The high performance of two-dimensional (2D) channel membranes is generally achieved by preparing ultrathin or forming short channels with less tortuous transport through self-assembly of small flakes, demonstrating potential for highly efficient water desalination and purification, gas and ion separation, and organic solvent waste treatment. Here, we report the construction of vertical channels in graphene oxide (GO) membrane based on a substrate template with asymmetric pores. The membranes achieved water permeance of 2647 L m⁻² h⁻¹ bar⁻¹ while still maintaining an ultrahigh rejection rate of 99.9% for heavy metal ions, which is superior to the state-of-the-art 2D membranes reported. Furthermore, the membranes exhibited excellent stability during long-term filtration experiments for at least 48 h, as well as resistance to ultrasonic treatment for over 100 minutes. The vertical channels possess very short pathway for almost direct water transport and a highly effective channel area, meanwhile the asymmetric porous template enhances the packing of the inserted GO nanosheets to avoid the swelling effect of membrane. Our work provides a simple way to fabricate vertical channels of 2D nanofiltration membranes with high water purification performance.

Black phosphorus (BP) and its two-dimensional derivative (2D-BP) have garnered significant attention as promising anode materials for electrochemical energy storage devices, including next-generation fast-charging batteries. However, the interactions between BP and light metal ions, as well as how these interactions influence BP’s electronic properties, remain poorly understood. Here, we employed density functional theory (DFT) to investigate the effects of monovalent (Li⁺ and Na⁺) and divalent (Mg²⁺ and Ca²⁺) ions on the valence electronic structure of 2D-BP. Molecular orbital analysis revealed that the adsorption of divalent cations can significantly reduce the band gap, suggesting an enhancement in charge transfer rates. In contrast, the adsorption of monovalent cations had minimal impact on the band gap, suggesting the preservation of 2D-BP’s intrinsic electrical properties. Energetic and charge analyses indicated that the extent of charge transfer primarily governs the ability of ions to modulate 2D-BP’s electronic structure, especially under high-pressure conditions where ions are in close proximity to the 2D-BP surface. Moreover, charge polarization calculations revealed that, compared with monovalent cations, divalent cations induced greater polarization, disrupting the symmetry of the pristine 2D-BP and further influencing its electronic characteristics. These findings provide a molecular-level understanding of how ion interactions influence 2D-BP’s electronic properties during ion-intercalation processes, where ions are in close proximity to the 2D-BP surface. Moreover, the calculated diffusion barrier results revealed the potential of 2D-BP as an effective anode material for lithium-ion, sodium-ion, and magnesium-ion batteries, though its performance may be limited for calcium-ion batteries. By extending our understanding of interactions between ions and 2D-BP, this work contributes to the design of efficient and reliable energy storage technologies, particularly for the next-generation fast-charging batteries.

The two-dimensional (2D) “sandwich” structure composed of a cation plane located between two anion planes, such as anion-rich CrI₃, VS₂, VSe₂, and MnSe₂, possesses exotic magnetic and electronic structural properties and is expected to be a typical base for next-generation microelectronic, magnetic, and spintronic devices. However, only a few 2D anion-rich “sandwich” materials have been experimentally discovered and fabricated, as they are vastly limited by their conventional stoichiometric ratios and structural stability under ambient conditions. Here, we report a 2D anion-rich NaCl₂ crystal with sandwiched structure confined within graphene oxide membranes with positive surface potential. This 2D crystal has an unconventional stoichiometry, with Na:Cl ratio of approximately 1:2, resulting in a molybdenite-2H-like structure with cations positioned in the middle and anions in the outer layer. The 2D NaCl₂ crystals exhibit room-temperature ferromagnetism with clear hysteresis loops and transition temperature above 320 K. Theoretical calculations and X-ray magnetic circular dichroism (XMCD) spectra reveal the ferromagnetism originating from the spin polarization of electrons in the Cl elements of these crystals. Our research presents a simple and general approach to fabricating advanced 2D unconventional stoichiometric materials that exhibit half-metal and ferromagnetism for applications in electronics, magnetism, and spintronics.

The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au³⁺ and other ions by rGO membranes. The maximum adsorption capacity for Au³⁺ ions was about 16 times that of Cu²⁺ ions and 10 times that of Fe³⁺ ions in a mixture solution with equal proportions of Au³⁺/Cu²⁺ and Au³⁺/Fe³⁺. In a mixed-ion solution containing Au³⁺:Cu²⁺:Na⁺:Fe³⁺:Mg²⁺ of printed circuit board (PCB), the mass of Au³⁺:Cu²⁺:Na⁺:Fe³⁺:Mg²⁺ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector.

Membrane separation technology has shown significant potential in the treatment of mixed dye wastewater. In this study, a reduced graphene oxide (AH-rGO) membrane was prepared using an amino-hydrothermal method and applied for the first time in mixed dye separation. These membranes can selectively recover high-value dyes while addressing the technical challenges of balancing permeability and selectivity in traditional membrane materials, which are often at odds with each other in the treatment of mixed dye wastewater. We simulated actual dye wastewater using four dyes: methyl orange (MO), methyl blue (MB), rhodamine B (RB), and Victoria Blue B (VBB). The four combinations of mixed dyes were MO/VBB, RB/VBB, MO/MB, and RB/MB, all of which demonstrated high water permeability and separation efficiency. Notably, the MO/VBB combination achieved a maximum water permeability rate of 118.79 L m⁻² h⁻¹ bar⁻¹ and a separation factor of 24.2. The AH-rGO membrane is currently the highest-permeability membrane available, achieving excellent separation results with typical mixed dye wastewater. Additionally, it demonstrates good stability. The experimental results indicate that the overall performance of the AH-rGO membrane is superior to that ofother graphene oxide (GO) membranes, which reveals the significant application potential of this membrane in the field of mixed dye wastewater treatment.