The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

https://iopscience.iop.org/article/10.1088/1468-6996/16/2/023501/pdf

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications.

Magnetocaloric effect: From materials research to refrigeration devices

The biorelated degradability and clearance of siliceous nanomaterials have been questioned worldwide, since they are crucial prerequisites for the successful translation in clinics. Typically, the degradability and biocompatibility of mesoporous silica nanoparticles (MSNs) have been an ongoing discussion in research circles. The reason for such a concern is that approved pharmaceutical products must not accumulate in the human body, to prevent severe and unpredictable side-effects. Here, the biorelated degradability and clearance of silicon and silica nanoparticles (NPs) are comprehensively summarized. The influence of the size, morphology, surface area, pore size, and surface functional groups, to name a few, on the degradability of silicon and silica NPs is described. The noncovalent organic doping of silica and the covalent incorporation of either hydrolytically stable or redox- and enzymatically cleavable silsesquioxanes is then described for organosilica, bridged silsesquioxane (BS), and periodic mesoporous organosilica (PMO) NPs. Inorganically doped silica particles such as calcium-, iron-, manganese-, and zirconium-doped NPs, also have radically different hydrolytic stabilities. To conclude, the degradability and clearance timelines of various siliceous nanomaterials are compared and it is highlighted that researchers can select a specific nanomaterial in this large family according to the targeted applications and the required clearance kinetics.

Degradability and Clearance of Silicon, Organosilica, Silsesquioxane, Silica Mixed Oxide, and Mesoporous Silica Nanoparticles.

The efficient handling of wastewater pollutants is a must, since they are continuously defiling limited fresh water resources, seriously affecting the terrestrial, aquatic, and aerial flora and fauna. Our vision is to undertake an exhaustive examination of current research trends with a focus on nanomaterials (NMs) to considerably improve the performance of classical wastewater treatment technologies, e.g. adsorption, catalysis, separation, and disinfection. Additionally, NM-based sensor technologies are considered, since they have been significantly used for monitoring water contaminants. We also suggest future directions to inform investigators of potentially disruptive NM technologies that have to be investigated in more detail. The fate and environmental transformations of NMs, which need to be addressed before large-scale implementation of NMs for water purification, are also highlighted.

Recent advances in nanomaterials for water protection and monitoring.

Enhanced electromagnetic wave absorption of nanoporous Fe3O4 @ carbon composites derived from metal-organic frameworks

Magnetic vortex core-shell Fe3O4@C nanorings with enhanced microwave absorption performance

Where does the toxicity of metal oxide nanoparticles come from: The nanoparticles, the ions, or a combination of both?

Electromagnetic pollution has been causing a series of problems in people’s life, and electromagnetic absorbers with lightweight and broad absorbing bandwidth properties are widely desired. In this work, novel sandwich-like 2D laminated Fe&TiO2 nanoparticles@C nanocomposites were rationally designed and successfully developed from the MXene–MOFs hybrids. The formation of Fe and rutile-TiO2 nanoparticles sandwiched by the two-dimensional carbon nanosheets provided strong electromagnetic energy attenuation and good impedance matching for electromagnetic wave (EMW) absorption. As expected, the nanocomposites achieved a broad effective absorption bandwidth of 6.5 GHz at a thickness of only 1.6 mm and the minimum reflection loss (RL) value of − 51.8 dB at 6.6 GHz with a thickness of 3 mm. This work not only provides a good design and fabricating concept for the laminated metal and functional nanoparticles@C nanocomposites with good EMW absorption, but also offers an important guideline to fabricate various two-dimensional nanocomposites derived from the MXene precursors.

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Sandwich-Like Fe&TiO 2 @C Nanocomposites Derived from MXene/Fe-MOFs Hybrids for Electromagnetic Absorption

Developing electromagnetic absorption materials with a strong absorption ability and wide absorption bandwidth has attracted widespread attention in the field of electromagnetic shielding, but it still remains a great challenge. Herein, we successfully developed 2D hierarchically laminated Fe3O4@nanoporous carbon (NPC)@rGO magnetic/dielectric nanocomposites as high-performance microwave absorbers through a facile microwave-assisted approach. The rational design of the composition (Fe3O4, NPC and rGO) and the hierarchical microstructure provided the nanocomposite with a micro-scale 3D magnetic coupling network, a hierarchical dielectric carbon network and good impedance matching, which were identified by the off-axis electronic holography and electromagnetic characterization. As expected, the Fe3O4@NPC@rGO composites achieved a strong reflection loss of −72.6 dB, a matching thickness of 2.0 mm and a broad bandwidth of 5.5 GHz. Such excellent achievements encourage the development of hierarchical magnetic EMA absorbers and provide remarkable inspiration for designing high-performance microwave absorbers.

https://pubs.rsc.org/en/content/articlepdf/2020/tc/c9tc06526a

Rational design of 2D hierarchically laminated Fe3O4@nanoporous carbon@rGO nanocomposites with strong magnetic coupling for excellent electromagnetic absorption applications

Wei Lu

Papers

Enhanced electromagnetic wave absorption of nanoporous Fe3O4 @ carbon composites derived from metal-organic frameworks

Magnetic vortex core-shell Fe3O4@C nanorings with enhanced microwave absorption performance

Where does the toxicity of metal oxide nanoparticles come from: The nanoparticles, the ions, or a combination of both?

Sandwich-Like Fe&TiO 2 @C Nanocomposites Derived from MXene/Fe-MOFs Hybrids for Electromagnetic Absorption

Rational design of 2D hierarchically laminated Fe3O4@nanoporous carbon@rGO nanocomposites with strong magnetic coupling for excellent electromagnetic absorption applications