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Quantitative identification of mixed-valence metal ions in solution by the distinctive fluorescence responses of graphene quantum dots. [Display omitted] • Quantitative mixed-valence state identification of Fe3+/Fe2+ solution by graphene quantum dots (GQDs). • The real-time monitoring of the dynamic changes in mixed-valence states triggered by the redox process was realized. • This method can be extended to other metal ions (Cr3+/Cr2+ or Cu2+/Cu+) and typically functionalised GQDs. • A universal and facile method for the quantitative mixed-valence state identification of metal ions in a solution. Quantitative identification of mixed-valence metal ions is essential for gaining deeper insights into critical chemical and biological processes in environmental science, chemical engineering, and biological systems. However, a simple approach of quantitative identification mixed-valence metal ions in solution has remained a challenge. In this study, we have experimentally observed a significant linear correlation (R2 = 0.99) between the concentration of high-valence metal ions (using iron ions as an example) and the fluorescence intensity of graphene quantum dots (GQDs). Utilizing the distinct fluorescence responses of GQDs to high-valence and low-valence metal ions, reliable quantitative detection of mixed-valence metal ions has been successfully achieved. Remarkably, we introduced real-time monitoring of mixed-valence metal ions, revealing a shift from a molar ratio of approximately 4.0 to 2.0. Density functional theory calculations have revealed significant differences in charge transfer between high-valence and low-valence states of metal ions adsorbed onto GQDs. Furthermore, the versatility of this method can extend to various types of GQDs and metal ions, highlighting its universal applicability. This work presents a simple, convenient, and cost-effective approach for quantitatively identifying mixed-valence metal ions in solution, offering a new avenue and opportunity for applications in biochemistry, environmental science, catalysis and materials science. [ABSTRACT FROM AUTHOR]

In this paper, ultra-fine Ti(C,N)–TiB 2 –Co cermets were prepared by reactive hot processing from the Co–Ti–C–BN system. Microstructure observation indicated that Co and TiB 2 uniformly distributed in the ultra-fine Ti(C,N) matrix. Carbon contents in the reactants had a great influence on the porosity and properties of synthesized cermets. In the range of 11.76–13.79 at.% carbon, dense samples were obtained. With increasing carbon contents, the relative density and hardness decreased due to the existence of residual carbon. The wear resistance of dense Ti(C,N)–TiB 2 –Co cermets were better than that of YT15 cemented carbide. In addition, the reaction process in the Co–Ti–C–BN system was explored by differential scanning calorimeter and X-ray diffraction. Results revealed that Ti(C,N) was synthesized through the solid solution of carbon into TiN, and the addition of Co to Ti–C–BN mixtures promoted the production of Ti(C,N) by the formation of Co–Ti liquid. [ABSTRACT FROM AUTHOR]

Lamellar MoS 2 has attracted widespread attention as a potential electrocatalytic HER (Hydrogen evolution reaction) catalyst. However, it is difficult to further improve its catalytic activity due to two major drawbacks: the limited number of active sites and its poor conductivity. Here, we adopt a one-step method utilizing an ultrafast pulsed laser treatment to produce multiple decorations on lamellar MoS 2 , where nanocrystallization and amorphization of lamellar MoS 2 are achieved simultaneously, along with an additional characteristic of atomic steps. Due to this special microstructure, laser-treated MoS 2 exhibits excellent electrocatalytic performance with a low overpotential and a small Tafel slope (217 mV @ 10 mA cm−2 and 74.5 mV dec−1, respectively), which is superior to that of untreated lamellar MoS 2 (461 mV @ 10 mA cm−2 and 142.6 mV dec−1, respectively). The MoS 2 prepared in this way has a high catalytic activity and a high stability, which indicates potential for electrocatalysis applications. • We proposed a one-step method using ultrafast pulsed laser treatment to enhance the HER performance of lamellar MoS 2. • We prepared ultra-small MoS 2 nanoparticles, amorphization, and atomic steps in situ on lamellar MoS 2. • The performance of treated MoS 2 is far superior to that of MoS 2 before laser treatment. [ABSTRACT FROM AUTHOR]