Floatable artificial leaf to couple oxygen-tolerant CO2 conversion with water purification

Abstract

To enable open environment application of artificial photosynthesis, the direct utilization of environmental CO₂ via an oxygen-tolerant reductive procedure is necessary. Herein, we introduce an in situ growth strategy for fabricating two-dimensional heterojunctions between indium porphyrin metal-organic framework (In-MOF) and single-layer graphene oxide (GO). Upon illumination, the In-MOF/GO heterostructure facilitates a tandem CO₂ capture and photocatalytic reduction on its hydroxylated In-node, prioritizing the reduction of dilute CO₂ even in the presence of air-level O₂. The In-MOF/GO heterostructure photocatalyst is integrated with a porous polytetrafluoroethylene (PTFE) membrane to construct a floatable artificial leaf. Through a triphase photocatalytic reaction, the floatable artificial leaf can remove aqueous contaminants from real water while efficiently reducing CO₂ at low concentrations (10%, approximately the CO₂ concentration in combustion flue gases) upon air-level O₂. This study provides a scalable approach for the construction of photocatalytic devices for CO₂ conversion in open environments.

Fig. 1. Schematic illustration of the catalyst application.

Schematic illustration depicting the design of a floatable artificial leaf to function as an integrated system for environmental CO₂ reduction and water purification.

Fig. 2. Characterization of 2D In-MOF/GO.

a Schematic showing the synthesis process of In-MOF/GO. b TEM images and c XRD at indicated elapsed growth time, the red spectrum in Fig.1c represents the synthesized In-MOF nanosheets. d HR-TEM images and e HAADF mapping of In-MOF/GO-4h, where 4 h represents the elapsed growth time. Source data for Fig. 2c is provided as a Source Data file.

Fig. 3. Photocatalytic activity of the floatable artificial leaf loaded with In-MOF/GO.

a Schematic showing the photocatalytic reaction on a floatable artificial leaf loaded with In-MOF/GO. b Comparison of the CO generation rates from aerobic CO₂ reduction using In-MOF/GO-4h synthesized via in situ growth, In-MOF, GO, and In-MOF/GO synthesized via ex situ assembly. c GC-MS spectra of CO produced on In-MOF/GO-4h using ordinary ¹²CO₂ and ¹³CO₂. d Cycling test results of aerobic CO₂ photoreduction on In-MOF/GO-4h. e Dependence of CO generation rate on O₂ levels. f Product generation rates of oxidative half-reaction products in the In-MOF/GO-4h loaded artificial leaves under oxygen-free conditions. g CO generation rate as a function of time obtained from coupling of aerobic CO₂ reduction with water purification; the lower section displays the variation of COD in lake water during photoreactions, the inset shows photographic images of the lake water before and after purification. The error bar represents the standard deviation of the measurements. Reaction conditions: For b, c, d, and g, the gas atmosphere was 10% CO₂, 20% O₂ and 70% Ar; for (e), O₂ level ranged from 0% to 20%, balanced with Ar; for (f), the atmosphere was O₂-free (10% CO₂ and 90% Ar). For b–f, deionized water was used, whereas lake water collected from Beijing Olympic Park was employed for (g). Source data for Fig. 3b–g are provided as a Source Data file.

Fig. 4. Investigation of CO₂ adsorption on In-MOF/GO.

Calculated charge difference when CO₂ adsorbed on (a) In-MOF/GO and (b) self-supported In-MOF; yellow regions represent regions of electron accumulation, whereas blue regions denote areas of electron depletion. c Calculated adsorption energy for CO₂ and O₂ on In-MOF/GO and self-supported In-MOF. d Adsorption–desorption curves of CO₂ and O₂ on In-MOF/GO. Source data for Fig. 4c, d are provided as a Source Data file.

Fig. 5. Monitoring photocatalytic CO₂ reduction on In-MOF/GO using in situ FT-IR spectroscopy.

a Reference FT-IR spectra of self-supported In-MOF with KBr as background; In situ FT-IR spectra collected during the photocatalytic CO₂ reduction on In-MOF/GO under b 10% CO₂ and 90% Ar, c 100% ¹³CO₂, and d 10% CO₂, 20% O₂ and 70% Ar atmospheres. The FT-IR spectra shown in (a–d) were collected per 0.6 s (bottom to top); the total illumination time was 6 s. The top spectrum in (b) was collected after the illumination was terminated to show the reversible structural alternation of the catalyst. The background for (b–d) was collected right before illumination for each sample. e Schematic illustration of the photocatalytic CO₂ reduction on one structural unit of In-MOF; In, C, O, and H are shown as green, gray, red and white circles, respectively. Source data for Fig. 5a–d are provided as a Source Data file.