Electrostatic Self-Assembly of Nanosized Carbon Nitride Nanosheet onto a Zirconium Metal–Organic Framework for Enhanced Photocatalytic CO2 Reduction

TLDR: In this article, the UiO-66/carbon nitride nanosheet heterogeneous photocatalyst exhibits a much higher photocatalytic activity for the CO2 conversion than that of bare carbon nitride nano-heets.

Abstract: UiO-66, a zirconium based metal–organic framework, is incorporated with nanosized carbon nitride nanosheets via a facile electrostatic self-assembly method. This hybrid structure exhibits a large surface area and strong CO2 capture ability due to the introduction of UiO-66. We demonstrate that electrons from the photoexcited carbon nitride nanosheet can transfer to UiO-66, which can substantially suppress electron–hole pair recombination in the carbon nitride nanosheet, as well as supply long-lived electrons for the reduction of CO2 molecules that are adsorbed in UiO-66. As a result, the UiO-66/carbon nitride nanosheet heterogeneous photocatalyst exhibits a much higher photocatalytic activity for the CO2 conversion than that of bare carbon nitride nanosheets. We believe this self-assembly method can be extended to other carbon nitride nanosheet loaded materials.

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Figure 2. (a)-(c) XRD patterns, diffuse-reflectance UV/Vis spectrum and PL spectra of bulk CN and CNNS. (d)-(f) XRD patterns, diffuse-reflectance UV/Vis spectrum and N2 adsorption-desorption isotherms of UiO-66 and UiO-66/CNNS. The CNNS content in UiO66/CNNS composite is 10 wt%.

Figure 3. (a)-(b) CO2 adsorption isotherms and ESR spectra of UiO-66, CNNS and UiO66/CNNS. (c)-(d) PL spectra and decay curve of CNNS and UiO-66/CNNS. The CNNS content in UiO-66/CNNS composite is 10 wt%.

Table 1. Comparison of the properties and photocatalytic activity of different samples. For hybrid structure photocatalysts, the carbon nitride content is 10 wt%. The photocatalytic reaction was conducted for 6 hours. Light source: 400 nm <λ< 800 nm

Figure 4. (a) Time course of CO evolution over bulk CN, CNNS, UiO-66/bulk CN and UiO66/CNNS photocatalysts. (b) Production yields of CO over UiO-66/CNNS photocatalyst in the recycling tests. For hybrid structure photocatalysts, the carbon nitride content is 10 wt%.

Figure 5. Proposed mechanism of photocatalytic reduction of CO2 by UiO-66/CNNS heterogeneous photocatalyst under visible light irradiation.

Figure 1. (a) Schematic illustration of the preparation of the UiO-66/CNNS heterogeneous photocatalyst. (b) TEM and HRTEM images of CNNS; (c) -(d) AFM and corresponding height images of CNNS. (e) -(f) SEM, TEM and HRTEM images of UiO-66. (g) TEM and HRTEM images of UiO-66/CNNS. The CNNS content in UiO-66/CNNS composite is 10 wt%.