In the present study, highly fluorescent carbon dots were prepared by using citric acid as the carbon source with the binary dopants, i.e. melamine and formaldehyde, named as MF-CDs. The co-dopants played a crucial role to enhance the fluorescence quantum yield of the MF-CDs, reaching 48%, in which melamine was the major nitrogen source, while formaldehyde was the co-dopant to regulate the state of nitrogen in the MF-CDs. The fluorescence of the MF-CDs was found to be quenched by Hg 2+ , and then recovered equally by individual halogen ions (eg. Cl − , Br − and I − ). Correspondingly, the “turn off” and “turn off-on” sensing systems were separately established to detect Hg 2+ and total halogen ions with good accuracy and reliability. In addition, the fluorescence of the MF-CDs was quenched by ClO − , and recovered by Fe 2+ ; the “turn off” sensor was established to detect ClO − in tap water with low limit of detection of 0.18 μM, and the “turn off-on” sensor was to determine the ferrous succinate in ferrous succinate tablets. Furthermore, owing to the low cytotoxicity, the MF-CDs were successful for cellular labeling on HepG2 cells. The developed binary dopants were effective to enhance the fluorescence quantum yield and endow the MF-CDs with some special properties, which would help to widen the applicability of the carbon dots.
Jie Wang,Qiming Liu,Shiyue Cao,Huijuan Zhu,Yilin Wang
Na 3 V 2 (PO 4 ) 2 F 3 (NVPF), recognized for its Na superionic conductor architecture, emerges as a promising candidate among polyanion-type cathodes for sodium ion batteries (SIBs). However, its adoption in practical applications faces obstacles due to its inherently low electronic conductivity. To address this challenge, we employ a binary co-doped strategy to design Na 3.3 K 0.2 V 1.5 Mg 0.5 (PO 4 ) 2 F 3 cathode with nitrogen-doped carbon (NC) coating layer. This configuration enhances electronic conductivity and reduces diffusion barriers for sodium ion (Na + ). The strategy of incorporating nitrogen-doped carbon coating not only facilitates the formation of a porous structure but also introduces additional defects and active sites. Such modifications accelerate the reaction kinetics and augment electrolyte interaction through an expanded specific surface area, thus streamlining the electrochemical process. Concurrently, strategic heteroatom substitution leads to a more efficient engagement of Na + in the electrochemical activities, thereby bolstering the cathode's structural integrity. The vanadium fluorophosphate Na 3.3 K 0.2 V 1.5 Mg 0.5 (PO 4 ) 2 F 3 @NC exhibits an electrochemical performance, including a high discharge specific capacity of 124.3 mA h g −1 at 0.1C, a long lifespan of 1000 cycles with a capacity retention of 93.1 % at 10C, and a rate property of 73.2 mA h g −1 at 20C. This research provides a method for preparing binary doped NVPF for energy storage electrochemistry.
Photocatalytic H 2 production from seawater splitting is a promising method for sustainable energy conversion technology. The vanadium-oxygen binary doped carbon nitride (VO X -CN) is successfully prepared for H 2 production. Benefiting from the electronic structure alteration, the maximum H 2 yield on VO X -CN in artificial seawater reaches 4475.74 μmol h −1 g −1 , 10 times higher than that of CN in deionized water. The impact of ions on the photocatalytic activity of VO 2 -CN is followed by Na + > Mg 2+ > K + > Ca 2+ . The adsorption of electrolyte ions promotes the formation of delocalized electron clouds on the surface of VO 2 -CN, facilitating more electrons to participate in H + reduction. Screening based on six machine models, the decision tree regression algorithm is used to reveal the interaction between cation type, their concentration and H 2 yield. Pearson heatmap indicates that Na + , Mg 2+ , and K + ions are positively correlated with H 2 yield, whereas Ca 2+ shows a negative correlation. The interactions among Na + , Mg 2+ and K + atoms facilitate H 2 production in multi-ion system, whereas Ca 2+ ions do the opposite, especially for high concentration. This work proposes new insights into the interference on H 2 yield between the structure alteration of CN framework and the change of ion type and concentration.
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