[Show abstract][Hide abstract] ABSTRACT: A purified natural kaolinite was functionalized with titanium(IV) isopropoxide via the hydrolytic sol-gel route and thermally treated at several temperatures, between 100 and 1000 °C, for 24 h. The resulting solids were used for photodegradation (λ=365 nm, 30 W) of Methylene Blue (MB) and Methyl Orange II (MOII) dyes. All the solids efficiently degraded the dyes and almost total bleaching of the aqueous solutions was observed after 1 h. The best results were found for the solid heated at 400 °C, which degraded 93% of MOII and 99% of MB. Comparative studies with titanium oxide P25 from Degussa were tested and the results reveal lower yields than our systems (45% MB and 15% MOII, 1 h). Kaolinite could promote the dispersion of TiO2 on the clay surface allowing a fast degradation of dyes. This effect was confirmed by comparison of the results from isolated components (titanium oxide and kaolinite) and titanium oxide-kaolinite nanocomposites.
[Show abstract][Hide abstract] ABSTRACT: This study aimed to assess the capacity of saponite modified with n-hexadecyltrimethylammonium bromide (CTAB) and/or 3-aminopropyltriethoxysilane (APTS) to adsorb and remove caffeine from aqueous solutions. Powder X-ray diffraction (PXRD) revealed increased basal spacing in the modified saponites. Small-angle X-ray scattering (SAXS) confirmed the PXRD results; it also showed how the different clay layers were stacked and provided information on the swelling of natural saponite and of the saponites functionalized with CTAB and/or APTS. Thermal analyses, infrared spectroscopy, scanning electron microscopy, element chemical analysis, and textural analyses confirmed functionalization of the natural saponite. The maximum adsorption capacity at equilibrium was 80.54 mg/g, indicating that the saponite modified with 3-aminopropyltriethoxysilane constitutes an efficient and suitable caffeine adsorbent.
[Show abstract][Hide abstract] ABSTRACT: New heterogeneous catalysts were prepared by immobilization of Me(II)-dipicolinate complexes (Me = Co, Mn or Ni) on kaolinite (Ka). The precursor material was kaolinite grafted with dipicolinic acid (dpa) obtained via melting of the acid. The catalysts were prepared by suspending the Ka-dpa precursors (lamellar or exfoliated) in Me2' solutions with a cation/ligand ratio of 1:3. The grafted complexes were characterized by thermal analyses, X-ray diffraction, UV/Vis and infrared spectroscopies, and transmission electron microscopy. The catalysts were tested in three reactions: (i) epoxidation of cis-cyclooctene to cis-cyclooctenoxide reaching 55% yield, with total selectivity to cyclooctenoxide; (ii) oxidation of cyclohexane, reaching 22% yield, with total selectivity towards cyclohexanone; and (iii) Fenton-like decolorization of the dyes metanil yellow, methylene blue and green light, reaching 70-100% decolorization, the maximum effectiveness being observed for methylene blue degradation. The high conversion in the oxidation reactions and the high levels of decolorization of dyes confirmed the versatility of these heterogeneous catalysts based on kaolinite.
[Show abstract][Hide abstract] ABSTRACT: We report on a novel transparent, flexible, rubbery, and insoluble tri-ureasil organic–inorganic hybrid material with multifunctional characteristics and potential application in drug delivery, water purification, and photochromic materials. We obtained the tri-ureasil gels by the one-pot sol–gel route using 3-isocyanatopropyltriethoxysilane and glyceryl poly(oxypropylene)triamine of molecular weight 5000 g mol−1 (Jeffamine® T5000). This approach generated a silica backbone covalently connected with poly(oxyalkylene) chains PPO(OCH–CH3CH2)n through urea bridges. We characterized the obtained materials by DSC, swelling tests, XRD, 29Si NMR, and small-angle X-ray scattering (SAXS). The results attested that the tri-ureasil hybrids are potentially applicable as photochromic devices, drug delivery systems, and adsorbents of pollutants from contaminated waters.
[Show abstract][Hide abstract] ABSTRACT: The sol-gel process was employed in the preparation of titania-doped spherical nanosilica for application in photocatalysis. To this end, the silica matrix was doped with 1 and 10% titania, and the catalytic activity of the resulting solids in the degradation of rhodamine was tested. The synthesized materials were thermally treated at 120, 400, and 800°C. Differential thermal analysis did not evidence the titania-phase transition from anatase to rutile. Scanning electron microscopy revealed the formation of monodisperse spherical nanoparticles with sizes varying between 400 and 500 nm. The UV-Vis absorption spectra showed that the silica doped with 10% titania promoted 86% rhodamine degradation within 90 minutes, as compared to 40% in the case of the silica containing 1% titania. The silica matrix was demonstrated to affect the titania-phase transformation.
[Show abstract][Hide abstract] ABSTRACT: The immobilization of Fe(III) picolinate and Fe(III) dipicolinate complexes on kaolinite furnished heterogeneous catalysts, whose catalytic activity was evaluated. The precursor materials were kaolinite grafted with picolinic (Ka-pa) and dipicolinic (Ka-dpa) acids obtained by melting of the pyridine carboxylic acids. To obtain the catalysts Fe(Ka-pa)-n and Fe(Ka-dpa)-n (n = 1, 2, or 3 is the ligand/Fe ratio), the precursors were suspended in Fe3+ solutions with cation/ligand ratios of 1:1, 1:2, or 1:3. The resulting materials were characterized by thermal analyses (simultaneous TG/DTA), X-ray diffraction, UV/vis and infrared spectroscopies, and transmission electron microscopy. The grafted complexes were employed as heterogeneous catalysts in the epoxidation of cis-cyclooctene to cis-cyclooctenoxide and in the oxidation of cyclohexane to cyclohexanol and cyclohexanone at ambient temperature and pressure. Hydrogen peroxide was used as oxygen donor at a catalyst/oxidant/substrate molar ratio of 1:300:100. Fe(Ka-pa)-n catalysts were very efficient for cis-cyclooctene epoxidation (38% conversion). For cyclohexane oxidation, Fe(Ka-dpa)-n was 100% selective for cyclohexanone formation, with substrate conversion of 14%. This last series of catalysts was also very effective in the Baeyer–Villiger reaction, with 60% substrate conversion and 100% selectivity for ξ-caprolactone. After reuse (5 times), the catalysts still led to high substrate conversion.
[Show abstract][Hide abstract] ABSTRACT: The catalytic efficiency of takovite-aluminosilicate-chromium catalysts obtained by adsorption of Cr(3+) ions from aqueous solutions by a takovite-aluminosilicate nanocomposite adsorbent is reported. The adsorbent was synthesized by the coprecipitation method. The catalytic activity of the final Cr-catalysts depended on the amount of adsorbed chromium. (Z)-cyclooctene conversion up to 90% with total selectivity for the epoxide was achieved when the oxidation was carried out with hydrogen peroxide, at room temperature. After five consecutive runs, the catalysts maintained high activity, although after the sixth reuse, the epoxide yields strongly decreased to 35%. The catalysts were also efficient for cyclohexane oxidation, reaching up to 18% conversion, with cyclohexanone/cyclohexanol selectivity close to 1.2. On the whole, their use as catalysts gives a very interesting application for the solids obtained by adsorption of a contaminant cation such as Cr(3+).
[Show abstract][Hide abstract] ABSTRACT: This work reports the application of a natural clay and an alumina-pillared clay as adsorbents for the removal of a basic dye, Methylene Blue, from aqueous solutions. The intercalation and pillaring processes improve the adsorption capacity of the montmorillonite. The adsorption kinetics of the dye has been studied in terms of pseudo-first-order and pseudo-second-order models. The equilibrium data are mathematically modelled using Freundlich, Langmuir and Sips isotherm adsorption models.
Desalination and water treatment 02/2012; 39(1):316-322. DOI:10.1080/19443994.2012.669181 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amino-functionalized titanosilicate materials were prepared as an alternative for developing efficient adsorbents of azo dyes. Functionalization of the titanosilicates with ethylenediamine groups was carried out via the sol−gel process, using the hydrolytic route. The obtained xerogels were characterized by thermal analysis, elemental chemical analysis, infrared absorption spectroscopy, textural analysis, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Adsorption of the azo dye Orange II from aqueous solutions by the functionalized titanosilicate materials was investigated by adsorption isotherms and kinetic studies. The Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms and to obtain the isotherm constants.
[Show abstract][Hide abstract] ABSTRACT: This work reports on the application of a takovite−aluminosilicate nanocomposite, synthesized by a coprecipitation procedure, as adsorbent for the removal of Cr(III) and Pb(II) from aqueous solutions. Experimental studies to determine the maximum fixation capacities, the adsorption isotherms, and the affinity order of the adsorption process were carried out. The sorption of Pb(II) ions is fast, and the equilibrium is reached within 20 min, while 180 min is necessary for the equilibrium to be reached in the case of Cr(III) ions. The adsorption kinetics of cations has been studied in terms of pseudofirst-order and pseudosecond-order kinetics. The Freundlich and Sips isotherm models have also been applied to the equilibrium adsorption data. The takovite−aluminosilicate nanocomposite material has excellent textural properties and can be used as an efficient adsorbent of Cr(III) and Pb(II) cations.
Journal of Chemical & Engineering Data 02/2009; DOI:10.1021/je800221a · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The thermal stability of vegetable oils is an important factor that affects their quality. In this study, we investigated the thermal stability of oil and lecithin extracted from soybeans by two distinct processes: mechanical extraction (pressing) and physical extraction (solvent). Thermal analysis was used to obtain information about different methodologies of extraction. The physically extracted products proved more stable than those extracted mechanically. Raman and UV-Vis techniques were applied to underpin the discussion of process differences.
Química Nova 01/2008; 31(3). DOI:10.1590/S0100-40422008000300012 · 0.66 Impact Factor