Exploring the distribution of copper-Schiff base complex covalently anchored onto the surface of mesoporous MCM 41 silica

A series of copper-Schiff base MCM 41 materials, synthesised by post-synthetic grafting, was studied by X-ray photoelectron spectroscopy (XPS) and nitrogen sorption(77 K) to explore distribution of the copper-Schiff base complex immobilised on the porous Si-MCM 41. Additional information on the physico-chemical properties of the functionalised materials was obtained by powder X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), CHN microanalysis, FTIR spectroscopy, 29Si and 13C CP MAS NMR spectroscopy. The effect of copper-Schiff base complex loading and reaction times on the surface properties of Si-MCM 41 (surface area and pore parameters) in addition to its distribution within the Si-MCM 41 was explored by nitrogen sorption and XPS coupled with argon etching. Argon etching of the surface to a surface depth of 45 A confirmed that the copper-Schiff base complex was distributed both on the external surface (pore end) and within the pores of Si-MCM 41. The amount of complex located in the pores at this depth was about one-third of the amount detected on the external surface of MCM 41. Nitrogen sorption isotherm measured at 77 K confirmed the reduction in total pore volume and surface area was the result of pore narrowing of Si-MCM 41 following grafting of the complex in the 8 h samples. A significant decrease in surface area and pore volume for the 20 h sample (longer reaction time), with the highest copper loading (0.65 mmol per g), confirmed pore blocking in this material. The uneven distribution of the copper complex between the external and internal surface of Si-MCM 41 was attributed to the bulky nature of the complex, which restricted access to the pores