A simple, one-step electrodeposition approach has been used to fabricate MnO x on an indium-doped tin oxide substrate for highly sensitive As 3+ detection. We report an experimental limit of detection of 1 ppb through anodic stripping voltammetry with selectivity to As 3+ in the presence of 10 times higher concentrations of several metal ions. Additionally, we report the simultaneous phase evolution of active material occurring through multiple stripping cycles, wherein MnO/Mn 2 O 3 eventually converts to Mn 3 O 4 as a result of change in the oxidation states of manganese. This occurs with concomitant changes in morphology. Change in the electronic property (increased charge transfer resistance) of the material due to sensing results in an eventual decrease in sensitivity after multiple stripping cycles. In a nutshell, this paper reports stripping-voltammetry-induced change in morphology and phase of as-prepared Mn-based electrodes during As sensing.
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Arsenic ( As ), an elemental metalloid, occurs primarily in metallic and sulfide ores. Both natural (e.g. volcanoes, weathering, and leaching) and anthropogenic activities (e.g. mining, wood preservation, etc.) determine its current global distribution. Water sources (particularly groundwater), soil, and air are all likely to contain arsenic‐based species in regions near to the sources. From a human ecology standpoint, As enters the human body primarily through food (which contains As via bioaccumulation) and contaminated water. The World Health Organization (WHO) and leading environmental monitoring agencies have declared As contamination as a serious concern. To address concerns, As mitigation methods have been developed focusing on human beings (primarily using iron‐based supplements), and remediation of waters (primarily through As removal). Ongoing scientific activities in this area include (i) research leading to increased understanding of As geochemistry (e.g. occurrence, mobilization, geochemical cycles); (ii) revisiting water standards in a location‐specific manner; (iii) biochemistry/cellular toxicology, and its use in therapeutics; and (iv) efforts to mitigate impact of As on humans subjected to chronic exposure. This article provides a comprehensive view of state‐of‐the‐art science and technology regarding As .
Two-dimensional nanostructures with atomically precise building blocks have potential applications in catalysis and sensing. However, structural instability and surface reactivity limit their practical use. In this work, we demonstrate the formation of vertically aligned nanoplates of the [Co6S8DPPE6Cl6] cluster (Co6 in short), protected by 1,2-bis(diphenylphosphino)ethane, using ambient electrospray deposition (ESD). Charged microdroplets of Co6 formed by ESD on a water surface created such nanostructures. Preferential arrangement of clusters in the nanoplates with enhanced surface area results in sensitive and selective electrochemical response toward arsenite down to 5 parts per billion, in tap water. Density functional theory calculations reveal the preferential binding of arsenite with Co6. Our work points to a practical application of atomically precise clusters of large societal relevance.
The Gibbs free energy difference between seawater and river water can be tapped by selective ion transport across charged nanochannels, referred to as reverse electrodialysis (RED). However, existing single pore and micro/nanofluidic RED systems have shown poor prospects for scalability and practical implementation. Herein, we present a macroscopic RED system, utilizing a cation-selective membrane or an anion-selective membrane. The membranes comprise reduced graphene oxide (rGO) nanosheets decorated uniformly with TiO2 nanoparticles. The nanosheets are covalently functionalized with polystyrene (PS) and subsequently linked to sulfonate or quaternary amine functional groups to obtain cation and anion selectivity, respectively. The membranes show excellent ion transport properties along with high power densities demonstrated under artificial salinity gradients. The cation-exchange membrane (CEM) delivered a power density of 448.7 mW m–2 under a 500-fold concentration gradient, while the anion-exchange membrane (AEM) produced a substantial power output of 177.8 mW m–2 under a similar gradient. The efficiencies ranged from 10.6% to 42.3% for CEM and from 9.7% to 46.1% in the case of AEM. Testing under varying pH conditions revealed higher power output under acidic conditions and substantial power output across the entire pH range, rendering them practically viable for sustainable energy harvesting in acidic and alkaline wastewaters.
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