Novel coassembly route to Cu-SiO₂ MCM-41-like mesoporous materials

A series of mesostructured Cu-SiO₂ composites have been synthesized with sodium metasilicate (Na₂SiO₃) and cuprammonia nitrate (Cu(NH₃)₄(NO₃)₂) respectively used as Si and Cu sources. The synthetic procedures were conducted at room temperature, and cetyltrimethylammonia bromide was used as a template. Under our experimental conditions, ordered mesoporous Cu-SiO₂ composites could be obtained with a copper content up to 16.8 wt%. Average pore diameters (2.80-3.15 nm), wall thickness (1.30-2.20 nm), and specific surface area (1020-690 m²/g) are found to vary linearly with copper content (0-16.8 wt %). Results of thermal gravimetry-differential thermal analysis reveal the collapse temperature of the order structure starts at ∼1250 K for mesoporous Cu-SiO₂ with 16.8 wt % copper content. As indicated by the outcomes of inductively coupled plasma and X-ray photoelectron spectroscopy studies, copper is mainly incorporated inside the pore wall rather than embedded on the wall surface. Copper species strongly interact with silica, and calcination at high temperatures cannot cause phase separation between silica and copper oxide. Cu status in mesoporous Cu-SiO₂ composites is similar to that in copper silicate in neighboring structures. Based on the results, a S⁺I^-I⁺I^- mechanism is proposed in which copper entities are surrounded by silicon species during synthesis of the mesostructured composite.