Aqueous Cu(ii) ion adsorption by amino-functionalized mesoporous silica KIT-6.

To find an alternative adsorbent with high adsorption performance, KIT-6 was prepared by hydrothermal crystallization synthesis using tetraethyl orthosilicate as a silicon source and triblock copolymer P123 as a template. Then the silane coupling agent (3-chloropropyl)trimethoxysilane was first grafted onto KIT-6 mesoporous material and then the polyethyleneimine (PEI) was further grafted through the substitution reaction between amino groups and chlorine atoms. The functionalized KIT-6 was denoted as PEI/KIT-6. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N adsorption-desorption, elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The Cu adsorption performance was determined by inductively coupled plasma (ICP). The results showed that the average loading of the amino groups was 3.74 mmol g, and the modified KIT-6 still has a stable mesoporous structure without pore blockage. With the dosage of 1 g L PEI/KIT-6 and at room temperature, the optimum pH value for adsorption of 100 mg L Cu was 6.0. The adsorption capacity of PEI/KIT-6 for Cu increased with the increase of reaction temperature, and the maximum adsorption capacity of Cu was 36.43 mg g. The adsorption capacity tends to reach equilibrium after 120 min, and the optimum adsorption temperature was 35 °C. The pseudo-second-order kinetic model was found to be well suited for the adsorption process of Cu. Adsorption equilibrium data could also be described well by the classical Langmuir and Freundlich isotherm models. The adsorption tends to be the chemisorption of a monolayer.