Low-temperature fluorination of silica by a nonaqueous solution of NH4F. Journal of Physical Chemistry A 2003, 107, (22), 4497-4505.
The fluorination of silica by ammonia fluoride in several organic solvents has been studied by diffuse reflectance Fourier transform infrared spectroscopy with in situ thermal treatment, 19F magic angle spinning nuclear magnetic resonance, 1H29Si and 19F29Si cross-polarization techniques, and temperature-programmed analysis followed mass spectrometrically. The extent of surface fluorination and the type of fluorinated species depend on the solvent and treatment procedure. The silicas that were studied show evidence of the formation of two types of surface-fluorinated silicon species: suface-bonded tetrahedral species with a general formula of On-Si(OH)4 - n - mFm and, to a lesser extent, octahedral species [FnSi(OH)6 - n]2-, which were formed already at low temperature. The thermal decomposition of [FnSi(OH)6 - n]2- leads to the removal of corresponding silicon fluorides and hydroxyfluorides, and surface-bonded O3Si-F and O-SiF3 can be additionally formed. Heating to 500-600
C causes the surface migration of fluorine in O3Si-F
over siloxane bridges and the formation of silicon fluorides and their
subsequent removal from the surface (complete removal at 600
C). The hydrophobic nature of fluorinated silica has
been shown by infrared spectroscopy and by the thermal dependence of water
desorption from the surface.Synthesis and structure of grafted layer of silicas modified with alkanesulfonic acid (2003) Russian Chemical Bulletin, 52 (2), pp. 364-369.
A convenient method for preparation of silicas modified with alkanesulfonic acid through the reaction of NaHSO3 with the C 2H3 groups grafted on the SiO2 surface was proposed. The influence of the carrier and the structure of the grafted layer on the modification process was studied by DRIFT, MAS NMR, and temperature-programmed desorption mass spectrometry (TPD-MS). It was found that at most 40% of the C2H3 groups transform to the acid sites, which mostly have the structure of 2-Si-ethanesulfonic acid. The mechanism of the thermal decomposition of the grafted groups, which are stable up to 240°C, was proposed. The monomeric structure of the grafted layer leads to partial olygomerization of the C2H3 groups through the C=C bonds.
Structural features of grafted phosphates in mesopores of Si-MCM-41 and Ti,Si-MCM-41 molecular sieves (2003) Theoretical and Experimental Chemistry, 39 (3), pp. 195-200.
We have used 31P NMR (MAS) and IR spectroscopy and also chemical analysis to show that when Si- and Ti,Si-MCM-41 mesoporous molecular sieves are treated with phosphorus oxychloride, surface-anchored silicophosphate and titanophosphate compounds are formed of the type ≡(Si-O) x-{PO(OH)3-x} and ≡(Ti-O)x-{PO(OH) 3-x} (x = 1, 2), and also compounds with the structure of titanium hydrophosphate and pyrophosphate.
Chemically modified complexing silica: Predicting analytical applications (2003) Zhurnal Analiticheskoj Khimii, 58 (7), p. 688.
