Katia J. Ciuffi

New synthesis strategies for effective functionalization of kaolinite and saponite with silylating agents

Functionalization of Brazilian São Simão kaolinite and Spanish Yunclillos saponite with the alkoxysilanes 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane is reported. The resulting hybrids were characterized by X-ray diffraction, thermal analysis, infrared absorption spectroscopy, and scanning electron microscopy, which demonstrated the effectiveness of the interlamellar grafting process. The X-ray diffractograms revealed incorporation of the alkoxide molecules into the interlayer space of the clays. The displacement of the stretching bands of interlayer hydroxyls in the infrared spectra of the modified kaolinites and the increased intensity of the Mg-OH vibrations in the spectra of the modified saponites confirmed the functionalization of the clays. The thermal behavior of the organoclays confirmed the stability of the hybrids, which was dependent on the clay used for preparation of the materials.

New highly luminescent hybrid materials: terbium pyridine-picolinate covalently grafted on kaolinite.

Luminescent hybrid materials derived from kaolinite appear as promising materials for optical applications due to their specific properties. The spectroscopic behavior of terbium picolinate complexes covalently grafted on kaolinite and the influence of the secondary ligand and thermal treatment on luminescence are reported. The resulting materials were characterized by thermal analysis, element analysis, X-ray diffraction, infrared absorption spectroscopy, and photoluminescence. The thermogravimetric curves indicated an enhancement in the thermal stability up to 300 °C for the lanthanide complexes covalently grafted on kaolinite, with respect to the isolated complexes. The increase in the basal spacing observed by X-ray diffraction confirmed the insertion of the organic ligands into the basal space of kaolinite, involving the formation of a bond between Al-OH and the carboxylate groups, as evidenced by infrared spectroscopy. The luminescent hybrid material exhibited a stronger characteristic emission of Tb(3+) compared to the isolated complex. The excitation spectra displayed a broad band at 277 nm, assigned to a ligand-to-metal charge transfer, while the emission spectra presented bands related to the electronic transitions characteristic of the Tb(3+) ion from the excited state (5)D(4) to the states (7)F(J) (J=5, 4, and 3), with the 4→5 transition having high intensity with green emission.

Hybrid materials prepared by interlayer functionalization of kaolinite with pyridine-carboxylic acids

This paper presents the results of the functionalization of Brazilian São Simão kaolinite with pyridine-2-carboxylic and pyridine-2,6-dicarboxylic acids. The functionalization involved refluxing of the pyridine-carboxylic acid in the presence of kaolinite previously intercalated with dimethyl sulfoxide; both acids effectively displaced dimethyl sulfoxide from the clay interlayer. The resulting materials were characterized by X-ray diffraction, thermal analysis, infrared absorption spectroscopy, and C and N elemental analysis. The X-ray diffractograms revealed the incorporation of the acid molecules into the interlayer space of kaolinite. The thermogravimetric curves of the kaolinite samples functionalized with the pyridine-carboxylic acids indicated that the materials were thermally stable up to 300 degrees C. The displacements of the bands due to interlayer hydroxyls in the infrared absorption spectra also confirmed the functionalization of the kaolinite with the pyridine-carboxylic acids.

Ureasil-Poly(ethylene oxide) Hybrid Matrix for Selective Adsorption and Separation of Dyes from Water

Herein, we present a cross-linked ureasil-polyether-siloxane hybrid (labeled PEO500) that can function as a stimuli-sensitive material; it swells or shrinks in response to changes in the environmental conditions and it can also, effectively and selectively, remove dyes from water solution. We also developed a methodology to separate a mixture of cationic and anionic dyes present in water. Addition of PEO500 to an aqueous solution of the anionic orange II (OII) or the ponceau S (PS) dye rendered the solution colorless, but an aqueous solution of cationic methylene blue (MB) remained unchanged after 2 h of contact with the insoluble matrix. In situ small-angle X-ray scattering (SAXS) showed that the distance of siloxane nanodomains are strongly affected by the swelling or shriking. By in situ UV-vis adsorption experiments, we found that the kinetics of OII and PS removal followed a pseudo-first-order rate equation. We accomplished B3LYP calculations, to establish which sites on the matrix interacted with the dyes and to investigate the nature of the matrix-dye chemical bonds. On the basis of the experimental and theoretical investigations, we proposed some mechanisms to explain how PEO500 adsorbs anionic dyes efficiently. This smart matrix is potentially applicable as an efficient, fast, selective, and convenient device in water treatment and stimuli-sensitive response materials.

Organically Modified Saponites: SAXS Study of Swelling and Application in Caffeine Removal

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.

Incorporation of anti-inflammatory agent into mesoporous silica

The unique properties of macroporous, mesoporous, and microporous systems, including their ability to accommodate molecules of different sizes inside their pores and to act as drug delivery systems, have been the object of extensive studies. In this work, mesoporous silica with hexagonal structure was obtained by template synthesis via the sol-gel process. The resulting material was used as support to accommodate the anti-inflammatory agent indomethacin. The alkaline route was used to prepare the mesoporous silica; cetyltrimethylammonium bromide was employed as porogenic agent. The silica particles were functionalized with 3-aminopropyltriethoxysilane alkoxide (APTES) by the sol-gel post-synthesis method. Indomethacin was incorporated into the silica functionalized with APTES and into non-functionalized silica. The resulting systems were characterized by x-ray diffraction (XRD), specific area, infrared spectroscopy, and thermal analyses (TGA). XRD attested to formation of mesoporous silica with hexagonal structure. This structure remained after silica functionalization with APTES and incorporation of indomethacin. Typical infrared spectroscopy vibrations and organic material decomposition during TGA confirmed silica functionalization and drug incorporation. The specific surface area and pore volume of the functionalized material incorporated with indomethacin decreased as compared with the specific surface area and pore volume of the non-functionalized silica containing no drug, suggesting both the functionalizing agent and the drug were present in the silica. Cytotoxicity tests conducted on normal fibroblasts (GM0479A) cells attested that the silica matrix containing indomethacin was less toxic than the free drug.

Effect of calcium phosphate coating on polyamide substrate for biomaterial applications

A new type of material from polyamide coated with calcium phosphate was developed aiming to have potential application as biomaterial. Coating was obtained by the sol-gel method and calcium phosphate was obtained after contact with body fluid solution. The coated polyamide (before and after contact with body fluid solution) was characterized by thermogravimetric and differential thermal (TGA/DTA) analyses, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). These characterizations revealed that the calcium phosphate coating has a thickness of less than 3 µm, which resulted in an increase in the melting point and improved the thermal stability of polyamide. After contact with body fluid, the interactions between the coating and the substrate remained, and there was formation of crystalline and amorphous phosphates on polyamide surface.

Low temperature synthesis of bioactive materials

Bioactive materials possess properties that allow them to interact with natural tissues to induce reactions that favor the development and regeneration of those tissues. In this study, silica was prepared by the sol-gel method, using tetraethylorthosilicate as the precursor. The calcium and phosphor sources used here were calcium ethoxy and phosphoric acid, respectively, in ethanol solvent. The solid obtained was dried at 50 oC. In vitro bioactivity assays were performed by soaking the materials in simulated body fluid (SBF). The samples were characterized by transmission electron microscopy (TEM), thermal analysis and photoluminescence. TEM images of the samples before contact with SBF revealed amorphous aggregates and after 12 days in SBF showed two phases, one amorphous with large quantities of Si and O, and the other a crystalline phase whose composition contained Ca and P. The electron diffraction pattern showed a planar distance of 2.86 A, corresponding to 2θ = 32.2o. This was ascribed to hydroxyapatite. The Eu III was used as structural probe. The relative band intensity correspondent the transition 5D0 → 7F2 / 5D0 → 7F1 showed a high symmetry surrounding the Eu III ion. These materials, produced by the sol-gel route, open up new possibilities for obtaining bioactive biomaterials for medical applications.

Effect of high-energy ball milling in the structural and textural properties of kaolinite

Por meio do processo de moagem de alta energia e possivel obter materiais solidos com elevadas areas superficiais e diferentes tamanhos de particulas. Estas caracteristicas sao muito importantes para algumas aplicacoes, tais como adsorcao. Alem disso, as aplicacoes de algumas argilas dependem da funcionalizacao que, para a caulinita, ocorrem nos grupos aluminois. Modificacoes nas propriedades estruturais e texturais de caulinita por moagem de alta energia podem melhorar a funcionalizacao da caulinita devido a exposicao dos grupos aluminois. Neste trabalho, estudos foram feitos sobre a influencia da moagem de alta energia nas propriedades morfologicas da caulinita levando-se em conta parâmetros tais como o preenchimento do moinho, o numero de bolas utilizadas na moagem e a quantidade de massa a ser moida e tambem, estudos sobre a cinetica de moagem de caulinita purificada foram feitos com a finalidade de verificar a variacao na morfologia da caulinita com o tempo de moagem.

Influence of the Percentage of TiO2 Doped into SiO2 Matrix on Photocatalysis

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 500u2009nm. The UV-Vis absorption spectra showed that the silica doped with 10% titania promoted 86% rhodamine degradation within 90u2009minutes, as compared to 40% in the case of the silica containing 1% titania. The silica matrix was demonstrated to affect the titania-phase transformation.