Adsorption of Copper(II) on NH2-MCM-41 and Its Application for Epoxidation of Styrene

Amine functionalized MCM-41 (NH2-MCM-41) with varying amine amount (6.4, 10.2, 12.8, and 20 wt %) was prepared by the cocondensation method using cetyltrimethylammonium bromide (CTAB) as structure-directing agent (SDA), 3-aminopropyltriethoxysilane (APTES), and tetraethylorthosilicate (TEOS). The characterizations of the synthesized samples were performed by X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy, and Fourier transform infrared spectral studies. The results revealed that the ordered hexagonal structure of MCM-41 was well retained after the amine functionalization irrespective of the amount of amine loading. Adsorption of Cu(II) from the aqueous state with varying parameters such as concentration, temperature, and pH was performed over as-synthesized and surfactant-removed NH2-MCM-41. Atomic adsorption spectroscopy investigations reported a higher percentage of adsorption in the case of as-synthesized NH2-MCM-41 compared to surfactant-removed samples. The experimental data fitted well to Langmuir and Freundlich adsorption isotherms. The sample (12.8)NH2-MCM-41 showed the highest copper adsorption at pH 5.5, Cu(II) concentration of 59.6 ppm, and temperature 323 K. The sample (12.8)NH2-MCM-41–Cu(59.6) was used as a catalyst for epoxidation of styrene using hydrogen peroxide as the oxidant. GC analyses reported a significant conversion of 17.2% with 64% selectivity toward formation of styrene epoxide.