Cícero Coelho de Escobar

Synthesis of molecularly imprinted photocatalysts containing low TiO2 loading: Evaluation for the degradation of pharmaceuticals.

A molecularly imprinted (MI) photocatalyst containing a low TiO2 loading (7.00-16.60mgL(-1) of TiO2) was prepared via an acid-catalyzed sol-gel route using different classes of pharmaceutical compounds (i.e., Atorvastatin, Diclofenac, Ibuprofen, Tioconazole, Valsartan, Ketoconazole and Gentamicine) as the template. Herein, our main goal was to test the hypothesis that photocatalysts based on molecular imprinting may improve the degradation performance of pharmaceutical compounds compared to that of a commercial sample (Degussa P25) due to presence of specific cavities in the silica domain. To elucidate certain trends between the performance of photocatalysts and their structural and textural properties, as well the effect of the structure of the drugs on molecular imprinting, the data were analyzed in terms of pore diameter, pore volume, surface area, zeta potential and six-membered ring percentage of silica. In comparison to the commercial sample (P25), we have shown that adsorption and degradation were enhanced from 48 to 752% and from 5 to 427%, respectively. A comparison with the control system (non-imprinted) indicates that the increased performance of the MI systems was due to the presence of specific cavities on the silica domain, and the textural and structural aspects also support this conclusion. The MI photocatalyst was reusable for seven cycles of reuse in which approximately 60% of its photocatalytic efficiency was preserved for the system containing Diclofenac as the template.

The role of the sol–gel route on the interaction between rhodamine B and a silica matrix

A series of silica xerogels having rhodamine B (RhB) as a template and Ti centers were synthesized by distinct sol–gel routes, namely, acid-catalyzed, base-catalyzed, acid-catalyzed with base-catalyzed (two steps) hydrolytic routes and a FeCl3-catalyzed non-hydrolytic route. The interaction of RhB with the prepared silica matrix was investigated by Fourier transform infrared spectroscopy, attenuated total reflectance, diffuse reflectance spectroscopy in the ultraviolet–visible region, Raman spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and confocal microscopy. Raman spectroscopy suggested the presence of Ti–O and Si–O–Ti moieties within the silica matrix. Infrared band shifts provided insight into potential interaction sites. Taking into account the results from ART, XPS, PL and confocal microscopy, encapsulation of RhB preferentially occurs inside the silica network for acid 1, basic and two-steps routes, and the presence of Ti occurs on the surface of the silica occurs for acid 2, basic and two-steps routes. Also, we have shown that although the structural characteristics of the encapsulated and extracted systems are affected by the route, the molecular structure is conserved during and after the encapsulation process.

Alternative Approaches in Development of Heterogeneous Titania-Based Photocatalyst

Three alternative approaches for the development of heterogeneous photocatalysts are comparatively evaluated, namely (i) the use of molecular imprinting concept for the development of heterogeneous catalysts employing rhodamine B as template and sol– gel as synthesis route; (ii) the impregnation of TiCl4 on mixed nanoand micro-metric silicas, followed by calcination; (iii) the use of industrial and academic chemical residues as source of potential photocatalyst species impregnated on supports. All tests were carried on with rhodamine B as target molecule. For comparative reasons, photocatalytic tests were carried out with commercial titania (P25). The solids were characterized by nitrogen porosimetry, small-angle X-ray scattering (SAXS), zeta potential (ZP), diffuse reflec‐ tance spectroscopy in the ultraviolet region (DRS-UV), diffuse reflectance infrared Fourier transmission spectroscopy (DRIFTS), and Rutherford backscattering spectrometry (RBS). The supported catalysts resulting from silica nanoparticles and residue of the petrochem‐ ical industry achieved higher percentage of the dye degradation under ultraviolet (68.0 and 66.8%, respectively) radiation. The industrial waste reached the highest photocata‐ lytic activity under visible (61%) radiation, while the commercial P25 achieved 82.0and 12.3% for ultraviolet and visible radiation, respectively. The textural and structural characteristics of the supported catalyst prepared with fumed silica and petrochemical waste (SiPe), namely the low-energy bandgap (1.8 eV), large surface area (280 m2 g−1), high pore volume (1.9 cm3 g−1), and high zeta potential value (−36.4 mV), may have been responsible for their high activity.

Molecularly imprinted photocatalyst for glyceraldehyde production

AbstractIn this work, a ZnO-based molecularly imprinted photocatalyst (MIP) bearing acid Lewis sites (Al) was evaluated for photocatalytic oxidation of glycerol. The MIP was characterized by porosimetry using nitrogen adsorption/desorption, Fourier transform infrared spectroscopy and X-ray diffraction. Characterization provided evidence of the presence of zincide crystalline phase and Al–O–Si bonds. Experiments were carried out in a batch reactor (slurry) under UV radiation. The oxidation products were analysed by HPLC. Until 1 h of reaction under UV-light, the molar fraction of glyceraldehyde (GAD) was 4.5% with formation of minor subproducts (carboxylic acid). Compared to the control samples (NIP), the presence of imprinted sites has enhanced the GAD production. The MIP was shown to be highly selective for glyceraldehyde until 1 h of reaction, since no other degradation products, such as glycolaldehyde and 1,3-dihydroxyacetone, were produced. Graphical abstract shows glyceraldehyde (GAD) and 1,2-dihydroxycetone DHA molar fraction obtained from glycerol oxidation using Molecularly Imprinted Polymer (MIP).HighlightsZnO-based molecularly imprinted photocatalyst was studied for photocatalytic oxidation of glycerol.Experiments were carried out in a batch reactor (slurry) under UV radiation.The photocatalyt was shown to be highly selective for glyceraldehyde (GAD).Compared to the control samples, the presence of imprinted sites has enhanced the GAD production.

Synthesis of Peptides in Prebiotic Environment: Implications for the Chemical Evolution

Since Millers experiment in 1951, research on prebiotic chemistry has received much attention of chemists. However, there are a few lines of research with the focus directed to this science in Brazil. Therefore, the objective of this paper is to describe some of the research in this field, with emphasis on peptide synthesis under prebiotic conditions and the implication of these studies in the context of molecular enrichment on the primitive earth. We also want to encourage new researchers conducting research in this area as well as promoting scientific debate related to the topic of the origin of life.