[en] Highlights: • Porous nanostructure carbon quantum dots/polypyrrole composite film was successfully synthesized by direct electrochemical method. • A flexible all-solid-state supercapacitor device was fabricated using the carbon quantum dots/polypyrrole composite electrode. • The flexible supercapacitor exhibits high specific capacitance, excellent reliability and long cycling life. - Abstract: Recently, carbon quantum dots (CQDs) as a new zero-dimensional carbon nanomaterial have become a focus in electrochemical energy storage. In this paper, flexible all-solid-state supercapacitors (ASSSs) were electrochemically synthesized by on-step co-deposition of appropriate amounts of pyrrole monomer and CQDs in aqueous solution. The different electrodeposition time plays an important role in controlling morphologies of stainless steel wire meshes (SSWM)-supported CQDs/PPy composite film. The morphologies and compositions of the obtained CQDs/PPy composite electrodes were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectrum and X-ray photoelectron spectroscopy (XPS). Furthermore, a novel flexible ASSS device was fabricated using CQDs/PPy composite as the electrode and separated by polyvinyl alcohol/LiCl gel electrolyte. Benefiting from superior electrochemical properties of CQDs and PPy, the as-prepared CQDs/PPy composite ASSSs exhibit outstanding electrochemical performance with the areal capacitance 315 mF cm⁻² (corresponding to specific capacitance of 308 F g⁻¹) at a current density of 0.2 mA cm⁻² and long cycle life with 85.7% capacitance retention after 2 000 cycles.

[en] Highlights: • An electrostatic self-assembly strategy was proposed to prepare CQDs/HpCN nanocomposite. • Carbon quantum dots (CQDs) attached onto surface of proton-functionalized graphitic carbon nitride (HpCN) through electrostatic attraction. • The CQDs/HpCN nanocomposite exhibited excellent photocatalytic and photoelectrochemical properties. - Abstract: Carbon quantum dots (CQDs) and graphitic carbon nitride (g-C_3N_4), as advanced metal-free material catalysts have been the focus of considerable attention because of their superior photocatalytic activities. In this study, we developed a novel approach to obtain CQDs/g-C_3N_4 nanocomposite with effective interfacial contact by incorporating negatively charged CQDs and tailor-made proton-functionalized g-C_3N_4via the electrostatic self-assembly strategy. Then, the morphology and microstructure of the new nanocomposite were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The CQDs and proton-functionalized g-C_3N_4 nanocomposite exhibited excellent electron transfer properties though electrochemical impedance spectroscopy (EIS), significantly enhanced photoactivity in the photoelectrochemical i–t curve test and degradation of methylene blue solution under visible light irradiation. These results demonstrated that the electrostatic self-assembly strategy process is a promising method of fabricating uniform metal-free material catalysts for an extensive range of applications.

[en] A carbon ceramic electrode was modified with a thin film composed of over oxidized polypyrrole, CuO and multi-walled carbon nanotubes. The surface morphology, electrochemical properties and electrocatalytic activity towards the oxidation of glucose of the modified electrode were studied in detail. Benefiting from the high electrocatalytic activity of CuO, the selectivity of OPpy film, and the fast electron transfer rate promoted by MWCNTs, this modified electrode displays good stability, selectivity, high electrocatalytic activity and a low detection limit for the determination of glucose in pH 13 solution. Under the optimum conditions, the linear range for the determination of glucose by cyclic voltammetry is from 20 μM to 10 mM, and the detection limit is 4.0 μM (at an SNR of 3). The amperometric calibration plot covers the 0.20 μM to 2.0 mM concentration range, and the detection limit is 50 nM. The highest sensitivity for the determination of glucose is 3922.6 μA mM⁻¹ cm². (author)

[en] Narrowband amplitude demodulation is an effective tool for extracting characteristic features in the fault diagnosis of rolling element bearings. The quality of demodulation largely depends on the frequency band selected for the demodulation. Numerous criteria have been constructed to determine the optimal frequency band. However, independent frequency interferences and in-band noises in narrowband signals can greatly affect the values of the criteria, which may lead to an inaccurate result in locating the optimal band, in demodulating fault features, and finally in the fault detection. Inspired by the nonlocal means (NL-means) denoising method that has been widely used in image processing, this paper proposes a narrowband envelope spectra fusion (NESF) method to enhance fault features and suppress in-band noises before criterion calculation. The method suppresses in-band noises by averaging envelope spectra at neighboring narrow bands. Meanwhile, some minor improvements are made to the conventional narrowband envelope spectrum calculation method to enhance the similarity of the narrowband envelope spectra containing fault features, and finally optimize the fusion process. Then, sparsity values of these denoised envelope spectra, which can lower the impact of independent frequency interferences, are utilized to determine the optimal band and select the optimal envelope spectrum. Frequency signatures of the extracted envelope spectrum can be utilized to indicate the status and fault types of rolling element bearings. A simulated bearing fault signal and three real bearing fault signals are used to validate the effectiveness of the proposed method through comparison studies with protrugram and sparsogram. The results show that the proposed method can effectively extract fault characteristics, even in a harsh environment. (paper)

[en] The coupled CO₂–water curing technique has been used for curing Portland cement-based materials, enabling the cement/concrete products with rapid strength development and lower carbon footprints. However, there is still a lack of convincing understanding on the mechanism of the accelerated carbonation reactions of cement. This current work mainly focused on characterizing the C–S–H gel formed in the bulk cement paste prepared with a low water to cement ratio (w/c = 0.18) subjected to a coupled CO₂–water curing regime, by using solid state ²⁹Si NMR and infrared spectroscopy together with other common tools. The results indicated that the CO₂ curing process led to the formation of C–S–H gel containing more Q² species than that in the corresponding hydrated pastes. Prolonged CO₂ curing incorporated more Al tetrahedra into the C–S–H gel. Meanwhile, both the amorphous carbonates and calcite were formed during the accelerated carbonation reactions, and the calcite crystals could serve as nuclei to accelerate the cement hydration at the early age. Excessive CO₂ curing resulted in a deficiency of lime in solution, yielding a structurally modified C–S–H with the absence of interlayered Ca(OH)₂, and longer silicate chains as well as a higher polymerization degree when compared to the C–S–H formed in the normally hydrated cement samples.

[en] Highlights: • 3D carambola-like nanostructure MXene/PPy composite was synthesized by one-step electrochemical co-deposition method. • The MXene/PPy composite film electrode demonstrated an outstanding electrocapacitive performance. • The as-fabricated symmetric supercapacitor exhibited high specific capacitance, excellent reliability and long cycling life. -- Abstract: Two-dimensional (2D) MXenes have been extensively investigated for electrochemical energy storage because of their excellent electronic properties. In this work, a facile and effective method was developed to fabricate MXene/polypyrrole (MXene/PPy) composite film electrodes via one-step co-electrodeposition. In this process, 2D Ti₃C₂T_x-MXene nanosheets acted as a core polymer because of the functional groups, such as –F, –OH, or –O, on their surface, and pyrrole monomer radical cations (Py·⁺) would gradually polymerize on the surface and layer space of the 2D MXene nanosheets to form three-dimensional (3D) carambola-like MXene/PPy composite films. The 3D structure composite facilitated electron transfer and ionic diffusion, so the MXene/PPy composite film electrodes exhibited an outstanding electrochemical performance with a high gravimetric capacitance of 416 F g⁻¹ at a current density of 0.5 A g⁻¹ in a three-electrode system. The as-fabricated symmetric supercapacitors of ITO-glasses coated with MXene/PPy composite films also exhibited a high specific capacitance (184 F g⁻¹ at a scan rate of 10 mV s⁻¹), excellent reliability and good cycling stability (approximately 86.4% retention after 5000 cycles, at 5 A g⁻¹).