One-step fluorine-free synthesis of delaminated, OH-terminated Ti3C2: High photocatalytic NOx storage selectivity enabled by coupling TiO2 and Ti3C2-OH

Difficulties associated with MXene fabrication typified by an environmentally hazardous fluorine-based etching process followed by delamination and fluorine reduction steps create obstacles against the expansion of this outstanding material and its application in air purification. Herein, we demonstrate a one-step hydrothermal process that involves alkali (NaOH)-assisted aluminum etching in the presence of a delaminating agent (hy-drazine) for synthesis of delaminated, OH-terminated MXene (Ti3C2-OH). The process does not require the use of fluorine-containing compounds and produces Ti3C2-OH sheets without the need for post-synthesis treatment. Ti3C2-OH shows a strong synergistic effect as a co-catalyst when coupled with TiO2 during photocatalytic oxidation of NOx. Excellent NOx storage selectivity (91 %) and a positive DeNOx index (+ 0.30) were achieved at NO conversion of 54 %. The photocatalytic activity of the hybrid shows high sensitivity to the surface chemistry of the co-catalyst as Ti3C2-OH outperforms delaminated, F-terminated Ti3C2 (fabricated via the traditional process), which shows low NO2 storage selectivity (65 %) and a negative DeNOx index (-0.05) at NO conversion of 47 %. We envision that these findings will benefit ongoing efforts aimed at developing effective alternative methods for MXene synthesis and provide a pathway for rational design of efficient NOx abatement photocatalysts.