Layer-Controlled Synthesis of a Silanol-Graphene Oxide Nanosheet Composite Forward Osmosis Membrane by Surface Self-Assembly

Layer-by-Layer Assembled Graphene Oxide on Carbon Fiber toward Phosphate Bonded Coatings with Excellent Interfacial Bond and Tribological Performance

To enhance the interfacial property, carbon fiber (CF) was modified with graphene oxide (GO) using a layer-by-layer self-assembly method and subsequently incorporated into phosphate bonded coatings as a reinforcement. CF modified with GO (CF-GO) was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometer, Raman spectroscopy, and thermogravimetric analysis. Additionally, the tribological behavior of phosphate bonded coatings with CF-GO was investigated. The results show that GO is grafted onto the CF surface through electrostatic interactions. Besides, the CF surface becomes rougher due to the modification of GO, leading to a stronger interfacial bond between CF and the coating. Notably, as the content of CF-GO increases, both the friction coefficient and the wear rate of the coating decrease. CF-GO can form a lubricant film on the worn surface, which leads to a decrease in the friction coefficient and wear rate. Moreover, in CF-GO, CF assumes the role of a tree trunk, while GO functions as branches, collaboratively bridging cracks, as well as altering and impeding crack propagation pathways, which can consume the fracture energy and improve the cohesive strength of the coating, further contributing to a lower wear rate. Specifically, the coating with 15 wt % CF-GO exhibits a 34% reduction in the friction coefficient and a 58% decrease in the wear rate compared to those of the coating without CF-GO. These findings highlight the significant potential of CF-GO in enhancing the tribological properties of phosphate bonded coatings, making them more durable for antiwear applications.

Enhanced Separation Performance of Radioactive Cesium and Cobalt in Graphene Oxide Membrane via Cationic Control

The great applications of nuclear power for the most promising clean energy sources have been challenged by a large amount of radioactive wastewater generated, specifically the Cs⁺/Co²⁺ separation for nuclear waste storage, retreatment or recycling of radioactive wastewater, because of their wide difference in half-life and high heat release. In this work, graphene oxide membranes (GOMs) with interlayer spacing controlled by cations were used to separate mixed Cs⁺/Co²⁺ ions. The separation factors of Cs⁺/Co²⁺ for K⁺-controlled graphene oxide membranes (K-GOMs) was 2∼3 times higher than that of GOMs without treatment. In addition, the separation factors of Cs⁺/Co²⁺ for K-GOMs can be further enhanced with the increase of membranes thickness and change the initial ratios of the two ions. Typically, the separation factors of K-GOMs with a thickness of ∼300 nm reached up to 73.7 ± 3.9. Moreover, the K-GOM showed outstanding stability of the separation performance under long-term operation within 7 days. First-principles calculation revealed that the enhanced ionic selectivity of controlled GOM is induced by the difference of adsorption energies between the hydrated cations and aromatic rings, resulting in a significant increase in the mobility differences between Cs⁺ and Co²⁺ through a fixed narrow interlayer spacing. This study demonstrated excellent separation performances of GO-based membranes based on their size-exclusion effect rather than electrostatic repulsion effect, and we believe this work can enable potential efficient treatment technologies for radioactive wastewater needed urgently.

Construction of a Self-Assembled Polyelectrolyte/Graphene Oxide Multilayer Film and Its Interaction with Metal Ions

In this study, a composite multilayer film onto gold was constructed from two charged building blocks, i.e., negatively charged graphene oxide (GO) and a branched polycation (polyethylenimine, PEI) via layer-by-layer (LbL) self-assembly technology, and this process was monitored in situ with quartz crystal microbalance (QCM) under different experimental conditions. This included the differences in frequency (Δf) as well as the changes in dissipation to yield information on the absorbed mass and viscoelastic properties of the formed PEI/GO multilayer films. The experimental conditions were optimized to obtain a high amount of the adsorbed mass of the self-assembled multilayer film. The surface morphology of the PEI/GO multilayer film onto gold was studied with atomic force microscopy (AFM). It was found that the positively charged PEI chains were combined with the oppositely charged GO to form an assembled film on the QCM sensor surface, in a wrapped and curled fashion. Raman and UV-vis spectra also showed that the intensities of the GO-characteristic signals are almost linearly related to the layer number. To explore the films for their use in divalent ion detection, the frequency response of the PEI/GO multilayer-modified QCM sensor to the exposure of aqueous solutions solution of Cu²⁺, Ca²⁺, Zn²⁺, and Sn²⁺ was further studied using QCM. Based on the Sauerbrey equation and the weight of different ions, the number of metal ions adsorbed per unit area on the surface of QCM sensors was calculated. For metal ion concentrations of 40 ppm, the adsorption capacities per unit area of Cu²⁺, Zn²⁺, Sn²⁺, and Ca²⁺ were found to be 1.7, 3.2, 0.7, and 4.9 nmol/cm², respectively. Thus, in terms of the number of adsorbed ions per unit area, the QCM sensor modified by PEI/GO multilayer film shows the largest adsorption capacity of Ca²⁺. This can be rationalized by the relative hydration energies.