1,720,989 research outputs found
High-Performance Nanofiltration Membrane with Dual Resistance to Gypsum Scaling and Biofouling for Enhanced Water Purification
No full textNanofiltration (NF) technology is pivotal for ensuring a sustainable and reliable supply of clean water. To address the critical need for advanced thin-film composite (TFC) polyamide (PA) membranes with exceptional permselectivity and fouling resistance for emerging contaminant purification, we introduce a novel high-performance NF membrane. This membrane features a selective polypiperazine (PIP) layer functionalized with amino-containing quaternary ammonium compounds (QACs) through an in situ interfacial polycondensation reaction. Our investigation demonstrated that precise QAC functionalization enabled the construction of the selective PA layer with increased surface area, enhanced microporosity, stronger electronegativity, and reduced thickness compared to the control PIP membrane. As a result, the QAC NF membrane exhibited an approximately 51% increase in water permeance compared to the control PIP membrane, while achieving superior retention capabilities for divalent salts (>99%) and emerging organic contaminants (>90%). Furthermore, the incorporation of QACs into the PIP selective layer was proved to be effective in mitigating mineral scaling by allowing selective passage of scale-forming cations, while simultaneously exhibiting strong antimicrobial properties to combat biofouling. The in situ QAC incorporation strategy presented in this study provides valuable guidelines for the fit-for-purpose design of the selective PA layer, which is crucial for the development of high-performance NF membranes for efficient water purification.
Omniphobic Membrane for Robust Membrane Distillation
Full text linkIn this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting.
ADVANCING THE FUNDAMENTAL UNDERSTANDING OF ACTIVE LAYER FORMATION FOR DEVELOPING HIGH-PERFORMANCE NANOFILTRATION MEMBRANE
No full textGrowing water scarcity is one of the leading challenges of our time, impacting over one-third of the world’s population. While several measures have been taken to improve water-usage efficiency among the industrial and domestic water consumption, these methods can only improve the usage of existing water resources instead of increasing them. The only approach to increasing the available water supply is through desalination and water purification. Pressure-driven membrane separation represents a highly-efficient approach to achieving molecular level separation because it requires only one-tenth energy to process an equivalent amount of liquid as compared to other industrial separation processes, e.g., evaporation and distillation, due to the latent heat of vaporization. Nanofiltration (NF) has received increasing interest in recent years due to its strong potential in addressing many of the environmental problems under growing stringent regulations and higher requirements for water quality in a variety of applications, e.g., desalination of brackish groundwater, water softening, and wastewater reuse. Increasing demands for more energy-efficient and more precise separations in the applications including desalination, chemical synthesis, and gas separation have stimulated the vigorous research interests in designing the next generation separation membranes. Herein, the overarching goal of this dissertation is to advance the fundamental understandings of the active layer formation mechanism of two most commonly used NF membranes, i.e., Thin-Film-Composite polyamide NF membranes and polyelectrolyte multilayer NF membranes in order to design and fabricate the next-generation nanofiltration membranes with multi-fold enhancement of perm-selectivity
Membrane-based Ion-ion Separation Processes: Nanofiltration and Electrodialysis
No full textSelective ion-ion separation is a critical research area due to its potential applications in resource extraction and recovery. One promising application is extracting lithium (Li) from brines rich in magnesium (Mg) to meet the growing demand of Li batteries. Nanofiltration (NF), a pressure-driven filtration process, and electrodialysis (ED), an electrical separation process, are two promising membrane processes for selective ion-ion separation. However, understanding ion-ion separation in NF and ED from microscopic ion transport to process-scale performance remains a challenge. This dissertation aims to advance the understanding of ion-ion separation with experiments and modeling, for tackling the specific challenge of Li extraction from brine lakes with a high mass ratio of Mg over Li. The dissertation first demonstrates the cross-method incomparability of ion-ion selectivity and the deficiency of using selectivity as the only performance metric. A standard protocol for membrane selectivity evaluation is recommended. A new framework for evaluating ion-ion separation based on the success criteria of product purity and recovery is established for NF at both material level and process level. Next, a multi-pass NF process with brine recirculation is proposed to achieve high Li/Mg selectivity without sacrificing Li recovery. The dissertation then extends the counter-ion condensation model to mixed salts scenarios for describing ion partition and mobility inside ion exchange membranes when used in ED. Finally, the performance of NF and ED based Li/Mg separation is compared under a unified mass transport model from coupon-scale to module-scale. The impacts of membrane properties and operating conditions on the separation performance are investigated and an important operational tradeoff between Li/Mg selectivity and Li recovery at the module-scale is elucidated for both NF and ED. This dissertation can contribute to the development of novel membranes with superior ion-ion selectivity and to process innovation for precise ion-ion separations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Toward Using Membrane Distillation for Brine Treatment: Understanding Energy Efficiency and the Challenge of Mineral Scaling
No full textMembrane distillation (MD) is an emerging technology that carries potential for brine treatment. Energy efficiency analysis and mineral scaling, which are the most critical challenges in MD, remain unresolved and poorly understood. Energy efficiency analysis of MD thus far has been unintuitive and difficult to draw conclusions from, especially when the MD process is coupled with latent heat recovery or driven by waste heat. Scaling is problematic because it directly hinders vapor transport across the membrane, which leads to inefficiency in the production of pure water, and eventually leads to pore wetting, which can allow for contamination of the produced water. In this work, I 1) develop intuitive metrics for the evaluation of energy efficiency in MD in varying contexts, and 2) evaluate scaling-related failure in the MD process when operated with highly saline and complex feed waters composed of sparingly soluble salts. Specifically, I explore the thermodynamics of an MD system coupled with heat exchangers for waste heat delivery and/or the delivery of latent heat stored within the distillate solution. Also, I investigate how operating parameters and feed solution composition contribute to the precipitation of minerals onto the surface of an MD membrane. This work informs the necessary discussion surrounding the optimization of MD for the cheap and efficient treatment of high-salinity brine
Simultaneous removal of phosphate (PO43-) and ammonium (NH4+) by nanofiltration for phosphorus recovery as struvite
No full textIn this study, we studied the transport of PO43- and NH4+ in synthetic wastewater (mixture) using three commercial nanofiltration (NF) membranes to elucidate the impact of charge on the membrane surface on the concurrent rejection of PO43- and NH4+ at different water recovery (WR) levels. Initially, we examined the transport of NH3-N and PO43- in each single salt across a range of pH levels at zero WR, encompassing two different concentrations, to understand the influence of pH and feed concentration on ion transport behavior. We found that the rejection of NH3-N in the single salt solutions, governed by Donnan exclusion, increased as pH rose up to pH 7.5, but decreased as the pH became alkaline due to an increased proportion of NH3 species. Conversely, PO43- species were retained over 90% in single salt solutions due to their larger hydrated radius, with a minor increase in rejection caused by increasing electrostatic repulsion against higher valence PO43- species as pH increased. Next, we examined ions transport in synthetic wastewater at zero and high WR. We observed that the magnitude of the negative membrane increased the retention of PO43- by electrostatic repulsion at zero WR. NH4+ was rejected by charge neutrality, predominantly determined by Cl- retention zero WRs in the mixture for all membranes. At high WR, the rejection sequences among ions remained unchanged across all membranes tested. A degree of reduction in rejections on ions were observed due to membrane fouling at this WR in all membranes. This study deepened our understanding of the fundamental processes involved in simultaneous PO43- and NH4+ transport in NF. This work contributed to alleviating environmental issues caused by phosphorus contamination and facilitating the circulation of phosphorus for reuse
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