Novel Radiation-Induced Properties of Graphene and Related Materials

Impact of Proton Irradiation on Medium Density Polyethylene/Carbon Nanocomposites for Space Shielding Applications

The development of novel materials with improved radiation shielding capability is a fundamental step towards the optimization of passive radiation countermeasures. Polyethylene (PE) nanocomposites filled with carbon nanotubes (CNT) or graphene nanoplatelets (GNP) can be a good compromise for maintaining the radiation shielding properties of the hydrogen-rich polymer while endowing the material with multifunctional properties. In this work, nanocomposite materials based on medium-density polyethylene (MDPE) loaded with different amounts of multi-walled carbon nanotubes (MWCNT), GNPs, and hybrid MWCNT/GNP nanofillers were fabricated, and their properties were examined before and after proton exposure. The effects of irradiation were evaluated in terms of modifications in the chemical and physical structure, wettability, and surface morphology of the nanocomposites. The aim of this work was to define and compare the MDPE-based nanocomposite behavior under proton irradiation in order to establish the best system for applications as space shielding materials.

Lateral dimension and amino-functionalization on the balance to assess the single-cell toxicity of graphene on fifteen immune cell types

Given the wide variety of potential applications of graphene oxide (GO), its consequent release into the environment poses serious concerns on its safety. The future production and exploitation of graphene in the years to come should be guided by its specific chemical-physical characteristics. The unparalleled potential of single-cell mass cytometry (CyTOF) to dissect by high-dimensionality the specific immunological effects of nanomaterials, represents a turning point in nanotoxicology. It helps us to identify the safe graphene in terms of physical-chemical properties and therefore to direct its future safe production. Here we present a high-dimensional study to evaluate two historically indicated as key parameters for the safe exploitation: functionalization and dimension. The role of lateral dimension and the amino-functionalization of GO on their immune impact were here evaluated as synergistic players. To this end, we dissected the effects of GO, characterized by a large or small lateral size (GO 1.32 μm and GO 0.13 μm, respectively), and its amino-functionalized counterpart (GONH₂ 1.32 μm and GONH₂ 0.13 μm, respectively) on fifteen cell types of human primary peripheral blood mononuclear cells (PBMCs). We describe how the smallest later size not only evokes pronounced toxicity on the pool of PBMCs compared to larger GOs but also towards the distinct immune cell subpopulations, in particular on non-classical monocytes, plasmacytoid dendritic cells (pDCs), natural killer cells (NKs) and B cells. The amino-functionalization was able to improve the biocompatibility of classical and non-classical monocytes, pDCs, NKs, and B cells. Detailed single-cell analysis further revealed a complex interaction of all GOs with the immune cells, and in particular monocyte subpopulations, with different potency depending on their physicochemical properties. Overall, by high-dimensional profiling, our study demonstrates that the lateral dimension is an important factor modulating immune cells and specifically monocyte activation, but a proper surface functionalization is the dominant characteristic in its immune effects. In particular, the amino-functionalization can critically modify graphene impact dampening the immune cell activation. Our study can serve as a guide for the future broad production and use of graphene in our everyday life.

Borophene: New Sensation in Flatland

Borophene, a 2D allotrope of boron and the lightest elemental Dirac material, is the latest very promising 2D material owing to its unique structural and electronic characteristics of the X₃ and β₁₂ phases. The high atomic density on ridgelines of the β₁₂ phase of borophene provides a substantial orbital overlap, which leads to an excellent electron density in the conduction level and thus to a highly metallic behavior. These unique structural characteristics and electronic properties of borophene attract significant scientific interest. Herein, approaches for crystal growth/synthesis of these unique nanostructures and their potential technological applications are discussed. Various substrate-supported ultrahigh-vacuum growth techniques for borophene, such as molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition, along with their challenges, are also summarized. The sonochemical exfoliation and modified Hummer's technique for the synthesis of free-standing borophene are also discussed. Solution-phase exfoliation seems to address the scalability issues and expands the applications of these unique materials to various fields, including renewable energy devices and ultrafast sensors. Furthermore, the electronic, optical, thermal, and elastic properties of borophene are thoroughly discussed and are compared with those of graphene and its "cousins." Numerous frontline applications are envisaged and an outlook is presented.

Graphene-oxide/TiO2 nanocomposite films with electron-donors for multicolor holography

Graphene oxide (GO) with an ideal two-dimensional structure, presents outstanding optical, electric, and mechanical properties which draws great attention in advanced information devices. Recently, GO-based films were found to show photochromic behavior, especially for the TiO₂ involved system which has potential data processing capability, such as storing holograms. However, expanding spectral response range and increasing exposure sensitivity are still challenges for such a film, due to the limited photo-quantum efficiency in reduction reaction. Here, an innovative method of "Immersion-Dropping" technology is proposed to fabricate GO-based continuous films. We, for the first time, achieve colored holography from violet to yellow regions on GO/TiO₂ nanocomposite films with introduction of weak acid molecules. A "diffraction self-enhancement" is observed. The obtained results benefit from the broadband photo-response of weak acid molecules and photo-triggered transferring of electrons in multi-channels. This work provides a research strategy for the large-capacity information storage and colorful display device.

The effect of proton irradiation on the properties of a graphene oxide paper

A graphene oxide paper (GOP) was irradiated with 500 keV proton for total fluence of 2 × 10¹³ cm⁻² to 2 × 10¹⁵ cm⁻² in a ground-based irradiation simulator. The spacing of layer, surface chemical composition, structural defects, thermal conductivity and electrical property of the GOP before and after irradiation was measured. The results indicated that the spacing of layer decreased after irradiation. The ratio of total carbon atom and total oxygen atom increased from 2.40 to 4.31 as well as the sp² hybridized carbons obviously increased after 2 × 10¹⁵ cm⁻² irradiation. The XPS analysis suggested the occurrence of reduction, and the Raman spectra indicated that the defects were produced after proton irradiation. Furthermore, the thermal conductivity of GOP decreased, and then increased smoothly as the irradiation fluences were increased, and the electrical property showed the similar trend. The change in the thermal and electrical properties for GOP could be attributed to the defects and the removal of oxygen-containing functional groups, which lead to the phonon conduct path and scattering centers changed under proton irradiation. This study could promote the application of GOP in future space expeditions.

The 500 keV proton irradiaiton effect on a graphene oxide paper was studied in a ground-based irradiation simulator.

Differential cytotoxic effects of graphene and graphene oxide on skin keratinocytes

Impressive properties make graphene-based materials (GBMs) promising tools for nanoelectronics and biomedicine. However, safety concerns need to be cleared before mass production of GBMs starts. As skin, together with lungs, displays the highest exposure to GBMs, it is of fundamental importance to understand what happens when GBMs get in contact with skin cells. The present study was carried out on HaCaT keratinocytes, an in vitro model of skin toxicity, on which the effects of four GBMs were evaluated: a few layer graphene, prepared by ball-milling treatment (FLG), and three samples of graphene oxide (GOs, a research-grade GO1, and two commercial GOs, GO2 and GO3). Even though no significant effects were observed after 24 h, after 72 h the less oxidized compound (FLG) was the less cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 62.8 μg/mL (WST-8 assay) and 45.5 μg/mL (propidium iodide uptake), respectively. By contrast, the largest and most oxidized compound, GO3, was the most cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 5.4 and 2.9 μg/mL, respectively. These results suggest that only high concentrations and long exposure times to FLG and GOs could impair mitochondrial activity associated with plasma membrane damage, suggesting low cytotoxic effects at the skin level.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.

Microstructure and properties of carbon nanosheet/copper composites processed by particle-assisted shear exfoliation

Graphite was exfoliated to CNSs with the help of copper particles by going through the narrow gaps between the stator and rotor of the stator–rotor mixer.

One-step green synthesis of a ruthenium/graphene composite as a highly efficient catalyst

Ruthenium particles with an average size of 3.17 nm are uniformly anchored on supercritical water-reduced graphene oxide (WRG).

High apparent strengthening efficiency for reduced graphene oxide in copper matrix composites produced by molecule-lever mixing and high-shear mixing

The RGO sheets are homogeneously distributed in the RGO/Cu composite produced by the molecular-level mixing and high-shear mixing method and the composites with high mechanical properties are obtained.

A novel magnetic polysaccharide–graphene oxide composite for removal of cationic dyes from aqueous solution

Magnetic adsorbents with more adsorption sites can realize efficient adsorption of cationic dyes.

Synthesis of graphene-like g-C3N4/Fe3O4 nanocomposites with high photocatalytic activity and applications in drug delivery

Graphene-like g-C₃N₄ nanosheet/Fe₃O₄ nanocomposites with high photocatalytic activity and applications for magnetically targeted drug delivery.

Organic functionalisation of graphene catalysed by ferric perchlorate

We have developed a method to prepare covalently functionalised graphene using ferric perchlorate as the catalyst.

A universal strategy for the hierarchical assembly of functional 0/2D nanohybrids

We report a universal strategy for the hierarchical assembly of nanoparticles on various 2D materials, resulting in functional 0/2D nanohybrids holding great promise in catalysis, energy storage, and chemical and biological sensing.