Cu-based MOF-derived architecture with Cu/Cu2O nanospheres anchored on porous carbon nanosheets for efficient capacitive deionization

Enhanced iodide removal from aqueous solutions using 3D-printed PLA scaffold coated with Cu/Cu2O nanoparticles

In nuclear power plant accidents, radioactive iodine (129I, 131I) can enter the environment, accumulate in the food chain, and pose significant health risks. We developed a novel scaffold using Cu/Cu2O nanoparticles immobilized on a polylactic acid 3D-printed scaffold for efficient iodide removal. The PLA scaffold was fabricated using a fused deposition modeling 3D printer, then surface-modified for enhanced hydrophilicity and functionalized with carboxyl groups via hydrolysis and acrylic acid grafting. Cu/Cu2O nanoparticles were immobilized on the modified surface. The adsorption capacity, determined using the Langmuir model, was 4.85 mg/g, and adsorption kinetics followed a pseudo-second-order model. The iodide removal mechanism was primarily driven by redox reactions between Cu(0), Cu(I) and iodide, leading to the formation of copper iodide (CuI), as confirmed by X-ray diffraction and Raman spectroscopy. Importantly, the Cu/Cu2O scaffold exhibited excellent structural stability during adsorption, with minimal copper leaching (<0.08 mg/L). Characterization of the Cu/Cu2O scaffold using scanning electron microscopy with energy-dispersive spectroscopy and X-ray photoelectron spectroscopy analysis supported these results. The scaffold demonstrated high selectivity for iodide ions even with competing anions. The scaffold maintained its effectiveness across a wide pH range, and continuous column tests separately confirmed its suitability for practical applications in environmental remediation and wastewater treatment systems. In summary, we successfully fabricated a 3D-printed Cu/Cu2O-PLA scaffold, demonstrated its efficient iodide removal performance, and elucidated the underlying redox-driven adsorption mechanism.

Coexistence of Redox-Active Metal and Ligand Sites in Copper-Based Two-Dimensional Conjugated Metal-Organic Frameworks as Active Materials for Battery-Supercapacitor Hybrid Systems

Two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) are promising materials for supercapacitor (SC) electrodes due to their high electrochemically accessible surface area coupled with superior electrical conductivity compared to traditional MOFs. In this work, porous and non-porous HHB-Cu (HHB=hexahydroxybenzene), derived through surfactant-assisted synthesis are studied as representative 2D c-MOF models with different characteristics, showing diverse reversible redox reactions with Na+ and Li+ in aqueous (10 M NaNO3) and organic (1.0 M LiPF6 in ethylene carbonate and dimethyl carbonate) electrolytes, respectively. These redox activities were here deployed to design negative electrodes for hybrid SCs (HSCs), combining the battery-like property of HHB-Cu at the negative electrode and the high capacitance and robust cyclic stability of activated carbon (AC) at the positive electrodes. In the organic electrolyte, porous HHB-Cu-based HSC achieves a maximum cell specific capacity (Cs) of 22.1 mAh g-1 at 0.1 A g-1, specific energy (Es) of 15.55 Wh kg-1 at specific power (Ps) of 70.49 W kg-1, and 77 % cyclic stability after 3000 gravimetric charge-discharge (GCD) cycles at 1 A g-1 (specific metrics calculated on the mass of both electrode materials). In the aqueous electrolyte, porous HHB-Cu-based HSC displays a Cs of 13.9 mAh g-1 at 0.1 A g-1, Es of 6.13 Wh kg-1 at 44.05 W kg-1, and 72.3 % Cs retention after 3000 GCD cycles. The non-porous sample, interesting for its superior electrical conductivity despite its limited surface area compared to its porous counterpart, shows lower Es performance but better rate capability compared to the porous one. This study indicates the potential of assembling a battery-SC hybrid system by rationally exploiting the battery-like behavior of 2D c-MOFs and the electrochemical double-layer capacitance of AC.

A mini review on metal-organic framework-based electrode materials for capacitive deionization

Capacitive deionization (CDI) is an electrochemical method of extracting ions from solution at potentials below electrolysis. It has various applications ranging from water remediation and desalination to heavy metal removal and selective resource recovery. A CDI device applies an electrical charge across two porous electrodes to attract and remove ions without producing waste products. It is generally considered environmentally friendly and promising for sustainability, yet ion removal efficiency still falls short of more established filtration methods. Commercially available activated carbon is typically used for CDI, and its ion adsorption capacity is low at approximately 20-30 mg g-1. Recently, much interest has been in the highly porous and well-structured family of materials known as metal-organic frameworks (MOFs). Most MOFs are poor conductors of electricity and cannot be directly used to make electrodes. A common workaround is to pyrolyze the MOF to convert its organic components to carbon while maintaining its underlying microstructure. However, most MOF-derived materials only retain partial microstructure after pyrolysis and cannot inherit the robust porosity of the parent MOFs. This review provides a systematic breakdown of structure-performance relationships between a MOF-derived material and its CDI performance based on recent works. This review also serves as a starting point for researchers interested in developing MOF-derived materials for CDI applications.

The electrosorption behavior of shuttle-like FeP: performance and mechanism

Owing to its high electrochemical ability, the FeP is envisioned to be the potential electrode for capacitive deionization (CDI) with enhanced performance. However, it suffers from poor cycling stability due to the active redox reaction. In this work, a facile approach has been designed to prepare the mesoporous shuttle-like FeP using MIL-88 as the template. The porous shuttle-like structure not only alleviates the volume expansion of FeP during the desalination/salination process but also promotes ion diffusion dynamics by providing convenient ion diffusion channels. As a result, the FeP electrode has demonstrated a high desalting capacity of 79.09 mg g⁻¹ at 1.2 V. Further, it proves the superior capacitance retention, which maintained 84% of the initial capacity after the cycling. Based on post-characterization, a possible electrosorption mechanism of FeP has been proposed.

In this work, mesoporous shuttle-like FeP for electrosorption is prepared. As an electrode, it achieves a high salt adsorption capacity of 79.09 mg g⁻¹ and superior capacitance retention. The conversion of Fe^II to Fe^III is responsible for the removal of salty ions.