MXenes are a novel family of two-dimensional (2D) transition metal carbides, carbonitrides and nitrides, directly prepared from selective etching of the A-site element in MAX phase precursors. Their general chemical formula Mn+1XnTx describes comprising n+1 layers (n=1–4) of early transition metals (‘M’), interleaved by n layers of carbon and/or nitrogen atoms (‘X’), with Tx representing surface terminations bonded to the outer M layers (i.e. –F, –O, –OH). Thus, their unique morphology mechanical, electronic, chemical, and optical properties makes them promising materials for advanced applications, such as in the consolidated role in the field of photocatalysis [1].

The development of new photo-thermal catalysts for the efficient valorisation of CO2 and N2 into high value chemical is of great interest.[2] Herein we deal with multi-layered titanium nitride (Ti2N) MXene as promising photothermal catalysts, see figure 1a. Selectivity of Ti2N can be easily controlled modifying its chemical surface partially oxidating the superficial layers of Ti2N MXene during the purification process, (figure 1b). Results show that when multi-layered titanium nitride (Ti2N) MXene is not oxidized the activity towards CO2 photothermal reduction is less favoured, whereas shows selectivity in the N2 fixation to NH3. Terminal nitrogen on the multi-layered Ti2N MXene surface offered an active role in the activation of N2 molecules by occupying the nitrogen vacancies produced during photothermal-catalytic reaction and efficiency shows sensitivity to the persulfate (PS) precursor that is used in the purification see figure 1c. In the counterpart, partially oxidation of T2N surfaces induces a kind of passivation by the formation of a thin layer of TiO2 avoiding the N2 molecules to occupy nitrogen vacances. Moreover, partial oxidation induced the formation of heterojunction between TiO2 and Ti2N, switching selectivity and improving overall catalytic efficiency of original Ti2N MXene. Passivation of Ti2N creates new active sites (TiO2) on top of titanium nitride layers that are able now to easily activate CO2 molecules to make possible the reduction of CO2 to CO and CH4. Formed TiO2 layer, also favours the formation of a third-party junction composites with perovskite nanoparticles enhancing light harvesting, improving photoactivity of the partially oxidized MXene (POM), see figure 1d.