Search

Background: Using novel technologies and solutions is crucial for producing clean water. There are different ways to remove dissolved salts from water. Methods: This study aimed to analyze the effect of an external force (EF) on the morphology of channels, the dispersion of particles, and the permeability of substances via carbon nanotubes in reverse electrodialysis. It was done using a computer simulation that studied the movement of molecules. This research aimed to study the effect of EF on the dispersion of particles and permeability of substances via carbon nanotubes using a reverse electrodialysis approach. The results show that increasing the EF from 0.0001 to 0.0005 eV/Å increased the electric current and fluid flow intensity from 5.31 e/ns and 211.31 atom/ns to 5.62 e/ns and 263.01 atom/ns. Moreover, the density decreased from 4.83 to 4.66 atom/nm3. Furthermore, the number of broken hydrogen bonds increased from 116 to 166. Significant findings: By understanding the effect of EF on particle movement and material passage through carbon nanotubes, researchers can optimize the design of reverse electrodialysis systems to enhance their performance. This can lead to more effective and cost-efficient water treatment solutions, crucial for producing clean water.

This study employed molecular dynamics simulations to investigate water transport through a carbon nanotube under an electric current, focusing on how varying ion atomic ratios influence key system parameters. These parameters include electric current intensity, fluid current intensity, maximum density, hydrogen bond count, and interaction energy as ion concentration changed. The research aimed to examine the effects of these changes on ion mobility, water permeability, and ion–carbon nanotube interactions. The study is conducted in two phases: equilibration, followed by the analysis of atomic transformations and the creation of various atomic ratios in samples. In the first phase, the kinetic energy of the atomic sample converges to 0.162 eV, and the potential energy reaches to 2.048 eV after 10 ns, indicating limited structural mobility and attractive forces among atoms. After equilibration, we achieved the atomic transformation process and created different atomic ratios. The results indicate that increasing ion ratios in the fluid led to a rise in electric current intensity, from 5.31 to 5.52 e/ns. Higher ion concentrations resulted in a greater density of charge carriers, enhancing ionic mobility and ion transport through the carbon nanotube. Moreover, higher ionic concentrations not only reduced the maximum density from 4.83 to 4.65 atoms/nm³ but also increases the number of broken hydrogen bonds, which could impact water transport and flow dynamics. Finally, according to the findings, there are 133 broken hydrogen bonds instead of 116, and the strength of the nanofluid flow, as well as the electric current, both increased when the ionic percentage of atoms rose to 5 %.

The study explores the technical feasibility of using abandoned mining site wastewater, specifically acid mine drainage (AMD), as an electrode solution in a reverse electrodialysis (RED) stack for energy production. Through experiments using a RED cell with varying electrode solutions, it was determined that the system achieved a maximum power density of 0.327 W m−2cell pair (5.01 W m−2electrode) when using simple mixtures of Cu2+ and Fe2+ ions, aligning with previous research on the Fe2+/Fe3+ redox pair. Synthetic solutions mimicking AMD composition also yielded promising results. When operating the system with real AMD effluent from an abandoned mine, a slightly lower maximum power density of 0.137 W m−2cell pair was achieved, only 5.5 % lower than with synthetic AMD. An extended-duration test showed a minor increase in pH in the electrode solution, but importantly, no metal deposition occurred on the electrode surface, as the pH consistently remained below 3.5 throughout the test. These findings indicate the potential of AMD as a viable electrode solution, offering a promising avenue for further research in the development of more sustainable RED systems.

Anion Exchange Membranes (AEMs) are positively charged polymer membrane used in many applications. In RED systems, AEMs could be used to separate ions to produce energy, and on the other hands remove unwanted molecules in wastewater. This study used three masses of colloidal silica (SiO2) as inorganic filler, three mass ratios of polymer mixture (where; PVA as an inert polymer and PDDA as an active polymer) and three different solvents (H2O, DMSO, and DMF), to produce composite AEMs. The properties of fabricated membranes, were measured to be used in the RED systems. RED membranes produced by DMSO showed the best yields where area resistance (AR), swelling degree (SD), and fixed charged density (FCD) were 1.69 k.Ω.cm2, 31.56%, and 0.26 mmol/g H2O, respectively, at the mixed mass ratio φ(PDDA/PVA)/SiO2 of AEM (0.528:0.4; DMSO). SiO2 can create a layer that can strengthen the matrix membrane, formed through -C(=O)-O-C- and -Si-O-Si- bonds. SiO2 can also encourage the formation of quaternary ammonium bonds. The higher the ratio of the mixture used can increase the number of quaternary ammonium bonds to improve AR and permselectivity. The use of water as solvent in the preparation of AEMs from PVA/PDDA/SiO2 mixture is also promising, by produce equivalent ion exchange properties, yet environmentally-safe.

Inorganic material-incorporated cation exchange membranes (CEMs) with improved properties have drawn attention for reverse electrodialysis (RED). This paper deals with improving CEMs properties by incorporating silica–magnetite inorganic materials from natural resources. First, silica and magnetite were extracted from rice husk and iron sand, respectively. CEMs were prepared using the phase inversion method by incorporating various ratios. The results showed that both silica and magnetite were in micron size with yields of 76.6% and 59.2% wt., respectively. The CEMs containing magnetite materials showed higher ion exchange capacity (IEC) and ionic conductivity than PVC membranes. However, they had a greater swelling degree. The presence of silica reduced the swelling degree from 18.38% to 7.15% leading to membrane strengthening. A maximum IEC and conductivity of CEMs of 0.26 meq/g and 0.524 S/cm were obtained for the membrane prepared with a SiO2/Fe3O4 ratio of 0:4, respectively. However, considering all aspects, the addition of a SiO2/Fe3O4 ratio of 1:3 was the most significant for increasing the fixed cation density and conductivity by 27.49% and 2815%, respectively, compared to other ratios. Thus, this SiO2/Fe3O4 ratio (1:3) should be considered for practical implementation. Performance examination using RED confirmed that the PVC/SiO2/Fe3O4 can be used as CEM for power generating and had comparable performance to commercial membrane.

Efficiently utilizing the low-grade heat contributes to improving energy consumption structure and energy utilization efficiency, as well as preventing environmental deterioration. To harvest low-grade heat below 80 °C, advanced adsorption-based osmotic heat engines are constructed, which consist of an adsorption-based desalination module for thermally separating the salt solution into concentrated and diluted streams, and a reverse electrodialysis module for converting produced salinity gradient into electricity. Two different heat recovery configurations are employed to improve the heat-to-electricity performance: one is that the cooling power generated in the evaporator is used to cool the condenser and the other is that evaporator is coupled inside the condenser. The transient responses are analyzed and the effects of adsorption/desorption time, switching time, working concentration and heat source temperature on the heat-to-electricity performance are discussed. The efficiency with respect to Carnot efficiency is also presented to provide information on effectively utilized level of the available exergy. Compared with original configuration, the reduced effective condensing temperature in Configuration I and the pressurization effect in Configuration II significantly elevate the working capacity, thus to boost the work extracted. At lower working concentrations and adsorption times, the electric efficiency can be improved via Configuration II, while at higher working concentrations and adsorption times, the advanced configurations hinder the electrical efficiency. In Configuration II, compared with original configuration, the electric power and efficiency are improved by 68.3% and 15.2%, respectively, at a heat source temperature of 333.15 K with 2 mol/kg NaCl solution. While with 7 mol/kg NaCl solution, the electric power is augmented by 11.8% while the electric efficiency is decreased by 19.8%. This study may contribute to designing advanced adsorption-based osmotic heat engines to achieve an upgraded heat-to-electricity performance.

Power generation from renewable energy sources is becoming increasingly significant as global energy consumption increases. The non-renewable energy sources we use now are on the verge of extinction. Reverse electrodialysis and pressure retarded osmosis are two methods of harvesting renewable energy using salinity gradients. There are non-polluting sources of energy that can be found at the interface of two solutions with varying salinity gradients. Reverse electrodialysis makes use of ion-selective membranes while uses salt rejecting membranes. It is necessary to employ membranes. Unlike pressure retarded osmosis membranes, ion-exchange membranes involve controlled mixing. The ion flux is employed by ion-exchange membranes in reverse electrodialysis to extract energy. Pressure retarded osmosis is an emerging membrane process uses for harvesting energy and desalination applications. Salinity gradient energy is a zero-emission and sustainable technology that can be practically applied worldwide. By employing a semipermeable membrane to control the mixing process, the osmotic pressure gradient energy can be generated in terms of electrical power via pressure retarded osmosis without causing adverse environmental impacts. In this study, the thin film nanocomposite membrane was fabricated by forming a polyamide thin film on the polysulfone substrate through the interfacial polymerization process.

How to optimize ion-exchange membrane materials has been the key for researchers recently working on the use of reverse electrodialysis to harvest osmotic energy. Based on the considerations of improving membrane performance and conversion to large-area industrial production, this work first proposes an easy-industrialized strategy to treat bacterial cellulose membranes by hot pressing and hot pressing with etherification modification, and then to obtain anion-selective and cation-selective membrane pairs (PBC-M and NBC-M) with opposite charges. The PBC-M obtained by multi-step treatment has excellent hydrophobicity, good surface charge density, and more favorable nanochannel size for the functioning of double layer. The maximum output power density of 44.1 mW m -2 was obtained in artificial river water and seawater simulated salinity gradient power generation. Applied to a larger test area, the power output of the system where a single membrane is located can reach 2.2 × 10 -3  mW, which is ahead of similar experimental products. The two membranes prepared can also be used in combination, which provides a new idea for full cell design. It's important to open up a new route for optimizing nanofluidic channel design, regulating ion flux transport, and advancing the large-scale industrialization of biomass nanofluidic membrane RED system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Reverse electrodialysis (RED) using nanofluidic ion-selective membrane may convert the salinity difference between seawater and river water into electricity. However, heterogeneous modification reactions of cellulose commonly leads to the inhomogeneous distribution of surface charges, thereby hampering the improvement of cellulose-based nanofluidic membranes for energy conversion. Herein, RED devices based on cellulose nanofibers (CNF) membranes with opposite charge characteristics were developed for the generation of salinity gradient power. Anion-CNF membrane (A-CNF) with varying negative charge densities was synthesized using 2,2,6,6-Tetramethylpiperidine 1-oxy radical (TEMPO) oxidation modification, whereas cation-CNF membrane (C-CNF) was prepared through etherification. By mixing artificial seawater and river water, the output power density of CNF RED device is up to 2.87 W m -2 . The output voltage of 30 RED units connected in series may reach up to 3.11 V, which can be used to directly power tiny electronic devices viz. LED lamp, calculator, etc. The results of this work provide a feasible possibility for widespread application of ion exchange membranes for salinity gradient energy harvesting., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

In this study, stack design for high concentration gradient reverse electrodialysis operating in recycle is addressed. High concentration gradients introduce complex transport phenomena, which are exacerbated when recycling feeds; a strategy employed to improve system level energy efficiency. This unique challenge indicates that membrane properties and spacer thickness requirements may differ considerably from reverse electrodialysis for lower concentration gradients (e.g. seawater/river water), drawing closer parallels to electrodialysis stack design. Consequently, commercially available electrodialysis and reverse electrodialysis stack design was first compared for power generation from high concentration gradients. Higher gross power densities were identified for the reverse electrodialysis stack, due to the use of thinner membranes characterised by a higher permselectivity, which improved current. However, energy efficiency of the electrodialysis stack was twice that recorded for the reverse electrodialysis stack at low current densities, which was attributed to: (i) an increased residence time provided by the larger intermembrane distance, and (ii) reduced exergy losses of the electrodialysis membranes, which provided comparatively lower water permeance. Further in-depth investigation into membrane properties and spacer thickness identified that membranes characterised by an intermediate water permeability and ohmic resistance provided the highest power density and energy efficiency (Neosepta ACS/CMS), while wider intermembrane distances up to 0.3 mm improved energy efficiency. This study confirms that reverse electrodialysis stacks for high concentration gradients in recycle therefore demand design more comparable to electrodialysis stacks to drive energy efficiency, but when selecting membrane properties, the trade-off with permselectivity must also be considered to ensure economic viability., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2021 The Author(s).)