P. Duarte

Effect of solvents on ZnO nanostructures synthesized by solvothermal method assisted by microwave radiation: a photocatalytic study

The present work reports the synthesis of zinc oxide (ZnO) nanoparticles with hexagonal wurtzite structure considering a solvothermal method assisted by microwave radiation and using different solvents: water (H2O), 2-ethoxyethanol (ET) and ethylene glycol (EG). The structural characterization of the produced ZnO nanoparticles has been accessed by scanning electron microscopy, X-ray diffraction, room-temperature photoluminescence and Raman spectroscopies. Different morphologies have been obtained with the solvents tested. Both H2O and ET resulted in rods with high aspect ratio, while EG leads to flower-like structure. The UV absorption spectra showed peaks with an orange shift for synthesis with H2O and ET and blue shift for synthesis with EG. The different synthesized nanostructures were tested for photocatalyst applications, revealing that the ZnO nanoparticles produced with ET degrade faster the molecule used as model dye pollutant, i.e. methylene blue.Graphical Abstract

Office Paper Platform for Bioelectrochromic Detection of Electrochemically Active Bacteria using Tungsten Trioxide Nanoprobes

Electrochemically active bacteria (EAB) have the capability to transfer electrons to cell exterior, a feature that is currently explored for important applications in bioremediation and biotechnology fields. However, the number of isolated and characterized EAB species is still very limited regarding their abundance in nature. Colorimetric detection has emerged recently as an attractive mean for fast identification and characterization of analytes based on the use of electrochromic materials. In this work, WO3 nanoparticles were synthesized by microwave assisted hydrothermal synthesis and used to impregnate non-treated regular office paper substrates. This allowed the production of a paper-based colorimetric sensor able to detect EAB in a simple, rapid, reliable, inexpensive and eco-friendly method. The developed platform was then tested with Geobacter sulfurreducens, as a proof of concept. G. sulfurreducens cells were detected at latent phase with an RGB ratio of 1.10 ± 0.04, and a response time of two hours.

Characterization of geodesic acoustic modes in the ISTTOK edge plasma

ISTTOK is equipped with two probe systems that allow the simultaneous measurement of the three-dimensional characteristics of the edge fluctuations with high temporal resolution. Electrostatic fluctuations consistent with the geodesic acoustic mode (GAM) are observed in the edge plasma. The radial, poloidal and toroidal structure of the fluctuations are investigated and good agreement with the GAM theoretical predictions is found. Furthermore, experimental evidence is presented suggesting that the GAM is modulating long-range correlations and the ambient turbulent fluctuations.

Chitin-glucan complex production by Komagataella pastoris: downstream optimization and product characterization

Purified chitin-glucan complex (CGCpure) was extracted from Komagataella pastoris biomass using a hot alkaline treatment, followed by neutralization and repeated washing with deionized water. The co-polymer thus obtained had a β-glucan:chitin molar ratio of 75:25 and low protein and inorganic salts contents (3.0 and 0.9 wt%, respectively). CGCpure had an average molecular weight of 4.9 × 10(5)Da with a polydispersity index of 1.7, and a crystallinity index of 50%. Solid-state NMR provided structural insight at the co-polymer. X-ray diffraction suggests that CGCpure has α-chitin in its structure. CGCpure presented an endothermic decomposition peak at 315°C, assigned to the degradation of the saccharide structures. This study revealed that K. pastoris CGC has properties similar to other chitinous biopolymers and may represent an attractive alternative to crustacean chitin derived-products, being a reliable raw material for the development of new/improved pharmaceutical, cosmetic or food products.

Edge plasma pressure measurements using a mechanical force sensor on the tokamak ISTTOK

In the present paper we report on a novel mechanical probe, which is able to measure the plasma pressure directly. The probe consists of two pendulums whose heads are exposed to the tokamak edge plasma, while the deflection is measured very sensitively outside the plasma by means of semi-conductor strain gauges. The plasma pressure was successfully measured in the ISTTOK edge plasma, its value being in good agreement with that derived from the electrical probe data (pp = 1–10 Pa). Furthermore, we discuss the possibility of determining the ion temperature Ti = pp/n − Te by combining the pressure measurement with those of n and Te from the electrical probes. Although the derived ion temperatures—besides that in the region close to the limiter—were reasonable, its uncertainty is still very large.

Phloxine B as a Probe for Entrapment in Microcrystalline Cellulose

The photophysical behaviour of phloxine B adsorbed onto microcrystalline cellulose was evaluated by reflectance spectroscopy and laser induced time-resolved luminescence in the picosecond-nanosecond and microsecond-millisecond ranges. Analysis of the absorption spectral changes with concentration points to a small tendency of the dye to aggregate in the range of concentrations under study. Prompt fluorescence, phosphorescence and delayed fluorescence spectral decays were measured at room temperature and 77 K, without the need of sample degassing because cellulose protects triplet states from oxygen quenching. In all cases, spectral changes with time and lifetime distribution analysis were consistent with the dye coexisting in two different environments: dyes tightly entrapped between polymer chains in crystalline regions of cellulose showed longer fluorescence and phosphorescence lifetimes and more energetic triplet states, while dyes adsorbed in more amorphous regions of the support showed shorter lifetimes and less energetic triplet states. This behaviour is discussed in terms of the different dye-support interactions in both kinds of adsorption sites.

Eosin Y Triplet State as a Probe of Spatial Heterogeneity in Microcrystalline Cellulose

The photophysical behavior of eosin Y adsorbed onto microcrystalline cellulose was evaluated by reflectance spectroscopy, steady‐state fluorescence spectroscopy and laser induced time‐resolved luminescence. On increasing the concentration of the dye, small changes in absorption spectra, fluorescence redshifts and fluorescence quenching are observed. Changes in absorption spectra point to the occurrence of weak exciton interactions among close‐lying dye molecules, whereas fluorescence is affected by reabsorption and excitation energy trapping. Phosphorescence decays are concentration independent as a result of the negligible exciton interaction of dye pairs in the triplet state. Lifetime distribution and bilinear regression analyses of time‐resolved phosphorescence and delayed fluorescence spectra reveal the existence of two different environments: long‐lived, more energetic triplet states arise from dyes tightly entrapped within the cellulose chains, while short‐lived, less‐energetic states result from dyes in more flexible environments. Stronger hydrogen bond interactions between the dye and cellulose hydroxyl groups lead in the latter case to a lower triplet energy and faster radiationless decay. These effects, observed also at low temperatures, are similar to those encountered in several amorphous systems, but rather than being originated in changes in the environment during the triplet lifetime, they are ascribed in this case to spatial heterogeneity.

Characterization of the poloidal asymmetries in the ISTTOK edge plasma

Edge plasma in/out and up/down asymmetries have been directly investigated on ISTTOK with a probe system that simultaneously samples the plasma at four poloidal angles. An experimental investigation of the asymmetries is presented as a function of the direction of plasma current and toroidal magnetic field. The edge plasma parameters show significant in/out asymmetries in both equilibrium and fluctuating parameters. Asymmetries favoring the outboard side are observed in density, turbulent particle flux and diffusion coefficient independently of the toroidal magnetic field and plasma current directions, suggesting a ballooning-like transport. This interpretation is supported by the characteristics of the fluctuations as they are found to be more intermittent on the outboard side. In addition, smaller up/down asymmetries reversing with the reversal of the toroidal magnetic field direction and favoring the ion ∇B drift direction are found. Significant poloidal asymmetries were also measured in the parallel flow that can be attributed mainly to Pfirsch–Schluter flows.

Surface Photochemistry: 3,3′-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose

In this work, thia and selenocarbocyanines with n-alkyl chains of different length, namely with methyl, ethyl, propyl, hexyl and decyl substituents, were studied in homogeneous and heterogeneous media for comparison purposes. For both carbocyanine dyes adsorbed onto microcrystalline cellulose, a remarkable increase in the fluorescence quantum yields and lifetimes were detected, when compared with solution. Contrary to the solution behaviour, where the increase in the n-alkyl chains length increases to a certain extent the fluorescence emission ΦF and τF, on powdered solid samples a decrease of ΦF and τF was observed. The use of an integrating sphere enabled us to obtain absolute ΦF’s for all the powdered samples. The main difference for liquid homogeneous samples is that the increase of the alkyl chain strongly decreases the ΦF values, both for thiacarbocyanines and selenocarbocyanines. A lifetime distribution analysis for the fluorescence of these dyes adsorbed onto microcrystalline cellulose, evidenced location on the ordered and crystalline part of the substrate, as well as on the more disordered region where the lifetime is smaller. The increase of the n-alkyl chains length decreases the photoisomer emission for the dyes adsorbed onto microcrystalline cellulose, as detected for high fluences of the laser excitation, for most samples.

Room Temperature Synthesis of Cu 2 O Nanospheres: Optical Properties and Thermal Behavior

The present work reports a simple and easy wet chemistry synthesis of cuprous oxide (Cu2O) nanospheres at room temperature without surfactants and using different precursors. Structural characterization was carried out by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy coupled with focused ion beam and energy-dispersive X-ray spectroscopy. The optical band gaps were determined from diffuse reflectance spectroscopy. The photoluminescence behavior of the as-synthesized nanospheres showed significant differences depending on the precursors used. The Cu2O nanospheres were constituted by aggregates of nanocrystals, in which an on/off emission behavior of each individual nanocrystal was identified during transmission electron microscopy observations. The thermal behavior of the Cu2O nanospheres was investigated with in situ X-ray diffraction and differential scanning calorimetry experiments. Remarkable structural differences were observed for the nanospheres annealed in air, which turned into hollow spherical structures surrounded by outsized nanocrystals.