Tuning the feature sizes and surface moiety groups of a two-dimensional (2D) sheet material has been regarded as the most effective strategy for achieving desired physical and chemical properties. The newly emerging transition-metal carbide or nitride sheets, generally referred to as MXenes, are of interest to the research community owing to their versatile behavior. While the chemical stability of MXenes is of pivotal importance to their real applications, a systematic study of examining the effect of their surface and lateral size on the resulting chemical stability is still lacking. Herein, by systematically varying the synthesis parameters, we obtained both regular and ultrasmall Ti3C2 sheets with different surfaces, namely, Al oxyanions or OH/F. To investigate the chemical stability and sustainability of each Ti3C2 sheet in an oxidizing environment, including an ambient atmosphere and a H2O2 medium, the evolution of phase, morphology, and optical behavior was carefully studied. The sheets covered with Al oxyanions had greater structural stability than those covered with the other species considered in this study, which may be due to the Al oxyanions acting like a shield and passivating the surface in the oxidizing atmosphere. Regarding the effect of feature size, thinner sheets or those with smaller lateral dimensions showed improved oxidation resistance, which could be due to the difficulty encountered in the structural recrystallization from Ti3C2 to oxidized product TiO2. This study provides a deeper understanding of MXenes and a method to efficiently engineer structures with desired performances.
Congyang Mao,Wanyu Jin,Yiming Xiang,Yizhou Zhu,Jun Wu,Xiangmei Liu,Shuilin Wu,Yufeng Zheng,Kenneth M. C. Cheung,Kelvin Wai Kwok Yeung
Conferring catalytic defects in sonosensitizers is of paramount importance in reinforcing sonodynamic therapy. However, the formation of such 0D defects is governed by the Schottky defect principle. Herein, 2D catalytic planar defects are designed within Ti 3 C 2 sheets to address this challenge. These specific planar slip dislocations with abundant Ti 3+ species (Ti 3 C 2 -SD(Ti 3+ )) can yield surface-bound O due to the effective activation of O 2 , thus resulting in a substantial amount of 1 O 2 generation and the 99.72% ± 0.03% bactericidal capability subject to ultrasound (US) stimulation. It is discovered that the 2D catalytic planar defects can intervene in electron transfer through the phonon drag effect—a coupling effect between surface electrons and US-triggered phonons—that simultaneously contributes to a dramatic decrease in O 2 activation energy from 1.65 to 0.06 eV. This design has achieved a qualitative leap in which the US catalytic site has transformed from 0D to 2D. Moreover, it is revealed that the electron origin, electron transfer, and visible O 2 activation pathway triggered by US can be attributed to the phonon–electron coupling effect. After coating with neutrophil membrane (NM) proteins, the NM-Ti 3 C 2 -SD(Ti 3+ ) sheets further demonstrate a 6-log 10 reduction in methicillin-resistant Staphylococcus aureus burden in the infected bony tissue.
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