The equilibrium of intergranular stress and strain can be realized simultaneously, whereas five independent slip systems of the Taylor principle and the criterion of minimal internal work are unnecessary. In fact, the Taylor principle applied in current theories is incorrect both in practice and theory, in which the activation mechanism of plastic deformation systems must violate the Schmid’s law and deviate from the elastic–plastic characteristics of deformed matrix. The intergranular reaction stress (RS) during deformation can be calculated according to Hooke’s law and elastic limit without additional subjective presupposition, therefore the RS theory is established intuitively. Under the combination of the RS (the intergranular elastic effect) and the external loading the slips penetrating grains are activated and produce deformation texture, but certain non-penetrating slips near grain boundaries will become active (the intergranular plastic effect) and produce some random texture when a RS reaches the yield strength of grains. The RS theory is simple, intuitive and reasonable, based on which the texture simulation can well reproduce the texture formation of various metals under different external loadings and under different crystallographic mechanisms.
Currently, δ-MnO2 is one of the popularly studied cathode materials for aqueous zinc-ion batteries (ZIBs) but impeded by the sluggish kinetics of Zn2+ and the Mn cathode dissolution. Here, we report our discovery in the study of crystalline/amorphous MnO2 (disordered MnO2), prepared by a simple redox reaction in the order/disorder engineering. This disordered MnO2 cathode material, having open framework with more active sites and more stable structure, shows improved electrochemical performance in 2 mol·L−1 ZnSO4/0.1 mol·L−1 MnSO4 aqueous electrolyte. It delivers an ultrahigh discharge specific capacity of 636 mA·h·g−1 at 0.1 A·g−1 and remains a large discharge capacity of 216 mA·h·g−1 even at a high current density of 1 A·g−1 after 400 cycles. Hence disordered MnO2 could be a promising cathode material for aqueous ZIBs. The storage mechanism of the disordered MnO2 electrode is also systematically investigated by structural and morphological examinations of ex situ, ultimately proving that the mechanism is the same as that of the δ-MnO2 electrode. This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.
Tricobalt tetroxide (Co3O4) is one of the promising anodes for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, the poor electrical conductivity and the rapid capacity decay hamper its practical application. In this work, we design and fabricate a hierarchical Co3O4 nanorods/N-doped graphene (Co3O4/NG) material by a facile hydrothermal method. The nitrogen-doped graphene layers could buffer the volume change of Co3O4 nanorods during the delithium/lithium process, increase the electrical conductivity, and profit the diffusion of ions. As an anode, the Co3O4/NG material reveals high specific capacities of 1873.8 mA·h·g−1 after 120 cycles at 0.1 A·g−1 as well as 1299.5 mA·h·g−1 after 400 cycles at 0.5 A·g−1. Such superior electrochemical performances indicate that this work may provide an effective method for the design and synthesis of other metal oxide/N-doped graphene electrode materials.
Conductive films have emerged as appealing electrode materials in flexible supercapacitors owing to their conductivity and mechanical flexibility. However, the unsatisfactory electrode structure induced poor output performance and undesirable cycling stability limited their application. Herein, a well-designed film was manufactured by the vacuum filtration and in-situ polymerization method from cellulose nanofibrils (CNFs), molybdenum disulfide (MoS2), and polypyrrole. The electrode presented an outstanding mechanical strength (21.3 MPa) and electrical conductivity (9.70 S·cm−1). Meanwhile, the introduce of hydrophilic CNFs induced a desirable increase in diffusion path of electrons and ions, along with the synergistic effect among the three components, further endowed the electrode with excellent specific capacitance (0.734 F·cm−2) and good cycling stability (84.50% after 2000 charge/discharge cycles). More importantly, the flexible all-solid-state symmetric supercapacitor delivered a high specific capacitance (1.39 F·cm−2 at 1 mA·cm−2) and a volumetric energy density (6.36 mW·h·cm−3 at the power density of 16.35 mW·cm−3). This work provided a method for preparing composite films with desired mechanical and electrochemical performance, which can broaden the high-value applications of nanocellulose.
Carbon–molybdenum disulfide (C–MoS2) ultrathin nanosheets were prepared by a hydrothermal process, and then AgI/C–MoS2 were synthesized via an in-situ deposition method. This ternary heterojunction composite exhibited better photocatalytic activity compared with those of one-component (pristine MoS2) and bi-component (AgI/MoS2 and C–MoS2) materials for the degradation of organic dyes under the visible-light irradiation. In particular, by comparing with AgI/MoS2, the significant role of conductive amorphous carbon in AgI/C–MoS2 in enhancing the charge transfer during the photocatalytic degradation of dyes was first confirmed by photocurrent response and electrochemical impedance spectroscopy (EIS). A possible photocatalytic mechanism was proposed based on the capture experiment results. Furthermore, a straightforward and interesting way had been applied to test the recycled/newly-prepared AgI/C–MoS2 composite for revealing its distinctive self-cleaning performance and recyclability characteristic besides its good photocatalytic activity. This work could provide a reference for the design of other new ternary heterojunction composite materials with special structures and properties.
High fluorescence quantum yield (QY), excellent fluorescence stability, and low toxicity are essential for a good cellular imaging fluorescent probe. Green-emissive carbon quantum dots (CQDs) with many advantages, such as unique fluorescence properties, anti-photobleaching, low toxicity, fine biocompatibility and high penetration depth in tissues, have been considered as a potential candidate in cell imaging fluorescent probes. Herein, N, S-codoped green-emissive CQDs (QY= 64.03%) were synthesized by the one-step hydrothermal method, with m-phenylenediamine as the carbon and nitrogen source, and L-cysteine as the nitrogen and sulfur dopant, under the optimum condition of 200 °C reaction for 2 h. Their luminescence was found to originate from the surface state. In light of the satisfactory photobleaching resistance and the low cytotoxicity, CQDs were used as a cell imaging probe for HeLa cell imaging. The results clearly indicate that cells can be labeled with CQDs, which can not only enter the cytoplasm, but also enter the nucleus through the nuclear pore, showing their broad application prospect in the field of cell imaging.
Adsorption of drug powder is caused by triboelectrification on the surface of starch capsule during filling process. Furthermore, high wear rate and poor water lubricity also hinder the further practical applications of traditional starch capsule. To solve these problems, a glycerol-modified starch capsule with perfect anti-triboelectrification and enhanced lubrication performance was fabricated. Hydrogen bond between glycerol and starch molecules could reduce the bound water content on the capsule surface and thus realizes anti-triboelectrification. By adding glycerol, a three-tier structure composed of starch-glycerol-water is formed through hydrogen bonding on the surface of the starch film, which has been proven to be favorable for lubrication performance. When 5% glycerol is added, the short-circuit current (Isc) of starch-based triboelectric nanogenerator (TENG) is reduced by 86%, and the wear volume of the starch film is reduced by 89%. Under water lubrication condition, the lubrication performance of the starch-glycerol film can reach the super lubricated level with a friction coefficient of about 0.005. This work provides a new route to obtain modified starch capsules with improved anti-triboelectrification property, reduced wear rate and superlubricity property.
The synergistic effect of polyethylene glycol (PEG) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) can effectively reduce the protein absorption, which is beneficial to theranostics. However, PEG–PMPC-based polymers have rarely been used as nanocarriers in the theranostic field due to their limited modifiability and weak interaction with other materials. Herein, a plain method was proposed to endow them with the probable ability of loading small active agents, and the relationship between the structure and the ability of loading hydrophobic agents was explored, thus expanding their applications. Firstly, mPEG–PMPC or 4-arm-PEG–PMPC polymer was synthesized by atom transfer radical polymerization (ATRP) using mPEG-Br or 4-arm-PEG-Br as the macroinitiator. Then a strong hydrophobic segment, poly(butyl methacrylate) (PBMA), was introduced and the ability to load small hydrophobic agents was further explored. The results showed that linear mPEG–PMPC–PBMA could form micelles 50–80 nm in size and load the hydrophobic agent such as Nile red efficiently. In contrast, star-like 4-arm-PEG–PMPC–PBMA, a monomolecular micelle (10–20 nm), could hardly load any hydrophobic agent. This work highlights effective strategies for engineering PEG–PMPC-based polymers and may facilitate the further application in numerous fields.
