Nature-Inspired, Highly Durable CO₂ Reduction System Consisting of a Binuclear Ruthenium(II) Complex and an Organic Semiconductor Using Visible Light

Abstract

A metal-free organic semiconductor of mesoporous graphitic carbon nitride (C3N4) coupled with a Ru(II) binuclear complex (RuRu') containing photosensitizer and catalytic units selectively reduced CO2 into HCOOH under visible light (λ > 400 nm) in the presence of a suitable electron donor with high durability, even in aqueous solution. Modification of C3N4 with Ag nanoparticles resulted in a RuRu'/Ag/C3N4 photocatalyst that exhibited a very high turnover number (>33000 with respect to the amount of RuRu'), while maintaining high selectivity for HCOOH production (87-99%). This turnover number was 30 times greater than that reported previously using C3N4 modified with a mononuclear Ru(II) complex, and by far the highest among the metal-complex/semiconductor hybrid systems reported to date. The results of photocatalytic reactions, emission decay measurements, and time-resolved infrared spectroscopy indicated that Ag nanoparticles on C3N4 collected electrons having lifetimes of several milliseconds from the conduction band of C3N4, which were transferred to the excited state of RuRu', thereby promoting photocatalytic CO2 reduction driven by two-step photoexcitation of C3N4 and RuRu'. This study also revealed that the RuRu'/Ag/C3N4 hybrid photocatalyst worked efficiently in water containing a proper electron donor, despite the intrinsic hydrophobic nature of C3N4 and low solubility of CO2 in an aqueous environment.

A spongy nickel-organic CO 2 reduction photocatalyst for nearly 100% selective CO production

“…The CO production rate is also superior compared with many other reported heterogeneous CO evolution photocatalysts to the best our knowledge ( 17 ), such as the Co 3 O 4 platelets with [Ru(bpy) 3 ]Cl 2 as a photosensitizer (3523 μmol hour −1 g −1 ) ( 18 ), the sensitized TiO 2 particles with enzyme as a cocatalyst (300 μmol hour −1 g −1 ) ( 31 ), and the sensitized BaLa 4 Ti 4 O 15 particles with Ag as a cocatalyst (22 μmol hour −1 g −1 ) ( 16 ). Note that the soluble homogeneous metal complex catalysts, which have also been investigated for controlled CO 2 reduction ( 32 – 34 ), are not categorized here for comparison.…”

Full‐Spectrum Solar‐Light‐Activated Photocatalysts for Light–Chemical Energy Conversion

“…Recently, the photocatalysis of Z-scheme heterostructures, adopted from natural photosynthesis, has been well studied in order to identify the charge transport pathway. [11,[102][103][104][105] For example, Ho et al [100] studied CdS-WO 3 heterostructures as a photocatalyst for CO 2 reduction. As illustrated in Figure 7a, for the normal band structure alignment of the heterostructure, the red (dashed) lines from the CB of CdS and that from the VB of WO 3 should be the electron and hole transport pathways, respectively.…”

“…The photocatalytic reduction of CO 2 can convert solar energy into chemical energy, stored as CH 4 , CO, CH 3 OH, etc. [11][12][13] These processes can help reduce the pressure of the global warming crisis and supply usable renewable energy. Due to the precise control of photocatalytic reduction and oxidation, photocatalytic molecular synthesis has also attracted much interest, which provides a sustainable pathway for green synthesis.…”

Boron-doped diamond semiconductor electrodes: Efficient photoelectrochemical CO2 reduction through surface modification

“…Selective, efficient conversion of CO 2 into a valuable chemical fuel is not only important for sustainability but also economically favourable151617. Natural photosynthesis is an indispensable tool to capture CO 2 , but gross destruction of green plants and rapid civilization have forced researchers to search for alternatives to natural photosynthesis to efficiently and selectively convert CO 2 into high-value chemicals.…”