Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion.

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Origin of Limiting and Overlimiting Currents in Bipolar Membranes.

Bipolar membranes (BPMs), a special class of ion exchange membranes with the unique ability to electrochemically induce either water dissociation or recombination, are of growing interest for environmental applications including eliminating chemical dosage for pH adjustment, resource recovery, valorization of brines, and carbon capture. However, ion transport within BPMs, and particularly at its junction, has remained poorly understood. This work aims to theoretically and experimentally investigate ion transport in BPMs under both reverse and forward bias operation modes, taking into account the production or recombination of H+ and OH-, as well as the transport of salt ions (e.g., Na+, Cl-) inside the membrane. We adopt a model based on the Nernst-Planck theory, that requires only three input parameters─membrane thickness, its charge density, and pK of proton adsorption─to predict the concentration profiles of four ions (H+, OH-, Na+, and Cl-) inside the membrane and the resulting current-voltage curve. The model can predict most of the experimental results measured with a commercial BPM, including the observation of limiting and overlimiting currents, which emerge due to particular concentration profiles that develop inside the BPM. This work provides new insights into the physical phenomena in BPMs and helps identify optimal operating conditions for future environmental applications.

Direct Air Capture Using Electrochemically Regenerated Anion Exchange Resins.

Direct air capture (DAC) aims to remove CO2 directly from the atmosphere. In this study, we have demonstrated proof-of-concept of a DAC process combining CO2 adsorption in a packed bed of amine-functionalized anion exchange resins (AERs) with a pH swing regeneration using an electrochemical cell (EC). The resin bed was regenerated using the alkaline solution produced in the cathodic compartment of the EC, while high purity CO2 (>95%) was desorbed in the acidifying compartment. After regenerating the AERs, some alkaline solution remained on the surface of the resins and provided additional CO2 capture capacity during adsorption. The highest CO2 capture capacity measured was 1.76 mmol·g-1 dry resins. Moreover, as the whole process was operated at room temperature, the resins did not show any apparent degradation after 150 cycles of adsorption-desorption. Furthermore, when the relative humidity of the air source increased from 33 to 84%, the water loss of the process decreased by 63%, while CO2 capture capacity fell 22%. Finally, although the pressure drop of the adsorption column (5 ± 1 kPa) and the energy consumption of the EC (537 ± 33 kJ·mol-1 at 20 mA·cm-2) are high, we have discussed the potential improvements toward a successful upscaling.

Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture.

CO2 capture from the atmosphere (or direct air capture) is widely recognized as a promising solution to reach negative emissions, and technologies using alkaline solutions as absorbent have already been demonstrated on a full scale. In the conventional temperature swing process, the subsequent regeneration of the alkaline solution is highly energy-demanding. In this study, we experimentally demonstrate simultaneous solvent regeneration and CO2 desorption in a continuous system using a H2-recycling electrochemical cell. A pH gradient is created in the electrochemical cell so that CO2 is desorbed at a low pH, while an alkaline capture solution (NaOH) is regenerated at high pH. By testing the cell under different working conditions, we experimentally achieved CO2 desorption with an energy consumption of 374 kJ·mol-1 CO2 and a CO2 purity higher than 95%. Moreover, our theoretical calculations show that a minimum energy consumption of 164 kJ·mol-1 CO2 could be achieved. Overall, the H2-recycling electrochemical cell allowed us to accomplish the simultaneous desorption of high-purity CO2 stream and regeneration of up to 59% of the CO2 capture capacity of the absorbent. These results are promising toward the upscaling of an energy-effective process for direct air capture.

Endovascular Treatment of Multiple Ruptures of Postdissecting Thoraco Abdominal Aortic Aneurysm with a Custom Branched Device Used as an Off-the-shelf Device.

Endovascular treatment of postdissection aortic aneurysms (PDAAs) is fascinating and challenging. The Colt branched graft (Jotec/Cryolife, Kennesaw, Georgia), because of its characteristics, can be used as an off-the-shelf device especially in urgent/emergency settings. In this report, we describe the first case of a PDAA successfully treated with a Colt device.

Combined Electrospinning-Electrospraying for High-Performance Bipolar Membranes with Incorporated MCM-41 as Water Dissociation Catalysts.

Electrospinning has been demonstrated as a very promising method to create bipolar membranes (BPMs), especially as it allows three-dimensional (3D) junctions of entangled anion exchange and cation exchange nanofibers. These newly developed BPMs are relevant to demanding applications, including acid and base production, fuel cells, flow batteries, ammonia removal, concentration of carbon dioxide, and hydrogen generation. However, these applications require the introduction of catalysts into the BPM to allow accelerated water dissociation, and this remains a challenge. Here, we demonstrate a versatile strategy to produce very efficient BPMs through a combined electrospinning-electrospraying approach. Moreover, this work applies the newly investigated water dissociation catalyst of nanostructured silica MCM-41. Several BPMs were produced by electrospraying MCM-41 nanoparticles into the layers directly adjacent to the main BPM 3D junction. BPMs with various loadings of MCM-41 nanoparticles and BPMs with different catalyst positions relative to the junction were investigated. The membranes were carefully characterized for their structure and performance. Interestingly, the water dissociation performance of BPMs showed a clear optimal MCM-41 loading where the performance outpaced that of a commercial BPM, recording a transmembrane voltage of approximately 1.11 V at 1000 A/m2. Such an excellent performance is very relevant to fuel cell and flow battery applications, but our results also shed light on the exact function of the catalyst in this mode of operation. Overall, we demonstrate clearly that introducing a novel BPM architecture through a novel hybrid electrospinning-electrospraying method allows the uptake of promising new catalysts (i.e., MCM-41) and the production of very relevant BPMs.

Understanding the Impact of the Three-Dimensional Junction Thickness of Electrospun Bipolar Membranes on Electrochemical Performance.

The use of electrospun bipolar membranes (BPMs) with an interfacial three-dimensional (3D) junction of entangled nano-/microfibers has been recently proposed as a promising fabrication strategy to develop high-performance BPMs. In these BPMs, the morphology and physical properties of the 3D junction are of utmost importance to maximize the membrane performance. However, a full understanding of the impact of the junction thickness on the membrane performance is still lacking. In this study, we have developed bipolar membranes with the same composition, only varying the 3D junction thicknesses, by regulating the electrospinning time used to deposit the nano-/microfibers at the junction. In total, four BPMs with 3D junction thicknesses of ∼4, 8, 17, and 35 µm were produced to examine the influence of the junction thickness on the membrane performance. Current-voltage curves for water dissociation of BPMs exhibited lower voltages for BPMs with thicker 3D junctions, as a result of a three-dimensional increase in the interfacial contact area between cation- and anion-exchange fibers and thus a larger water dissociation reaction area. Indeed, increasing the BPM thickness from 4 to 35 µm lowered the BPM water dissociation overpotential by 32%, with a current efficiency toward HCl/NaOH generation higher than 90%. Finally, comparing BPM performance during the water association operation revealed a substantial reduction in the voltage from levels of its supplied open circuit voltage (OCV), owing to excessive hydroxide ion (OH-) and proton (H+) leakage through the relevant layers. Overall, this work provides insights into the role of the junction thickness on electrospun BPM performance as a crucial step toward the development of membranes with optimal entangled junctions.

Effect of Recycling on the Mechanical Properties of 6000 Series Aluminum-Alloy Sheet.

Sustainability is one of the biggest values of today and for the future of our society; a responsible usage of material in every sector is fundamental to achieving sustainability goals. Aluminum alloys are some of the most promising materials in terms of strength and weight, but their production implies the emission of a high amount of CO2. For that reason, the study and development of aluminum alloys with increasing scrap content play a central role in future applications. In the current study, two sheet-aluminum 6181 alloys with different scrap content were analyzed and compared with a 6181 alloy coming from primary production. The alloys were compared in terms of chemical composition, microstructure, tensile properties, and forming behaviors. The results showed that the alloys coming from secondary productions contained a higher amount of manganese, iron, and copper. The metallurgical and mechanical behaviors were very similar to those of the primary produced alloy. Nevertheless, a drop in formability was shown in the aluminum alloys containing a high scrap amount when stressed in a biaxial condition. The study demonstrated the viability of 6181 alloy production using a high scrap amount, highlighting the main difference with the same alloy coming from primary route production.

Entanglement-Enhanced Water Dissociation in Bipolar Membranes with 3D Electrospun Junction and Polymeric Catalyst.

With the use of bipolar membranes (BPMs) in an expanding range of applications, there is an urgent need to understand and improve the catalytic performance of BPMs for water dissociation, as well as to increase their physical and chemical stability. In this regard, electrospinning BPMs with 2D and 3D junction structures have been suggested as a promising route to produce high-performance BPMs. In this work, we investigate the effect of entangling anion and cation exchange nanofibers at the junction of bipolar membranes on the water dissociation rate. In particular, we compare the performance of different tailor-made BPMs with a laminated 2D junction and a 3D electrospun entangled junction, while using the same type of anion and cation exchange polymers in a single/dual continuous electrospinning manufacturing method. The bipolar membrane with a 3D entangled junction shows an enhanced water dissociation rate as compared to the bipolar membrane with laminated 2D junction, as measured by the decreased bipolar membrane potential. Moreover, we investigate the use of a third polymer, that is, poly(4-vinylpyrrolidine) (P4VP), as a catalyst for water dissociation. This polymer confirmed that a 3D entangled junction BPM (with incorporated P4VP) gives a higher water dissociation rate than does a 2D laminated junction BPM with P4VP as the water dissociation catalyst. This work demonstrates that the entanglement of the anion exchange polymer with P4VP as the water dissociation catalyst in a 3D junction is promising to develop bipolar membranes with enhanced performance as compared to the conventionally laminated membranes.

Microbial electrosynthesis: Towards sustainable biorefineries for production of green chemicals from CO2 emissions.

Decarbonisation of the economy has become a priority at the global level, and the resulting legislative pressure is pushing the chemical and energy industries away from fossil fuels. Microbial electrosynthesis (MES) has emerged as a promising technology to promote this transition, which will further benefit from the decreasing cost of renewable energy. However, several technological challenges need to be addressed before the MES technology can reach its maturity. The aim of this review is to critically discuss the bottlenecks hampering the industrial adoption of MES, considering the whole production process (from the CO2 source to the marketable products), and indicate future directions. A flexible stack design, with flat or tubular MES modules and direct CO2 supply, is required for site-specific decentralised applications. The experience gained for scaling-up electrochemical cells (e.g. electrolysers) can serve as a guideline for realising pilot MES stacks to be technologically and economically evaluated in industrially relevant conditions. Maximising CO2 abatement rate by targeting high-rate production of acetate can promote adoption of MES technology in the short term. However, the development of a replicable and robust strategy for production and in-line extraction of higher-value products (e.g. caproic acid and hexanol) at the cathode, and meaningful exploitation of the currently overlooked anodic reactions, can further boost MES cost-effectiveness. Furthermore, the use of energy storage and smart electronics can alleviate the fluctuations of renewable energy supply. Despite the unresolved challenges, the flexible MES technology can be applied to decarbonise flue gas from different sources, to upgrade industrial and wastewater treatment plants, and to produce a wide array of green and sustainable chemicals. The combination of these benefits can support the industrial adoption of MES over competing technologies.

The Acid-Base Flow Battery: Sustainable Energy Storage via Reversible Water Dissociation with Bipolar Membranes.

The increasing share of renewables in electric grids nowadays causes a growing daily and seasonal mismatch between electricity generation and demand. In this regard, novel energy storage systems need to be developed, to allow large-scale storage of the excess electricity during low-demand time, and its distribution during peak demand time. Acid-base flow battery (ABFB) is a novel and environmentally friendly technology based on the reversible water dissociation by bipolar membranes, and it stores electricity in the form of chemical energy in acid and base solutions. The technology has already been demonstrated at the laboratory scale, and the experimental testing of the first 1 kW pilot plant is currently ongoing. This work aims to describe the current development and the perspectives of the ABFB technology. In particular, we discuss the main technical challenges related to the development of battery components (membranes, electrolyte solutions, and stack design), as well as simulated scenarios, to demonstrate the technology at the kW-MW scale. Finally, we present an economic analysis for a first 100 kW commercial unit and suggest future directions for further technology scale-up and commercial deployment.

Visceral adiposity and arterial stiffness: echocardiographic epicardial fat thickness reflects, better than waist circumference, carotid arterial stiffness in a large population of hypertensives.

AIMS: Relationship between obesity and cardiovascular (CV) disease depends not only on the amount of body fat, but also on its distribution. For example, individuals with increased fat accumulation in the abdominal region have atherogenic lipid profiles and are at increased CV risk. The loss of elasticity in medium and large arteries is an early manifestation of atherosclerosis. The aim of this study was to evaluate whether echocardiographic epicardial adipose tissue, an index of cardiac adiposity, is related to carotid stiffness and carotid intima-media thickness (IMT), indexes of subclinical atherosclerosis, better than waist circumference in hypertensive patients. METHODS AND RESULTS: We studied 459 patients with Grade I and II essential hypertension who were referred to our outpatient clinic over a period from May 2007 to March 2008. The population was first sorted by waist circumference and then by epicardial fat < or = 7 or >7 mm. We measured epicardial fat thickness, waist circumference, carotid artery stiffness, and carotid IMT in all patients. Patients divided according to waist circumference showed no statistical differences in carotid artery stiffness between the two groups. Subjects with epicardial fat >7 mm were older, had higher systolic, diastolic, and pulse pressure, increased left ventricular mass index, carotid IMT, diastolic parameters, and stiffness parameters compared with those with epicardial fat < or = 7 mm (P < 0.001). A positive correlation was found between epicardial fat and age, pulse pressure, stiffness parameters, carotid IMT, systolic blood pressure, and duration of hypertension, and a negative correlation was found with diastolic parameters. Age, carotid IMT, and stiffness parameters were independently related to epicardial fat. CONCLUSION: Our findings indicate that epicardial fat reflects carotid artery stiffness in hypertension-induced organ damage.

New and low-cost auto-algometry for screening hypertension-associated hypoalgesia.

OBJECTIVE: The aim of the present work was to measure the pain threshold in hypertensive patients with a new auto-algometry method. DESIGN AND SETTING: Auto-algometry consists of asking the subjects to push their fingers against a fixed round-tip needle until they feel a pain sensation. An electronic force transducer permits the measurement of the force applied by the subjects and storage of the data on a personal computer. Eight tests are performed twice on each subject on the tip and back of four fingers. For each test, the maximal applied force (grams) is defined as pain threshold. The overall discomfort during the entire procedure is reported by the subjects on a 0 (no discomfort) to 10 (intolerable pain) scale. PATIENTS AND INTERVENTIONS: A group of hypertensive patients (n = 22) and a group of normotensive subjects (n = 22) underwent the auto-algometry examination. RESULTS: The pain threshold was higher in hypertensive patients compared with normotensive subjects. All discomfort scores referred by the subjects fell within the 4-6 range. CONCLUSION: The data obtained from this study indicate that the auto-algometer as described here can detect hypoalgesia associated with hypertension.

Evaluation of retinal abnormalities in essential hypertension: qualitative fundoscopy versus central retinal artery resistance index as indicators of target organ damage.

PURPOSE: To compare qualitative fundoscopy with resistance index (RI) of the central retinal artery determined using color Doppler examination as indicators of target organ damage in a large population of patients with essential hypertension. METHOD: We compared qualitative fundoscopy and central retinal artery RI (CRARI) in 459 patients with grade I and II essential hypertension. Correlations with left ventricular mass, carotid structural changes, and diastolic function were investigated. The results were analyzed according to the degree of retinopathy (grade I versus grade II) and CRARI (<0.70 versus >or=0.70). All patients underwent carotid sonography, echocardiography, diastolic function, a sonographic examination of the eye with measurement of CRARI, and examination of the fundus oculi. RESULTS: There was no statistical difference in the parameters studied between patients with grade I and patients with grade II retinopathy on fundoscopy. Patients with CRARI >or=0.70 were older and had higher systolic and pulse pressure, more years of hypertension, increased left ventricular mass index, carotid intima media thickness, and diastolic parameters compared with patients with CRARI <0.70 (p < 0.001). A positive correlation was found between CRARI and age, pulse pressure, carotid intima media thickness, systolic blood pressure, and duration of hypertension, whereas a negative correlation was found between CRARI and diastolic parameters. Age, pulse pressure, carotid intima media thickness, and left ventricular mass index were independently related to CRARI. CONCLUSION: Our findings indicate that CRARI is more reliable than traditional fundoscopy in the evaluation of hypertension-induced organ damage and should be used to measure global cardiovascular risk for tailored therapy.

Feasibility, accuracy, and clinical relevance of a rapid thyroid evaluation during carotid duplex ultrasonography in hypertensive patients.

Carotid ultrasonography can detect thyroid nodules without increasing examination duration. The authors analyzed whether management is influenced by reporting such findings during routine carotid ultrasonography in hypertensive patients vs waiting for 6 months to repeat them. This is a population-based study of 1216 hypertensive patients. During carotid ultrasonography, nodule cystic/solid characteristics and size of thyroid changes were recorded. Patients with nodules were divided into those with nodules reported at the moment of diagnosis (group A) and those reported 6 months after diagnosis (group B). The authors monitored patients who underwent thyroid treatment 12 months after carotid ultrasonography. A total of 255 participants had thyroid nodules detected on screening and 99 patients started therapy after discovery. Six months later, as expected, there were more patients undergoing thyroid treatment in the group with nodules reported at time of diagnosis. This difference between groups was not significant, however, 6 months after reporting the nodules, in group B, because the number of patients on therapy significantly increased. Thyroid nodules cannot be ignored during carotid ultrasonography, and reporting their presence is valuable to general practitioners. Thyroid screening during carotid ultrasonography is cost-effective, rapid, sensitive, and specific and may affect the patient's diagnostic and therapeutic management.

Counter-ion transport number and membrane potential in working membrane systems.

In this work we use the general space-charge (SC) theory for a combined transport model of fluid and ion through cylindrical nanopores to derive equations for the membrane potential and counter-ion transport numbers. We discuss this approach for ion exchange membranes assuming aqueous domains as interconnected network of cylindrical pores. The transport number calculations from the SC theory are compared with the corresponding ones from the uniform potential (UP) and Teorell-Meyer-Sievers (TMS) models in the case of both zero and non-zero concentration gradient across the membrane and with an applied current density. By using this approach we suggest the optimal conditions for performing membrane potential experiments (i.e. choice of electrolyte and concentration difference) depending on an easily accessible membrane property, namely the volumetric charge density. We also theoretically describe a novel dynamic method to determine in a single experiment the membrane potential and membrane conductivity. To exemplify the use of the dynamic method we report the calculations based on typical operating conditions of the reverse electrodialysis process. The numerical results are presented in terms of the electrical potential difference versus the average pore radius and charge density. The resulting map is a useful tool for a rational design of an effective membrane morphology for a specific electrochemical application.

Reverse electrodialysis performed at pilot plant scale: Evaluation of redox processes and simultaneous generation of electric energy and treatment of wastewater.

This paper describes the experimental campaign carried out with a reverse electrodialysis (RED) demonstration plant (Marsala, Italy) with the main aims of: (i) evaluating the effect of various operating parameters, including the redox processes, on the system performances; (ii) using the plant for the simultaneous generation of electric energy and treatment of wastewater. The prototype (44 × 44 cm2, 500 cell pairs) was tested using both real (brackish water and brine) and artificial solutions. Tests with two different electrode rinse solutions (with or without iron redox couples) were performed. In agreement with the data obtained in the laboratory, the presence of iron ions contributes positively to the power production. The effect of flow rates in the electrode and saline compartments, as well as aging of the electrode rinse solution was also investigated. The possibility to remove an organic pollutant (the azoic dye Acid Orange 7) from the electrode solution was tested, obtaining a very fast and total removal of the pollutant. This experimental campaign represents the first demonstration in a real environment of the abilities of a RED plant to treat wastewater, thus giving useful indications for the spreading of RED technology in the near future.

Long-term effects of nicotine on the forced swimming test in mice: an experimental model for the study of depression caused by smoke.

Large evidence showing an association between depression and tobacco smoking is known. Nicotine is the active chemical responsible for smoking addiction, and its withdrawal may induce in smokers greater sensitivity to stress. Our aim has been to investigate the links between tobacco addiction and depression by studying the long-term effects of repeated administration of nicotine followed by dependence, to forced swimming test, serotonin content and 5-HT(1A) expression in diencephalon. Dependence has been induced by daily subcutaneous injection in mice of nicotine (2mg/kg four injections daily) for 15 days and assessed after nicotine withdrawal with an abstinence scale; control animals received daily subcutaneous injection of saline for the same period. Experiments on forced swimming test have been carried out at t=0 (last day of nicotine or saline treatment), and 15, 30, 45 and 60 days after saline or nicotine withdrawal. Both control mice and nicotine mice have been pre-treated with oral 5-hydroxy-tryptophan (12.5-50mg/kg), precursor of serotonin, before forced swimming test. Nicotine mice have shown on forced swimming test a significant increase of immobility time compared to control mice. This increase was not evident in nicotine mice treated with 5-hydroxy-tryptophan and treatment with the selective serotonin receptorial antagonist WAY 100635 (WAY) abolished 5-hydroxy-tryptophan effects. Evaluation of diencephalic serotonin, performed at t=0 showed an increase of diencephalic serotonin content, while serotonin measured 15, 30, 45 and 60 days after nicotine withdrawal, was significantly reduced in nicotine mice compared to control mice. Western blot analysis showed a great reduction of 5-HT(1A) receptor expression in nicotine mice measured at t=0 (last day of treatment) and at 15 and 30 days after nicotine withdrawal compared to control mice. Our results show that (i) behavioural alterations estimated with forced swimming test and (ii) changes in diencephalic serotonin content and 5-HT(1A) receptor expression, are present since nicotine is withdrawn even after a long time, suggesting a role of serotonin in mood disorders eventually occurring following smoking cessation.

Effects of monotherapy and combination therapy on blood pressure control and target organ damage: a randomized prospective intervention study in a large population of hypertensive patients.

This prospective, randomized trial evaluated the effect of monotherapy and different combination therapies on cardiovascular target organ damage and metabolic profile in 520 hypertensive patients. Patients were allocated to a single agent: carvedilol 25 mg, amlodipine 10 mg, enalapril 20 mg, or losartan 50 mg (groups C, A, E, and L, respectively). After 2 months (level 2), nonresponders received a low-dose thiazide diuretic, and after 4 months (level 3), amlodipine (groups E, C, and L) and carvedilol (group A). Twenty-four-hour blood pressure was significantly lowered in all treatment groups. Blood pressure control was more pronounced in patients receiving two or three drugs. At the end of the study, the carotid intima-media thickness decreased in group L (P<.01), left ventricular mass index in groups E and L (P<.05 and P<.001, respectively), with a concomitant reduction in cholesterol in group L (P<.03). Diastolic function improved significantly in group L (P<.05). This study describes the need to control blood pressure with two or more drugs in most hypertensive patients and illustrates good clinical outcomes, independent of blood pressure lowering, using combination therapy with losartan, low-dose thiazide, and amlodipine.