Hierarchical S-scheme titanium dioxide@cobalt-nickel based metal–organic framework nanotube photocatalyst for selective carbon dioxide photoreduction to methane.

[Display omitted] • Hierarchical S-scheme TiO 2 @CoNi-MOF nanotubes were fabricated. • S-scheme heterojunction accelerates charge transfer and separation. • Hierarchical hybrid possesses more active sites and visible-light absorption. • Hierarchical hybrid exhibits enhanced activity and CH 4 selectivity. Efficient photocatalysts are of great importance for the photochemical conversion of CO 2 into fuels. Herein, S-scheme titanium dioxide@cobalt-nickel based metal–organic framework (TiO 2 @CoNi-MOF) heterojunction photocatalysts with high surface area and porosity are designed and fabricated by a multi-step controllable strategy. The photocatalytic activity of the composites can be optimized by adjusting the loading content of CoNi-MOF in TiO 2 @CoNi-MOF and molar ratios of Co2+ and Ni2+ in CoNi-MOF. The optimized hybrid photocatalyst showed a much higher CO 2 photoreduction activity than the control single-component samples (TiO 2 and CoNi-MOF) with a high CH 4 yield (41.65 μmol g−1 h−1) and selectivity (93.2%). The accelerated charge carrier separation induced by the S-scheme heterojunction significantly promoted the photocatalytic performance of TiO 2 @CoNi-MOF NTs. Meanwhile, the introduction of bimetallic CoNi-MOF nanosheets significantly resulted in the increase of active sites, CO 2 adsorbability, visible-light utilization, and CH 4 selectivity. Moreover, the S-scheme photoinduced charge transfer model of the TiO 2 @CoNi-MOF NTs photocatalyst was confirmed by photoluminescence spectroscopy, free radical trapping tests, and work function calculated from Kelvin probe. The work aims to design and fabricate heterojunction photocatalysts with high efficiency for solar fuel production. [ABSTRACT FROM AUTHOR]