Controllable synthesis of superparamagnetic NiCo-graphene quantum dot-graphene composite with excellent dispersion for high performance magnetic field-controlled electrochemical flow hybrid supercapacitor

CoO/Co-graphene quantum dots as an oxidative mimetic nanozyme for the colorimetric detection of L-cysteine

The preparation of cobalt-based nanozymes with high oxidase-like activity still needs more efforts. In this paper, we report the synthesis of a CoO/Co-tryptophan-functional graphene quantum dot hybrid (CoO/Co-Try-GQD). Firstly, cobalt ions coordinate with the indole nitrogen on Try-GQD to form a complex, followed by thermal reduction and oxidation. The resulting hybrid presents a three-dimensional network structure, and CoO/Co nanoparticles are uniformly dispersed on the graphene sheet with an average size of 10 ± 0.24 nm. This unique structure improved the oxidase-like activity of the hybrid, enabling it to catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to rapidly produce deep blue ox-TMB with a strong absorbance at 652 nm (A652). A colorimetric method was developed for the highly sensitive determination of L-cysteine (L-cys) based on the inhibition of the hybrid's oxidase-like activity and low A652 caused by the binding of L-cys with Co atoms on CoO/Co via the Co-S bond. The A652 linearly decreased with increasing L-cys concentration in the range of 0.05-2 μM, and the detection limit was 0.032 μM. Further, the established method has been successfully applied to the determination of L-cys in milk.

Facile Synthesis of Nitrogen-Doped Graphene Quantum Dots/MnCO3/ZnMn2O4 on Ni Foam Composites for High-Performance Supercapacitor Electrodes

This study reports the facile synthesis of rationally designed composite materials consisting of nitrogen-doped graphene quantum dots (N-GQDs) and MnCO3/ZnMn2O4 (N/MC/ZM) on Ni foam using a simple hydrothermal method to produce high-performance supercapacitor applications. The N/MC/ZM composite was uniformly synthesized on a Ni foam surface with the hierarchical structure of microparticles and nanosheets, and the uniform deposition of N-GQDs on a MC/ZM surface was observed. The incorporation of N-GQDs with MC/ZM provides good conductivity, charge transfer, and electrolyte diffusion for a better electrochemical performance. The N/MC/ZM composite electrode delivered a high specific capacitance of 960.6 F·g-1 at 1 A·g-1, low internal resistance, and remarkable cycling stability over 10,000 charge-discharge cycles. Additionally, an all-flexible solid-state asymmetric supercapacitor (ASC) device was fabricated using the N/MC/ZM composite electrode. The fabricated ASC device produced a maximum energy density of 58.4 Wh·kg-1 at a power density of 800 W·kg-1 and showed a stable capacitive performance while being bent, with good mechanical stability. These results provide a promising and effective strategy for developing supercapacitor electrodes with a high areal capacitance and high energy density.

MXene/Ferrite Magnetic Nanocomposites for Electrochemical Supercapacitor Applications

MXene has been identified as a new emerging material for various applications including energy storage, electronics, and bio-related due to its wider physicochemical characteristics. Further the formation of hybrid composites of MXene with other materials makes them interesting to utilize in multifunctional applications. The selection of magnetic nanomaterials for the formation of nanocomposite with MXene would be interesting for the utilization of magnetic characteristics along with MXene. However, the selection of the magnetic nanomaterials is important, as the magnetic characteristics of the ferrites vary with the stoichiometric composition of metal ions, particle shape and size. The selection of the electrolyte is also important for electrochemical energy storage applications, as the electrolyte could influence the electrochemical performance. Further, the external magnetic field also could influence the electrochemical performance. This review briefly discusses the synthesis method of MXene, and ferrite magnetic nanoparticles and their composite formation. We also discussed the recent progress made on the MXene/ferrite nanocomposite for potential applications in electrochemical supercapacitor applications. The possibility of magnetic field-assisted supercapacitor applications with electrolyte and electrode materials are discussed.