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Mesoscopic modeling and experimental validation of thermal and mechanical properties of polypropylene nanocomposites reinforced by graphene-based fillers. (arXiv:2211.13148v1 [cond-mat.mtrl-sci])

2022-11-24T02:29:39+00:00November 24th, 2022|Categories: Publications|Tags: , , |

The development of nanocomposites relies on structure-property relations, which necessitate multiscale modeling approaches. This study presents a modelling framework based on mesoscopic models to predict the thermal and mechanical properties of nanocomposites starting from their molecular structure. Mesoscopic models of polypropylene (PP) and graphene based nanofillers (Graphene (Gr), Graphene Oxide (GO) and reduced Graphene Oxide (rGO)) were analyzed and compared against experiments. The developed mesoscopic model has been validated with the experimental characterization of the thermal and mechanical properties of PP/Gr nanocomposite samples, showing better prediction capabilities with respect to traditional continuum models. Results demonstrate that with the modest addition of nanofillers (up to 2 wt.%), the Young’s modulus and thermal conductivity show up to 35% and 25% enhancement, respectively, while the Poisson’s ratio slightly decreases. Among the different combinations tested, PP/Gr nanocomposite shows the best mechanical properties, whereas PP/rGO the best thermal conductivity. This mesoscopic model validated by experiments will contribute to the development of smart materials with enhanced mechanical and thermal properties based on polypropylene, especially for mechanical, energy storage, and sensing applications.

Published in: "arXiv Material Science".

Acidity of graphene oxide aqueous solutions: the origin unveiled. (arXiv:2211.10208v1 [cond-mat.mtrl-sci])

2022-11-21T02:29:34+00:00November 21st, 2022|Categories: Publications|Tags: , |

Nonempirical modeling of hydrated single-layer graphene oxide (GO) fragments revealed that the probable origin of the acidity of aqueous GO solutions is the dissociation in closely grouped hydroxyls. The process is further promoted by the adjacent $pi$-conjugated carbon subsystem at the edges of GO flakes or their inner defects. The apparent $pK_a$ values of the groups fall in a range of ca. 2.0 to 5.3.

Published in: "arXiv Material Science".

Bioinspired Gradient Stretchable Aerogels for Ultrabroad‐Range‐Response Pressure‐Sensitive Wearable Electronics and High‐Efficient Separators

2022-11-09T13:07:47+00:00November 9th, 2022|Categories: Publications|Tags: , |

Broad-range-response pressure-sensitive wearable electronics are urgently needed but their preparation remains a challenge. Herein, we report unprecedented bioinspired wearable electronics based on stretchable and superelastic reduced graphene oxide/polyurethane nanocomposite aerogels with gradient porous structures by a sol-gel/hot pressing/freeze casting/ambient pressure drying strategy. The gradient structure with a hot-pressed layer promotes strain transfer and resistance variation under high pressures, leading to an ultrabroad detection range of 1 Pa-12.6 MPa, one of the broadest ranges ever reported. They can withstand 10000 compression cycles under 1 MPa, which can’t be achieved by traditional flexible pressure sensors. They can be applied for broad-range-response electronic skins and monitoring various physical signals/motions and ultrahigh pressures of automobile tires. Moreover, the gradient aerogels can be used as high-efficient gradient separators for water purification.

Published in: "Angewandte Chemie International Edition".

Synergistic Interfacial Bonding in Reduced Graphene Oxide Fiber Cathodes Containing Polypyrrole@sulfur Nanospheres for Flexible Energy Storage

2022-09-11T13:07:34+00:00September 11th, 2022|Categories: Publications|Tags: , , |

Flexible lithium sulfur batteries with high energy density and good mechanical flexibility are highly desirable. Here, we report a synergistic interface bonding enhancement strategy to construct flexible fiber-shaped composite cathodes, in which polypyrrole@sulfur (PPy@S) nanospheres are homogeneously implanted into the built-in cavity of self-assembled reduced graphene oxide fibers (rGOFs) by a facile microfluidic assembly method. In this architecture, sulfur nanospheres and lithium polysulfides are synergistically hosted by carbon and polymer interface, which work together to provide enhanced interface chemical bonding to endow the cathode with good adsorption ability, fast reaction kinetics, and excellent mechanical flexibility. Consequently, the PPy@S/rGOFs cathode shows enhanced electrochemical performance and high-rate capability. COMSOL Multiphysics simulations and density functional theory (DFT) calculations are conducted to elucidate the enhanced electrochemical performance. In addition, a flexible Li-S pouch cell is assembled and delivers a high areal capacity of 5.8 mAh/cm 2 at 0.2 A/g. Our work offers a new strategy for preparation of advanced cathodes for flexible batteries.

Published in: "Angewandte Chemie International Edition".

Hydrogen‐Bonded Organic Framework Ultrathin Nanosheets for Efficient Visible Light Photocatalytic CO2 Reduction

2022-09-07T13:07:20+00:00September 7th, 2022|Categories: Publications|Tags: , |

Post-modification of robust guanine-quadruplex-linked 2,2′-pyridine-containing HOF-25 with Ni(ClO) 4 ·6H 2 O followed by exfoliation using sonication method affords hydrogen-bonded organic framework (HOF) nanosheets (NSs) of HOF-25-Ni in the yeild of 56%. TEM and AFM technologies disclose the ultrathin nature of HOF-25-Ni NSs with thickness of 4.4 nm. STM observation determines the presence of sql segments assembled from HOF-25-Ni building blocks at the heptanoic acid/highly oriented pyrolytic graphite interface, supporting the simulated 2D supramolecular framework. ICP analysis, XAS, and XPS spectra prove the successful immobilization of atomic nickel sites on the 20% total 2,2′-pyridine moieties in crystalline HOF-25-Ni. With the aid of [Ru(bpy) 3 ] 2+ and triisopropanolamine, 10 wt% HOF-25-Ni NSs dispersed on graphene oxide efficiently promotes visible light-driven CO 2 reduction, showing a 96.3% CO selectivity with a prominent conversion rate up to 24323 μmol g −1 h −1 .

Published in: "Angewandte Chemie International Edition".

Stimulus‐responsive Tubular Conjugated Polymer 2D Nanosheets

2022-09-01T13:07:30+00:00September 1st, 2022|Categories: Publications|Tags: , |

Creation of new 2D architectures has attracted significant attention in the field of self-assembly for structural diversity and new functionalization. Although numerous 2D polymer nanosheets have been reported, 2D nanosheets with tubular channels have been unexplored. Herein, we describe a new strategy for the fabrication of stimulus-responsive conjugated polymer 2D nanosheets with hollow cavities. Amphiphilic macrocyclic diacetylenes self-assembled in an aqueous solution in a columnar manner to afford bilayered 2D nanosheets with intrinsically tubular nanochannels. UV-induced polymerization resulted in the generation of blue-colored tubular conjugated polydiacetylene 2D nanosheets. Immobilization of gold nanoparticles, fluorescence labeling with FRET phenomenon and colorimetric DNA sensing were demonstrated with these new 2D nanosheets. In addition, the free NH 2 containing polymerized 2D nanosheet was utilized for conductivity behavior and grafting on graphene oxide (GO)

Published in: "Angewandte Chemie International Edition".

Fiber‐spinning Asymmetric Assembly for Janus‐structured Bifunctional Nanofiber Films towards All‐Weather Smart Textile

2022-08-26T13:07:56+00:00August 26th, 2022|Categories: Publications|Tags: , , |

Given health threat by global warming and increased energy consumption in regulating body temperature, it is an urgent need to construct smart temperature-regulating materials. Herein, a novel fiber-spinning asymmetric chemical assembly (FACA) method is proposed to construct nanofiber materials with asymmetric photothermal properties. The silver nanowires (AgNWs) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with opposite thermal radiation are assembled on reduced graphene oxide (rGO) film, imparting AgNW/rGO/PVDF-HFP film with Janus structure that can realize the AgNWs side consistently keeps temperature of ca. 11 o C lower than the side of PVDF-HFP nanofiber regardless of the irradiation directions under 1 sun, suggesting the adjustable photothermal regulation. Such photothermally selective hybrid nanofiber film provides great potential as fabrics to achieve all-weather smart clothes, promoting controllable and comprehensive utilization of solar energy.

Published in: "Angewandte Chemie International Edition".

Efficient Gene Silencing in Intact Plant Cells Using siRNA Delivered By Functional Graphene Oxide Nanoparticles

2022-08-04T13:08:02+00:00August 4th, 2022|Categories: Publications|Tags: , |

Delivery of small interfering RNA (siRNA) to intact plants for gene silencing mainly relies on viral vectors and Agrobacterium- mediated transformation due to the barrier of intact plant cell wall. Here, we reported that polymer functionalized graphene oxide nanoparticles (GONs) enable siRNA transfer into intact plant cells and bring about efficient gene silencing. We found that sheeted GONs could efficiently load siRNA to form small sized, near-spheroidal GONs-siRNA complex, which could be across the cell wall and internalize in the plant cell. The GONs-siRNA exhibited transient and strong silencing (97.2% efficiency) in plant tissues at 24 h after treatment and returned to normal level at 5 days after treatment. This method has the obvious advantages of efficient, transient, simple, stability and well biocompatibility, which should greatly stimulate the application of nanomaterials as gene-engineering tools in plant research.

Published in: "Angewandte Chemie International Edition".

Layered, Tunable Graphene Oxide-Nylon Heterostructures for Wearable Electrocardiogram Sensors. (arXiv:2109.12739v2 [cond-mat.mtrl-sci] UPDATED)

2022-08-03T04:30:19+00:00August 3rd, 2022|Categories: Publications|Tags: , , |

Nanoscale engineered materials combined with wearable wireless technologies can deliver a new level of health monitoring. A reduced graphene oxide-nylon composite material is developed and tested, demonstrating its usefulness as a material for sensors in wearable, long-term electrocardiogram (ECG) monitoring via a comparison to one of the widely used ECG sensors. The structural analysis by scanning electron (SEM) and atomic force microscopy (AFM) shows a limited number of defects on a macroscopic scale. Fourier Transform Infrared (FTIR) and Raman spectroscopy confirm the presence of rGOx, and the ratio of D- and G-features as a function of thickness correlates with the resistivity analysis. The negligible effect of the defects and the tunability of electrical and optical properties, together with live ECG data, demonstrate its signal transduction capability.

Published : "arXiv Mesoscale and Nanoscale Physics".

Highly Efficient and Selective Extraction of Gold by Reduced Graphene Oxide. (arXiv:2208.01435v1 [cond-mat.mtrl-sci])

2022-08-03T02:29:21+00:00August 3rd, 2022|Categories: Publications|Tags: , |

Materials that are capable of extracting gold from complex sources, especially electronic waste (e-waste) with high efficiency are needed for gold resource sustainability and effective e-waste recycling. However, it remains challenging to achieve high extraction capacity to trace amount of gold, and precise selectivity to gold over a wide range of complex co-existing elements. Here we report a reduced graphene oxide (rGO) material that has an ultrahigh extraction capacity for trace amounts of gold (1,850 mg/g and 1,180 mg/g to 10 ppm and 1 ppm gold). The excellent gold extraction behavior is accounted to the graphene areas and oxidized regions of rGO. The graphene areas spontaneously reduce gold ions to metallic gold, and the oxidized regions provide a good dispersibility so that efficient adsorption and reduction of gold ions by the graphene area can be realized. The rGO is also highly selective to gold ions. By controlling the protonation process of the functional groups on the oxidized regions of rGO, it shows an exclusive gold extraction without adsorption of 14 co-existing elements seen in e-waste. These discoveries are further exploited in highly efficient, continuous gold recycling from e-waste with good scalability and economic viability, as exemplified by extracting gold from e-waste using a rGO membrane based flow-through process.

Published in: "arXiv Material Science".

Mechanism for selective binding of aromatic compounds on oxygen-rich graphene nanosheets based on molecule size/polarity matching

2022-07-30T04:36:55+00:00July 30th, 2022|Categories: Publications|Tags: , |

Abstract Selective binding of organic compounds is the cornerstone of many important industrial and pharmaceutical applications. Here, we achieved highly selective binding of aromatic compounds in aqueous solution and gas phase by oxygen-enriched graphene oxide (GO) nanosheets via a previously unknown mechanism based on size matching and polarity matching.

Published in: "Science Advances".

News at a glance: Debate over classifying research, giant water lilies, and new hummingbird feather colors

2022-07-06T21:08:49+00:00July 6th, 2022|Categories: Publications|Tags: |

ECOLOGY Scientists find new hummingbird colors The plumage of hummingbirds has more color diversity than the feathers of all other birds combined, a recent study finds. Researchers from Yale University collected feathers from specimens of 114 hummingbird species and, using a spectrometer, documented the wavelengths of light they reflected. These wavelengths were then compared with those found in a previous study of 111 other bird species, including penguins and parrots. The researchers were surprised to find new colors in the hummers, which widened the known avian color gamut by 56% and included rarely seen saturated greens and blues, they report in Communications Biology . The newfound variation largely includes colors in the ultraviolet scale that are invisible to humans and probably only seen by hummingbirds themselves. Researchers note the variation is likely due to the reflective qualities of nanostructures present in the small barbs that protrude from the end of each hummingbird feather. The new colors were mostly found on the crowns and throats of the birds, suggesting a role in mating displays and communication. RESEARCH SECURITY New debate over secrecy Science has learned that the U.S. National Science Foundation (NSF) has asked the National Academies to take a fresh look this fall at a Cold War-era presidential directive that regards openness in basic research as a boon to both innovation and national security. Advocates of classifying as little information as possible say additional restrictions would harm U.S. research without deterring countries seen as adversaries. China’s aggressive pursuit of

Published in: "Science".

Functionalization of graphene sponge electrodes with two-dimensional materials for tailored electrocatalytic activity towards specific contaminants of emerging concern. (arXiv:2206.04111v1 [cond-mat.mtrl-sci])

2022-06-10T02:29:23+00:00June 10th, 2022|Categories: Publications|Tags: , , |

Low-cost graphene sponge electrodes were functionalized with two-dimensional (2D) materials, i.e., borophene and hexagonal boron nitride (hBN), using a one-step, hydrothermal self-assembly method. Borophene and hBN-modified graphene sponge anode and N-doped graphene sponge cathode were employed for electrochemical degradation of model persistent contaminants of emerging concern in one-pass, flow through mode, and using low-conductivity supporting electrolyte. Functionalization of the reduced graphene oxide (RGO) coating with 2D materials led to specific modifications in the electrode electrocatalytic performance and interactions with the target contaminants. For instance, addition of hBN promoted the adsorption of more hydrophobic organic contaminants via van der Waals and {pi}-{pi} interactions. Functionalization of the graphene sponge anode with borophene enhanced the generation of oxidant species such as H2O2 and O3 and yielded an order of magnitude higher concentration of hydroxyl radicals (HO) compared with the non-functionalized graphene sponge anode, thus enhancing the removal of target contaminants. Experiments conducted with the selective radical scavengers indicated the key role of surface-bound hydroxyl radicals (HOads) and singlet oxygen (1O2) in electrochemical degradation. The study demonstrates that functionalization of graphene sponge electrodes with 2D materials can enhance their electrocatalytic activity and modulate the interaction with specific organic contaminants, thus opening new possibilities for designing electrodes tailored to remove specific groups of pollutants.

Published in: "arXiv Material Science".

Surface‐Adaptive Capillarity Enabling Densified 3D Printing for Ultra‐High Areal and Volumetric Energy Density Supercapacitors

2022-06-07T13:07:40+00:00June 7th, 2022|Categories: Publications|Tags: , , |

Innovative densified 3D printing enabled by a surface-adaptive capillarity strategy is proposed for fabrication of highly loaded supercapacitors. Coupling with controllable capillary densification, the printed symmetric supercapacitor delivers a double leap in areal and volumetric energy densities in both aqueous and organic electrolytes, a rarely achieved yet gravely desired attribute for 3D printed energy storage devices. Abstract Endowing supercapacitors with higher energy density is of great practical significance but remains extremely challenging. In this work, an innovative densified 3D printing enabled by a surface-adaptive capillarity strategy is proposed for the first time. The printable ink formulated with pyrrole surface-modified reduced graphene oxide renders the printed electrodes excellent surface tension regulability to the subsequent capillary densification, creating an intensely condensed electrode with well-maintained structural integrity. Furthermore, simultaneous in situ nitrogen doping and hierarchical micro–meso porosity are readily realized upon post-carbonization, encouraging enhanced capacitance and fast reaction dynamics. As a result, the printed symmetric supercapacitor delivers a double leap in areal and volumetric energy densities in both aqueous and organic electrolytes, a rarely achieved yet gravely desired attribute for 3D printed energy storage devices.

Published in: "Angewandte Chemie International Edition".

The $omega^3$ scaling of the vibrational density of states in quasi-2D nanoconfined solids. (arXiv:2108.07521v2 [cond-mat.mtrl-sci] UPDATED)

2022-05-02T04:31:52+00:00May 2nd, 2022|Categories: Publications|Tags: , |

Atomic vibrations play a vital role in the functions of various physical, chemical, and biological systems. The vibrational properties and the specific heat of crystalline bulk materials are well described by Debye theory, which successfully predicts the quadratic $omega^{2}$ low-frequency scaling of the vibrational density of states (VDOS) in bulk ordered solids from few fundamental assumptions. However, the analogous framework for nanoconfined materials with fewer degrees of freedom has been far less well explored. Using inelastic neutron scattering, we characterize the VDOS of amorphous ice confined to a thickness of $approx 1$ nm inside graphene oxide membranes and we observe a crossover from the Debye $omega^2$ scaling to an anomalous $omega^3$ behaviour upon reducing the confinement size $L$. Additionally, using molecular dynamics simulations, we confirm the experimental findings and also prove that such a scaling of the VDOS appears in both crystalline and amorphous solids under slab-confinement. We theoretically demonstrate that this low-frequency $omega^3$ law results from the geometric constraints on the momentum phase space induced by confinement along one spatial direction. Finally, we predict that the Debye scaling reappears at a characteristic frequency $omega_times= v L/2pi$, with $v$ the speed of sound of the material, and we confirm this quantitative estimate with simulations. This new physical phenomenon, revealed by combining theoretical, experimental and simulations results, is relevant to a myriad of systems both in synthetic and biological contexts and it could impact various technological applications for systems under confinement such as nano-devices or thin films.

Published : "arXiv Mesoscale and Nanoscale Physics".

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