributed on the cell wall of carbon foam in the form of nanoparticles after carbonization. The presence of MgO had a negligible effect on the specific surface area of carbon foam but increased the micropore volume instead. Furthermore, to evaluate the Cd(II) removal ability of Mg/CF composite in water, batch adsorption experiments were carried out. The findings indicated that this adsorbent exhibited excellent removal ability for Cd(II) in water, with a theoretical maximum adsorption capacity of 308.51 mg.g(-1), which was approximately 2.0 times as neat as MgO adsorbent. Further, the equilibrium time (12 h) of this adsorbent was significantly shorter than that of MgO (24 h). Meanwhile, the thermodynamic analysis showed that the Cd(II) removal was a spontaneous, endothermic, and entropy-increasing process. The removal behavior of Mg/CF for Cd(II) satisfied the pseudo-second-order kinetic equation and Langmuir adsorption isotherm model. It was proposed that the Cd(II) removal by Mg/CF composite adsorbent could be mainly attributed to ion exchange and chemical precipitation, accompanied by physisorption.