High-performance capacitive deionization electrodes through regulated electrodeposition of manganese oxide and nickel-manganese oxide/hydroxide onto activated carbon

Improved MnO2 based electrode performance arising from step by step heat treatment during electrodeposition of MnO2 for determination of paracetamol, 4-aminophenol, and 4-nitrophenol

The design of electrochemical sensors is crucial considering important factors such as efficiency, low cost, biocompatibility, and availability. Manganese oxides are readily available, low-cost, and biocompatible materials, but their low conductivity limits their efficiency as sensors. Today, morphology engineering of manganese oxide has been one of the most common research topics, because manganese oxides' electrochemical properties are highly dependent on their morphologies. In this study, a method for reducing the charge transfer resistance (Rct) of MnO2-based electrodes was established by the cyclic voltammetry technique accompanied by step-by-step heat treatment to electrodeposition MnO2 nanofilm, which remarkably improved the Rct. Next, the sensing performance of MnO2/FTO for two separate measurements was examined, one for the simultaneous measurement of paracetamol (PAR) and 4-aminophenol (4-APh), and the other for the measurement of 4-nitrophenol (4-NP). Under the optimum conditions, the linear ranges of 4-APh, PAR, and 4-NP, were 0.8 to 22.0 µM, 2.0 to 55.0 µM, and 0.1-250 µM, with limits of detection (LOD) of 0.19 µM, 0.60 µM, and 0.01 µM, respectively. It also was unaffected by a 200-fold excess of interferences. In addition, the designed sensor was successfully applied to the analysis of real samples.

Hydrolyzed Hydrated Titanium Oxide on Laser-Induced Graphene as CDI Electrodes for U(VI) Adsorption

Recently, laser-induced graphene (LIG), which has been successfully applied in CDI technology (directly without a complex preparation process), has gained considerable attention. However, the raw LIG electrode with a limited number of active sites exhibits low adsorption efficiency. Therefore, the search for a suitable and effective method to modify LIG to improve its electroadsorption performance is significant. Herein, a very simple titration hydrolysis method is adopted to modify LIG, resulting in a layer of hydrated titanium oxide (HTO) being synthesized on the surface of LIG. The LIG/HTO composites possess a good adsorption property since covering the surface of LIG with a layer of HTO can greatly improve the adsorption capacity of LIG. Moreover, with the addition of HTO, not only the proton transfer ability of LIG has been enhanced but also considerable specific capacitance has been enlarged. As a result, LIG/HTO composite as CDI electrode displays a maximum theoretical adsorption capacity of 1780.89 mg/g at 1.2 V, and the capacitance of LIG/HTO composite material is 4.74 times higher than LIG. During the electroadsorption process, Ti4+ is reduced to Ti3+ under external voltage, and O2- is produced through oxidation. Meanwhile, part of the U (VI) is hydrolyzed into UO3·2H2O under the action of -OH, and some combine with O2- to produce UO4·4H2O.

Unraveling the Ion Uptake Capacitive Deionization of Sea- and Highly Saline-Water by Sulfur and Nitrogen Co-Doped Porous Carbon Modified with Molybdenum Sulfide

In parallel to the depletion of potable water reservoirs, novel technologies have been developed for seawater softening, as it is the most abundant source for generating deionized water. Although salt removal at subosmotic pressures and ambient temperatures by applying low-operating potentials with high energy efficiency made capacitive deionization (CDI) an advantageous water-softening process, its practical application is limited by insufficient ion removal capacity and low concentration influent. The performance of a CDI system is in progress with engineering the electrode active materials, also facilitating the advance design in highly saline- and seawater study. Herein, an innovative strategy was developed to provide high-performance CDI systems based on efficient and electrochemical ion-uptake active materials with a simple initial preparation. Nitrogen-doped porous carbons (N-pCs) received benefits from a high specific surface area and good surface wettability. The N-pCs were modified with molybdenum oxide/sulfide intercalative array and developed as CDI electrode active materials for desalination of both low/medium saline- and seawater. The MoS2/S,N-pC electrode materials exhibited perfect optimized salt adsorption capacity (SACs) of 47.9 mg g-1 when compared to N-pC (37.9 mg g-1) and MoO3/N-pC (39.6 mg g-1) counterparts at 1.4 V in a 750 ppm NaCl solution. In addition, the assembled CDI cells exhibited reasonable cycle stability and retained 96.7% of their initial SAC in continuous CDI cycles for 128,000 s. The fabricated CDI cell rendered an excellent salt removal efficiency (SRE, %) of 13.34% from the real seawater sample at 1.2 V. In detail, the SRE % of the NaCl, KCl, MgCl2, and CaCl2 soluble salts with respect to seawater sample exhibited a remarkable SRE % of 30.8%, 36%, 32.6%, and 19.3%, respectively. These SRE % values (>13.34%) provide convincing evidence on the reasonable ion uptake capability of the fabricated CDI cells for removing Na+, K+, Mg2+, and Ca2+ ions compared to other soluble component. The advanced cell design parallel to the promising outcomes provided herein makes these CDI systems immensely propitious for efficient water softening.