Development of nitric acid-modified activated carbon electrode for removal of Co2+/Mn2+/Ni2+ by electrosorption

Enhanced Pore Structure of Powdered Activated Carbon Can Boost Its Performance in Catalyzing Mn(II) Oxidation by Chlorine

Mn(II) oxidation by chlorine under neutral pH conditions is inherently slow. Previous studies have demonstrated that a few milligrams per liter of powdered activated carbon (PAC) can dramatically accelerate this process, but catalytic efficiency varies widely across different PAC types. In this study, various chemical and physical modifications were applied to coal- and straw-based PAC to enhance their catalytic efficiency and identify the key characteristics decisively influencing catalysis. The results showed that chemical treatments with HNO3 or NaOH had no notable impact on the PAC-catalyzed Mn(II) oxidation. In contrast, physical modifications, steam-reactivation, and ultrasonication substantially enhanced PAC's catalytic performance, increasing Mn(II) oxidation rates by 50-300%. Characterization revealed that alterations in surface functional groups, induced by chemical treatments, had no noticeable impact on the Mn(II) oxidation. Instead, enhancements in pore structure achieved through physical modifications remarkably accelerated the Mn(II) oxidation process. The specific surface area of PAC exhibited a strong positive correlation with both the Mn(II) oxidation and chlorine decay rates. Mn(II) oxidation by chlorine retained by PAC (not chlorine in water) demonstrated the occurrence of Mn(II) and chlorine reactions in PAC pores. The increased local concentrations of the reactants and confined catalysis in nanoscale pores were proposed to interpret the rapid Mn(II) oxidation.

Recovery of Metal Ions (Cd2+, Co2+, and Ni2+) from Nitrate and Sulfate on Laser-Induced Graphene Film Using Applied Voltage and Its Application

The urgent removal of Cd, Co, and Ni from nitrate and sulfate is essential to mitigate the potential risk of chemical pollution from large volumes of industrial wastewater. In this study, these metal ions were rapidly recovered through applying voltage on nitrate and sulfate, utilizing laser-induced graphene/polyimide (LIG/PI) film as the electrode. Following the application of external voltage, both the pH value and conductivity of the solution undergo changes. Compared to Co2+ and Ni2+, Cd2+ exhibits a lower standard electrode potential and stronger reducibility. Consequently, in both nitrate and sulfate solutions, the reaction sequence follows the order of Cd2+ > Co2+ > Ni2+, with the corresponding electrode adsorption quantities in the order of Cd2+ > Co2+ ~ Ni2+. Additionally, using the recovered Co(OH)2 as the raw material, a LiCoO2 composite was prepared. The assembled battery with this composite exhibited a specific capacity of 122.8 mAh g-1, meeting practical application requirements. This research has significance for fostering green development.

Adsorption and desorption behavior of Zn2+ in a flow-through electrosorption reactor

As heavy metal industrial wastewater increases in volume and complexity, we need more efficient, cheaper, and renewable technologies to curb its environmental impact. Compared to advection electrosorption, through-flow electrosorption is a hotspot technique that makes more efficient use of the adsorption capacity of activated carbon fiber mats. A cascade flow-through electrosorption assembly based on activated carbon fiber was used to obtain the best adsorption of Zn2+ in water at a voltage of 2 V, pH value of 8, plate spacing of 3 mm, and temperature of 15°C. The process is more closely fitted to the secondary adsorption kinetic equation and the Langmuir equation. The adsorption capacity of the module decreases at a progressively slower rate with the number of cycles and will eventually retain 75% of its peak value with significant regenerability. The study of this module can provide technical support for treating heavy metal wastewater.

Preparation of heterogeneous cation exchange membrane and its contributions in enhancing the removal of Ni2+ by capacitive deionization system

Capacitive deionization (CDI), an emerging method to eliminate ions from water at a low cost, has garnered significant interest in recent years. This study evaluates the implication of cation exchange resin loading on the membrane via the nonsolvent-induced phase inversion method. After determining the quantity of resins efficiently loaded on the membrane, it was subsequently utilized as a cation exchange membrane in the membrane capacitive deionization (MCDI) unit to examine the performance removal of Ni2+. The results show that the amount of resins influenced the membrane structure and significantly improved the efficiency of Ni2+ removal. The sulfonic acid group show a strong intensity directly proportional to the quantity of resins based on the FTIR measurement. In conjunction with the enhanced resin amount, ion exchange capacity and water content were increased. Simultaneously, there was an observed elevation in the water contact angle and the roughness of the membrane surface with increased resin amount. In the MCDI unit, membrane M20 (20% by weight resin) was employed to elucidate its roles in the CDI unit, encompassing an examination of various concentrations and flow rates, with Ni2+ utilized as a test contaminant. The results demonstrated that using membrane M20 in the MCDI (MCDI-M20) unit consistently exhibited higher adsorption levels than the CDI unit, reaching 19.80 mg g-1 ACC in the MCDI-M20 unit, while CDI unit achieved 10.27 mg g-1 ACC at 200 mg L-1 Ni2+ concentration and a flow rate of 10 mL min-1 at 1.2 V. Additionally, Ni2+ concentrations and flow rates in CDI system had an evident impact on the duration of adsorption due to the mechanisms of ions transport on the membrane. This study suggests that employing the prepared membrane in the MCDI unit enhanced the removal of Ni2+ from the solution, contributing to sustainable development goals.

Recent progress of particle electrode materials in three-dimensional electrode reactor: synthesis strategy and electrocatalytic applications

With the complete promotion of a green, low-carbon, safe, and efficient economic system as well as energy system, the promotion of clean governance technology in the field of environmental governance becomes increasingly vital. Because of its low energy consumption, great efficiency, and lack of secondary pollutants, three-dimensional (3D) electrode technology is acknowledged as an environmentally beneficial and sustainable way to managing clean surroundings. The particle electrode is an essential feature of the 3D electrode reactor. This study provides an in-depth examination of the most current advancements in 3D electrode technology. The significance of 3D electrode technology is emphasized, with an emphasis on its use in a variety of sectors. Furthermore, the particle electrode synthesis approach and mechanism are summarized, providing vital insights into the actual implementation of this technology. Furthermore, by a metrological examination of the research literature in this sector, the paper expounds on the potential and obstacles in the development and popularization of future technology.

Insight into the Mechanism of Cobalt-Nickel Separation Using DFT Calculations on Ethylenediamine-Modified Silica Gel

The separation of Co(II) and Ni(II) from leaching solution is gaining interest because Co(II) and Ni(II) are increasingly used in emerging strategic areas, such as power batteries. Herein, the surface of silica gel is functionalized with 1,2-ethylenediamine and used for the separation of Co(II) and Ni(II). The Co(II) removal efficiency of the modified silica is 80.2%, with a 4-fold improvement in the separation factor. The geometry, frequency, and electrostatic potential of the ethylenediamine modified silica gel (en/SG) are calculated. The corresponding properties of M²⁺ (M-Co, Ni) adsorbed on en/SG in an aqueous solution are simulated and analyzed. The results show that ethylenediamine tends to form [Men(H₂O)₄]²⁺ after binding to M²⁺, and the binding ability of Co(II) to ethylenediamine is stronger. Besides, the thermodynamic calculations show that en/SG has a more negative Gibbs free energy when absorbing Co(II) in aqueous solution, so en/SG is more inclined to bind with Co(II) preferentially. It is the difference in complexation ability between Ni, Co, and ethylenediamine that enlarges the difference in the original physical adsorption, thus strengthening the separation performance. This work will provide guidance for a rational design of high-performance nickel-cobalt adsorption materials.