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

摘要

A series of copper-Schiff base MCM 41 materials, synthesized 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 immobilized on the porous Si-MCM 41. Additional information on the physico-chemical properties of the functionalized materials was obtained by powder X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), CHN microanalysis, FTIR spectroscopy, Si-29 and C-13 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 a surface to a depth of 45 angstrom 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 isotherms 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 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 g(-1)), 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. (c) 2005 Elsevier Inc. All rights reserved.