Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth

Overview of Functionalized Porous Materials for Rare-Earth Element Separation and Recovery

The exceptional photoelectromagnetic characteristics of rare-earth elements contribute significantly to their indispensable position in the high-tech industry. The exponential expansion of the demand for high-purity rare earth and related compounds can be attributed to the swift advancement of contemporary technology. Nevertheless, rare-earth elements are finite and limited resources, and their excessive mining unavoidably results in resource depletion and environmental degradation. Hence, it is crucial to establish a highly effective approach for the extraction and reclamation of rare-earth elements. Adsorption is regarded as a promising technique for the recovery of rare-earth elements owing to its simplicity, environmentally friendly nature, and cost-effectiveness. The efficacy of adsorption is contingent upon the performance characteristics of the adsorbent material. Presently, there is a prevalent utilization of porous adsorbent materials with substantial specific surface areas and plentiful surface functional groups in the realm of selectively separating and recovering rare-earth elements. This paper presents a thorough examination of porous inorganic carbon materials, porous inorganic silicon materials, porous organic polymers, and metal-organic framework materials. The adsorption performance and processes for rare-earth elements are the focal points of discussion about these materials. Furthermore, this work investigates the potential applications of porous materials in the domain of the adsorption of rare-earth elements.

Constructing Two-Dimensional (2D) Heterostructure Channels with Engineered Biomembrane and Graphene for Precise Scandium Sieving

The special properties of rare earth elements (REE) have effectively broadened their application fields. How to accurately recognize and efficiently separate target rare earth ions with similar radii and chemical properties remains a formidable challenge. Here, precise two-dimensional (2D) heterogeneous channels are constructed using engineered E. coli membranes between graphene oxide (GO) layers. The difference in binding ability and corresponding conformational change between Lanmodulin (LanM) and rare earth ions in the heterogeneous channel allows for precisely recognizing and sieving of scandium ions (Sc3+). The engineered E. coli membranes not only can protect the integrity of structure and functionality of LanM, the rich lipids and sugars, but also help the Escherichia coli (E. coli) membranes closely tile on the GO nanosheets through interaction, preventing swelling and controlling interlayer spacing accurately down to the sub-nanometer. Apparently, the 2D heterogeneous channels showcase excellent selectivity for trivalent ions (SFFe /Sc≈3), especially for Sc3+ ions in REE with high selectivity (SFCe/Sc≈167, SFLa/Sc≈103). The long-term stability and tensile strain tests verify the membrane's outstanding stability. Thus, this simple, efficient, and cost-effective work provides a suggestion for constructing 2D interlayer heterogeneous channels for precise sieving, and this valuable strategy is proposed for the efficient extraction of Sc.

Macroscopic Heterostructure Membrane of Graphene Oxide/Porous Graphene/Graphene Oxide for Selective Separation of Deuterium Water from Natural Water

Deuterium water (D₂ O) is a strategic material that is widely used in and scientific research and has applications in fields such as nuclear energy generation. However, its content in natural water is extremely low. Therefore, the development of a room-temperature technology for achieving simple, efficient, and low-cost separation of D₂ O from natural water is challenging. In this study, porous graphene (PG) nanosheets with "crater-like" pores are sandwiched between two layers of graphene oxide (GO) membranes to prepare a GO/PG/GO membrane with a macroscopic heterostructure, which can be used to separate D₂ O and H₂ O by pressure-driven filtration. At 25 °C, the rejection rate of D₂ O is ≈97%, the selectivity of H₂ O/D₂ O is ≈35.2, and the excellent performance can be attributed to the difference of transmembrane resistance and flow state of H₂ O and D₂ O in the confinement state. In addition, the D₂ O concentration in natural water is successfully enriched from 0.013% to 0.059% using only one stage, and the membrane exhibits excellent structural and cycling stability. Therefore, this method does not require ultralow temperatures, high energy supplies, complex separation equipment, or the introduction of toxic chemicals. Thus, it can be directly applied to the large-scale industrial production and removal of D₂ O.

Highly selective adsorption of rare earth elements by honeycomb-shaped covalent organic frameworks synthesized in deep eutectic solvents

One of the key factors to obtain a highly pure individual rare earth element (REE) is to prepare adsorbents with high selectivity and adsorption capacity. Covalent organic frameworks (COFs), which encompass a variety of properties, including regular/tunable pore size, high specific surface area and easy functionalization, could be effective as adsorbents for separating rare earth elements (REEs). In this paper, TpPa COFs were successfully synthesized using an eco-friendly deep eutectic solvent (DES) as the reaction medium instead of toxic organic solvents at room temperature. TpPa COFs have a good separation effect on the nine REEs investigated in this work. Among them, the separation factors (β) of Eu/Yb, Eu/Tm and Eu/La are 15.34, 14.70 and 10.78, respectively, indicating that the TpPa COFs have good separation performance. Further discoveries showed that the adsorption and separation mechanism of the TpPa COFs for REEs in this experiment may be due to the coordination of REE ions with O to form a stable structure. This study blazed a trial for a green and facile synthesis strategy of TpPa COFs and expanded its implementation as a solid adsorbent in the separation of REEs.

Graphene Quantum Dots prepared by Electron Beam Irradiation for Safe Fluorescence Imaging of Tumor

Graphene quantum dots (GQD) have attracted much attention due to their unique properties in biomedical application, such as biosensing, imaging, and drug delivering. However, scale preparing red luminescing GQD is still challenging now. Herein, with the help of electron beam irradiation, a simple, rapid, and efficient up-to-down strategy was developed to synthesize GQD with size of 2.75 nm emitting 610 nm luminescence. GQD were further functionalized with polyethylene glycol (PEG) and exhibited good solubility and biocompatibility. The potential in vivo toxicity of PEGylated GQD could completely be eliminated by the clinic cholesterol-lowering drug simvastatin. PEGylated GQD could selectively accumulate in tumor after intravenous injection as a security, reliable and sensitive tumor fluorescence imaging agent. Therefore, this work presented a new method preparing red luminescing GQD for biomedical application.

Metal-Organic Framework-Intercalated Graphene Oxide Membranes for Selective Separation of Uranium

Design and construction of a membrane that can achieve selective separation of uranium from spent fuel or seawater is a big challenge in the field of separation science. In this work, 1,3,5-benzenetricarboxylic acid (BTC) and three different nitrates (Zn/Ni/Cu) were used to prepare metal-organic frameworks (BTC-MOFs) with different pore sizes, and then, BTC-MOFs were intercalated into the interlayers of graphene oxide (GO) for preparing the composite membranes which presented selective separation of uranium with strong acid resistance. Composite membranes prepared by Zn/Ni/Cu-BTC-MOFs and GO can achieve the separation between ions of different valence states, and their permeability and selectivity depend on the membrane thickness, the acidity of driving solution, and the pore sizes of MOFs. Importantly, Cu-BTC-MOF-intercalated GO membranes can not only achieve the selective separation of Th⁴⁺ and UO₂²⁺ with a selectivity of ≈6 but also induce the ultra-high selectively separation of UO₂²⁺ and Ce³⁺ because the rejection rate of Ce³⁺ is about 100%. Moreover, the Zn-BTC-MOF-intercalated GO membrane shows an excellent selectivity of Th⁴⁺ and UO₂²⁺ with a selectivity of ≈25, and it may also achieve selective separation of uranium from seawater.

Template-synthesis of a poly(ionic liquid)-derived Fe1-x S/nitrogen-doped porous carbon membrane and its electrode application in lithium-sulfur batteries

This study deals with the facile synthesis of Fe1-x S nanoparticle-containing nitrogen-doped porous carbon membranes (denoted as Fe1-x S/N-PCMs) via vacuum carbonization of hybrid porous poly(ionic liquid) (PIL) membranes, and their successful use as a sulfur host material to mitigate the shuttle effect in lithium-sulfur (Li-S) batteries. The hybrid porous PIL membranes as the sacrificial template were prepared via ionic crosslinking of a cationic PIL with base-neutralized 1,1'-ferrocenedicarboxylic acid, so that the iron source was molecularly incorporated into the template. The carbonization process was investigated in detail at different temperatures, and the chemical and porous structures of the carbon products were comprehensively analyzed. The Fe1-x S/N-PCMs prepared at 900 °C have a multimodal pore size distribution with a satisfactorily high surface area and well-dispersed iron sulfide nanoparticles to physically and chemically confine the LiPSs. The sulfur/Fe1-x S/N-PCM composites were then tested as electrodes in Li-S batteries, showing much improved capacity, rate performance and cycle stability, in comparison to iron sulfide-free, nitrogen-doped porous carbon membranes.

A Nanoporous Graphene/Nitrocellulose Membrane Beneficial to Wound Healing

Adequate treatment of skin wounds is vital to health. Nitrocellulose bandage as a traditional wound dressing is widely used for wound healing, but its limited air permeability and poor sterilization need to be improved for enhancing the actual efficacy. Here, nanoporous graphene (NPG) is used to mix into nitrocellulose for preparing a composite membrane, which exhibits a moderate transmission rate of water vapor, excellent toughness performance, and good biocompatibility. Moreover, the membrane shows an excellent broad-spectrum antibacterial property (>98%, Escherichia coli; >90%, Staphylococcus aureus) and can reduce the risk of microbial infection for the body after trauma. Importantly, after using the nanoporous graphene/nitrocellulose membrane, the wound closure percentage reaches 93.03 ± 1.08% at 7 days after the trauma, and the degree of skin tissue recovery is also improved significantly. Therefore, this study develops a highly efficient wound healing dressing, which is expected to be used directly in clinics.

Graphene Oxide-Based Nanofiltration for Hg Removal from Wastewater: A Mini Review

Mercury (Hg) is one of heavy metals with the highest toxicity and negative impact on the biological functions of living organisms. Therefore, many studies are devoted to solving the problem of Hg separation from wastewater. Membrane-based separation techniques have become more preferable in wastewater treatment area due to their ease of operation, mild conditions and also more resistant to toxic pollutants. This technique is also flexible and has a wide range of possibilities to be integrated with other techniques. Graphene oxide (GO) and derivatives are materials which have a nanostructure can be used as a thin and flexible membrane sheet with high chemical stability and high mechanical strength. In addition, GO-based membrane was used as a barrier for Hg vapor due to its nano-channels and nanopores. The nano-channels of GO membranes were also used to provide ion mobility and molecule filtration properties. Nowadays, this technology especially nanofiltration for Hg removal is massively explored. The aim of the review paper is to investigate Hg removal using functionalized graphene oxide nanofiltration. The main focus is the effectiveness of the Hg separation process.