Understanding ionic transport in the macrostructure of polysaccharide bound electrodes for capacitive deionization

Capacitive deionization (CDI) is increasingly being considered as a promising desalination alternative to reverse osmosis and other well-established technologies, especially when it comes to treating low salinity water, such as groundwater. Lifetime and charge efficiency (CE) are the two metrics which determine the competitiveness of CDI technologies, which is why enhancing design is a major developmental challenge. It is known that ion-exchange membranes (IEMs) and chemical surface modification contribute to this goal by eliminating the effects of co-ion repulsion. Previous research conducted in our lab, showed how the use of charged biodegradable polysaccharide compounds, namely chitosan (CS) and carboxymethylcellulose (CMC), as anodic and cathodic electrode binders respectively, improved charge efficiency and lifetime values of the electrodes in which they were employed, compared to a symmetric cell where electrodes were bound with the traditionally used, petrochemically derived, polyvinylidene fluoride (PVDF). As a means of comparison, surface-modified electrodes were also fabricated and their performance assessed when assembling them in another CDI unit. The specific salt adsorption (SSA) behavior of the CS-CMC bound cell, combined with the cyclic voltammetry (CV) results and SSA at various discharge voltages, suggested the binder was enhancing salt adsorption performance and mitigating co-ion repulsion by modifying the macrostructure, producing a similar effect to an IEM. In this work, we propose a mechanism for the enhanced salt adsorption and charge efficiency observed with the charged polysaccharide binders, where a hybrid system composed of CDI and MCDI sub-units can illustrate the effects of the improved electrode macrostructure. We fit the untreated carbon data using the Amphoteric Donnan Model (ADM) to consider the asymmetry in acidic and basic groups in the pristine carbon surface, which is the main cause of co-ion repulsion. The SSA value calculated for this system only differs by 5% from that obtained experimentally and charge efficiency shows a similar trend. To simulate impact of charged binders on ionic transport within the electrode macropores, MCDI sub-units were introduced. At a MCDI surface coverage of 7.5% we observe the co-ion repulsion peak disappears as a result of the addition of fixed charge. When decreasing the membrane thickness, thus resembling the polysaccharide coating of the carbon, the diffusion timescale across the selective interface is significantly reduced, and therefore governs the overall cell behavior by modifying the concentration in the flow channel for subsequent units. The model discretizes rapid transport across these selective interfaces and slower transport across traditional CDI sub-units, although in reality the electrode structure is much more complex and thus differences between the simulated results and the actual behavior can find reason in this simplification. Finally, we determine that an anode binder pKa should be one log unit greater than the influent pH to make the system less sensitive to pH fluctuations

Teaching and learning experience in soil consolidation aided by computer software

[EN] The present article shows how the learning and personal motivation of the students in Geotechnics are improved through the realization of computer practices and thanks to the use of a software adapted to their needs. By means of a simple interface of data entry and output of results, students will master abstract concepts such as the excess pore pressure and the average degree of consolidation, while reinforcing their personal motivation, both to face the content of the subject and those of other disciplines of the Civil Engineering Degree.http://ocs.editorial.upv.es/index.php/HEAD/HEAD18García Ros, G.; Sánchez Pérez, JF.; Fernández García, M.; Del Cerro Velázquez, F. (2018). Teaching and learning experience in soil consolidation aided by computer software. Editorial Universitat Politècnica de València. 725-732. https://doi.org/10.4995/HEAD18.2018.8070OCS72573

Effect of Gamma Radiation on the Processability of New and Recycled PA-6 Polymers

The growing quantities of plastic waste have raised environmental concerns, with almost a quarter of disposed plastics being sent to landfill. This has motivated research efforts into various recycling technologies to ease dependence on fossil resources, increasing circularity. Irradiation of various kinds, such as electron beam, beta and gamma rays, has been studied in the past as a way of revamping end-of-life polymer properties. The present work focuses on the effects of gamma radiation on the processability of new and recycled polymers, which is intimately linked with their rheological properties. In this study, both virgin and recycled polymers were irradiated under different radiation doses and the effects of the radiation on their viscosity assessed and compared. Results were analyzed making use of different theoretical relationships, and the causes of the changes in rheology were investigated by means of various characterization techniques, such as GPC, FTIR, EPR and DSC. Finally, the rheological curves of all samples were fitted to the Ostwald–de Waele relationship and the dependence of its parameters on the absorbed dose fitted to a function

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Reducing impedance to ionic flux in capacitive deionization with Bi-tortuous activated carbon electrodes coated with asymmetrically charged polyelectrolytes

Capacitive deionization (CDI) with electric double layers is an electrochemical desalination technology in which porous carbon electrodes are polarized to reversibly store ions. Planar composite CDI electrodes exhibit poor energetic performance due the resistance associated with salt depletion and tortuous diffusion in the macroporous structure. In this work, we investigate the impact of bi-tortuosity on desalination performance by etching macroporous patterns along the length of activated carbon porous electrodes in a flow-by CDI architecture. Capacitive electrodes were also coated with thin asymmetrically charged polyelectrolytes to improve ion-selectivity while maintaining the bitortuous macroporous channels. Under constant current operation, the equivalent circuit resistance in CDI cells operating with bi-tortuous electrodes was approximately 2.2 times less than a control cell with unpatterned electrodes, leading to significant increases in working capacitance (20–22 to 26.7–27.8 F g−1), round-trip efficiency (52–71 to 71–80%), and charge efficiency (33–59 to 35–67%). Improvements in these key performance indicators also translated to enhanced salt adsorption capacity, rate, and most importantly, the thermodynamic efficiency of salt separation (1.0–2.0 to 2.2–4.1%). These findings demonstrate that the use of bi-tortuous electrodes is a novel approach of reducing impedance to ionic flux in CDI. Keywords: Capacitive deionization, Polyelectrolyte coating, Bi-tortuous electrode