Comprehensive Study of Surface Chemistry of MCM-41 Using²⁹Si CP/MAS NMR, FTIR, Pyridine-TPD, and TGA

Abstract

A comprehensive study was conducted on mesoporous MCM-41. Spectroscopic examinations demonstrated that three types of silanol groups, i.e., single, (SiO)3Si−OH, hydrogen-bonded, (SiO)3Si−OH-OH−Si(SiO)3, and geminal, (SiO)2Si(OH)2, can be observed. The number of silanol groups/nm2, αOH, as determined by NMR, varies between 2.5 and 3.0 depending on the template-removal methods. All these silanol groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol-1, respectively. However, only free silanol groups (involving single and geminal silanols) are highly accessible to the silylating agent, chlorotrimethylsilane. Silylation can modify both the physical and chemical properties of MCM-41.

Covalent Heterogenization of a Discrete Mn(II) Bis-Phen Complex by a Metal-Template/Metal-Exchange Method: An Epoxidation Catalyst with Enhanced Reactivity

“…600 m 2 g −1 . 43 At 1 mmol g −1 loadings, however, the ligands are sufficiently close to allow a single metal center to be ligated by two 1 C . 42 Assuming a tether length of ca.…”

Solid state, dry zinc/MCM-41/air cell as relative humidity sensor

“…The most dominant is Q 3 which is responsible for the water absorption property and serves as the hydration site. This group forms 40-60% of the silanol group [10,18]. The hydrophilic characteristic of MCM-41 material is attributed to this type of silanol group.…”

“…The MCM-41 surface structure is covered with silanol groups (Si-OH) formed during the synthesis of the material [9,10]. The hydrophilic characteristic of the material is attributed to the existence of these Si-OH groups.…”

Large Pore Methylene-Bridged Periodic Mesoporous Organosilicas: Synthesis, Bifunctionalization and Their Use as Nanotemplates

“…The pore size distributions (PSDs) were calculated using the Barret-JoynerHalenda (BJH) method based on the adsorption branches of the sorption isotherms, and the pore sizes were estimated from the position of the maximum in the PSDs. Both solid state 29 Si magic angle spinning (MAS) NMR and 13 C cross polarization (CP) MAS NMR were collected on a Bruker DRX-400 NMR spectrometer. The 29 Si MAS NMR spectra were recorded in a 4 mm ZrO 2 rotor at 79.4 MHz, with a pulse width of 3.0 µs, MAS rate of 4 kHz, and acquisition time of 40.96 ms.…”

“…Both solid state 29 Si magic angle spinning (MAS) NMR and 13 C cross polarization (CP) MAS NMR were collected on a Bruker DRX-400 NMR spectrometer. The 29 Si MAS NMR spectra were recorded in a 4 mm ZrO 2 rotor at 79.4 MHz, with a pulse width of 3.0 µs, MAS rate of 4 kHz, and acquisition time of 40.96 ms. The 13 C CP MAS NMR spectra were measured at 100.5 MHz, with a pulse time of 5.6 µs, MAS rate of 4 kHz, and acquisition time of 25.60 ms. Quantitative analyses were performed to explain the NMR spectra.…”