Tuning Crystallinity and Surface Hydrophobicity of a Cobalt Phosphide Cocatalyst to Boost CO2 Photoreduction Performance

Designing covalent organic frameworks with Co-O4 atomic sites for efficient CO2 photoreduction

Cobalt coordinated covalent organic frameworks have attracted increasing interest in the field of CO₂ photoreduction to CO, owing to their high electron affinity and predesigned structures. However, achieving high conversion efficiency is challenging since most Co related coordination environments facilitate fast recombination of photogenerated electron-hole pairs. Here, we design two kinds of Co-COF catalysts with oxygen coordinated Co atoms and find that after tuning of coordination environment, the reported Co framework catalyst with Co-O₄ sites exhibits a high CO production rate of 18000 µmol g^-1 h^-1 with selectivity as high as 95.7% under visible light irradiation. From in/ex-situ spectral characterizations and theoretical calculations, it is revealed that the predesigned Co-O₄ sites significantly facilitate the carrier migration in framework matrixes and inhibit the recombination of photogenerated electron-hole pairs in the photocatalytic process. This work opens a way for the design of high-performance catalysts for CO₂ photoreduction.

Tailoring Copper Chemical Status and Hydrophobicity of Biomimetic Photocatalytic Films for Carbon Dioxide Conversion

Naturally hierarchical nanostructures of leaves were successfully replicated on thermally stable polyimide (PI) films to obtain biomimetic substrates for the grafting of p-type semiconductor, cuprous oxide (Cu₂O). The chemical states of Cu₂O and the hydrophobicity on the photocatalytic films were tunable by altering the process time of ion-exchange or chemical reduction. The obtained photocatalytic films showed activity to photocatalytically convert carbon dioxide (CO₂) into carbon monoxide (CO) under visible light illumination. The yield of CO was initially improved with the increasing hydrophobicity on the film but then leveled off. The photocatalytic activity could be further improved by tailoring the amount or composition of copper oxides. An optimum ratio of Cu₂O and moderate basicity on the surface, as well as more metallic Cu from the bulk, will achieve more efficient interfacial charge transfer, resulting in a higher CO production rate.

Promoting the reduction of CO2 to formate and formaldehyde via gas-liquid interface dielectric barrier discharge using a Zn0.5Cd0.5S/CoP/multiwalled carbon nanotubes catalyst

A Zn_0.5Cd_0.5S (ZCS) solid solution was prepared using a hydrothermal method, in which CoP nanowires were added as a co-catalyst and co-deposited with multiwalled carbon nanotubes (MWNTs) on sponge to prepare a series of ZCS/CoP/MWNTs/sponge electrodes. The microstructures of catalysts were analyzed to confirm ZCS and CoP were successfully loaded in MWNTs/sponge. The CO₂ reduction products (formate and formaldehyde) produced via dielectric barrier discharge (DBD) using the different catalysts proved that the introduction of the CoP nanowires co-catalyst can enhance the catalytic activity of ZCS/MWNTs/sponge in the DBD system. Using 10% CoP and a ZCS/CoP concentration of 2.5 g·L^-1, the resulting ZCS/CoP/MWNTs/sponge catalyst exhibited the best catalytic of CO₂ reduction ability toward formate (7894.6 μmol·L^-1) and formaldehyde (308.5 μmol·L^-1) after 60 min of discharge, respectively. The proposed DBD catalytic mechanism for the reduction of CO₂ was analyzed according to the Tafel slope, density functional theory calculations, photocurrent density and plasma reaction process. Furthermore, the application of the DBD catalytic technology for CO₂ capture and reduction was shown to be efficient in a seawater system, and as such, it could be useful for marine CO₂ storage and conversion.

Photocatalytic CO2 Reduction Coupled with Alcohol Oxidation over Porous Carbon Nitride

The photocatalytic transformation of CO2 to valuable man-made feedstocks is a promising method for balancing the carbon cycle; however, it is often hampered by the consumption of extra hole scavengers. Here, a synergistic redox system using photogenerated electron-hole pairs was constructed by employing a porous carbon nitride with many cyanide groups as a metal-free photocatalyst. Selective CO2 reduction to CO using photogenerated electrons was achieved under mild conditions; simultaneously, various alcohols were effectively oxidized to value-added aldehydes using holes. The results showed that thermal calcination process using ammonium sulfate as porogen contributes to the construction of a porous structure. As-obtained cyanide groups can facilitate charge carrier separation and promote moderate CO2 adsorption. Electron-donating groups in alcohols could enhance the activity via a faster hydrogen-donating process. This concerted photocatalytic system that synergistically utilizes electron-hole pairs upon light excitation contributes to the construction of cost-effective and multifunctional photocatalytic systems for selective CO2 reduction and artificial photosynthesis.

Chromatic Fulleropyrrolidine as Long-Lived Metal-Free Catalyst for CO2 Photoreduction Reaction

Conversion of CO₂ into carbonaceous fuels with the aid of solar energy has been an important research subject for decades. Owing to their excellent electron-accepting capacities, fullerene derivatives have been extensively used as n-type semiconductors. This work reports that the fulleropyrrolidine functionalized with 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole, abbreviated as DTBT-C₆₀ , could efficiently catalyze the photoreduction of CO₂ to CO. The novel C₆₀ -chromophore dyad structure facilitated better usage of solar light and effective dissociation of excitons. Consequently, the DTBT-C₆₀ exhibited a promising CO yield of 144 μmol g_cat ^-1 under AM1.5G solar illumination for 24 h. Moreover, the isotope experiments demonstrated that water molecules could function as an electron source to reactivate DTBT-C₆₀ . Impressively, DTBT-C₆₀ exhibited an extremely durable catalytic activity for more than one week, facilitating the practical application of photochemical CO₂ reaction.

Well-defined Co9S8 cages enable the separation of photoexcited charges to promote visible-light CO2 reduction

Exploring affordable cocatalysts with high performance for boosting charge separation and CO₂ activation is an effective strategy to reinforce CO₂ photoreduction efficiency. Herein, well-defined Co₉S₈ cages are exploited as a nonprecious promoter for visible-light CO₂ reduction. The Co₉S₈ cages are prepared via a multistep strategy with ZIF-67 particles as the precursor and fully characterized by physicochemical techniques. The hollow Co₉S₈ cocatalyst with a high surface area and profuse catalytically active centers is discovered to accelerate separation and transfer of light-induced charges, and strengthen concentration and activation of CO₂ molecules. In a hybrid photosensitized system, these Co₉S₈ cages efficiently promote the deoxygenative reduction of CO₂ to generate CO, with a high yield rate of 35 μmol h^-1 (i.e., 35 mmol h^-1 g^-1). Besides, this cocatalyst is also of high stability for the CO₂ photoreduction reaction. Density functional theory (DFT) calculations reveal that the Ru(bpy)₃²⁺ photosensitizer is strongly absorbed on the Co₉S₈ (311) surface through forming four Co-C bonds, which can serve as the "bridges" to ensure quick electron transfer from the excited photosensitiser to the active Co₉S₈ cocatalyst, thus promoting the separation of photoexcited charges for ehannced CO₂ reduction performance.

Prolonging the Triplet State Lifetimes of Rhenium Complexes with Imidazole-Pyridine Framework for Efficient CO2 Photoreduction

The photocatalytic reduction of CO₂ into fuels offers the prospect for creating a new CO₂ economy. Harnessing visible light-driven CO₂ -to-CO reduction mediated by the long-lived triplet excited state of rhenium(I) tricarbonyl complexes is a challenging approach. We here develop a series of new mononuclear rhenium(I) tricarbonyl complexes (Re-1-Re-4) based on the imidazole-pyridine skeleton for photo-driven CO₂ reduction. These catalysts are featured by combining pyridyl-imidazole with the aromatic ring and different pendant organic groups onto the N1 position of 1,3-imidazole unit, which display phosphorescence under Ar-saturated solution even at ambient conditions. By contrast, {Re[9-(pyren-1-yl)-10-(pyridin-2-yl)-9H-pyreno[4,5-d]imidazole)](CO)₃ Cl} (Re-4) by introducing pyrene ring at the N1 position of pyrene-fused imidazole unit exhibits superior catalytic performance with a higher turnover number for CO (TON_CO =124) and >99.9 % selectivity, primarily ascribed to the strong visible light-harvesting ability, long-lived triplet lifetimes (164.2 μs) and large reductive quenching constant. Moreover, the rhenium(I) tricarbonyl complexes derived from π-extended pyrene chromophore exhibit a long lifetime corresponding to its ligand-localized triplet state (³ IL) evidenced from spectroscopic investigations and DFT calculations.

Energy Band Alignment and Redox-Active Sites in Metalloporphyrin-Spaced Metal-Catechol Frameworks for Enhanced CO2 Photoreduction

Two new chemically stable metalloporphyrin-bridged metal-catechol frameworks, InTCP-Co and FeTCP-Co, were constructed to achieve artificial photosynthesis without additional sacrificial agents and photosensitizers. The CO₂ photoreduction rate over FeTCP-Co considerably exceeds that obtained over InTCP-Co, and the incorporation of uncoordinated hydroxyl groups, associated with catechol, into the network further promotes the photocatalytic activity. The iron-oxo coordination chain assists energy band alignment and provides a redox-active site, and the uncoordinated hydroxyl group contributes to the visible-light absorptance, charge-carrier transfer, and CO₂ -scaffold affinity. With a formic acid selectivity of 97.8 %, FeTCP-OH-Co affords CO₂ photoconversion with a reaction rate 4.3 and 15.7 times higher than those of FeTCP- Co and InTCP-Co, respectively. These findings are also consistent with the spectroscopic study and DFT calculation.

Highly Selective Production of Ethanol Over Hierarchical Bi@Bi2 MoO6 Composite via Bicarbonate-Assisted Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction is a sustainable and inexpensive method to solve the energy crisis and the greenhouse effect. However, the major stumbling blocks such as poor product selectivity, low yield of the multi-carbon products, and serious recombination of electron-hole pairs hinder practical application of photocatalysts. Herein, a high-performance Bi@Bi₂ MoO₆ photocatalyst, Bi nanoparticles grown on the surface of Bi₂ MoO₆ nanosheets with oxygen vacancies, was fabricated via a simple solvothermal approach. Benefiting from the abundant active sites and effective separation of photogenerated carriers of Bi₂ MoO₆ nanosheets, and the localized surface plasmon resonance effect of Bi nanoparticles, the Bi@Bi₂ MoO₆ sample exhibited great photocatalytic CO₂ reduction activity. Furthermore, adding NaHCO₃ into the system not only significantly increased the C₂ H₅ OH generation rate but also enhanced the product selectivity. In the photocatalytic measurement (0.17 mol L^-1 CO₂ -saturated NaHCO₃ solution), the highest formation rates of CO, CH₃ OH, and C₂ H₅ OH were reached at 0.85, 0.59, and 17.93 μmol g^-1  h^-1 (≈92 % selectivity), respectively.