Fernando J.V.E. Oliveira

Useful aminoalcohol molecules incorporated in an epoxide silylating agent for silica organofunctionalization and thermodynamics of copper removal

Ethanolamine (E) and diethanolamine (D) molecules were incorporated onto a precursor 3-glycidoxypropyltrimethoxysilane (G) agent, followed by organofunctionalization of the silica gel through homogeneous (A) and heterogeneous (B) routes, to yield SiEA, SiDA, SiEB and SiDB hybrids. These chemically organofunctionalized silicas were characterized by several techniques, including infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (13C and 29Si NMR using CP/MAS), thermogravimetry and elemental analysis. Based on the obtained nitrogen percentages, the amount of pendant organic groups attached to the inorganic matrices SiEB, SiEA, SiDB and SiDA were calculated as 0.22 ± 0.04, 1.05 ± 0.03, 0.29 ± 0.02 and 0.89 ± 0.01, respectively. The infrared spectra presented characteristic bands attributed either to the inorganic framework or to the immobilized chains. Solid-state 13C NMR results clearly demonstrated that the organic moieties are covalently bonded to the inorganic framework, while 29Si NMR revealed the silicon atoms with distinct environments, Q and T, in agreement with the covalent attachment of organic moieties. The basic centers attached on the pendant groups have the ability to sorb copper from aqueous solution. This process was adjusted to the Langmuir model, to obtain maximum sorption values of 0.28 ± 0.02, 0.40 ± 0.02, 0.29 ± 0.03, 0.76 ± 0.02 mmol g−1 for SiEB, SiEA, SiDB and SiDA hybrids, respectively, from the isotherms. Thermodynamic data obtained from calorimetric titrations reflected the spontaneity of the reactions, which are also enthalpically and entropically favorable for the proposed cation/basic center interactions for these chelating processes at the solid/liquid interface.

The use of molecular probes for the characterization of dispersions of functionalized silica nanoparticles

Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of fumed silica nanoparticles with butanol and characterized by 13C and 29Si NMR and thermogravimetry. The molecular probes benzophenone (BP) and safranine-T were used to investigate the BSN suspensions in water:acetonitrile. Laser flash-photolysis experiments at lambda(exc)=266 nm performed with BSN suspended in acetonitrile:aqueous phosphate buffer supported previous results of our group obtained by time-resolved phosphorescence experiments and showed that only free and adsorbed excited triplet states of BP and diphenylketyl radicals contribute to the signals. The UV-vis spectroscopic and photophysical properties of safranine-T are strongly solvent-dependent. Thus, the analysis of the emission spectra and fluorescence lifetimes yielded information on the localization of this probe molecule in suspensions of BSN and of the bare silica nanoparticles. The values of the equilibrium constant for the adsorption of the ground-state safranine-T on the particles were found to be (9.2+/-0.8)x10(4), (7.2+/-0.8)x10(5), and (3.0+/-0.1)x10(4) for the BSN in 1:1 acetonitrile:water, SiO2 in 1:1 acetonitrile:water, and SiO2 in acetonitrile, respectively.

Generation of Chemisorbed Benzyl Radicals on Silica Nanoparticles

Functionalized silica nanoparticles (NP) were obtained by esterification of the silanol groups of fumed silica nanoparticles with benzyl alcohol. These particles were characterized by Fourier transform infrared spectroscopy, 13C and 29Si NMR spectroscopy, thermogravimetry, total organic carbon, Brunauer–Emmett–Teller analysis, UV‐visible spectroscopy, and transmission electron microscopy. NP suspensions in water/acetonitrile mixtures were used as quenchers of benzophenone (BP) phosphorescence in time‐resolved experiments at the excitation wavelength of 266 nm. The phosphorescence signals obtained in the presence of the nanoparticles were fitted to biexponential decays. Both decays were accelerated in the presence of increasing amounts of NP. A model, including the reversible adsorption of BP on the NP, which was supported by computer simulations accounts for the observed results. Laser flash‐photolysis experiments with excitation at 266 nm of NP suspensions in water/acetonitrile in the presence of BP generated benzyl radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (320 nm) by transient optical techniques.