Synthesis of nanostructured metal oxides for their use in gas sensors

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2020, Tutor: Paolo PellegrinoGallium oxide (Ga2O3) nanowires (NW) were successfully grown using the Vapour-Liquid-Solid method from a metallic source and were later characterized by means of Scanning Electron Microscopy (SEM). X-ray diffraction, SEM and photoluminescence (PL) data from previously grown mixed indium oxide (In2O3) and Ga2O3 nanowires were also analysed. From the analysis of the Ga2O3 nanowires, a severe hindering effect of a marginal concentration of oxygen on the carrier gas mix was observed regarding the synthesis. For the mixed nanowires, an additional PL band to the main direct band-to-band transition was observed in photoluminescence, which may be attributed to optical transitions from surface states located at the outer shell of the nanowires, and possibly involving impurities such as Ga and C. In addition, a coherent shift was observed of both PL bands, probably caused by changes in the dimensions of the crystalline domain

Trace ions rejection tunning in NF by selecting solution composition: Ion permeances estimation

Nanofiltration (NF) is suggested to selectively remove ionic species in aqueous process streams taking benefit of both membrane and aqueous solution composition. The importance of predicting and optimizing selective ion rejections by NF not only of major compounds (e.g. NaCl, Na2SO4, MgCl2, MgSO4) but also of minor ones such as ammonium (NH4+), nitrate (NO3-), bromide (Br-), iodide (I-) typically present in natural and industrial process streams is crucial. The current work explores ion rejection patterns and membrane ion permeances using the phenomenological Solution-Electro-Diffusion-Film (SEDF) model. It makes possible rapid calculations that account for the effects of spontaneously arising electric fields on rejections. Experimental ion rejection data of several inorganic ions species at various transmembrane pressures and at fixed cross-flow velocity have been obtained with NF270 membrane. A number of trace ions (Na+, K+, Cl-, Ca2+, Mg2+, SO42-, NO3-, NH4+, Br-and I-) have been used in combination with various dominant salts (NaCl, MgCl2, MgSO4) as model feed solutions. Results showed that dominant salts were moderately (NaCl) and highly (MgCl2, MgSO4) rejected when some ions are divalent, while trace ions exhibited quite variable rejection, including negative ones mainly at low transmembrane volume flows. The electric field of membrane potential can accelerate or retard the ion flows to the permeate, so negative or unexpectedly high rejections could be observed. Ions transport was shown to be affected by the membrane chemistry (e.g. acid-base properties of the un-crosslinked carboxylic and amine groups) and the dielectric exclusion phenomena. From the modelling procedure, ionic membrane permeances were determined for various multi-ion systems studied. Results showed that nature of dominant salt composition can be used to control the rejection of minor components.Peer ReviewedPostprint (author's final draft

Selectrodialysis and bipolar membrane electrodialysis combination for industrial process brines treatment: Monovalent-divalent ions separation and acid and base production

Chemical industries generate large amounts of wastewater rich in different chemical constituents. Amongst these, salts at high concentrations are of major concern, making necessary the treatment of saline effluents before discharge. Because most of these rejected streams comprise a combination of more than one salt at high concentration, it is reasonable to try to separate and revalorize them to promote circular economy at industry site level. For this reason, ion-exchange membranes based technologies were integrated in this study: selectrodialysis (SED) and electrodialysis with bipolar membranes (EDBM). Different process brines composed by Na2SO4 and NaCl at different concentrations were treated first by SED to separate each salt, and then by EDBM to produce base (NaOH) and acids (HCl and H2SO4) from each salt. The optimum of both electrolyte nature and concentration of the SED stack streams was evaluated. Results indicated that it was possible to separate Cl- and SO42- depending on the anionic membrane, initial electrolytes and concentrations of each stream. Pure NaOH and a mixture of HCl and H2SO4 with different purities could be obtained. Energy consumption evolutions were plotted and an optimal zone work was found where the consumption values were acceptable.Peer ReviewedPostprint (author's final draft

Integration of monopolar and bipolar electrodialysis for valorization of seawater reverse osmosis desalination brines: Production of strong acid and base

Water scarcity in the Mediterranean basin has been solved by using seawater desalination reverse osmosis technology (SWD-RO). This technology produces brine which is discharged back into the sea resulting in an environmental impact on marine ecosystems. Under the circular economy approach, the aim of this work is to recover resources from NaCl-rich brine (~60-70 g/L), e.g. in the form of NaOH and HCl, by integration of two ion exchange-based membrane technologies and quantify the electrical energy consumption. Electrodialysis (ED) incorporating monovalent selective cation exchange membranes as divalent ions purification and concentration of the NaCl present in the SWD-RO brine, was integrated with bipolar membrane ED (EDBM) to produce NaOH and HCl. Current densities of 0.30–0.40 kA/m2 at two temperature ranges simulating different seawater temperature regimes (15-18 ºC and 22-28ºC) were tested and a pure NaCl solution was used as starting concentrate stream. NaCl-rich brines with 100 or 200 gNaCl/L were obtained by ED and then introduced in the EDBM stack producing HCl and NaOH up to 2 M, depending on the initial concentrations. A minimum energy consumption of 1.7 kWh/kgNaOH was calculated when working by EDBM with initial concentrations of 104 g NaCl/L and 0.24 M HCl and NaOH.Peer ReviewedPostprint (author's final draft

Introducció a l'acústica de la tenora. Part II.

En aquest article es exposada la modelització matemàtica del comportament acústic de la tenora i dels instruments del mateix tipus, desenvolupada al Laboratori de Vibracions de 1'ETSEIB. Aquesta modelització es limita a la columna d'aire de l'interior de l'instrurnent i es refereix al càlcul de la impedància acústica —a la secció on s'acobla amb la canya— a partir de la geometria del tub i dels forats. Els càlculs es basen en la teoria de la propagació d'ones longitudinals amb esmorteiment en tubs cilíndrics i cònics. Horn presenta també un model simplificat previst per al càlcul de les freqüències de ressonància emprant recursos de càlcul reduïts. A partir d'aquest model hom obté resultats generals il•lustratius de la influència en les freqüències de ressonància del truncament del tub principal, de la posició i mida dels forats, i de la variació local del perfil del tub. A 1'últim apartat de 1'article hom fa una introducció a la modelització de 1'instrument complet, en la qual es planteja l'acoblament entre la columna d'aire i la canya. En aquesta modelització, que ha de permetre l'estudi tant del règim estacionari com del transitori, la columna d'aire es caracteritzada per la seva resposta impulsional