Reconstruction of Highly-Defective MgO and Exceptional Photochemical Activity on CO 2 Upgrade in Aqueous Solution.

Defects on metal oxide have attracted extensive attention in photo-/electrocatalytic CO 2 reduction. Herein, porous MgO nanosheets with abundant oxygen vacancies (V o s) and three-coordinated oxygen atoms (O 3c ) at corners are reported, which reconstruct into defective MgCO 3 ·3H 2 O exposing rich surface unsaturated -OH groups and vacancies to initiate photocatalytic CO 2 reduction to CO and CH 4 . In consecutive 7-cycle tests (each run for 6 h) in pure water, CO 2 conversion keeps stable. The total production of CH 4 and CO attains ≈367 µmol g cata -1 h -1 . The selectivity of CH 4 gradually increases from ≈3.1% (1 st run) to ≈24.5% (4 th run) and then remains unchanged under UV-light irradiation. With triethanolamine (3.3 vol.%) as the sacrificial agent, the total production of CO and CH 4 production rapidly increases to ≈28 000 µmol g cata -1 in 2 h reaction. Photoluminescence spectra reveal that V o s induces the formation of donor bands to promote charge carrier seperation. A series of trace spectra and theoretical analysis indicate Mg-V o sites in the derived MgCO 3 ·3H 2 O are active centers, which play a crucial role in modulating CO 2 adsorption and triggering photoreduction reactions. These intriguing results on defective alkaline earth oxides as potential photocatalysts in CO 2 conversion may spur some exciting and novel findings in this field.