Sérgio Lima

Multi-functional rare-earth hybrid layered networks: photoluminescence and catalysis studies

Hydrothermal reactions between rare-earth (RE) chloride salts and N-(carboxymethyl)iminodi(methylphosphonic acid) (H5cmp) led to the isolation of a series of layered networks formulated as [RE(H2cmp)(H2O)] [RE3+ = Y3+, La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+ and Er3+]. All compounds were isolated as micro-crystalline powders (many of which were nano-sized in thickness), with the plate-like crystallites found to exhibit preferential growth perpendicular to the [002] vector, a feature which seems to favour catalytic performance. Full structural elucidation was attained by the combination of synchrotron radiation (micro-crystal and powder) diffraction data, solid-state NMR studies (1H, 13C and 31P) and photophysical measurements. Materials consist of ∞2[RE(H2cmp)(H2O)] layers in the ab plane of the unit cell, constructed from a single RE3+ centre (in a highly distorted dodecahedral coordination environment with one water molecule in the first coordination sphere) and one H2cmp3− ligand present in a zwitterionic form. Connections between layers along the c-axis are assured by strong and highly directional O–H⋯O hydrogen bonds involving the protonated phosphonate group (donor) of one layer and one oxygen atom (acceptor) of the carboxylate group in the adjacent layer. The network is an unprecedented 12-connected uninodal plane net with total Schafli symbol 330.434.52. The Eu3+ material is photoluminescent at room temperature and 12 K with 5D0 lifetimes of 0.86 ± 0.01 ms and 0.89 ± 0.01 ms, respectively. Studies of the mixed-lanthanide diluted [(Gd0.95Eu0.05)(H2cmp)(H2O)] material showed that Gd3+-to-Eu3+ energy transfer occurs within the layers. The coordinated water molecule plays a decisive role in the non-radiative relaxation process of the Eu3+ emission. All synthesised materials were further tested in the cyclodehydration of xylose to furfural, with the observed results comparing quite favourably with those from other solid acid catalysts used in the same reaction under similar conditions. A detailed catalytic study was performed for [Y(H2cmp)(H2O)]: selectivity increased to 84% as the conversion reached 83%; this solid was also re-used successfully in three consecutive 4 h runs after separation from the liquid phase by centrifugation and regeneration using either thermal treatment at 280 °C or repeated washing with solvents. All materials have been routinely characterized using vibrational spectroscopy (ATR-FT-IR and FT-Raman), thermogravimetric analyses, SEM investigations and CHN elemental composition.

Acid-Catalysed Conversion of Saccharides into Furanic Aldehydes in the Presence of Three-Dimensional Mesoporous Al-TUD-1

The one-pot acid-catalysed conversion of mono/di/polysaccharides (inulin, xylan, cellobiose, sucrose, glucose, fructose, xylose) into 2-furfuraldehyde (FUR) or 5-hydroxymethylfurfural (HMF) in the presence of aluminium-containing mesoporous TUD-1 (denoted as Al-TUD-1, Si/Al = 21), at 170 ºC was investigated. Xylose gave 60% FUR yield after 6 h reaction; hexose-based mono/disaccharides gave less than 20% HMF yield; polysaccharides gave less than 20 wt % FUR or HMF yields after 6 h. For four consecutive 6 h batches of the xylose reaction in the presence of Al-TUD-1, the FUR yields achieved were similar, without significant changes in Si/Al ratio.

Catalytic dehydration of xylose to furfural: vanadyl pyrophosphate as source of active soluble species

The acid-catalysed, aqueous phase dehydration of xylose (a monosaccharide obtainable from hemicelluloses, e.g., xylan) to furfural was investigated using vanadium phosphates (VPO) as catalysts: the precursors, VOPO(4)·2H(2)O, VOHPO(4)·0.5H(2)O and VO(H(2)PO(4))(2), and the materials prepared by calcination of these precursors, that is, γ-VOPO(4), (VO)(2)P(2)O(7) and VO(PO(3))(2), respectively. The VPO precursors were completely soluble in the reaction medium. In contrast, the orthorhombic vanadyl pyrophosphate (VO)(2)P(2)O(7), prepared by calcination of VOHPO(4)·0.5H(2)O at 550°C/2 h, could be recycled by simply separating the solid acid from the reaction mixture by centrifugation, and no drop in catalytic activity and furfural yields was observed in consecutive 4 h-batch runs (ca. 53% furfural yield, at 170°C). However, detailed catalytic/characterisation studies revealed that the vanadyl pyrophosphate acts as a source of active water-soluble species in this reaction. For a concentration of (VO)(2)P(2)O(7) as low as 5 mM, the catalytic reaction of xylose (ca. 0.67 M xylose in water, and toluene as solvent for the in situ extraction of furfural) gave ca. 56% furfural yield, at 170°C/6 h reaction.

Production of biomass-derived furanic ethers and levulinate esters using heterogeneous acid catalysts

Mesoporous aluminosilicates of the type Al-TUD-1, prepared via “green”, low-cost, non-surfactant templating routes, are effective and versatile heterogeneous acid catalysts for the production of useful bio-based furanic ethers and levulinate esters, via the reactions of the biorenewable substrates 5-hydroxymethyl-2-furfural (Hmf) or furfuryl alcohol (FA) with aliphatic alcohols. The identification of reaction intermediates and products by comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry was carried out, giving mechanistic insights. Ethyl levulinate (EL) was formed from FA or Hmf as substrates, with higher EL yields being reached in the former case. Different types of alkyl levulinates may be synthesized from FA using Al-TUD-1 catalysts. On the other hand, 5-(ethoxymethyl)furan-2-carbaldehyde may be formed as the main product from Hmf. Modifications of the properties of Al-TUD-1 involved varying the Si/Al ratio and applying a post-synthesis acid treatment. The influence of these factors and of the reaction conditions on the catalytic reactions was investigated. The efficient regeneration and recyclability of Al-TUD-1 was assessed.

Ionic Liquids as Tools for the Acid‐Catalyzed Hydrolysis/Dehydration of Saccharides to Furanic Aldehydes

One of the measures associated with the socio‐political and environmental protection policies towards sustainability is the use of biomass as a renewable source of energy, fuels, and chemical products. The chemical valorization of carbohydrate biomass, in particular, the acid‐catalyzed conversion of saccharides into the furanic aldehydes, furfural and 5‐hydroxymethyl‐2‐furfuraldehyde, has been a matter of intensive research. These products possess wide application profiles in different sectors of the chemical industry and are thus considered as important platform chemicals. High expectations have been put on the use of ionic liquids (ILs) as tools for these reaction systems, partly due to the singular solubilizing properties of ILs for polysaccharides (important for process intensification), leading to favorable effects when coupled with different types of acid catalysts or when the actual IL is functionalized with acid groups, allowing it to play a dual solvent‐acid role. An assessment of the present state‐of‐the art on this topic is made in this review, showing that promising results have been reported using mild reaction conditions.

Microwave-assisted coating of carbon nanostructures with titanium dioxide for the catalytic dehydration of D-xylose into furfural

Titanium dioxide was selectively grown on reduced graphene oxide (TiO2/RGO) and carbon black (TiO2/CB) by a microwave-assisted synthesis in benzyl alcohol to produce nanocomposite catalysts (consisting of 8–9 nm anatase nanoparticles dispersed on the carbon surface) with interesting properties for the production of furfural from renewable carbohydrate biomass. The materials efficiently catalyze the aqueous-phase dehydration of xylose into furfural at 170 °C with high furfural yields (67–69%) at high conversions (95–97%). The catalytic performance was not significantly affected by the type of carbon support, suggesting that cheap amorphous carbons can be used to support the titania nanoparticles. Additionally, the catalysts were found to be stable under hydrothermal conditions and outstandingly stable towards coke formation in comparison to other solid acid catalysts reported in the literature. Both composites were reused after a simple wash and drying procedure without any detectable loss of catalytic activity in consecutive batch runs.

Bulk and composite catalysts combining BEA topology and mesoporosity for the valorisation of furfural

The sustainable conversion of biomass and biomass-derived platform chemicals demands efficient catalytic processes for which modified versions of zeolites can be strategically important. The catalytic potential of bulk and composite catalysts which simultaneously feature zeolite crystallinity, mesoporosity and Zr and Al sites were explored for the valorisation of furfural (Fur; industrially produced from hemicelluloses) via integrated reduction and acid reactions in alcohol media, to give useful bio-products (bioP), namely, furanic ethers, levulinate esters and angelica lactones. Different synthetic strategies were used starting from zeolite microcrystals or nanocrystals. A composite consisting of nanocrystals of Zr,Al-Beta embedded in a mesoporous matrix is reported for the first time. In a different synthesis approach, a bulk mesoporous zeotype material was prepared by post-synthesis alkaline/acid/impregnation treatments, and explored for the first time as a catalyst for a one-pot reduction/acid reaction system. Characterisation studies of the morphology, structure, texture and nature of the Al and Zr sites (27Al MAS NMR spectroscopy, FT-IR spectroscopy of adsorbed pyridine or deuterated acetonitrile) helped understand the influence of material properties on catalytic performance. These types of materials are active and stable catalysts for the integrated conversion of Fur to bioP.

Coupling of Nanoporous Chromium, Aluminium-Containing Silicates with an Ionic Liquid for the Transformation of Glucose into 5-(Hydroxymethyl)-2-furaldehyde

Micro/mesoporous chromium, aluminium-containing silicates of the type TUD-1 (Al-TUD-1, Cr-TUD-1, CrAl-TUD-1) and zeolite BEA, Cr-BEA, and related composites BEA/TUD-1 and Cr-BEA/TUD-1, were prepared, characterised, and tested as solid acids coupled with the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim]Cl) as solvent, in the transformation of d-glucose into 5-(hydroxymethyl)-2-furaldehyde (Hmf), at 120 °C. The chromium-containing catalytic systems lead to considerably higher Hmf yields in comparison to the related systems without chromium. The IL is a favourable solvent for this target reaction (in terms of Hmf yields reached) compared to water or dimethylsulfoxide. A detailed study on the stabilities of the nanoporous solid acids in the IL medium is presented.

Why do methylated and unsubstituted cyclodextrins interact so differently with sodium decanoate micelles in water

Small-angle neutron scattering is used to study the influence that methylated and unsubstituted cyclodextrins might have on sodium decanoate micelles in D(2)O aqueous solution. When the concentration of the cyclodextrin is varied in a 200 mM sodium decanoate solution (CMC approximately 116 mM), it is found that methylated and unsubstituted cyclodextrins exhibit distinct behaviors. In particular, permethyl-alphaCD, dimethyl-betaCD, and permethyl-betaCD display linear increases of the specific surface area S/V obtained from the Porod equation with slopes following the degree of methylation of the cyclodextrins, whereas alphaCD and betaCD present close S/V values which are approximately independent of the cyclodextrin concentration at least for the considered concentration range (from 5 mM up to 45 mM). When a cyclodextrin is added to the 200 mM perdeuterated sodium decanoate NaDec(d(19)) solution in D(2)O ([CD](o) = 30 mM), methylated cyclodextrins show correlation peaks in the I(Q) distributions, whereas alphaCD and betaCD do not originate any correlation maximum. On the whole, the experimental results point to the adsorption of methylated cyclodextrins on the surface of the formed decanoate micelles and are consonant with the existence of an equilibrium between the molecules in aqueous solution and those adsorbed by the micelles. In turn, unsubstituted cyclodextrins are not adsorbed by the decanoate micelles and so are involved in a guest-host equilibrium with the decanoate ion in solution. As the cyclodextrin concentration increases, this equilibrium leads to the shifting of the multiple equilibria involving micelles of successive aggregation numbers toward those of smaller dimensions and to the decrease of the average intermicellar distance. It is suggested that methylated cyclodextrins should be more easily adsorbed on the electric double layer of the decanoate micelle-water interface than the unsubstituted cyclodextrins, as the former tend to sample the environment that is most energetically favorable, where the dielectric permittivity is lower than in bulk water and so is closer to those of the methylated cyclodextrins.

ECCA - Endoscopic Capsule Capview cAtaloguer

Statistical pattern recognition research, namely in applied computer vision, typically needs highly accurate massive datasets to train and test its classifiers. This paper presents extensive work for creating a large clinically annotated dataset of high confidence events for gastroenterology. More specifically, we address images and videos obtained using endoscopic capsule imaging technology, which contain some kind of lesion. The purpose of such dataset is to boost scientific research in computer aided diagnostic systems for a technology that would clearly benefit from them.