No abstract

The synthesis and properties of three representatives of a new class of chemically modified silicas containing aminophosphonic acids, namely, (N-methyl-Npropylamino)methylenephosphonic, N-propylaminodi(methylenephosphonic), and N-[2-, covalently grafted on the silica surface are reported. The modified silicas were obtained by the two-step Kabachnik--Fields reaction in high yields. The concentrations of the grafted groups were determined by elemental analysis and pH-titration. The new materials were characterized by IR and 31p and J3C high resolution solid state NMR spectroscopy. The hydration of the modified silicas was found to result in a significant change in the structure of the grafted layer and to increase the mobility of the grafted groups.

The obtained samples are characterized by acidity measurements, TEM, powder XRD, NMR, and FTIR spectroscopy. The materials exhibit a mesoporous framework and an acidic surface functionalized with silicon and titanium phosphate species. Tests on esterefication catalysis show future perspectives of these materials as solid acid catalysts. -(KOVALCHUK, T. V.; SFIHI, H.; KORCHEV, A. S.; KOVALENKO, A. S.; IL'IN, V. G.; ZAITSEV, V. N.; FRAISSARD*, J.; J. Phys.

The reaction between an aqueous solution of a strong acid and the methylaminopropyl groups chemically bonded to a silica surface (A-NHCH3) was studied potentiometrically at various temperatures. Equilibrium constants were calculated on the basis of the law of mass action. It was shown that the interaction of acid with A-NHCH3 cannot be described within acceptable confidence levels by a single constant. At all temperatures studied, two types of chemical reactions had to be assumed: (1) protonation of an associate formed from adjacent amine molecules and (2) reaction of the charged associate with a second proton. The thermodynamic characteristics of the reactions were: ΔH1.2 = 25 ± 4 kJ/mol and ΔS1 = −17 J/(mol K), ΔS2 = +49 J/(mol K). The dynamic change in the structure of the interfacial layer was evaluated from the data obtained. It seems that after the first step in the reaction the surface associates remain unchanged. The second proton promotes a significant change in the geometry of the interfacial layer.

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO(2)) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO(2) in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO(2) for phenol is 2.4 mg g(-1) with distribution coefficients up to 3.4 x 10(4) mL g(-1); corresponding data for 1-naphthol are 1.5 mg g(-1) and 3 x 10(3) mL g(-1). The distribution coefficient does not change significantly for solution volumes of 0.025-0.5 L and adsorbent mass less than 0.03 g; 1-90 microg analyte can be easily eluted by 1-3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A(540)) and phenol concentration (C) in water was found according to the equation A(540) = (6 +/- 1) x 10(-2) + (0.9 +/- 0.1) C (micromol L(-1)) with a detection range from 1 x 10(-8) mol L(-1) (0.9 microL g(-1)) to 2 x 10(-7) mol L(-1) (19 microL g(-1)), a limit of quantification of 1 microL g(-1) (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 microL g(-1) while the quantification limit is 20 microL g(-1). A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08-3.2 mL g(-1).