We have synthesized a porous Mo‐based composite obtained from a polyoxometalate‐based metal–organic framework and graphene oxide (POMOFs/GO) using a simple one‐pot method. The MoO2@PC‐RGO hybrid ...material derived from the POMOFs/GO composite is prepared at a relatively low carbonization temperature, which presents a superior activity for the hydrogen‐evolution reaction (HER) in acidic media owing to the synergistic effects among highly dispersive MoO2 particles, phosphorus‐doped porous carbon, and RGO substrates. MoO2@PC‐RGO exhibits a very positive onset potential close to that of 20 % Pt/C, low Tafel slope of 41 mV dec−1, high exchange current density of 4.8×10−4 A cm−2, and remarkable long‐term cycle stability. It is one of the best high‐performance catalysts among the reported nonprecious metal catalysts for HER to date.
Nanocomposite catalyst: A novel Mo‐based catalyst for the hydrogen‐evolution reaction has been synthesized by directly carbonizing a composite obtained from polyoxometalate‐based metal–organic frameworks and graphene oxide at a relatively low temperature. The Mo‐based catalyst exhibits a positive onset potential, low Tafel slope, high exchange current density, and long‐term stability for the hydrogen‐evolution reaction in acidic media.
The high fracture toughness of mollusk nacre is predominantly attributed to the structure‐associated extrinsic mechanisms such as platelet sliding and crack deflection. While the nacre‐mimetic ...structures are widely adopted in artificial ceramics, the extrinsic mechanisms are often weakened by the relatively low tensile strength of the platelets with a large aspect ratio, which makes the fracture toughness of these materials much lower than expected. Here, it is demonstrated that the fracture toughness of artificial nacre materials with high inorganic contents can be improved by residual stress‐induced platelet strengthening, which can catalyze more effective extrinsic toughening mechanisms that are specific to the nacre‐mimetic structures. Thereby, while the absolute fracture toughness of the materials is not comparable with advanced ceramic‐based composites, the toughness amplification factor of the material reaches 16.1 ± 1.1, outperforming the state‐of‐the‐art biomimetic ceramics. The results reveal that, with the merit of nacre‐mimetic structural designs, the overall fracture toughness of the artificial nacre can be improved by the platelet strengthening through extrinsic toughening mechanisms, although the intrinsic fracture toughness may decrease at platelet level due to the strengthening. It is anticipated that advanced structural ceramics with exceeding performance can be fabricated through these unconventional strategies.
This work illustrates an anti‐intuitive strategy that, with the merit of biomimetic designs, residual stress that is conventionally harmful to ceramics can inversely help improve the fracture toughness of biomimetic ceramics through nanoscale residual stress‐induced platelet strengthening. This provides new insights into the design principles of nacre‐like materials at the bottom level.
Energy shortage, environmental crisis, and developing customer demands have driven people to find facile, low‐cost, environmentally friendly, and nontoxic routes to produce novel functional materials ...that can be commercialized in the near future. Amongst various techniques, the hydrothermal carbonization (HTC) process of biomass (either of isolated carbohydrates or crude plants) is a promising candidate for the synthesis of novel carbon‐based materials with a wide variety of potential applications. In this Review, we will discuss various synthetic routes towards such novel carbon‐based materials or composites via the HTC process of biomass. Furthermore, factors that influence the carbonization process will be analyzed and the special chemical/physical properties of the final products will be discussed. Despite the lack of a clear mechanism, these novel carbonaceous materials have already shown promising applications in many fields such as carbon fixation, water purification, fuel cell catalysis, energy storage, CO2 sequestration, bioimaging, drug delivery, and gas sensors. Some of the most promising examples will also be discussed here, demonstrating that the HTC process can rationally design a rich family of carbonaceous and hybrid functional carbon materials with important applications in a sustainable fashion.
A hydrothermal carbonization process from biomass allows fabrication of various novel carbon‐based materials or composites with special chemical and/or physical properties, which have great potential for environmental, catalytic, biochemical, electric, and sensing applications (see figure).
Biomedical applications of nontoxic amorphous calcium carbonate (ACC) nanoparticles have mainly been restricted because of their aqueous instability. To improve their stability in physiological ...environments while retaining their pH‐responsiveness, a novel nanoreactor of ACC–doxorubicin (DOX)@silica was developed for drug delivery for use in cancer therapy. As a result of its rationally engineered structure, this nanoreactor maintains a low drug leakage in physiological and lysosomal/endosomal environments, and responds specifically to pH 6.5 to release the drug. This unique ACC–DOX@silica nanoreactor releases DOX precisely in the weakly acidic microenvironment of cancer cells and results in efficient cell death, thus showing its great potential as a desirable chemotherapeutic nanosystem for cancer therapy.
Precise release of doxorubicin (DOX) in the weakly acidic microenvironment of cancer cells has been achieved with an amorphous calcium carbonate/doxorubicin@silica (ACC–DOX@silica) nanoreactor. Only low drug leakage occurs in physiological and lysosomal/endosomal environments, but at pH 6.5 the drug is specifically released and results in efficient cell death.
Recently, heteroatom‐doped three‐dimensional (3D) nanostructured carbon materials have attracted immense interest because of their great potential in various applications. Hence, it is highly ...desirable to exploit a simple, renewable, scalable, multifunctional, and general strategy to engineer 3D heteroatom‐doped carbon nanomaterials. Herein, a simple, eco‐friendly, general, and effective way to fabricate 3D heteroatom‐doped carbon nanofiber networks on a large scale is reported. Using this method, 3D P‐doped, N,P‐co‐doped, and B,P‐co‐doped carbon nanofiber networks are successfully fabricated by the pyrolysis of bacterial cellulose immersed in H3PO4, NH4H2PO4, and H3BO3/H3PO4 aqueous solution, respectively. Moreover, the as‐prepared N,P‐co‐doped carbon nanofibers exhibit good supercapacitive performance.
A simple, efficient, and general approach is developed for preparing cost‐effective, three‐dimensional, and large‐scale heteroatom‐doped carbon nanofibers, such as P‐doped, N,P‐co‐doped, and B,P‐co‐doped carbon nanofibers, by pyrolyzing bacterial cellulose (BC) previously immersed in H3PO4, NH4H2PO4, and H3BO3/H3PO4, respectively. Moreover, the as‐prepared N,P‐co‐doped carbon nanofibers exhibit good supercapacitive performance.
Various methods have been exploited to replicate nacre features into artificial structural materials with impressive structural and mechanical similarity. However, it is still very challenging to ...produce nacre-mimetics in three-dimensional bulk form, especially for further scale-up. Herein, we demonstrate that large-sized, three-dimensional bulk artificial nacre with comprehensive mimicry of the hierarchical structures and the toughening mechanisms of natural nacre can be facilely fabricated via a bottom-up assembly process based on laminating pre-fabricated two-dimensional nacre-mimetic films. By optimizing the hierarchical architecture from molecular level to macroscopic level, the mechanical performance of the artificial nacre is superior to that of natural nacre and many engineering materials. This bottom-up strategy has no size restriction or fundamental barrier for further scale-up, and can be easily extended to other material systems, opening an avenue for mass production of high-performance bulk nacre-mimetic structural materials in an efficient and cost-effective way for practical applications.Artificial materials that replicate the mechanical properties of nacre represent important structural materials, but are difficult to produce in bulk. Here, the authors exploit the bottom-up assembly of 2D nacre-mimetic films to fabricate 3D bulk artificial nacre with an optimized architecture and excellent mechanical properties.
Droplet dynamics on a solid substrate is significantly influenced by surfactants. It remains a challenging task to model and simulate the moving contact line dynamics with soluble surfactants. In ...this work, we present a derivation of the phase-field moving contact line model with soluble surfactants through the first law of thermodynamics, associated thermodynamic relations and the Onsager variational principle. The derived thermodynamically consistent model consists of two Cahn–Hilliard type of equations governing the evolution of interface and surfactant concentration, the incompressible Navier–Stokes equations and the generalized Navier boundary condition for the moving contact line. With chemical potentials derived from the free energy functional, we analytically obtain certain equilibrium properties of surfactant adsorption, including equilibrium profiles for phase-field variables, the Langmuir isotherm and the equilibrium equation of state. A classical droplet spread case is used to numerically validate the moving contact line model and equilibrium properties of surfactant adsorption. The influence of surfactants on the contact line dynamics observed in our simulations is consistent with the results obtained using sharp interface models. Using the proposed model, we investigate the droplet dynamics with soluble surfactants on a chemically patterned surface. It is observed that droplets will form three typical flow states as a result of different surfactant bulk concentrations and defect strengths, specifically the coalescence mode, the non-coalescence mode and the detachment mode. In addition, a phase diagram for the three flow states is presented. Finally, we study the unbalanced Young stress acting on triple-phase contact points. The unbalanced Young stress could be a driving or resistance force, which is determined by the critical defect strength.
The lifespan of high‐energy‐density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to ...obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3−) is proposed and validated to improve the homogeneity of the SEI in practical LMBs. NO3− is connected to an ether‐based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3− and improve the reducibility. The decomposition of non‐resonant −NO3 in ISDN enriches SEI with abundant LiNxOy and induces uniform lithium deposition. Lithium–sulfur batteries with ISDN additives deliver a capacity retention of 83.7 % for 100 cycles compared with rapid decay with LiNO3 after 55 cycles. Moreover, lithium–sulfur pouch cells with ISDN additives provide a specific energy of 319 Wh kg−1 and undergo 20 cycles. This work provides a realistic reference in designing additives to modify the SEI for stabilizing LMBs.
The modification of NO3− is achieved by connecting NO3− to an ether‐based moiety. The broken resonance structure of −NO3 improves its reducibility compared with NO3−. The decomposition of −NO3 forms a LiNxOy‐rich solid electrolyte interphase (SEI) and induces uniform Li deposition.
A new kind of nitrogen‐doped graphene/carbon nanotube nanocomposite can be synthesized by a facile hydrothermal process under mild conditions, which exhibits synergistically enhanced electrochemical ...activity for the oxygen reduction reaction. This research provides a new route to access a metal‐free electrocatalyst with high activity under mild conditions.
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