Efficient CO2 Photoreduction Research Articles

Construction of Co1-xZnxFe2xGa2-2xO4 (0

Solid solutions are garnering substantial attention in the realm of solar energy utilization due to their tunable electronic properties, encompassing band edge positions and charge-carrier mobilities. In this study, we designed and synthesized Co1-xZnxFe2xGa2-2xO4 (0<x≤0.6) as a photocatalyst for CO2 conversion using H2O. Careful optical and photo/electrochemical characterizations unveiled that the relative content of CoGa2O4 and ZnFe2O4 not only substantially influences light absorption in the full solar spectrum but also modulates valence and conduction band positions. We thoroughly assessed the photocatalytic activity of Co1-xZnxFe2xGa2-2xO4 and found that when x=0.35, the solid-solution catalyst achieved a remarkable CO2 reduction rate to CH4 and CO (31.5 μmol g-1 h-1). Furthermore, this optimized solid-solution catalyst demonstrated impressive photostability. Characterization and DFT calculations revealed that the formation of a solid solution not only reduces the band gap and promotes the separation of electron-hole pairs to accelerate efficient CO2 photoreduction, but also the introduction of more FeO6 octahedral active sites in Co1-xZnxFe2xGa2-2xO4 solid solutions enhanced the effective photoreduction of CO2. This design results in high conversion efficiencies for producing solar fuels through CO2 reduction with H2O.

2D/2D g-C3N4@BiOI S-scheme heterojunction with gas-liquid-solid triphase interface for highly efficient CO2 photoreduction

2D/2D g-C3N4@BiOI S-scheme heterojunction with gas-liquid-solid triphase interface for highly efficient CO2 photoreduction

Enhanced CO2 photoreduction over bismuth-rich Bi4O5Br2: Optimized charge separation and intrinsic barriers

Photocatalytic CO2 conversion into chemicals is one of effective strategies to overcoming the energy crisis and global warming. However, the CO2 photoreduction efficiency is hindered by poor charge separation and CO2 activation. The composition regulation of photocatalyst is a promising strategy to solve these issues. Herein, we constructed the Bi4O5Br2 in ionic liquid through a solvothermal approach. The electronic structure of photocatalyst has been regulated over Bi4O5Br2 through Bi-rich strategy, achieving enhanced charge separation and long carrier lifetime. Density-functional theory (DFT) calculations found that the intrinsic barriers for CO2 adsorption-activation can be effectively optimized over Bi4O5Br2, promoting the CO2 dissociation and facilitating the generation of *COOH. Therefore, Bi4O5Br2 possesses improved evolution rates of 23.81 and 1.33 μmol g−1 for CO and CH4 under irradiation of 300 W Xe lamp for 4 h. This work demonstrates a valuable strategy for the rational construction of efficient materials towards CO2 photoreduction.

Gas-Solid Phase Reaction Derived Silver Bismuth Iodide Rudorffite: Structural Insight and Exploring Photocatalytic Potential of CO2 Reduction.

Photocatalytic reduction of CO2 is a promising strategy to mitigate the effects of global warming by converting CO2 into valuable energy-dense products. Silver bismuth iodide (SBI) is an attractive material owing to its tunable bandgap and favorable band-edge positions for efficient CO2 photoreduction. In this study, SBI materials, including AgBi2I7, AgBiI4, Ag2BiI5, and Ag3BiI6 are first synthesized, through gas-solid reaction by controlling the stoichiometric ratio of reactants. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) results revealed that the distance between Ag-I is proportional to the degree of Ag ions delocalization, which occupies the vacant sites. That greatly retards the charge recombination at vacant sites. In addition, the surface potential via photo-assisted Kelvin probe force measurements of various SBI catalysts shows that Ag3BiI6 exhibits the highest surface potential change due to the rich delocalized Ag ions. This results in effective charge carrier transport and prevention of charge recombination at vacant sites. Taking the above advantages, the averaged CO and CH4 production rates for Ag3BiI6 achieved 0.23 and 0.10µmolg-1h-1, respectively. The findings suggest that Ag3BiI6 has a high potential as a novel photocatalyst for CO2 reduction and sheds light on the possibility of solving environmental contamination and sustainable energy crises.

Synthetic Leaves Based on Crystalline Olefin-Linked Covalent Organic Frameworks for Efficient CO2 Photoreduction with Water.

We report, for the first time, a new synthetic strategy for the preparation of crystalline two-dimensional olefin-linked covalent organic frameworks (COFs) based on aldol condensation between benzodifurandione and aromatic aldehydes. Olefin-linked COFs can be facilely crystallized through either a pyridine-promoted solvothermal process or a benzoic anhydride-mediated organic flux synthesis. The resultant COF leaf with high in-plane π-conjugation exhibits efficient visible-light-driven photoreduction of carbon dioxide (CO2) with water (H2O) in the absence of any photosensitizer, sacrificial agents, or cocatalysts. The production rate of carbon monoxide (CO) reaches as high as 158.1 μmol g-1 h-1 with near 100% CO selectivity, which is accompanied by the oxidation of H2O to oxygen. Both theoretical and experimental results confirm that the key lies in achieving exceptional photoinduced charge separation and low exciton binding. We anticipate that our findings will facilitate new possibilities for the development of semiconducting COFs with structural diversity and functional variability.

Construction of an Electron Capture and Transfer Center for Highly Efficient and Selective Solar-Light-Driven CO2 Conversion.

Exploring high-efficiency photocatalysts for selective CO2 reduction is still challenging because of the limited charge separation and surface reactions. In this study, a noble-metal-free metallic VSe2 nanosheet was incorporated on g-C3N4 to serve as an electron capture and transfer center, activating surface active sites for highly efficient and selective CO2 photoreduction. Quasi in situ X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and femtosecond transient absorption spectroscopy (fs-TAS) unveiled that VSe2 could capture electrons, which are further transferred to the surface for activating active sites. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations revealed a kinetically feasible process for the formation of a key intermediate and confirmed the favorable production of CO on the VSe2/PCN (protonated C3N4) photocatalyst. As an outcome, the optimized VSe2/PCN composite achieved 97% selectivity for solar-light-driven CO2 conversion to CO with a high rate of 16.3 μmol·g-1·h-1, without any sacrificial reagent or photosensitizer. This work offers new insights into the photocatalyst design toward highly efficient and selective CO2 conversion.

Hydrogen‐Bond‐Network Breakdown Boosts Selective CO2 Photoreduction by Suppressing H2 Evolution

AbstractConventional strategies for highly efficient and selective CO2 photoreduction focus on the design of catalysts and cocatalysts. In this study, we discover that hydrogen bond network breakdown in reaction system can suppress H2 evolution, thereby improving CO2 photoreduction performance. Photosensitive poly(ionic liquid)s are designed as photocatalysts owing to their strong hydrogen bonding with solvents. The hydrogen bond strength is tuned by solvent composition, thereby effectively regulating H2 evolution (from 0 to 12.6 mmol g−1 h−1). No H2 is detected after hydrogen bond network breakdown with trichloromethane or tetrachloromethane as additives. CO production rate and selectivity increase to 35.4 mmol g−1 h−1 and 98.9 % with trichloromethane, compared with 0.6 mmol g−1 h−1 and 26.2 %, respectively, without trichloromethane. Raman spectroscopy and theoretical calculations confirm that trichloromethane broke the systemic hydrogen bond network and subsequently suppressed H2 evolution. This hydrogen bond network breakdown strategy may be extended to other catalytic reactions involving H2 evolution.

Hydrogen-Bond-Network Breakdown Boosts Selective CO2 Photoreduction by Suppressing H2 Evolution.

Conventional strategies for highly efficient and selective CO2 photoreduction focus on the design of catalysts and cocatalysts. In this study, we discover that hydrogen bond network breakdown in reaction system can suppress H2 evolution, thereby improving CO2 photoreduction performance. Photosensitive poly(ionic liquid)s are designed as photocatalysts owing to their strong hydrogen bonding with solvents. The hydrogen bond strength is tuned by solvent composition, thereby effectively regulating H2 evolution (from 0 to 12.6 mmol g-1 h-1). No H2 is detected after hydrogen bond network breakdown with trichloromethane or tetrachloromethane as additives. CO production rate and selectivity increase to 35.4 mmol g-1 h-1 and 98.9 % with trichloromethane, compared with 0.6 mmol g-1 h-1 and 26.2 %, respectively, without trichloromethane. Raman spectroscopy and theoretical calculations confirm that trichloromethane broke the systemic hydrogen bond network and subsequently suppressed H2 evolution. This hydrogen bond network breakdown strategy may be extended to other catalytic reactions involving H2 evolution.

Enhanced conversion of CO2 into C2H4 on single atom Cu-anchored graphitic carbon nitride: Synergistic diatomic active sites interaction

Single atom metal–nitrogen–carbon materials have emerged as remarkably potent catalysts, demonstrating unprecedented potential for the photo-driven reduction of CO2. Herein, a unique Cu@g-C3N5 catalyst obtained by cooperation of single atom Cu and nitrogen-rich g-C3N5 is proposed. The particular CuN diatomic active sites (DAS) in Cu@g-C3N5 contribute to the formation of highly stable CuOCN adsorption, a key configuration for CO2 activation and CC coupling. The synergistic diatomic active sites interaction is found responsible for the efficient photoreduction of CO2 to C2H4 which has been demonstrated in our Gibbs free energy calculation and COHP analysis. The CO2 activation mechanism was studied, the charge density difference and DOS analysis show that the low oxidation state Cu atom significantly affects the electronic structure of g-C3N5 and then enhance the catalytic activity of CO2 hydrogenation.

Pd nanocubes/In2O3/hollow carbon microspheres with ultra-low interface resistance of Ohmic contact for efficient CO2 photoreduction

The utilization of CO2 photoreduction into valuable hydrocarbon fuels presents a promising avenue for mitigating climate change and providing a sustainable energy source. However, photogenerated carriers are highly prone to recombination, which adversely affects photocatalytic activity. In our study, we introduce a novel photocatalyst synthesis method, featuring an Ohmic contact (OC) structure that incorporates biomass-derived hollow carbon microspheres (HCM), Pd nanocubes (NC), and Indium Oxide (In2O3) through a simple yet effective thermal reduction method. This modification significantly enhances the photocatalytic efficiency of the Pd NC/In2O3/HCM (donated as PIC) system, achieving an optimal value of 496.89 μmol∙g−1 over 5 h without the need for additional additives, 8.7-fold higher than that of the pristine In2O3. Experimental and theoretical results reveal that the substantial enhancement in CO2 photoreduction performance can be attributed to the ultra-low resistance (122 Ω) interfaces within the PIC system, facilitating accelerated transfer of photogenerated electrons. This work provides a strategy for boosting CO2 photoreduction efficiency by the reduction of interface resistance to promote rapid photogenerated electron migration.

Nanostructured ZnO/ZnS with Type-II Hetero-junction for Efficient CO2 Photoreduction

Nanostructured ZnO/ZnS with Type-II Hetero-junction for Efficient CO2 Photoreduction

Effect of the Ti content and pore size of mesoporous catalysts on CO2 photoreduction

The photocatalytic conversion of CO2 into chemicals and fuels is a promising approach for reducing atmospheric CO2 and addressing energy demands. This study investigates the impact of titanium (Ti) content and pore size in mesoporous silica on CO2 photoreduction (CO2PR) efficiency. Ordered mesoporous silica with a large surface area and stability is used as a matrix for Ti dispersion. Two sets of photocatalysts with varying Ti contents and pore sizes are synthesized and assessed for their microstructures, photoelectric properties, and CO2PR efficiency in both solid–gas and liquid–gas modes. The results reveal that photocatalysts with only 3.0 wt% Ti perform comparably to commercial TiO2 (P25) and can be recycled and reused. Moreover, an enhancement in photocatalytic activity with increasing pore sizes of the photocatalysts is observed. Notably, a photocatalyst with 3.0 wt% Ti and about 8 nm pore size significantly outperforms P25, producing much higher CH4, CO, and CH3OH yields. These findings are crucial for optimizing photocatalyst efficiency and are applicable across various compositions.

Efficient Photoreduction of CO2 to CO with 100% Selectivity by Slowing Down Electron Transport.

It remains challenging to obtain a single product in the gas-solid photocatalytic reduction of CO2 because CO and CH4 are usually produced simultaneously. This study presents the design of the I-type nested heterojunction TiO2/BiVO4 with controllable electron transport by modulating the TiO2 component. This study demonstrates that slowing electron transport could enable TiO2/BiVO4-4 to generate CO with 100% selectivity. In addition, modifying TiO2/BiVO4-4 by loading a Cu single atom further increased the CO product yield by 3.83 times (17.33 μmol·gcat-1·h-1), while maintaining 100% selectivity for CO. Characterization and density functional theory (DFT) calculations revealed that the selectivity was mainly determined by the electron transport of the support, whereas CO2 was efficiently adsorbed and activated by the Cu single atom. Such a two-step regulation strategy of combining heterojunction with single atom enhances the possibility of simultaneously obtaining high selectivity and high yield in the photocatalytic reduction of CO2.

Construction of Au-modified CN-based donor-acceptor system coupled with dual photothermal effects for efficient photoreduction of carbon dioxide

Conversion of CO2 into high value-added fuels through the photothermal effect is an effective approach for utilizing solar energy. In this study, we prepared the CN-based photocatalyst Py-CTN-Au with both donor-acceptor (D-A) system and dual photothermal effects using a simple two-step method involving calcination and photo-deposition. Real-time monitoring with a thermal imaging camera revealed that Py-CTN-Au0.5 achieved a maximum stable temperature of 180 °C, which was approximately 1.2 times higher than that of Py-CTN (155 °C) and 1.9 times higher than that of g-CN (95 °C) under the same reaction conditions. Under the optimized reaction conditions, Py-CTN-Au0.5 exhibited a CO release rate of 30.59 umol g−1 after 4 h of reaction, which was 7.3 times higher than that of pure g-CN (4.18 umol g−1). The D-A system not only facilitated the separation and transformation of charge carriers but also induced a photothermal effect to accelerate the photoreduction of CO2. Additionally, the cocatalyst Au nanoparticles (Au NPs) further enhanced the charge carrier dynamics and photothermal effect by increasing the built-in electric field intensity and localized surface plasmon resonance (LSPR) effect, respectively. The dual photothermal effects resulting from the non-radiative photon conversion of the D-A structure and the Au NPs LSPR effect, along with the enhanced charge carrier dynamics, catalyzed the efficient photoreduction of CO2. DFT simulations were used to confirm the effect of D-A system and Au NPs. In-situ FTIR results demonstrated that the synergistic photothermal effect promoted the formation of the key intermediate species COOH*, which is beneficial for the photocatalytic reduction of CO2. This study provides valuable insights into the multiple photothermal synergistic effects in photocatalytic reactions.

Porous C3N4 nanosheet supported Au single atoms as an efficient catalyst for enhanced photoreduction of CO2 to CO

Artificial photosynthesis utilizing solar energy to convert carbon dioxide (CO2) and water (H2O) into fuels and high-value chemicals offers a promising technology for mitigating energy consumption and environmental pollution. However, the development of efficient photocatalysts with high product selectivity remains a big challenge due to the sluggish dynamic transfer of photogenerated charge carriers. Herein, porous C3N4 nanosheet supported Au single atoms photocatalyst (Au1@CN) with AuN4 coordination is fabricated via a facile “impregnation + freeze-drying” process. The as-synthesized Au1@CN exhibits efficient and stable CO2 photoreduction activity with a CO evolution rate of 0.58 μmol h−1 (amount of catalyst: 10 mg), CO selectivity of 94 %, and a turnover frequency (TOF) of 10.0 h−1 using H2O as the reductant, which exceed most previous works on C3N4-based single-atom photocatalysts for CO2 reduction. Experimental studies and density functional theory (DFT) calculations reveal that the unique Au—N4 coordination promotes the dynamic transfer of photogenerated charge carriers, facilitates the adsorption/activation of CO2 molecules and generation of *COOH intermediate, thereby significantly enhancing the CO2 photoreduction activity with high CO selectivity. This study demonstrates an effective strategy for the design of M—N4 coordinated single-atom catalyst toward efficient and selective photoreduction of CO2 to CO.

Defect-synergetic effect enhanced CO2 photoreduction efficiency of TiO2 nanostructures with Fe dopants

TiO2 nanostructures (NSs) doped with varying Fe concentrations are synthesized using the sol-gel process, followed by annealing in 1 atm environment at 470 ℃ for 3 h. Anatase TiO2 crystal structure and defect levels are characterized using XRD, HRTEM, SEM-EDS, XPS, Raman, EPR, PL, and TR-PL techniques. Remarkably, the addition of approximately 4 wt% Fe dopant had no discernible impact on the crystal structure of the anatase TiO2. Furthermore, energy levels including VO, Tii∙∙∙, Fe3+/Fe2+, Fe3+/Fe4+, and Ti3+/Ti4+ are identified. The optical band-gap of TiO2 is reduced from 3.077 to 2.352 eV and its carrier lifetime is extended from 6.53 ns to 9.12 ns with Fe contents ranging from 0 to approximately 2 wt%. The CO2 photoreduction results demonstrate that Fe-doped TiO2 outperforms commercial TiO2 (P25) in terms of the photoreduction rate. Particularly, TiO2 NSs doped with 2 wt% Fe exhibit the highest CO2 photoreduction rates, yielding approximately 35.19×102 and 66.84×102 μmol‧g1‧min1of CO and CH4, respectively; thereby surpassing P25 by factors of 1.26 and 3.1, respectively. Therefore, Fe-doping can reduce the optical band-gap and extend the carrier lifetime of TiO2 photocatalysts, resulting in superior CO2 photoreduction capabilities. Moreover, the significance of electrons in the CO2 photoreduction process, as evidenced by the findings from the EPR spectrum and CO2 photoreduction, underscores the importance of an appropriate Fe content, such as 2 wt% used in this study, for enhancing the photoreduction abilities and potential applications of TiO2 in CO2 photoreduction.

Trinuclear Cu-based covalent organic framework: π-conjugated framework regulating electron delocalization to promote photoreduction CO2

Sunlight-driven CO2 reduction to value-added chemicals is an effective strategy to promote carbon recycling. The exploration of catalysts with efficient charge separation is crucially important for highly efficient CO2 photoreduction. In this work, the preparation of metal-cluster-based covalent organic framework (CuABD) integrated features from both metal organic frameworks (MOFs) and covalent organic frameworks (COFs) through the condensation of diamines and functionalized trinuclear copper clusters demonstrate a thoughtful design strategy. The reported yield of 1.3 mmol g−1 h−1 for formic acid (HCOOH) under simulated solar irradiation is impressive, surpassing the performance of many COF- and MOF-based catalysts previously reported. Compared to its isomorphic metal-free structure (named BDFTD) and bare trinuclear Cu cluster which present extremely poor catalytic activities, CuABD displays remarkably enhanced CO2 reduction activity. Experimental and theoretical investigations reveal that the efficient charge transfer between diamine monomer and cyclic trinuclear copper (I) units, and the electron delocalization of the π-conjugated framework are responsible for the appealing catalytic performance. In summary, the work presents a well-structured and scientifically sound exploration of a metal-cluster-based covalent organic framework for efficient CO2 reduction under sunlight.

Defect and nanostructure engineering of polymeric carbon nitride for visible-light-driven CO2 reduction

Sunlight-induced photocatalytic carbon dioxide (CO2) reduction to energy-rich chemicals by metal-free polymeric carbon nitride (CN) semiconductor is a promising tactic for sustained solar fuel production. However, the reaction efficiency of CO2 photoreduction is restrained seriously by the rapid recombination of photogenerated carriers on CN polymer. Herein, we incorporate 2-aminopyridine molecule with strong electron-withdrawing group into the skeleton edge of CN layers through a facile one-pot thermal polymerization strategy using urea as the precursor, which renders a modified carbon nitride (ACN) with extended optical harvesting, abundant nitrogen defects and ultrathin nanosheet structure. Consequently, the ACN photocatalyst with desirable structural features attains enhanced separation and migration of photoexcited charge carriers. Under visible light irradiation with Co(bpy)32+ as a cocatalyst, the optimized ACN sample manifests a high CO2 deoxygnative reduction activity and high stability, providing a CO yielding rate of 17 μmol h−1, which is significantly higher than that of pristine CN. The key intermediates engaged in CO2 photoreduction reaction are determined by the in situ diffuse reflectance infrared Fourier transform spectroscopy, which sponsors the construction of the possible photocatalytic CO2 reduction mechanism on ACN nanosheets.

Precision engineering of Z-scheme interfacial charge transfer in CoPc/Bi2WO6 through W-based bonds and internal electric field for efficient CO2 photoreduction

The Z-scheme heterojunction offers hope for CO2 reduction due to its unique charge migration, superior separation, and high redox capacity. Yet, regulating charge transfer in nanoscale heterostructure interfaces remains a significant challenge. Herein, we systematically engineered interfacial dual tungsten (W) bonds and built-in electric field (BIEF) modulated Z-scheme heterostructure composed by CoPc and Bi2WO6 (BWO), stimulate a Z-scheme charge shuttle cascade, channelling electrons from BWO to CoPc, thereby optimizing charge separation and upholding a high redox potential. The optimized photocatalyst exhibits high CH4/CO2 rate of ∼2.5 compared to pure BWO under vis-light for efficient CO2 reduction. The improved photoactivity is confirmed through theoretical/experimental evidence, highlighting the significance of newly formed W-O-C and W-Co bonds and BIEF. These components function as atomic-level interfacial channels, efficiently accelerating Z-scheme interfacial electron shuttle and shortening the electron-shuttle distance. Furthermore, the extended visible-light range, enabled by the molecular dispersion of CoPc, and the favourable catalytic function of its central metal cation (Co2+) for CO2 activation, significantly contribute to the overall enhancement. This work offers a new platform to design emerging modulated CO2 photoreduction systems based on Z-scheme charge shuttle by regulating atomic-level interface and BIEF to remarkably encourage photocatalytic CO2 photo-reduction performance.

Amorphous Metallic Cobalt-Based Organophosphonic Acid Compounds as Novel Photocatalysts to Boost Photocatalytic CO2 Reduction

Photocatalytic carbon dioxide conversion is a promising method for generating carbon fuels, in which the most important thing is to adjust the catalyst material to improve the photocatalytic efficiency and selectivity to conversion products, but it is still very challenging. In order to enhance the efficiency of CO2 photoreduction, it is important to develop an appropriate photocatalyst. The present study focuses on developing a simple and effective hydrothermal reaction treatment to improve the catalytic efficiency of transition metal cobalt (Co) and organophosphonates. Photoexcited charge carriers are separated and transferred efficiently during this treatment, which enhances CO2 chemisorption. Under visible light exposure, the best performing catalyst, CoP-4, showed 2.4 times higher activity than Co3O4 (19.90 μmol h−1 g−1) for reducing CO2 into CO, with rates up to 47.16 μmol h−1 g−1. This approach provides a viable route to enhancing the efficiency of CO2 photoreduction.