Ionic Control of Functional Zeolitic Imidazolate Framework-Based Membrane for Tailoring Selectivity toward Target Ions

Near-complete recovery of phosphorus from fresh human urine: Combining magnesium-air fuel cells with modified granular attapulgite

In light of the urge demand for sustainable development and environmental protection, the recovery of phosphorus from source-separated urine holds great significance. This study proposed a novel approach combining magnesium-air fuel cells (MAFC) with modified granular attapulgite (GAT) to recover phosphorus from urine, producing a bulk blending fertilizer and soil amendment. The phosphorus adsorption capacity of GAT was enhanced by more than threefold following modification. The combined process attained a phosphorus recovery efficiency of 99.97 %, with the effluent phosphorus concentration decreased to 0.18 mg L-1, which complies with the discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002). In practical implementation, the process effectively treated real urine, yielding artificial phosphate ores (APOs) with a struvite content exceeding 88 % and a phosphate purity over 98 %. The pilot-scale assessment indicated a net benefit of 11.29 $·m-3 of urine, demonstrating significant economic feasibility. This work presents an innovative strategy for the efficient recovery of phosphorus from complex wastewater, showcasing its promising potential for practical applications.

External voltage regulates hydrogen and vivianite recovery from fermentation liquid in microbial electrolysis cell equipped with iron anode: Performance and mechanism

Employing an iron anode in microbial electrolysis cell (MEC) can promote hydrogen yield and vivianite recovery from waste biomass by accelerating electron transport, but the performance is highly dependent on the functional microbial community present and the ferrous ion content. An external voltage had a significant effect on enriching functional microbes and controlling the release of ferrous ions. In this study, the effects of different voltages, i.e., 0.4 V, 0.6 V, 0.8 V and 1.0 V, on hydrogen production and vivianite recovery were explored. The results indicated that an applied voltage of 0.8 V resulted in the maximum hydrogen productivity of 11.17 mmol/g COD, representing an increase of 18∼91 % compared with the other voltage conditions. The removal efficiency of phosphorus reached 100 % at 3 d in the 0.8 V group, with vivianite as the main product at a purity of 92.7 %. An external voltage of 0.8 V notably enhanced the electrochemical performance of the MEC. The relative abundances of bio-cathodic microbes, i.e., electrochemically active bacteria, anaerobic fermentation bacteria, dissimilatory iron-reducing bacteria and homoacetogens, greatly changed with different voltages, reaching 9.6 %, 3.2 %, 3.1 % and 23.7 %, respectively, in the 0.8 V group. The expression of key functional genes related hydrogen production, i.e., the ferredoxin-dependent hydrogenase pathway and pyruvate ferredoxin oxidoreductase pathway, was significantly upregulated, whereas that related to homo-acetogenesis was downregulated under 0.8 V. This work reveals the performance and mechanism of synergistic hydrogen production and phosphorus recovery under an applied voltage, and provides new insights and feasible measures for improving hydrogen production and phosphorus recovery in MECs.

Fundamental Perspectives on the Electrochemical Water Applications of Metal-Organic Frameworks

HIGHLIGHTS

The recent development and implementation of metal-organic frameworks (MOFs) and MOF-based materials in electrochemical water applications are reviewed. The critical factors that affect the performances of MOFs in the electrochemical reactions, sensing, and separations are highlighted. Advanced tools, such as pair distribution function analysis, are playing critical roles in unraveling the functioning mechanisms, including local structures and nanoconfined interactions. Metal-organic frameworks (MOFs), a family of highly porous materials possessing huge surface areas and feasible chemical tunability, are emerging as critical functional materials to solve the growing challenges associated with energy-water systems, such as water scarcity issues. In this contribution, the roles of MOFs are highlighted in electrochemical-based water applications (i.e., reactions, sensing, and separations), where MOF-based functional materials exhibit outstanding performances in detecting/removing pollutants, recovering resources, and harvesting energies from different water sources. Compared with the pristine MOFs, the efficiency and/or selectivity can be further enhanced via rational structural modulation of MOFs (e.g., partial metal substitution) or integration of MOFs with other functional materials (e.g., metal clusters and reduced graphene oxide). Several key factors/properties that affect the performances of MOF-based materials are also reviewed, including electronic structures, nanoconfined effects, stability, conductivity, and atomic structures. The advancement in the fundamental understanding of these key factors is expected to shed light on the functioning mechanisms of MOFs (e.g., charge transfer pathways and guest-host interactions), which will subsequently accelerate the integration of precisely designed MOFs into electrochemical architectures to achieve highly effective water remediation with optimized selectivity and long-term stability.

Poly(alkyl-biphenyl pyridinium)-Based Anion Exchange Membranes with Alkyl Side Chains Enable High Anion Permselectivity and Monovalent Ion Flux

Poly(alkyl-biphenyl pyridinium)-based anion exchange membranes with alkyl side chains were synthesized for permselective anion separation. By altering the length of the grafted side chain, the hydrophilicity and other attributes of the membranes could be controlled. The QDPAB-C5 membrane with the best comprehensive performance exhibited a Cl^- ion flux of 3.72 mol m^-2 h^-1 and a Cl^-/SO₄^2- permselectivity of 15, which are significantly better than the commercial Neosepta ACS membrane. The QDPAB-C5 membranes with distinct microscopic phase separation structures formed interconnected hydrophilic/hydrophobic ion channels and exhibited excellent ion flux and permselectivity for other anionic systems (NO₃^-/SO₄^2-, Br^-/SO₄^2-, F^-/SO₄^2-, NO₃^-/Cl^-, Br^-/Cl^-, and F^-/Cl^-) as well. Furthermore, the influence of alkyl side chain length on the membranes' ion flux and permselectivity in electrodialysis was investigated, which may be attributed to the alterations in ion channels and hydrophobic regions of the membranes. This work provides an effective strategy for the development of monovalent anion permselective membranes.

Advanced Covalent Organic Framework-Based Membranes for Recovery of Ionic Resources

Membrane technology has shown a viable potential in conversion of liquid-waste or high-salt streams to fresh waters and resources. However, the non-adjustability pore size of traditional membranes limits the application of ion capture due to their low selectivity for target ions. Recently, covalent organic frameworks (COFs) have become a promising candidate for construction of advanced ion separation membranes for ion resource recovery due to their low density, large surface area, tunable channel structure, and tailored functionality. This tutorial review aims to analyze and summarize the progress in understanding ion capture mechanisms, preparation processes, and applications of COF-based membranes. First, the design principles for target ion selectivity are illustrated in terms of theoretical simulation of ions transport in COFs, and key properties for ion selectivity of COFs and COF-based membranes. Next, the fabrication methods of diverse COF-based membranes are classified into pure COF membranes, COF continuous membranes, and COF mixed matrix membranes. Finally, current applications of COF-based membranes are highlighted: desalination, extraction, removal of toxic metal ions, radionuclides and lithium, and acid recovery. This review presents promising approaches for design, preparation, and application of COF-based membranes in ion selectivity for recovery of ionic resources.