Visible-light Driven CO2 Reduction Research Articles

Mononuclear Iron Pyridinethiolate Complex Promoted CO2 Photoreduction via Rapid Intramolecular Electron Transfer.

Designing earth-abundant metal complexes as efficient molecular photocatalysts for visible light-driven CO2 reduction is a key challenge in artificial photosynthesis. Here, we demonstrated the first example of a mononuclear iron pyridine-thiolate complex that functions both as a photosensitizer and catalyst for CO2 reduction. This single-component bifunctional molecular photocatalyst efficiently reduced CO2 to formate and CO with a total turnover number (TON) of 46 and turnover frequency (TOF) of 11.5 h-1 in 4 h under visible light irradiation. Notably, the quantum yield was determined to be 8.4 % for the generation of formate and CO at 400 nm. Quenching experiments indicate that high photocatalytic activity is mainly attributed to the rapid intramolecular quenching protocol. The mechanism investigation by DFT calculation and electrochemical studies revealed that the protonation of Febpy(pyS)2 is indispensable step for photocatalytic CO2 reduction.

Fabrication and optimization of perovskite-based photoanodes for solar-driven CO2 photoelectroreduction to formate

The photoelectrochemical reduction of CO2 to value-added products represents a promising strategy for mitigating CO2 emissions. However, further research efforts need to be undertaken to enable the technology for scale-up, including the design and fabrication of efficient photoelectrodes capable of yielding substantial photogenerated current densities. In this work, a photoanode combining a commercial calcium titanate perovskite (CaTiO3) and BiVO4 layers coated onto a transparent FTO substrate by automated spray pyrolysis is proposed. Different photoanode configurations are tested, with the most favourable results achieved when BiVO4 is positioned as the top layer with back illumination. The optimization of the catalytic loading is also assessed, finding an optimal at 1 mg cm−2 of CaTiO3 and 3 mg cm−2 of BiVO4, resulting in an impressive current density of –71 mA cm−2 at –1.8 V vs. Ag/AgCl. This optimal photoanode is then integrated into an electrolyzer for continuous visible light-driven CO2 reduction in the gas phase to formate, obtaining a concentration of 63.8 g L−1, with a Faradaic Efficiency of 79.1 %, and solar-to-fuel conversion efficiency of 7.6 %. These results represent a significant advancement in the development of photoanodes, offering promise for the future scalability of photoelectrochemical CO2 reduction processes.

Modulation of Fe–MOF via second-transition metal ion doping (Ti, Mn, Zn, Cu) for efficient visible-light driven CO2 reduction to CH4

This study developed metal–organic frameworks (MOFs) with enhanced properties for CO2 conversion by doping second- transition metal ions (Ti, Mn, Zn, and Cu) into Fe–MOF, which resulted in Fe-M−MOF (M = Ti, Mn, Zn, or Cu). The selection of different metal species in the metal cluster nodes of the MOFs significantly impacted the CO2 conversion efficiency. Among the different combinations, the Fe–Cu bimetallic cluster node was identified as the most optimal node. In addition, we investigated various variables and preparation conditions for determining the optimal synthesis conditions for Fe–Cu-MOFs. We observed that a synthesis temperature, time, and pH of 130 °C, 15 h, and 3.2, respectively, yielded the best results. The 13CO2 isotope labeling method confirmed that the carbon source of CO and CH4 were derived from CO2. Under simulated visible-light irradiation (λ ≥ 420 nm), Fe–Cu-T130 exhibited the highest photocatalytic activity, with a CH4 generation rate of up to 444.2 μmol g−1 h−1. This high activity was attributed to several factors. First, the presence of Fe2+, Fe3+, and Cu2+ on the surface of Fe–Cu-T130 resulted in photogenerated electrons and holes under visible-light excitation. Fe2+ accepted electrons to reduce CO2, whereas Fe3+ and Cu2+ oxidized H2O through holes. Second, the polycrystalline structure of Fe–Cu-T130 with abundant surface oxygen vacancies enhanced the chemical reactivity. Finally, the low conduction band position and narrower bandgap of Fe–Cu-T130 facilitated the excitation of electrons into the conduction band, thereby promoting the CO2 reduction reaction. This study successfully demonstrated the enhanced photocatalytic activity of Fe–Cu-T130 for CO2 conversion under visible light. The findings provide insight into the development of MOFs with improved properties for the sustainable and efficient utilization of CO2.

Localized surface plasmon resonance effect of bismuth nanoparticles in Bi/TiO2 catalysts for boosting visible light-driven CO2 reduction to CH4

Herein, the photocatalysts of metallic Bi-modified TiO2 microsphere (namely BTO) were synthesized by one-pot solvothermal method. The localized surface plasmon resonance (LSPR) effect of introduced metallic Bi nanoparticles is beneficial to improve the absorption efficiency for visible light, and its surface hot electrons can donate to the valence band of TiO2 for boosting the separation efficiency of light generated electron-hole pairs. BTO catalysts exhibit the super catalytic activity for visible light-driven CO2 reduction with H2O to CH4. The formation amount and selectivity of CH4 product over BTO-2 catalyst are 49.12 μmol g−1 and 85.48 % for 4 h, respectively. Based on the results of in-situ DRIFTS and density functional theory calculation, the mechanism for photocatalytic CO2 reduction is proposed: the visible light-driven LSPR effect on BTO catalyst can boost the key step of CO2* -to-HCO* for promoting selective generation of CH4 product. It inspires the design of efficient photocatalysts for CO2 conversion.

Construction of glucose precursor carbon/TiO2 heterojunction with high ligand-to-metal charge transfer (LMCT) for visible light driven CO2 reduction

Well-designed fabrication of glucose precursor carbon-doped TiO2 heterojunction with high Ligand-to-Metal Charge Transfer (LMCT) for enhancing photocatalytic CO2 conversion has been examined. Photocatalysts were fabricated using a single-step thermal method and tested in a fixed-bed reactor under visible light. The 6 % glucose precursor carbon-doped over TiO2 (6 %C/TiO2) photocatalyst has demonstrated excellent activity in converting CO2 to CO and CH4 under visible light. The main product yield, CO of 739.9 μmol g-cat−1 was produced over 6 %C/TiO2, which is 4.4 folds the amount of CO obtained over TiO2 (168.7 μmol g-cat−1). The XPS findings reveal the presence of different surface components containing C-OH, CC, and CO functional groups, which contribute to the formation of a ligand-metal-charge-transfer (LMCT) complex between carbon and TiO2 photocatalyst. Carbon-doped TiO2 possesses a narrow energy band and the ability to effectively absorb solar light, which enables efficient transportation of electrons generated by photon excitation. The mechanism of the carbon-doped TiO2 in CO2 conversion to CO and CH4 is postulated to be consistent with the LMCT complex phenomena. Therefore, carbon-doped TiO2 provides heterojunction for localization of electrons, impedes the rate at which charges recombine, and reduces the band gap energy, leading to improved photocatalytic performance when exposed to visible light.

Designing of cobalt doped pyridine based covalent organic frameworks for efficient visible light driven CO2 reduction

Covalent organic frameworks (COF) are the class of compounds that impulses the boundaries of organic/polymer chemistry and materials science to achieve the exceptional control of predesigned long-range ordered structures. The present work deals with one-pot reaction of pyridine-2,6-diamine and terephthalaldehyde in pyrex tube at slightly elevated temperature and resulted in the formation of PDT/COF. The obtained PDT/COF was then functionalized using cobalt (Co@PDT/COF). The formation of COF and metal incorporation is confirmed by Fourier transform Infrared spectroscopy (FTIR). The simulated AB staggered stacking model for both PDT/COF and Co@PDT/COF correlate well with the observed PXRD pattern than AA eclipsed stacking. The theoretical findings using materials studio software showed increase in the porosity and interlayer spacing after the addition of Co to PDT/COF. The superior photocatalytic CO2 reduction activity is observed in Co@PDT/COF compared to PDT/COF. Co@PDT/COF was able to produce 13, 24 and 45 μmol g−1h−1 of H2, CH4 and CO, respectively. The obtained experimental optical properties were correlated well with Density functional theory (DFT) studies. Based on the characterization results, mechanism of photocatalysis has been discussed. Good stability and efficiency towards photocatalytic reduction CO2 in presence of the Co@PDT/COF shows its suitability for further research on pyridine based COFs for different applications.

Oxygen vacancy-engineered ultrathin Bi24O31Br10 for visible light-driven CO2 reduction with nearly 100% CO selectivity in pure water

Photocatalytic CO2 reduction performance is still unsatisfactory main due to the low separation efficiency of photogenerated electron-hole pairs, insufficient of active sites, and poor activation of CO2. Defect engineering is an effective strategy to address these issues. Herein, we firstly reported that one ultrathin Bi24O31Br10 nanosheet with abundant oxygen vacancy is fabricated via one-step hydrothermal approach. Electron paramagnetic resonance (EPR) spectra confirmed that different concentrations of oxygen vacancies are deliberately created on the surfaces of Bi24O31Br10 nanosheets by adjusting the amount of ethylene glycol (EG). Density of states function theory (DFT) calculations revealed the generation of stronger local charge around the oxygen vacancies (Vo), which promoted the dissociation of CO2 and facilitated the production of COOH* intermediate conversed from CO2. Meanwhile, adsorption energy calculations indicated that the Vo favor the adsorption of CO2. As a result, without cocatalysts or sacrificial agents, the ultrathin Vo-R Bi24O31Br10 nanosheets delivers a nearly 100% of CO selectivity with high CO yield rate of 14.80 μmol g−1h−1 in pure water under visible light.

Enhanced visible light-driven CO2 reduction activity induced by Z-scheme heterojunction photocatalyst C60/TpPa (COF)

A family of heterojunction photocatalysts C60/TpPa have been constructed from fullerenes (C60) and TpPa-1 via in-situ solvothermal method firstly. The photocatalytic activity toward CO2 of C60/TpPa has been evaluated through the gas-solid reaction system under pure CO2 and low concentration CO2 (10 %) atmosphere, respectively. The results show that the maximum CO formation rates for C60/TpPa are as high as 48.16 μmol·g−1·h−1 and 90.25 μmol·g−1·h−1 under pure CO2 and 10 % CO2 environment, respectively. The attractive experimental phenomenon is assigned to the existence of CO groups in TpPa-1. Due to the presence of Z-scheme heterojunction, the separation of photoexcited electrons and holes is effectively enhanced, and the photocatalytic performances are significantly improved. This work suggests that the construction of COF-based photocatalysts with heterojunction for efficient photoreduction of CO2 is a promising strategy.

Vacancy defects engineering in Yolk-shelled Co-CeO2 for efficient visible Light-Driven CO2 reduction

Solar-driven photocatalytic CO2 conversion is considered as the most promising approach to eliminating atmospheric CO2 emissions. However, great challenges lie in the utilization of visible-infrared light and the activation of the inert CO2 molecule. Herein, we report the preparation of a yolk-shell Co-CeO2 octahedron and the strategy for surface defect engineering to optimize the photocatalyst by two-step calcination of a Ce-based metal–organic framework (Ce-UiO-66). As a result of the synergistic effect of incorporating the Co atom and rich oxygen vacancies, the energy barrier of activating and transforming the adsorbed CO2 to *COOH is significantly reduced. Benefiting from the structure with high surface area, cavity, and abundant defects, the optimized Co-CeO2 photocatalyst not only provides more exposed active sites and enhanced photoabsorption but also improves charge separation and transfer. Accordingly, 1%–Co-CeO2-H2 exhibits much higher photocatalytic activity in CO2 reduction under visible light irradiation with a CO generation rate of 46.9 μmol/h, which is 4.6 times than that of less defective 1%–Co-CeO2, and far more than that of pure CeO2.

Defective nano-silica loaded polymeric carbon nitride for visible light driven CO2 reduction and dye degradation

A hybrid composite of polymeric carbon nitride (PCN) and defective nano-silica (n-SiOx) photocatalyst has been synthesized, exhibiting a high surface area, improved light response, and reduced charge recombination. The synergistic formation of PCN-n-SiOx interface facilitated photoinduced charge transfer from PCN to n-SiOx, resulting in suppressed carrier recombination. The resultant hybrid PCN-n-SiOx sample demonstrated a three-fold photocatalytic reduction of CO2 into methanol and formic acid. Furthermore, photoelectrocatalytic CO2 reduction selectively yielded 283.0 μmol L−1 of formic acid, a five-fold increment compared to bare PCN (57.0 μmol L−1). These findings hold promise for the development of PCN-based hybrid composites for solar-powered applications.

Photocatalytic CO2 reduction with aminoanthraquinone organic dyes

The direct utilization of solar energy to convert CO2 into renewable chemicals remains a challenge. One essential difficulty is the development of efficient and inexpensive light-absorbers. Here we show a series of aminoanthraquinone organic dyes to promote the efficiency for visible light-driven CO2 reduction to CO when coupled with an Fe porphyrin catalyst. Importantly, high turnover numbers can be obtained for both the photosensitizer and the catalyst, which has not been achieved in current light-driven systems. Structure-function study performed with substituents having distinct electronic effects reveals that the built-in donor-acceptor property of the photosensitizer significantly promotes the photocatalytic activity. We anticipate this study gives insight into the continued development of advanced photocatalysts for solar energy conversion.

Variable valence Mo5+/Mo6+ ionic bridge in hollow spherical g-C3N4/Bi2MoO6 catalysts for promoting selective visible light-driven CO2 photoreduction into CO

Herein, the catalysts of ultrathin g-C3N4 surface-modified hollow spherical Bi2MoO6 (g-C3N4/Bi2MoO6, abbreviated as CN/BMO) were fabricated by the co-solvothermal method. The variable valence Mo5+/Mo6+ ionic bridge in CN/BMO catalysts can boost the rapid transfer of photogenerated electrons from Bi2MoO6 to g-C3N4. And the synergy effect of g-C3N4 and Bi2MoO6 components remarkably enhance CO2 adsorption capability. CN/BMO-2 catalyst has the best performances for visible light-driven CO2 reduction compared with single Bi2MoO6 and g-C3N4, i.e., its amount and selectivity of CO product are 139.50 μmol g−1 and 96.88% for 9 h, respectively. Based on the results of characterizations and density functional theory calculation, the photocatalytic mechanism for CO2 reduction is proposed. The high-efficient separation efficiency of photogenerated electron-hole pairs, induced by variable valence Mo5+/Mo6+ ionic bridge, can boost the rate-limiting steps (COOH*-to-CO* and CO* desorption) of selective visible light-driven CO2 conversion into CO. It inspires the establishment of efficient photocatalysts for CO2 conversion.

CdO decorated CdS nanorod for enhanced photocatalytic reduction of CO2 to CO.

Solar-driven CO2 reduction into fuels and sustainable energy has attracted increasing attention around the world. However, the photoreduction efficiency remains low due to the low efficiency of separation of electron-hole pairs and high thermal stability of CO2. In this work, we prepared a CdO decorated CdS nanorod for visible light driven CO2 reduction. The introduction of CdO facilitates the photoinduced charge carrier separation and transfer and acts as an active site for adsorption and activation of CO2 molecules. Compared with pristine CdS, CdO/CdS exhibits a nearly 5-fold higher CO generation rate (1.26 mmol g-1 h-1). In situ FT-IR experiments indicated that CO2 reduction on CdO/CdS may follow a COOH* pathway. This study reports the pivotal effect of CdO on photogenerated carrier transfer in photocatalysis and on CO2 adsorption, which provides a facile way to enhance photocatalytic efficiency.

Developing post-modified Ce-MOF as a photocatalyst: a detail mechanistic insight into CO2 reduction toward selective C2 product formation

Post-synthetically modified defect-regulated Ce-UiO-66 MOF produces selective C2-based product (acetic acid) by visible light-driven CO2 reduction reaction.

Phosphorus Tailors the d-Band Center of Copper Atomic Sites for Efficient CO2 Photoreduction under Visible-Light Irradiation.

Photoreduction of CO2 into solar fuels has received great interest, but suffers from low catalytic efficiency and poor selectivity. Herein, two single-Cu-atom catalysts with unique Cu configurations in phosphorus-doped carbon nitride (PCN), namely, Cu1 N3 @PCN and Cu1 P3 @PCN were fabricated via selective phosphidation, and tested in visible light-driven CO2 reduction by H2 O without sacrificial agents. Cu1 N3 @PCN was exclusively active for CO production with a rate of 49.8 μmolCO gcat -1 h-1 , outperforming most polymeric carbon nitride (C3 N4 ) based catalysts, while Cu1 P3 @PCN preferably yielded H2 . Experimental and theoretical analysis suggested that doping P in C3 N4 by replacing a corner C atom upshifted the d-band center of Cu in Cu1 N3 @PCN close to the Fermi level, which boosted the adsorption and activation of CO2 on Cu1 N3 , making Cu1 N3 @PCN efficiently convert CO2 to CO. In contrast, Cu1 P3 @PCN with a much lower Cu 3d electron energy exhibited negligible CO2 adsorption, thereby preferring H2 formation via photocatalytic H2 O splitting.

Visible-Light Driven CO2 Reduction to CO by Co3O4 Supported on Tungsten Oxide

Visible-Light Driven CO₂ Reduction to CO by Co₃O₄ Supported on Tungsten Oxide

Synthesis of Stable Lead-Free Cs3 Sb2 (Brx I1- x )9 (0 ≤ x≤ 1) Perovskite Nanoplatelets and Their Application in CO2 Photocatalytic Reduction.

Exploring photocatalysts to foster CO2 photoreduction into high value-added chemicals is of great significance. Lead halide perovskites (LHPs) have recently been extensively investigated as photocatalysts, owing to their facile fabrication and prominent optoelectronic properties. However, the toxicity of lead and instability will hinder their future large-scale applications. To address these challenges, a series of lead-free Sb-based all-inorganic mixed halide perovskite Cs3 Sb2 (Brx I1- x )9 (0 ≤ x≤ 1) nanoplatelets (NPLs) is synthesized. The perovskite NPLs are prepared using a ligand-assisted re-precipitation approach at 50 °C. The authors observe the tunability of their optical band gaps from 2.1 to 2.5eV, and they can maintain the excellent stability over 120 h under heating at 100 °C or UV light irradiation. The resultant materials are employed as efficient photocatalysts for visible-light driven CO2 reduction at the gas-solid interface. The Cs3 Sb2 (Br0.7 I0.3 )9 perovskite NPLs afford an impressive overall yield of 27.7µmol g-1 for the selective photocatalytic conversion of CO2 into CO. This study represents a significant demonstration for practical artificial photosynthesis by using LHP materials as photocatalysts.

Activating oxygen deficient TiO2 in the visible region by Bi2MoO6 for CO2 photoreduction to methanol.

Fast photogenerated charge recombination and inappropriate bandgap for visible light driven charge generation hinders the performance of TiO2. In this study, TiO2 was activated for visible light driven CO2 reduction in the presence of Bi2MoO6 as an electron donor. Furthermore, the introduction of oxygen vacancies resulted in enhanced CO2 adsorption and conversion. The best catalyst gives 27.1 μmol g-1 h-1 methanol formation. DRIFTS was used to explain the methanol formation mechanism on oxygen deficient TiO2.

2D Covalent Organic Frameworks with an Incorporated Manganese Complex for Light Driven Carbon Dioxide Reduction

AbstractCovalent organic frameworks (COFs) have emerged as a novel class of crystalline porous photocatalytic materials due to their unique properties such as large surface area, tunable porosity, and rigid structure. In this work, we report the direct incorporation of a manganese CO2 molecular catalyst (MC) into COFs (Mn−TTA‐COF) and the evaluation of its capability as photocatalyst for visible light driven CO2 reduction to form CO. We found that the photocatalytic activity of Mn−TTA‐COF is quite low, which mainly results from the elimination of the CO ligand in the Mn MC upon light illumination, rendering its short duration in the catalytic reaction. While this is a central concern for the further use Mn−TTA‐COF as a CO2 reduction catalyst, we found that the stability and efficiency of Mn MC is largely enhanced after being incorporated into COFs with respect to its homogeneous version, suggesting the capability of COFs as heterogeneous platform to incorporate MC and improve the catalytic performance of MC. Moreover, transient absorption spectroscopic studies show that the intramolecular charge transfer lifetime of the Mn‐incorporated COF is longer than that in the parent COF, which suggests that charge separation (CS) may occur from the parent COF to the Mn moiety. These results together suggest that COFs may show promise as a platform for creating next‐generation photocatalysts with a built‐in photosensitizer and MC, which can facilitate CS and enhance the stability and efficiency of the incorporated MC.

The heterojunction between 3D ordered macroporous TiO2 and MoS2 nanosheets for enhancing visible-light driven CO2 reduction

The photocatalytic CO2 and H2O conversion into CO and hydrocarbons over the semiconductors catalysts is an effective way to alleviate environmental pollution and resource shortage currently. Herein, three-dimensional ordered macroporous (3DOM) TiO2-supported two-dimensional layered MoS2 (MoS2/3DOM-TiO2) as two isolated photochemical systems were proposed to form heterojunction structure. The diffuse reflection of photonic crystal microstructure can raise the adsorption efficiency of visible light. The formation of TiO2-MoS2 heterojunction is favorable to the enhancing separation efficiency of photoexcitation electron and hole pairs. The binary MoS2/3DOM-TiO2 photocatalyst shows the higher catalytic performance for visible-light driven reduction of CO2 in the range of 420−900 nm. MoS2/3DOM-TiO2-1.5 photocatalyst shows the highest maximum formation yields of CO (22.6 μmol g-1) as well as CH4 (11.6 μmol g-1) products during 8 h, then its apparent quantum efficiency value is 6.7 %, which is far higher than the photosynthesis efficiency of green plants. The heterojunction of MoS2/3DOM-TiO2 photocatalysts with enhancing light adsorption and electron-hole separation efficiency is expected to provide more extensive reference for the evolution of high-efficient photocatalyst for CO2 conversion.