Engineering of PMo12@NiCo-LDH composite via in situ encapsulation-reassembly strategy for highly selective photocatalytic reduction of CO2 to CH4

Abstract

Polyoxometalate intercalated layered double hydroxide (POM-LDH) composites have drawn wide attention due to their tunable intrinsic properties, variable composition, and synergistic effects between LDHs and POMs. Herein, we report the fabrication of PMo₁₂@NiCo-LDH composite via an in situ encapsulation-reassembly strategy using PMo₁₂@ZIF-67 as the precursor, in which ZIF-67 was in situ converted to the corresponding NiCo-LDH in the presence of Ni(NO₃)₂ solution, and PMo₁₂ was confined within the NiCo-LDH nanocages. When applied for the photocatalytic reduction of CO₂ (CO₂PR), the PMo₁₂@NiCo-LDH composite exhibited excellent CH₄ selectivity of 86.2% (production rate of 2.01 μmol h⁻¹) and suppressed H₂ selectivity of only 3.3% under visible light irradiation (λ > 500 nm). Such excellent performance can be attributed to the following reasons: (1) PMo₁₂@NiCo-LDH modulated the band structure and promoted the efficient generation, transfer, and separation of photo-induced electron–hole pairs; (2) the presence of the crucial intermediates CH₃O* and CHO* facilitated the generation of CH₄. Moreover, PMo₁₂@NiCo-LDH composites could be recycled for at least five cycles without an obvious decrease in catalytic performance, benefitting from the stable confinement of PMo₁₂ within NiCo-LDH nanocages.