A Near-Isotropic Proton-Conducting Porous Graphene Oxide Membrane

In-situ strategies for melamine-functionalized graphene oxide nanosheets-based nanocomposite proton exchange membranes in wide-temperature range applications

The traditional preparation of nanocomposite proton exchange membranes (PEM) is hindered by poor organic-inorganic interface compatibility, insufficient proton-conducting sites, easy aggregation of nanoparticles, and difficulty in leveraging nanoscale advantages. In this study, a novel method involving electrochemical anodic oxidation exfoliation was employed to prepare melamine-coated graphene oxide (Me@GO), which was subsequently subjected to in-situ polymerization with poly(2,5-benzimidazole) (ABPBI) to prepare a Me@GO/ABPBI composite proton exchange membrane. Benefiting from the strong hydrogen bonding and large π stacking interactions, melamine (Me) tightly bound to graphene oxide (GO), effectively preventing the secondary aggregation of GO after exfoliation. Moreover, the abundant alkaline functional groups of melamine enhanced the enhancement of phosphoric acid (PA) retention in the Me@GO/ABPBI membranes, thereby increasing the number of proton-conducting sites. The experimental results indicated that the introduction of Me@GO enhanced membrane properties. For Me@GO at a concentration of 1 wt%, the tensile strength of the 1Me@GO/ABPBI composite membrane reached 207 MPa, nearly 2.52 times that of the pure membrane. The proton conductivity of the 1Me@GO/ABPBI composite membrane reached 0.01 S cm-1 across a wide temperature range (40-180 °C), peaking at 0.087 S cm-1 at 180 °C. Additionally, a single-cell incorporating the 1Me@GO/ABPBI composite membrane achieved a peak power density of 0.304 W cm-2 at 160 °C, nearly 1.46 times that of the pure membrane. Benefiting from the well-dispersed and PA-enriched proton channels provided by Me@GO, the Me@GO/ABPBI composite membrane exhibits excellent prospects for wide-temperature range (40-180 °C) applications.

Maternal exposure to sunlight-irradiated graphene oxide induces neurodegeneration-like symptoms in zebrafish offspring through intergenerational translocation and genomic DNA methylation alterations

The physiochemical properties of graphene oxide may be affected by sunlight irradiation. However, the underlying mechanisms that alter the properties and subsequent intergenerational effects are not sufficiently investigate. Epigenetics is an early sensitive marker for the intergenerational effects of nanomaterial exposure due to the epigenetic memory. In this study, we investigate changes in the physicochemical properties and the intergenerational effects of maternal exposure to simulated sunlight-irradiated polyethyleneimine-functionalized graphene oxide (SL-PEI-GO). Results show that the physicochemical properties of polyethyleneimine-functionalized graphene oxide (PEI-GO) can be altered significantly by the oxidation of carbon atoms with unpaired electrons present in the defects and on the edges of PEI-GO by sunlight. First, the positive charges, sharp edges, defects and disordered structures of SL-PEI-GO make it translocate from maternal zebrafish to offspring, thus catalyzing the production of reactive oxygen species and damaging mitochondria directly. In addition, changes in DNA methylation reduce the expression of protocadherin1a, protocadherin19 and cadherin4, thus destroying cell membrane integrity, cell adhesion and Ca2+ binding. The alteration of DNA methylation induced by maternal exposure activates the Ca2+-CaMKK-brsk2a pathway, which catalyzes the phosphorylation of Tau and eventually results in the appearance of neurodegeneration-like symptoms, including the loss of neurons and neurobehavioral disorders. This study demonstrates that maternal exposure to SL-PEI-GO induces clear neurodegeneration-like symptoms in offspring through both the intergenerational translocation of nanomaterials and differential DNA methylation. These findings may provide new insights into the health risks of nanomaterials altered by nature conditions.

Metal Confined in 2D Membranes for Molecular Recognition and Sieving towards Ethylene/Ethane Separation

Membranes with nanochannels have exhibited great potential in molecular separations, while it remains a great challenge to separate molecules with very close physical properties and kinetic diameters (e.g., ethylene/ethane) owing to the lack of size-sieving property and specific affinity. Herein, a metal confined 2D sub-nanometer channel is reported to successfully discriminate ethylene over ethane via molecular recognition and sieving. Transition metal cations are paired with polyelectrolyte anions to achieve high dissociation activity, forming reversible complexation with ethylene. Aberration-corrected transmission electron microscopy observes that the metals with size of ≈2 nm are uniformly confined in graphene oxide (GO) interlayer channels with average height of ≈0.44 nm, thereby cooperating the size-sieving effect with a molecular recognition ability toward ethylene and stimulating its selective transport over ethane. The resulting ultrathin (≈60 nm) membrane exhibits superior ethylene/ethane separation performance far beyond the polymeric upper-bound. Density functional theory (DFT) and molecular dynamic simulations reveal that the metal@2D interlayer channel provides a molecular recognition pathway for selective gas transport. The proposed metal confined in 2D channel with molecular recognition and sieving properties would have broad application in other related fields such as single-atom catalysis, sensor and energy conversion.

Conduction Mechanism in Graphene Oxide Membranes with Varied Water Content: From Proton Hopping Dominant to Ion Diffusion Dominant

Proton conductors, particularly hydrated solid membranes, have various applications in sensors, fuel cells, and cellular biological systems. Unraveling the intrinsic proton transfer mechanism is critical for establishing the foundation of proton conduction. Two scenarios on electrical conduction, the Grotthuss and the vehicle mechanisms, have been reported by experiments and simulations. But separating and quantifying the contributions of these two components from experiments is difficult. Here, we present the conductive behavior of a two-dimensional layered proton conductor, graphene oxide membrane (GOM), and find that proton hopping is dominant at low water content, while ion diffusion prevails with increasing water content. This change in the conduction mechanism is attributable to the layers of water molecules in GOM nanosheets. The overall conductivity is greatly improved by forming one layer of water molecules. It reaches the maximum with two layers of water molecules, resulting from creating a complete hydrogen-bond network within GOM. When more than two layers of water molecules enter the GOM nanosheets, inducing the breakage of the ordered lamellar structure, protons spread in both in-plane and out-of-plane directions inside the GOM. Our results validate the existence of two conduction mechanisms and show their distinct contributions to the overall conductivity. Furthermore, these findings provide an optimization strategy for the design of realizing the fast proton transfer in materials with water participation.