Unlocking photoredox selective organic transformation over metal-free 2D transition metal chalcogenides-MXene heterostructures

Two-dimensional (2D) transition metal carbide, known as MXene, has recently received enduring attention for solar energy conversion by virtue of its pivotal role as efficient interfacial charge transfer mediator for photocatalysis. However, controllable design of MXene-based heterostructured photosystems is still in the infant stage and MXene-dominated photoredox mechanism in photoredox selective organic catalysis has so far not yet been unleashed. Herein, we conceptually report the rational construction of 2D/2D heterostructures by a facile electrostatic self-assembly approach utilizing oppositely charged transition metal chalcogenides (TMCs: CdIn₂S₄, CdS, Zn₀.₅Cd₀.₅S, ZnIn₂S₄) nanosheets (NSs) and Ti₃C₂Tₓ (MXene) as the building blocks for photocatalytic selective organic transformation. The peculiar face-to-face stacking mode between the building blocks and suitable energy level alignment synergistically endow the MXene-TMCs NSs heterostructures with markedly enhanced photoactivities toward multifarious photoredox catalysis including anaerobic selective photoreduction of nitroaromatics to amino derivatives and photoxidation of aromatic alcohols to aldehydes under the irradiation of visible light. The considerably enhanced photoactivities of MXene-TMCs NSs heterostructures are caused by the integrated merits of Ti₃C₂Tₓ (MXene) including: (i) abundant hydrophilic groups on the Ti₃C₂Tₓ (MXene) surface for affording substantial interaction with TMCs NSs, which benefits the charge migration; (ii) strong redox activities of surface Ti sites which promotes multiple electron reduction; (iii) electrons-withdrawing capability of Ti₃C₂Tₓ (MXene) to boost the electron transfer from TMCs NS to Ti₃C₂Tₓ (MXene), thereby enhancing the charge separation. This work would open a new frontier for constructing a host of MXene-based heterostructured photosystems and unveiling the charge transfer mechanism of MXene for solar energy conversion.