We report a strategy to turn non-electrocatalytic 2D-titanium carbide MXene (Ti2CTx) into a highly active electrocatalyst by nitridation with sodium amide (NaNH2).

Sr 1-x , Zn x ) 1-y (Al 1.98 , B 0.02 )O 4 :Eu y 2+ green phosphor particles for ultraviolet light-emitting diodes (UV LEDs) were prepared by spray pyrolysis and their luminescent properties were investigated with changing the reducing temperature, the concentration of the activator, and the ratio of Sr to Zn. For the Sr(Al 1.98 , B 0.02 )O 4 :Eu 2+ phosphor, pure monoclinic SrAl 2 O 4 phase was formed when the post-treatment temperature was 1100-1200 °C. Over 1300 °C, however, the Sr 4 Al 14 O 25 phase appeared as a minor phase, which induced a blue shift in the emission peak. The highest intensity of Sr(Al 1.98 , B 0.02 )O 4 :Eu 2+ phosphor was achieved when the reducing temperature and the content of Eu 2+ were 1200 °C and 10 mol % of the strontium, respectively. It was found that the substitution of 10-50% Zn atoms instead of the strontium greatly enhanced the 520 nm green emission, especially for the excitation wavelength range from 380 to 420 nm. At the high Zn concentration (x > 0.7), a new blue (460 nm) emission was observed and stable even at ambient temperature. This blue emission disappeared when the Zn content became lower than 0.7. The excitation spectrum of (Sr 1-x , Zn x )(Al 1.98 , B 0.02 )O 4 :Eu 2+ phosphor (x e 0.7) well overlapped with the 460 nm blue emissions. Consequently, it was concluded that the new blue sites successfully played the role of sensitizer for the energy transfer, which is responsible for the enhancement of the luminescence intensity. Finally, the optimized phosphor (Sr 0.6 , Zn 0.4 ) 0.9 (Al 1.98 , B 0.02 )O 4 :Eu 2+ 0.1 showed 185% improved emission intensity compared with that of the Sr 0.9 (Al 1.98 , B 0.02 )O 4 :Eu 2+ 0.1 phosphor under ultraviolet (λ ex ) 393 nm) excitation.

2D transition metal carbides and nitrides, namely MXenes, are normally synthesized in acidic solutions and are delaminated in basic solutions. This results in versatile materials with unique physical/chemical properties suitable for various practical applications. However, solution‐based chemical treatments can affect the chemical structures of MXenes, which accelerates the oxidation reactions and degrades their intrinsic properties. Here, long‐term stable Ti3C2Tx dispersion in deep eutectic solvents (DESs) that resisted oxidation degradation for up to 28 weeks is demonstrated. As an anti‐oxidative dispersion medium, DESs helped prevent oxidation of Ti3C2Tx layers due to hydrogen bond accepting and donating molecules passivated surface of the Ti3C2Tx. In addition, DES molecules in bulk solution can also be hydrated in the presence of water, which stabilizes reactive oxygen by forming stable DES‐water cluster. Therefore, the use of DESs enhanced the delamination of the Ti3C2Tx nanosheets, while preventing oxidation of the nanosheets in solution and even in their dried state. As a result, thick and thin films of Ti3C2Tx fabricated using DESs exhibited stable sheet resistance in comparison with pristine‐Ti3C2Tx. In addition, Ti3C2Tx dispersed in DESs can be applied as electrodes for electrochemical capacitors, in which they showed higher chemical stability and better performance than pristine Ti3C2Tx.

No abstract