Liquid phase exfoliation of metal–organic frameworks in aqueous quaternary ammonium hydroxide solution enables highly efficient photocatalytic CO2 reduction.

[Display omitted] • Aqueous solution of quaternary ammonium hydroxide is used to exfoliate MONs from bulk MOF powder. • The exfoliation yield of MONs is high up to 27.5%. • The MONs is mainly in the range from 1 to 3 layers. • The basicity and molecular size of quaternary ammonium hydroxide play vital roles in exfoliation. • The CO production rate catalyzed by MON is 118.7 μmol g−1 h−1 and the selectivity for CO is ca.100%. Metal−organic framework nanosheets (MONs) show promising applications in many fields, but the production of large amounts of high-quality MONs remains a challenge. Here, we report a general liquid-phase stripped approach to exfoliate a benzoic acid linked MOF (Al 2 (OH) 2 TCPP-Co) in water by using quaternary ammonium hydroxides as deprotonation reagent, intercalator and stabilizer simultaneously. It is shown that the stripped yield is high up to 27.5%, the thickness of MONs is mainly 1–3 nm, and the horizontal size is less than one hundred nanometers. The molecular geometry and alkalinity of quaternary ammonium hydroxides play vital roles in the exfoliation of MONs. Moreover, the MONs have been applied as photocatalysts for the conversion of CO 2 to CO in a gas–solid model under UV–visible light illumination without using any photosensitizer and sacrificial agents. The productivity rate of CO is 118.7 μmol g−1 h−1, which outperforms most of the photocatalysts reported previously. Thus, the liquid phase stripping method reported in this work has great potential in the large-scale production of MONs for efficient photocatalysis of CO 2 reduction in the gaseous phase. [ABSTRACT FROM AUTHOR]