Atmospheric-pressure plasma seawater desalination: Clean energy, agriculture, and resource recovery nexus for a blue planet

Water connects every aspect of life. Only 4% of the world's water is fresh water, as most water sources have different degrees of salinity. As a result, billions of people face water scarcity, which is a global challenge. Desalination technologies that separate fresh water from solvated salt ions in saline water are attracting major attention. However, conventional desalination processes including thermally and pressure driven processes are highly energy intensive. To address this issue we demonstrate that the atmospheric-pressure plasma (APP) treatment of saline water can be a new potential alternative low-energy and green desalination route. Valuable salts are recovered by direct salt crystal precipitation within a short plasma processing time. During desalination and salt precipitation, plasma activated desalinated water (PADW) is generated and can be used for clean energy processes such as water electrolysis and sustainable agriculture by enhanced plant seed germination. In addition, functional nanomaterials can be extracted from the precipitated salt. The PADW exhibited a low salinity of 5.6 mS/cm with a low pH value of 2.1. The unique intrinsic PADW chemistries enabled electrochemical water splitting for both the hydrogen evolution reaction (HER) at a Pt electrode and the oxygen evolution reaction (OER) at a RuO2 electrode. Moreover, the feasibility of using PADW in sustainable agriculture was demonstrated by enhancing mungbean seed germination using tap water mixed with PADW. At optimum mix concentration, both seed germination rates and germination percentages increased. Finally, we demonstrated the feasibility of synthesizing high-value 2D nanomaterials exemplified by Mg(OH)2 nanosheets via a single step thermal process using the salt precipitated from the seawater by the plasma process. Combined with straightforward use of renewable electricity to generate APPs, this study reveals the plasma potential for sustainable recovery of clean water, clean energy applications, sustainable agriculture, and manufacturing of advanced functional nanomaterials – all from the greatest treasure of our blue planet – seawater.</p

2D MXenes: A New Family of Promising Catalysts for the Hydrogen Evolution Reaction

Developing highly conductive, stable, and active nonprecious hydrogen evolution reaction (HER) catalysts is a key step for the proposed hydrogen economy. However, few catalysts, except for noble metals, meet all the requirements. By using state-of-the-art density functional calculations, herein we demonstrate that 2D MXenes, like Ti2C, V2C, and Ti3C2, are terminated by a mixture of oxygen atoms and hydroxyl, while Nb2C and Nb4C3O2 are fully terminated by oxygen atoms under standard conditions [pH 0, p(H2) = 1 bar, U = 0 V vs standard hydrogen electrode], findings in good agreement with experimental observation. Furthermore, all these MXenes are conductive under standard conditions, thus allowing high charge transfer kinetics during the HER. Remarkably, the Gibbs free energy for the adsorption of atomic hydrogen (ΔGH∗0) on the terminated O atoms (e.g., Ti2CO2) is close to the ideal value (0 eV). Our results demonstrate terminated oxygens as catalytic active sites for the HER at these materials and highlight a family of promising two-dimensional catalysts for water splitting. (Chemical Equation Presented)

Electrochemical Behavior and Redox-Dependent Disassembly of Gallic Acid/Fe-III Metal-Phenolic Networks

Metal-phenolic networks (MPNs) are a versatile class of organic-inorganic hybrid systems that are generating interest for applications in catalysis, bioimaging, and drug delivery. These self-assembled MPNs possess metal-coordinated structures and may potentially serve as redox-responsive platforms for triggered disassembly or drug release. Therefore, a comprehensive study of the reduction and oxidation behavior of MPNs for evaluating their redox responsiveness, specific conditions required for their disassembly, and the kinetics of metal ion release, is necessary. Using a representative MPN gallic acid-iron (GA/FeIII) system, we conducted electrochemical studies to provide fundamental insights into the redox behavior of these MPNs. We demonstrate that GA/FeIII is redox active, and evaluate its electrochemical reversibility, identify the oxidation state of the redox-active species, and provide information regarding the stability of the networks toward reductive stimuli and specific redox conditions required for the "on-off" or continuous release of FeIII. Overall, through studying the redox properties of GA/FeIII films, we advance the understanding of multifunctional iron-containing MPN platforms that may have practical significance for biologically relevant applications

Utilization of plasma in water desalination and purification

© 2020 Elsevier B.V. Supplying fresh drinking water to the world population is a persistent global challenge. Therefore, effective and efficient desalination processes are becoming increasingly important. Oceans account for most of the water on Earth and the presence of salts and other contaminants in seawater prevents them from being used as a source of drinking water. Owing to this challenge, non-thermal plasma can be utilized in order to enhance the existing desalination processes via membrane or material modification while it can also be used as a direct tool for seawater desalination leading to significant process improvements. A direct non-thermal plasma-based desalination process is a new emerging area of research and recent efforts have shown its promise with many unexplored mechanisms, providing benefits that conventional desalination processes cannot offer. Here we critically review the use of plasma technologies in water desalination including membrane modification by plasma for pressure, thermal, photothermal processes and direct plasma-based desalination process. We also address the use of plasmas in water purification. Finally, the existing challenges and future prospects are outlined

Probing the surface oxidation of chemically synthesised gold nanospheres and nanorods

In this study, the electrochemical behaviour of commercially available gold spheres and rods stabilised by carboxylic acid and cetyl trimethyl ammonium bromide (CTAB) moieties, respectively, are investigated. The cyclic voltammetric behaviour in acidic electrolyte is distinctly different with the nanorods exhibiting unusual oxidative behaviour due to an electrodissolution process. The nanospheres exhibited responses typical of a highly defective surface which significantly impacted on electrocatalytic activity. A repetitive potential cycling cleaning procedure was also investigated which did not improve the activity of the nanorods and resulted in deactivating the gold spheres due to decreasing the level of surface defects

Electrocatalytic and SERS activity of Pt rich Pt-Pb nanostructures formed via the utilisation of in-situ underpotential deposition of lead

The controlled synthesis of nanostructured materials remains an ongoing area of research, especially as the size, shape and composition of nanomaterials can greatly influence their properties and applications. In this work we present the electrodeposition of highly dendritic platinum rich platinum-lead nanostructures, where lead acetate acts as an inorganic shape directing agent via underpotential deposition on the growing electrodeposit. It was found that these nanomaterials readily oxidise at potentials below monolayer oxide formation, which significantly impacts on the methanol electrooxidation reaction and correlates with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. Additionally these materials were tested for their surface enhanced Raman scattering (SERS) activity, where the high density of sharp tips provides promise for their application as SERS substrates