A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.

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Supramolecular Luminescent Sensors

Strategies to improve electrocatalytic and photocatalytic performance of two-dimensional materials for hydrogen evolution reaction

Carbon quantum dots (CQDs) are a class of carbon nanomaterials that have recently gained recognition as current entrants to traditional semiconductor quantum dots. CQDs have the desirable advantages of low toxicity, environmental friendliness, low cost, photostability, favorable charge transfer with enhanced electronic conductivity, and comparable easy-synthesis protocols. This review examines the advancements in CQD research and development, with a focus on their synthesis, functionalization, and energy applications. Initially, various synthesis methods are discussed briefly with pros and cons. Herein, first top-down methods including the arc-discharge technique, laser ablation technique, plasma treatment, ultrasound synthesis technique, electrochemical technique, chemical exfoliation, and combustion were discussed briefly. The later section presents bottom-up (microwave synthesis, hydrothermal synthesis, thermal pyrolysis, and metal–organic framework template-assisted approach) and waste-derived CQD synthesis methods. The next section is focused on the energy applications of CQDs including supercapacitors, lithium-ion batteries, photovoltaics, hydrogen evolution reaction and oxygen evolution reaction. Finally, challenges and future perspectives in this exciting and promising area are presented.

/pdf/carbon-quantum-dots-for-energy-applications-a-review-4lnlm2klr2.pdf

Carbon Quantum Dots for Energy Applications: A Review

Graphene quantum dot (GQD) is one of the youngest superstars of the carbon family. Since its emergence in 2008, GQD has attracted a great deal of attention due to its unique optoelectrical properties. Non-zero bandgap, the ability to accommodate functional groups and dopants, excellent dispersibility, highly tunable properties, and biocompatibility are among the most important characteristics of GQDs. To date, GQDs have displayed significant momentum in numerous fields such as energy devices, catalysis, sensing, photodynamic and photothermal therapy, drug delivery, and bioimaging. As this field is rapidly evolving, there is a strong need to identify the emerging challenges of GQDs in recent advances, mainly because some novel applications and numerous innovations on the ease of synthesis of GQDs are not systematically reviewed in earlier studies. This feature article provides a comparative and balanced discussion of recent advances in synthesis, properties, and applications of GQDs. Besides, current challenges and future prospects of these emerging carbon-based nanomaterials are also highlighted. The outlook provided in this review points out that the future of GQD research is boundless, particularly if upcoming studies focus on the ease of purification and eco-friendly synthesis along with improving the photoluminescence quantum yield and production yield of GQDs.

Synthesis, Applications, and Prospects of Graphene Quantum Dots: A Comprehensive Review

β-Cyclodextrin (β-CD) possess a hydrophobic inner cavity and a hydrophilic exterior surface. They exhibit excellent inclusion properties with the guest molecules that match cavity size, and β-CD-based materials drew widespread attention in electrochemical sensors. The hydroxy groups at the edge of the cavity can form hydrogen bonds and undergo electrostatic and dipole-dipole interactions with other molecules. This review (with 109 refs.) reveals β-CD-based detection mechanisms from the viewpoint of the size/shape-fit concept, and summarizes the current state of multiple electrochemical sensors based on the use of β-CD and functionalized β-CD such as carboxymethyl-β-CD, mono-(6-ethanediamine-6-deoxy)-β-CD, hydroxypropyl-β-CD, thio-β-cyclodextrin, and others.

Advances in the use of functional composites of β-cyclodextrin in electrochemical sensors.

Highly sensitive fluorescence sensor for mercury(II) based on boron- and nitrogen-co-doped graphene quantum dots.

Voltammetric enantiomeric differentiation of tryptophan by using multiwalled carbon nanotubes functionalized with ferrocene and β-cyclodextrin

Electrochemical chiral interface based on the Michael addition/Schiff base reaction of polydopamine functionalized reduced graphene oxide

A chiral sensor is described for the enantioselective recognition of L- and D-tryptophan (Trp). The sensor is based on the use of (a) Cu(II) ions coordinated with β-cyclodextrin (Cu-β-CD) that was self-assembled with carboxymethyl cellulose (CD-Cu-CMC) as a chiral selector, (b) of N-doped reduced graphene oxide (N-rGO) as substrate materials, and (c) of differential pulse voltammetry that was used for enantiorecognition. The 3D N-rGO was prepared by using reduced graphene oxide and pyrrole as the starting materials. Electrostatic interaction occurs between the carboxy groups of CMC and Cu(II) ions in Cu-β-CD. The FT-IR, SEM, XRD and XPS techniques showed that 3D N-rGO and the CD-Cu-CMC composite were successfully synthesized. The 3D N-rGO enabled the immobilization of the chiral selector (CD-Cu-CMC) and improves the active areas. A glassy carbon electrode was modified with N-rGO/CD-Cu-CMC and then showed a stronger electrochemical signal for L-Trp than for D-Trp, typically at a working potential of around 0.78 V (vs. SCE). UV-vis spectroscopy proved that CD-Cu-CMC has a higher affinity for D-Trp. The enantioselectivity for D-Trp over L-Trp is 4.72. The modified electrode had a limit of detection of 0.063 μM and 0.0035 μM for L-Trp and D-Trp, respectively, with a linear response range of 0.01 mM to 5 mM. The sensor was used to detect Trp (D- or L-Trp) in spiked real human urine and human serum protein samples.

Liu Zhenyu

Papers

Advances in the use of functional composites of β-cyclodextrin in electrochemical sensors.

Highly sensitive fluorescence sensor for mercury(II) based on boron- and nitrogen-co-doped graphene quantum dots.

Voltammetric enantiomeric differentiation of tryptophan by using multiwalled carbon nanotubes functionalized with ferrocene and β-cyclodextrin

Electrochemical chiral interface based on the Michael addition/Schiff base reaction of polydopamine functionalized reduced graphene oxide

Electrochemical chiral sensing of tryptophan enantiomers by using 3D nitrogen-doped reduced graphene oxide and self-assembled polysaccharides