Mechanism Of Ion Removal Research Articles

Construction of amidinothiourea crosslinked graphene oxide membrane by multilayer self-assembly for efficient removal of heavy metal ions

Abstract Amidinothiourea crosslinked graphene oxide membrane was prepared by a multilayer self-assembly method along with (3-aminopropyl) triethoxysilane modification, while different thicknesses of the membrane layer were obtained by regulating the volume of graphene oxide dispersion. The removal rate of the membrane layer with different thicknesses of heavy metal ions was explored and its removal mechanism was explained. The results show that the membrane can maintain high stability after 90 days of immersion in water. When the volume of graphene oxide dispersant increases from 9 ml to 15 ml, the thickness of the membrane layer enhances from about 120 nm to about 200 nm. After filtration of 140 ml of different nitrate solutions, the water fluxes of different membranes are about 22.6 l m−2 h−1·bar−1, 6.1 l m−2 h−1·bar−1, and 1.4 l m−2 h−1·bar−1, respectively. The removal rates of the preferred membrane for Pb2+, Cd2+, and Cu2+ are 43.3 %, 41.2 %, and 39.7 %, respectively. The ion removal mechanism is mainly due to the Dornan effect.

Tuning Surface Energy to Enhance MoS2 Nanosheet Production via Liquid-Phase Exfoliation: Understanding the Electrochemical Adsorption of Cesium Chloride.

Environmental pollution caused by radionuclides like Cs-137 and Cs-134 has increased global attention toward public health. Electrochemical adsorption has emerged as a feasible, rapid, and scalable method to treat contaminated water sources. However, graphene and its derivatives have limitations in ion adsorption via physisorption, forming a double layer that restricts the electrode's adsorption capacity. To address this, we propose the use of molybdenum disulfide (MoS2) with its extensive intercalation galleries of MoS2 nanosheets for cesium removal via an electrochemical route. Liquid-phase exfoliation with water and N-methyl-2-pyrrolidone (NMP) was then used to produce MoS2 nanosheets in a scalable quantity (high-yield production). The formation of a mixed solvent possessing relatively equivalent surface energy for exfoliation enabled us to achieve a remarkable exfoliation yield of up to ca. 1.26 mg mL-1, which is one of the highest yields reported to date (without a surfactant being added) and to the best of our knowledge. The 35% v/v of water in NMP displayed a maximum yield while maintaining the structure of the as-exfoliated one. Water exceeding over 66.7% v/v led to the formation of MoO3. Moreover, an insight into the cesium ion removal mechanism through the electrochemical route was demonstrated. It is found that the Cs+ removal follows electrochemical intercalation rather than adsorption. This work aids the understanding of cesium intercalation coupled with a mass-scale production method, which should lead to more efficient and cost-effective removal of radionuclides from contaminated water sources, opening new research avenues in materials and environmental science.

Recent Progress and Challenges in Faradic Capacitive Desalination: From Mechanism to Performance.

Due to substantial consumption and widespread contamination of the available freshwater resources, green, economical, and sustainable water recycling technologies are urgently needed. Recently, Faradic capacitive deionization (CDI), an emerging desalination technology, has shown great desalination potential due to its high salt removal ability, low consumption, and hardly any co-ion exclusion effect. However, the ion removal mechanisms and structure-property relationships of Faradic CDI are still unclear. Therefore, it is necessary to summarize the current research progress and challenges of Faradic CDI. In this review, the recent progress of Faradic CDI from five aspects is systematically reviewed: cell architectures, desalination mechanisms, evaluation indicators, operation modes, and electrode materials. The working mechanisms of Faradic CDI are classified as insertion reaction, conversion reaction, ion-redox species interaction, and ion-redox couple interaction in the electrolytes. The intrinsic and desalination properties of a series of Na+ and Cl- capturing materials are described in detail in terms of design concepts, structural analysis, and synthesis modulation. In addition, the effects of different cell architectures, operation modes, and electrode materials on the desalination performance of Faradic CDI are also investigated. Finally, the work summarizes the challenges remaining in Faradic CDI and provides the prospects and directions for future development.

Uvidi u dinamiku pH, varijabilnost rastvorenog kiseonika i efikasnost uklanjanja jona u biološkom sistemu sa plutajućim ostrvima

This paper aims to analyse the dynamic responses within FTW constructed on the riverbank, focusing on pH, dissolved oxygen (DO), and the dynamics of calcium and magnesium concentrations. While some research has been carried out on Ca and Mg behavior in constructed wetlands no papers specifically addressed the removal mechanisms of these ions in FTWs have been found. Results showed that both polluted and treated water exhibited characteristics consistent with a mildly alkaline environment. Extremely low DO levels in cells with floating islands were increased after water passing through cell with algae. Ca removal efficiency in cells with floating island cells ranged from 2% to 6%, while the cell with algae achieved 23% to 49% efficiency. Modest Mg removal (1-6%) could indicate potential challenges in Mg removal processes within the FTWs. The analysis of plant responses to polluted water exposure reveals species-specific variations in Ca and Mg concentrations in shoots and roots. Ca concentration in algae tissue increased over time contrasting the marked decrease of Mg content. The study also revealed a gradual decrease of Ca and Mg concentration in stone wool corresponding to exposure duration. This research contributes to a better understanding of the complex dynamics of water treatment in FTWs, emphasizing the need for continued investigation into ion removal mechanisms, plant responses to increased Ca and Mg concentrations, and the role of algae in these biological systems.

Analysis of the chloride ion removal mechanism from simulated wastewater by discarded vitamin tablets.

Vitamin (VM) tablets are often discarded or incinerated as medical waste, and untreated highly chlorinated wastewater is discharged, polluting the environment. In this study, Cu2+ was reduced by vitamin C (VC, a component of VM), and the precipitate formed by the reaction of its product with Cl- in water was used to remove Cl- from simulated wastewater. This allows for the resourceful use of waste VM, while also achieving the goal of dechlorinating wastewater. Meanwhile, the effect of various parameters on dechlorination was studied, and the dechlorination mechanism was analyzed. According to the results, the removal rate of Cl- increased first and then decreased with pH, removal time and reaction temperature. Using VC in VM to dechlorinate simulated wastewater, the removal rate of Cl- was 94.31% under optimum conditions: pH 2.5, temperature 30 °C and reaction time 10 minutes. According to the dechlorination process, it can be inferred that Cu2+ is reduced to Cu+ by VC, and Cu+ and Cl- coprecipitate to remove Cl-. Therefore, it is feasible to use discarded VM to treat high concentration chlorine-containing wastewater.

Comparison of Ion Selectivity in Electrodialysis and Capacitive Deionization

Ion-selective removal is an important frontier in water purification technologies. For many emerging applications, removing all ions indiscriminately can lead to excessive energy consumption, high levelized cost of water, poor effluent water quality, and increased waste brine volume. Electrodialysis and capacitive deionization are two electrochemical water purification technologies which are promising toward tunable, ion-selective purification. These technologies have fundamentally different ion removal mechanisms, as electrodialysis leverages electrodiffusion through ion-exchange membranes while capacitive deionization utilizes electrosorption into charged electrodes. We here provide a direct comparison of ion selectivity achieved by these two technologies, focusing on several important ion pairs. We highlight distinct differences in achieved selectivity between these technologies and provide theory results to connect such observations to ion removal mechanisms. Based on the experimental literature, we find that capacitive deionization demonstrates a wider range of achieved ion selectivities than electrodialysis for competing cations such as Na+ vs Ca2+ and Li+ vs Na+, while a wider range is observed for electrodialysis when separating anion pairs such as Cl– vs SO42– and Cl– vs NO3–. We conclude with reviewing “knobs” that can be adjusted to tune the achieved selectivities by both technologies, and emphasize important questions that should be answered in future studies to improve the selectivity of both technologies.

Modeling and optimization of electrodeionization process for the energy-saving of ultrapure water production

Electrodeionization (EDI) is essential for producing ultrapure water in power plants and high-tech industries. Compared with the traditional ion exchange process, EDI does not require high-pollution resin regeneration by acid and alkali reagents. However, the process is markedly energy-intensive, and thus it is crucial to reduce the energy consumption. The reduction may be achieved by optimizing the operating conditions and module design. Previous mathematical models of the EDI process have been based on the mass transfer mechanism of ion removal. However, the water dissociation reactions, which are crucial for the energy efficiency of ion removal and thus EDI optimization, have rarely been considered. In particular, the design of EDI modules has not been studied. In this study, the water dissociation reactions in the EDI model were considered to simulate the ion removal process and energy consumption. In addition, the design variables of the equipment configuration and the operating conditions of an industrial-scale EDI module were optimized to reduce the energy consumption via nonlinear programming. The results show that the energy consumption of the current industrial EDI operation can be reduced by 22.4% when only the operating conditions are optimized. Furthermore, the optimization of the design and operation, based on the annual cost, will lead to a 50.4% decrease in the annual cost. The developed modeling and optimization method will play a critical role in an energy-saving operation and low-cost design of the EDI process.

CaFe-Based Layered Double Oxides With Superior Iron Alloy Corrosion Inhibition Behaviors in Aggressive Seawater Environment.

Reinforced concrete is among the most multifaceted materials used in the construction field. Maintaining the resistance of reinforced concrete to weathering, abrasion, and chemical attack, particularly in aggressive natural conditions such as seawater environments, is challenging. The main factor in the degradation of reinforced-concrete durability is chloride penetration, which accelerates iron alloy corrosion and facilitates structural degradation. In this study, calcium-iron-based layered double hydroxides (CaFe-LDHs) were fabricated at room temperature, followed by structural modulation, and their effectiveness in mitigating iron alloy corrosion due to chloride ions (in 3.5 wt% of NaCl) was investigated. The synthesized CaFe-LDHs with phase transfer notably improved the Cl− removal capacity (Qmax) to 881.83 mg/g, which is more than three times that reported based on previous studies. The novelty of this research lies in the sophisticated structural and phase transformations of the as-synthesized CaFe-LDHs, determination of crucial factors for chloride ion removal, and suggestion of calcium-iron-based layered double oxide (CaFe-LDO)-based chloride ion removal mechanisms considering chemical and ion-exchange reactions. Moreover, when the phase-transformed LDHs, C-700 LDOs, were applied to inhibit iron alloy corrosion, a noticeable inhibition efficiency of 98.87% was obtained, which was an 11-fold improvement compared to the case of iron alloys without LDOs. We believe this work can provide new insights into the design of CaFe-LDOs for the enhancement of the lifespan of reinforced concrete structures.

Functionalized layered double hydroxides composite bio-adsorbent for efficient copper(II) ion encapsulation from wastewater

In this study, naturally abundant and inexpensive bamboo was used to make cheaper activated charcoal for efficient encapsulation of toxic copper (Cu(II)) ion from wastewater. The functionalized bamboo charcoal-Layered double hydroxides (BC-LDHs) composite bio-adsorbent was prepared using co-precipitation method. The composite bio-adsorbent was exploited to eliminate Cu(II) ion with high sensitivity and selectivity from contaminated water. The adsorption parameters including the effect of pH, contact time, adsorbent dose, and effect of initial concentration were optimized in systematic way and the adsorption kinetics and isotherms were investigated for potential use in real sample treatment. The physicochemical properties and morphological structure of the adsorbent were examined using X-ray Diffraction, Scanning Electronic Microscopy, Fourier Transform Infrared Spectroscopy and Thermogravimetric Analysis to understand the Cu(II) ion adsorption mechanism. The adsorption results revealed that the BC-LDH could remove almost 100% of Cu(II) ion from aqueous solution at pH range between 3.0 and 6.0 within 30 min. The maximum monolayer adsorption capacity was determined to be 85.47 mg/g based on the Langmuir isotherm. The adsorption equilibrium data were well-fitted by the Langmuir isotherm model (R2 = 0.998) and the experimental kinetic data were supported by the pseudo-second order model (R2 = 0.999). The BC-LDH could be reused without losing its adsorption performance in several cycles after successful regeneration with 0.10 M HCl. The Cu(II) ion removal mechanism was postulated with intercalated ion exchange, surface precipitation and interaction between BC-LDH and surface functionalities. Therefore, the highly functional BC-LDH composite could be a promising adsorbent for efficient Cu(II) ion removal from wastewater.

Molecular Dynamics Simulation of Ion Adsorption and Ligand Exchange on an Orthoclase Surface.

Orthoclase (K-feldspar) is one of the natural inorganic materials, which shows remarkable potential toward removing heavy metal ions from aqueous solutions. Understanding the interactions of the orthoclase and metal ions is important in the treatment of saline wastewater. In this paper, molecular dynamics simulations were used to prove the adsorption of different ions onto orthoclase. The adsorption isotherms show that orthoclase has remarkable efficiency in the removal of cations at low ion concentrations. Aluminol groups are the preferential adsorption sites of cations due to higher negative charges. The adsorption types and adsorption sites are influenced by the valence, radius, and hydration stability of ions. Monovalent cations can be adsorbed in the cavities, whereas divalent cations cannot. The hydrated cation may form an outer-sphere complex or an inner-sphere complex in association with the loss of hydration water. Na+, K+, and Ca2+ ions mainly undergo inner-sphere adsorption and Mg2+ ions prefer outer-sphere adsorption. On the basis of simulation results, the mechanism of ion removal in the presence of orthoclase is demonstrated at a molecular level.

Experimental Study of the Relationship Between Dissolved Iron, Turbidity, and Removal of Cu(II) Ion From Aqueous Solutions Using Zero-Valent Iron Nanoparticles

In this study, nanoscale zero-valent iron has been prepared through the reduction method by sodium borohydride and then was used for removal of Cu(II) from aqueous solutions. The XRD analysis proved the high crystallinity of synthesized nZVI particles, and the calculated particle size was found to be 72 nm, which corresponds to a specific surface area of 10.68 m2/kg. The SEM analysis provided images about the morphologies of nZVI particles before/after Cu(II) adsorption, which revealed that the nZVI particles are spherical and tend to aggregate together in chain-like agglomerates. Besides, after Cu(II) adsorption, the SEM image evidenced a disparity in the structure of nZVI particles. The mineral composition of nZVI particles before/after Cu(II) adsorption was examined using XRF, which demonstrated that the nZVI particles were mainly composed of iron metal by up to 74.16%, and further proved the successful adsorption for Cu(II) onto nZVI particles. Kinetics, isotherms, and thermodynamics studies were showed that the adsorption process obeyed the pseudo-second-order, well-fitted to monolayer Langmuir isotherm with a maximum adsorption capacity of 54.35 mg/g, and have endothermic spontaneously nature, respectively. Both the released dissolved iron ions and the yielded turbidity that co-occurred along with the nZVI/Cu reaction were monitored. The dissolved iron concentrations recorded the highest value reached up to 106.3 mg/L at pH 1.0, while the turbidity dramatically increased to 32, and 35 NTU with increases in nZVI dosages and initial Cu(II) ion concentrations, respectively. Finally, some explanations have been suggested to represent the Cu(II) ion removal mechanisms onto nZVI particles.

Trace-Fe-Enhanced Capacitive Deionization of Saline Water by Boosting Electron Transfer of Electro-Adsorption Sites.

Capacitive deionization (CDI) is a promising water purification technology. However, the current ion adsorption capacity of CDI electrode materials is still an issue, which cannot meet the rapid demand of clean water from saline water. Herein, trace-Fe-enhanced removal of ions from saline water via CDI is presented. The ion adsorption capacity of CDI electrodes is up to 36.25 mg g-1 in a 500 mg L-1 NaCl media at 1.2 V together with stable regeneration property. In situ Raman and ex situ XPS measurements unravel the removal mechanism of ions from saline water, and the reinforced adsorption of ions is due to the introduction of trace Fe boosting electron transfer of electro-adsorption sites during the CDI process. This work presents a promising solution to highly efficient capacitive deionization for saline water.

Metal removal efficiency of novel LD-slag-incorporated ceramic membrane from steel plant wastewater

ABSTRACT This work focuses on the preparation and characterisation of novel LD-slag (by product of Linz-Donawitz process in Steel Industry)-based ceramic membrane. LD-slag powder along with other pore forming and binding agents such as boric acid, sodium metasilicate, sodium carbonate and alumina, were blended and casted into membrane by the simple paste casting method. The prepared membrane sintered at 700 ºC was found to have enhanced temperature resistivity, mechanical strength and excellent separation efficiency. The prepared ceramic membrane had an average pore diameter of 0.73–1.77 µm and porosity ranging from 31.13 to 55.5%. The prepared membrane was further used for the microfiltration of electro-coagulated wastewater obtained from Tata Steel plant, India to retain the flocks and metal ions obtained after electrocoagulation process. A novel metal ion removal mechanism was proposed based on electrostatic attraction-repulsion phenomenon between the membrane surface and pollutants.

Removal of co-existing fluoride, calcium, magnesium, and carbonates, by non-chemical induced electrolysis system for drinking and industrial purposes

Abstract An electrolysis (ELC) system was proposed to remove co-existing F−, Ca2+, Mg2+, CO32−, and HCO3− from groundwater without the addition of any chemicals. The proposed system utilized an ELC cell composed of non-corrosive platinum and stainless steel electrodes. Ion removal mechanisms, performance against different ion concentrations, and charge loading were studied and compared with drinking and industrial water quality guidelines. System performance with real groundwater was also examined. Results revealed that ELC effectively removes (CO32− + HCO3−) in the anode as CO2, and (CO32− + HCO3−), Ca2+, and Mg2+ in cathode as MgCO3, CaCO3, and Mg(OH)2. F− was removed by co-precipitation with Mg(OH)2 and Coulomb transfer. Maximum removal of 58%-F−, 42%-Ca2+, and 95%-Mg2+ were observed at a charge loading of 1500 C/L. With increasing Ca2+ and Mg2+, removal increments of cathode F−, Ca2+, Mg2+, and (CO32− + HCO3−) were noticed. To meet drinking water guidelines value of 1.5 mg/L of F−, minimum initial ion concentration ranges should be within F− < 4.29–6 mg/L, Mg2+ < 75–125 mg/L, Ca2+ > 50 mg/L, and (CO32− + HCO3−) < 10–0 mmol/L for 1500 C/L. The anode delivered the quality water which meets industrial boiler water alkalinity guideline for the initial (CO32− + HCO3−) < 12.5 meq/L. The community-scale treatment system established in Sri Lanka confirmed smooth operation with a higher removal of F− and Ca2+ in the cathode and (CO32− + HCO3−) in the anode which can be slightly approximated with laboratory results.

Removal of fluoride, hardness and alkalinity from groundwater by electrolysis

A novel continuous flow electrolysis (ELC) system comprised of non-corrosive platinum-anode and stainless steel-cathode electrodes was proposed to remove fluoride (F−) and elements that cause hardness (magnesium (Mg2+), calcium (Ca2+), and alkalinity causing ions (carbonates (CO32−) and bicarbonates (HCO3−)) from naturally contaminated groundwater. Performances and ion removal mechanisms of the proposed system were studied with the effect of charge loading in electrolyte (C/L) and initial ion concentrations, in synthetic groundwater. Experimental results were used to design and build a community-level treatment facility in the Anuradhapura District, Sri Lanka, where high F−, elements causing hardness and alkalinity are found in the groundwater. It was noticed that the proposed ELC system (water recovery 100%) was capable of removing a significant amount of F− by adsorption to the calcite (CaCO3) phase and co-precipitating with amorphous Mg(OH)2. The chemical composition of precipitation demonstrated that 6–9 mol of Mg2+ can remove 1 mol of F− ions at higher charge loading (500–1500 C/L). For the initial levels of F−10, Ca2+100, Mg2+ 100 mg/L, and (HCO3− + CO32−) 9.42 mmol/L, it was found that a maximum of 57% of F−, 61% of Mg2+, 94% of Ca2+ and 82% of (HCO3− + CO32−) were effectively removed by the system. Moreover, the proposed system exhibited the capability of disinfecting the final water as an extra advantage. However, system efficiencies of contaminant removal varied with the varying initial Mg2+, CO32−, (HCO3− + CO32−), and charge loading. The water quality data from the community-level ELC plant established shows that the proposed system was competent for the removal of F−, Mg2+, Ca2+, HCO3− and CO32− ions from groundwater to meet desirable standard levels as a simple, robust and economical technology.

The stability of the compounds formed in the process of removal Pb(II), Cu(II) and Cd(II) by steelmaking slag in an acidic aqueous solution

The potential feasibility of steel slag as a low cost removal agent for heavy metal ions Pb(II), Cu(II) and Cd(II) in acidic conditions was investigated in this study. The initial pH effect on heavy metal ion removal efficiency, the compounds formed after heavy metal ion removal, and the binding force of metals with the compounds were determined. The results showed that the efficiency of removing heavy metal ions by steel slag was low at low initial pH levels, yet it sharply increased and then became stable as the initial pH increased. The pseudo-second order model provided the best description for the removal of Pb, Cu, and Cd ions, indicating that the predominant heavy metal ion removal mechanism was chemisorption. The images obtained by the Fourier transform infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) analysis indicated that the main compounds formed after the removal of Pb, Cu, and Cd ions by steel slag in an aqueous solution were heavy metal ferrites, silicates, carbonates, hydroxides and oxides. Sequential extraction experiments showed that these three heavy metals bond to the compounds mainly in the carbonate fraction (F2), the Fe oxide bound fractions (F3 (a) and F3 (c)), and the residual fraction (F4) in which F2 corresponded to the carbonates, and F3(a), F3(c) and F4 corresponded to the amorphous or crystalline ferrites and silicates, respectively. The F3 (a), F3 (c) and F4 are relatively stable and do not tend to re-release metal ions in acidic solutions. However, F2 and heavy metal hydroxides have relatively low stability and dissolve readily, re-leaching heavy metal ions into the acid solution. When these three heavy metal ion mixtures were removed by steel slag, the Pb, Cu and Cd deposits were at higher levels in the F3 and F4 fractions. Therefore, it was concluded that the co-existence of heavy metal ions in an aqueous solution is beneficial for their removal by steel slag in acidic conditions.

Removal and Recovery of Heavy Metal Ions by Two-dimensional MoS2 Nanosheets: Performance and Mechanisms.

We investigated the removal of heavy metals from water by two-dimensional MoS2 nanosheets suspended in aqueous solution, and restacked as thin film membranes, respectively. From these studies we elucidated a new heavy metal ion removal mechanism that involves a reduction-oxidation (redox) reaction between heavy metal ions and MoS2 nanosheets. Ag+ was used as a model species and MoS2 nanosheets were prepared via chemical exfoliation of bulk powder. We found that the Ag+ removal capacity of suspended MoS2 nanosheets was as high as ∼4000 mg/g and adsorption accounted for less than 20% of removal, suggesting the reduction of Ag+ to metallic silver as a dominant removal mechanism. Furthermore, we demonstrated that MoS2 membranes were able to retain a similar high removal capacity, and attribute this capability to the formation of a conductive, permeable multilayer MoS2 structure, which enables a corrosion-type reaction involving electron transfer from a MoS2 site inside the membrane (anode) to another site on membrane surface (cathode) where heavy metal ions are reduced to metallic particles. The membrane surface remains active to efficiently recover metallic particles, because the primary oxidation products are soluble, nontoxic molybdate and sulfur species, which do not form an insulating oxide layer to passivate the membrane surface. Therefore, MoS2 membranes can be used effectively to remove and recover precious heavy metals from wastewater.

Water Desalination Via Hybrid Capacitive Deionization with Tunnel Manganese Oxides As Redox Active Electrodes

In this report, we show that inexpensive and environmentally friendly manganese oxides can achieve high ion removal capacities in a hybrid capacitive deionization (HCDI) configuration and highlight the importance of understanding the relationship between material crystal structure and ion size in electrochemical water desalination. As population and pollution levels continue to rise and threaten fresh water sources, the scarce availability of potable water has become a critical issue for society. Therefore, it is imperative to develop efficient water desalination techniques, and capacitive deionization (CDI) has emerged as a low cost and low pressure deionization technique [1]. In a typical CDI process, brackish water is flown through a channel between two carbon electrodes, and a potential is applied across the electrodes. Ions from the water are then attracted to the electric double layer on the surface of the carbon materials and removed from solution, resulting in a desalinated water stream exiting the channel. When the electrodes are saturated, the potential can be reversed, releasing ions from the surface of the carbon electrodes and regenerating them for subsequent desalination. The ion removal capacity of carbon electrodes in CDI is limited by the surface area of the carbon since the mechanism of ion removal is based on the electric double layer formed on the carbon surfaces. Recently, an approach has emerged (HCDI) that utilizes one carbon electrode and a redox active material as the opposite electrode [2]. This approach has the potential for higher ion removal capacities since the redox active material can remove and release ions from solution via oxidation and reduction reactions with bulk of the material and is therefore not limited by the available surface area. A tunnel manganese oxide (TuMO), Na4Mn9O18, demonstrated the effectiveness of this approach by achieving a high capacity in NaCl solution while in an HCDI configuration [2]. Motivated by this past work, we study the behavior of other TuMOs in an HCDI configuration. Manganese oxides are of great interest for electrochemical water desalination due to their inherently low cost, environmentally friendliness, high electrochemically activity, and stability in aqueous environments. More specifically, TuMOs consist of MnO6 octahedra arranged in various tunnel configurations around stabilizing cations. The large, open tunnel structures provide ample volume to store ions removed from solution. Further, by varying synthesis conditions, the size, shape, and ionic content of the structural tunnels can be modified, thus making TuMOs an attractive materials system to investigate for the relationship between crystal structure and ion removal capacity. TuMOs can all be synthesized with a flexible nanowire morphology as well, which allows for excellent access of water and ions to the surface of the materials. In this work, we investigate the ion removal behavior of four TuMOs in an HCDI configuration in NaCl, KCl, and MgCl2 solutions. Two of the phases studied are well-known tunnel structures, α-MnO2 with 2x2 octahedra square tunnels and manganese oxide with todorokite crystal structure (Tod-MnO2) containing tunnels of 3x3 octahedra dimensions. The other two phases are novel TuMOs with ordered (2xn-MnO2) and disordered (Hybrid-MnO2) combinations of structural tunnels with multiple different dimensions. The ion removal capacities of the four TuMOs are shown in Figure 1, and it was found that each material demonstrated high ion removal capacities above 20 mg g-1 in all solutions tested. α-MnO2, with the smallest tunnels, demonstrated lower capacities in the solution containing the largest hydrated cation, MgCl2. The other three phases, which contain larger structural tunnels, were found to demonstrate superior removal of larger hydrated ions from solution. Extended ion removal experiments showed the TuMOs to be stable for over 20 ion removal/ion release cycles, indicating the efficacy of using TuMOs for repeated water desalination via HCDI. Moreover, ex-situ XRD and EDS show that the ion removal mechanism is a result of chemical reaction between the ions in solution and the TuMO electrode. In summary, this work demonstrates not only the efficacy and high ion removal capacities of TuMOs in an HDCI configuration, but also shows the importance of understanding the relationship between material crystal structure and the size of ions in solution for maximizing performance in electrochemical water desalination.

Nanocellulose based functional membranes for water cleaning: Tailoring of mechanical properties, porosity and metal ion capture

Multi-layered nanocellulose membranes were prepared using vacuum-filtration of cellulose nanofibers suspensions followed by dip coating with cellulose nanocrystals having sulphate or carboxyl surface groups. It was possible to tailor the specific surface area, pore structure, water flux and wet strength of the membranes via control of drying conditions and acetone treatment. Cellulose nanofibers coated with cellulose nanocrystal with carboxyl surface groups showed the highest tensile strength (95MPa), which decreased in wet conditions (≈3.7MPa) and with acetone (2.7MPa) treatment. The membrane pore sizes, determined by nitrogen adsorption/desorption were in nanofiltration range (74Å) and the acetone treatment increased the average pore sizes to tight ultrafiltration range (194Å) with a concomitant increase (7000%) of surface area. The water flux, also increased from zero to 25Lm−2h−1 at a pressure differential of 0.45MPa, for acetone treated membranes. Modeling of the permeance showed that the middle layer of cellulose nanofibers was responsible for the majority of the resistance to flux and the flux can be improved by increasing the porosity or decreasing the thickness of this layer. The membranes irrespective of the surface functionality showed exceptional capability (≈100%) to remove Ag+, Cu2+ and Fe3+/Fe2+ ions from mirror industry effluents. Surface adsorption followed by micro-precipitation was considered as the possible mechanism of ion removal, which opens up a new generation of ultrafiltration membranes with high rejection towards metal ions.

Structure–performance relationship of bulk functionalized polyurethane foams designed for lead ion removal from water

Lead ion removal mechanism of bulk functionalized polyurethane foams were investigated by batch and column tests. The pH changes in the lead solution, before and after batch tests, indicate that both adsorption and ion exchange mechanisms are active in removing lead ions from water. The adsorption mechanism was benchmarked by comparing the adsorption isotherms of the control and functionalized PU foams with a commercially used adsorption media; such as granular activated carbon (GAC). Chemical structural analysis by FTIR shows a change in the peak intensities and wave numbers associated with the sulfonic groups after lead removal. Physical structure analysis by micro-CT reveals that fluid flow in the foams is through interconnected channels within and in between pores.