Materials Today Communications
Continuous electrochemical deionization by utilizing the catalytic redox effect of environmentally friendly riboflavin-5'-phosphate sodium
Introduction
With global warming and the climate change, the evolution of land desertification and freshwater shortage has become severe. Growing of population and the development of industrialization undoubtedly speed up the freshwater storage. Nearly 97.5 % of the world's total water resource is ocean water, and more than 70 % of the world's population lives within 70 km along the coastline. Since 1950s, desalination has been considered as the most practical method of sustainably providing fresh water sources and to remediate the enlarging in demands of fresh water. The desalination technology currently used in large-scale industrial applications includes multi-stage flashing, reverse osmosis, capacitive deionization and electrodialysis deionization [1]. Multi-stage flash is thermal treatment process with the advantages of high water quality, safe and reliable operation. However, acid and a scale inhibitor are required to do the regeneration. The thermal power consumption is large, and corrosion occurs in the system in previous developed methods [2]. RO is widely used in industry all over the world, however the energy consumption is still considered high [3]. Recently, CDI has been paid much attention as an emerging desalination technology based on the electrical double layer absorption from high-surface-area electrode materials such as carbon [4]. Conventional CDI [5,6], membrane capacitance deionization (MCDI) [7,8], hybrid capacitive deionization (HCDI) [9,10] and flow-electrode capacitive deionization (FCDI) [[11], [12], [13]] are widely investigated. When electrically applied, cation/anion can be electrostatically absorbed by the negative/positive electrodes respectively, resulting in deionization process [14]. Lots of research works were focused on electrode materials such as improvement on the surface area and conductivity in the last decade. The desalination technology with commercial potential possesses the embodiment of high salt removal capacity, economic energy consumption, and low maintenance cost. However, the desalination ability of CDI devices is not particularly desirable because of the limited capacitance of these carbon materials. In addition, another restriction of the conventional CDI or Faradic CDI is it can only work in intermittent desalination/salination exchanged mode [15]. In the practical application, the continuous process is highly demanded. Therefore, in our latest research work, an electrocatalytic redox desalination technique using TEMPO/TEMPO+ was proposed, which enables continuous desalination by the circulation of redox species between the electrode reservoirs [16]. However, these chemicals are potentially toxic in some extent (Oral-category 4, skin irritation-category 2, eye irritation-category 2A, specific target organ toxicity-category 3). Therefore, utilizing cheap and nontoxic candidate is necessary to develop desalination technology. FMN-Na has been proposed as a versatile electroactive molecule that catalyze diverse redox reactions in various biological organizations [17,18], and redox flow battery [17,[19], [20], [21]]. It serves as a cofactor in many enzymes in tissue and cell. In this current work, as a great importance to be environmentally friendly in desalination process, FMN-Na is utilized as a nontoxic redox mediator to achieve the continuous electrochemical deionization by circulating the electrode material between positive and negative electrodes. The salt removal efficiency up to 98.1 % can be attained by applying FMN-Na as flow electrolyte. By controlling the current density and salt feed concentrations, the desalination performance is examined. The cyclability and flow rate are also performed. In addition, energy consumption and salt feed concentration and other important electrochemical tests are also performed. This study suggests that pollution-free electro-catalytic technology will be huge significant for the future low cost and safe desalination.
Section snippets
Material and experimental method
The detailed preparation, device structure and desalination setup, electrochemical tests are provided in the supplementary information
Results and discussion
Continuous desalination of ED was shown in Fig. 1a. FMN-Na at the positive stream gains electron while the generation of FMN-Na at negative chamber. The sodium ions in stream A transport to positive chamber through CEM while the chloride ions move to stream B, occurring a salt removal in stream A. With the acceptance of sodium ions from negative chamber through CEM, the salt content in stream B becomes concentrated. Overall, the salt in stream A is removed to stream B, and the constituents of
Conclusion
The edible FMN-Na is utilized firstly for continuous desalination process in the ED cell that consists of the flow FMN-Na between positive and negative electrodes, two salt feeds, separated by two CEMs and one AEM. The electrochemical catalytic function of FMN-Na achieves an uninterrupted desalination effect, reducing the salt feed from 5200 ppm to 100 ppm drinking water level. A series of experiments were designed to explore the influence of applied current density, feed concentration, and
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.
Acknowledgments
This project was supported by Outstanding Young Scholar Project (8S0256), and the Scientific and Technological Plan of Guangdong Province (2018A050506078), and the Project of Blue Fire Plan (CXZJHZ201709).
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2022, DesalinationCitation Excerpt :Riboflavin-5′-phosphate sodium salt (FMN-Na) FMN-Na was also investigated by Zhang et al. as a feasible redox mediator for continuous redox desalination [118]. Sodium ions were captured and transferred in this system through the redox couple of FMN-Na/FMN-Na2, resulting in the realization of the salt removal efficiency of 98.1 %.
Continuous desalination via redox flow desalination using sodium 4-sulfonatooxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (NaSO<inf>4</inf>-TEMPO)
2022, Chemical Engineering JournalCitation Excerpt :MVCl2 extracted product with 284 ppm from 6000 ppm salt feed at salt removal efficiency of 95.3% and energy consumption of 160 kJ/mol[[32]]. In addition, nickel phthalocyanine tetrasulfonic acid tetrasodium salt (NiPcTATS) and riboflavin-5′-phosphate sodium salt (FMN-Na) were also validated the feasible redox mediator for continuous redox desalination architectures[33,34]. Compared with the complex synthesis and high cost of BYMAP-Fc and NiPcTATS, and highly toxic MVCl2, 4-hydroxy-2,2,6,6- tetramethylpiperidine 1-oxyl (HO-TEMPO) has the advantage of low cost and high electrochemical activity in the redox system[35].
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2022, Cell Reports Physical ScienceCitation Excerpt :Although most studies have focused on low concentrations,21,22 our past work applied MCDI in 600 mM NaCl to achieve a desalination capacity of 25 mg/g at a potential range of −1 to +1 V17; works such as ours and others show the possibility of applying MCDI for seawater desalination.10,23 In desalination batteries,23,24 carbon electrodes are replaced by charge-transfer materials, such as metal oxides,20 hexacyanoferrates,25 MXenes,26 redox-electrolytes,27 conversion materials,28,29 or alloying materials.30 More recent approaches include electrocatalytic processes.31,32