CO2 Photoreduction Activity Research Articles

The Facile Synthesis of a Re-Complex Heterogeneous Catalysis System for Enhancing CO2 Photoreduction Activity.

fac-Re(2,2'-bipyridine)(CO)3Cl] (denoted as ReCC) is an efficient molecule-catalyst with high selectivity in the photoreduction of CO2 to CO in a homogeneous system. However, the two major drawbacks of Re(I) complexes in the homogeneous system, easy degradation and difficult separation, seriously hinder its development in the field of industrial applications. In this paper, we designed and prepared two different Re-complex fixation systems (denoted as ReCC@TiO2-5 wt% and ReCC-TiO2-5 wt%) based on TiO2 gel via the sensitization method and sol-gel method, respectively. Compared with a pure ReCC complex, both of them exhibited excellent photocatalytic reduction activity. In particular, the sol-gel hybrid system (ReCC-TiO2-5 wt%) displayed outstanding positive synergistic effects on the photocatalytic activity and the long durability of the photocatalytic process. A series of characterizations were carried out to explore the probable photocatalytic reduction process mechanism, which provides the theoretical basis and technical support for the Re complex fixation method.

Understanding the unique S-scheme charge migration in triazine/heptazine crystalline carbon nitride homojunction

Understanding charge transfer dynamics and carrier separation pathway is challenging due to the lack of appropriate characterization strategies. In this work, a crystalline triazine/heptazine carbon nitride homojunction is selected as a model system to demonstrate the interfacial electron-transfer mechanism. Surface bimetallic cocatalysts are used as sensitive probes during in situ photoemission for tracing the S-scheme transfer of interfacial photogenerated electrons from triazine phase to the heptazine phase. Variation of the sample surface potential under light on/off confirms dynamic S-scheme charge transfer. Further theoretical calculations demonstrate an interesting reversal of interfacial electron-transfer path under light/dark conditions, which also supports the experimental evidence of S-scheme transport. Benefiting from the unique merit of S-scheme electron transfer, homojunction shows significantly enhanced activity for CO2 photoreduction. Our work thus provides a strategy to probe dynamic electron transfer mechanisms and to design delicate material structures towards efficient CO2 photoreduction.

One-step hydrothermal synthesis of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composites with enhanced photocatalytic CO2 reduction performance

In this study, a kind of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composite material is firstly prepared by one-step hydrothermal method through adjusting the molar amount of Bi source, which further improves the photocatalytic CO2 reduction performance compared with pure Bi2Sn2O7. Combined with work-enthalpy data using density functional theory calculations, the photoexcited electrons are directionally transferred from Bi2O3 to Bi2Sn2O7 for the formation of S-scheme mechanism, achieving the significant improvement in the photoinduced charge separation efficiency and CO2 photoreduction activity to CO for as-prepared Bi2O3/Bi2Sn2O7 composite. A feasible photocatalytic CO2 reduction mechanism of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composite is proposed and investigated. Our findings should provide the significant theoretical guidance and experimental data for achieving the S-scheme heterojunction construction and CO2 green conversion into low-carbon chemical fuels.

Contribution of CuO on lamellar BiVO4/Bi2O3-based semiconductor for photoconversion of CO2

Lamellar BiVO4 is a photocatalyst recognized as an effective visible-light-driven semiconductor that is active in CO2 reduction but faces challenges such as high recombination rate and low mobility of photogenerated charge carriers. Additionaly, CuXO are well-known materials for CO2 photosynthesis, and Bi2O3 improves the generation of organic compounds from CO2 reduction with more than one carbon. In this sense, this paper evaluates the influence of small amounts of copper oxide on lamellar BiVO4-Bi2O3 prepared by a microwave-assisted route on the CO2 photoreduction activity. Lamellar BiVO4-Bi2O3 powder catalysts modified by different percentages of CuO were synthesized using microwave heating at 140 °C and 1200 rpm for 15 min. Electrochemical and photochemical characterizations showed that small amounts of copper, such as 1.0%, enhanced the absorption of visible light, improved charge transfer, mitigated charge recombination, and increased the yield of products (acetone and methanol). Furthermore, the flat band potential of the catalyst modified with 1.0% of copper was located at a more negative potential than the unmodified sample, which favored the photocatalytic reduction of the CO2. As a result, the study achieved a 38-fold improvement in methanol generation (1373.5 µmol L−1 gcat−1) and a 62% increase in acetone formation (12.5 µmol L−1 gcat−1) under UV–Vis light incidence over 2 h of reaction at ambient pressure and temperature, compared to pure BiVO4 (36.3 µmol L−1 gcat−1 of methanol and 7.7 µmol L−1 gcat−1 of acetone).

Selective Photocatalytic Reduction of CO2 to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride

AbstractArtificial photosynthesis is a promising strategy for converting carbon dioxide (CO2) and water (H2O) into fuels and value‐added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C3N4 nanotubes (PCN) to form the photocatalyst Ag1@PCN with Ag−N3 coordination for CO2 photoreduction using H2O as the reductant. The as‐synthesized Ag1@PCN exhibits a high CO production rate of 0.32 μmol h−1 (mass of catalyst: 2 mg), a high selectivity (>94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal–support interactions (Ag−N3) favor *CO2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C3N4 and Ag single atoms, thereby accounting for the enhanced CO2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal–support interactions in enhancing the photoactivity and CO selectivity of CO2 photoreduction.

Selective Photocatalytic Reduction of CO2 to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride.

Artificial photosynthesis is a promising strategy for converting carbon dioxide (CO2 ) and water (H2 O) into fuels and value-added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C3 N4 nanotubes (PCN) to form the photocatalyst Ag1 @PCN with Ag-N3 coordination for CO2 photoreduction using H2 O as the reductant. The as-synthesized Ag1 @PCN exhibits a high CO production rate of 0.32 μmol h-1 (mass of catalyst: 2 mg), a high selectivity (>94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal-support interactions (Ag-N3 ) favor *CO2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C3 N4 and Ag single atoms, thereby accounting for the enhanced CO2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal-support interactions in enhancing the photoactivity and CO selectivity of CO2 photoreduction.

Partial disorder structured BiOI atomic layers boosting excitons dissociation for photocatalytic CO2 reduction and pollutant removal

Owing to atomic-thin thickness, reduced dielectric screening will usually happen in 2D atomic layers and lead to the formation of strong exciton effect, which is not energetically for some photocatalytic reactions. In this work, a scalable fast synthesis strategy is developed to fabricate BiOI atomic layers with partial disorder area (BiOI-D) at room temperature, as observed by HAADF-STEM image. This order–disorder interface in BiOI atomic layers favors boosting excitons dissociation to free charge carriers. Due to the atomic-thin thickness for rapid bulk charge diffusion and order–disorder interface for excitons dissociation, this BiOI-D atomic layers display greatly improved charge separation efficiency compared to BiOI nanosheets, thus contribute to enhanced photocatalytic activity for pollutants degradation and CO2 reduction. Compared to BiOI nanosheets, a 12.5 times increased CO2 photoreduction activity can be realized over BiOI-D atomic layers, with the CO generation rate of 15.1 μmol g−1 in 5 h. Profiting from the order–disorder interface, CO2 activation energy barrier can be lowered and rate-limiting step energy barrier for COOH* formation is decreased from 0.67 to 0.34 eV.

Selective CO2 photoreduction into CO over Ti3C2 quantum dots decorated NH2-MIL-101(Fe) heterostructures

Exploring effective photocatalyst to promote the conversion of CO2 into valuable chemical fuels remains a great challenge. Herein, a novel heterostructure, namely Ti3C2 quantum dots (QDs) decorated NH2-MIL-101(Fe), was designed and fabricated via an electrostatic adsorption method. The resultant heterostructure exhibited remarkably improved activity for CO2 photoreduction under visible-light illumination. The optimal NH2-MIL-101(Fe)@Ti3C2 QDs catalyst with 0.75 wt% Ti3C2 QDs achieved a CO-evolution rate of 55.7 μmol h−1 g−1, which was 2.6 times greater than that of pristine NH2-MIL-101(Fe). The enhanced activity of NH2-MIL-101(Fe)@Ti3C2 QDs was mainly due to the extended visible-light response and the effective charge separation and transfer benefiting from the formation of a Schottky junction at the interface. Isotope-labeling experiment indicated that CO was produced from CO2. Finally, the reaction intermediates and mechanism of photocatalytic CO2 reduction were investigated by in-situ FT-IR.

Graphene Oxide-Mediated Synthesis of Ultrathin Co-MOL for CO2 Photoreduction.

Metal-organic framework (MOF) materials have broad application prospects in catalysis because of their ordered structure and molecular adjustability. However, the large volume of bulky MOF usually leads to insufficient exposure of the active sites and the obstruction of charge/mass transfer, which greatly limits their catalytic performance. Herein, we developed a simple graphene oxide (GO) template method to fabricate ultrathin Co-metal-organic layer (2.0 nm) on reduced GO (Co-MOL@r-GO). The as-synthesized hybrid material Co-MOL@r-GO-2 exhibits highly efficient photocatalytic performance for CO2 reduction, and the CO yield can reach as high as 25,442 μmol/gCo-MOL, which is over 20 times higher than that of the bulky Co-MOF. Systematic investigations demonstrate that GO can act as a template for the synthesis of the ultrathin Co-MOL with more active sites and can be used as the electron transport medium between the photosensitizer and the Co-MOL to enhance the catalytic activity for CO2 photoreduction.

Construction of sandwich-like Ag/UiO-66@g-C3N4 Z-scheme ternary heterojunction for photocatalytic CO2 conversion to CH3OH and CO

Photocatalysis technology to convert CO2 into fuels is considered as one promising strategy to mitigate the greenhouse effect and energy crisis. Herein, the Z-scheme Ag/UiO-66@g-C3N4 (AUiO@CN) composites exhibit an improved CO2 photoreduction activity owing to the increased specific surface area, strong redox capacity, rapid separation of photoinduced h+/e− pairs and fast transfer of e− at the interface. As a result, CH3OH and CO evolution rates of AUiO@CN composite are roughly 3.09 and 2.40 times higher than those of g-C3N4, respectively. The Quantum yield (QY) of CO and CH3OH for AUiO@CN are 0.0217 % and 0.0986 %. The ESR characterization and a series of electrochemical results confirmed the Ag NPs acted as e− mediator, which could promote the photogenerated charge separation and transport and CO2 reduction ability. This work not only provides a simple photo-deposition assisted grinding calcination method to prepare ternary composites, but also shows that the prepared ternary heterojunction photocatalyst can realize an efficient photocatalytic CO2 conversion to methanol and CO.

Interface and Defect Engineering of a Hollow TiO2@ZnIn2S4 Heterojunction for Highly Enhanced CO2 Photoreduction Activity

Rational engineering of the interfaces or defects of heterojunctions provides an effective strategy to improve their photocatalytic performance but is still a challenge. Herein, we present an ingenious calcination strategy of simultaneously introducing sulfur vacancies and enhancing the interfacial interaction for a hollow TiO2@ZnIn2S4 heterojunction, thus greatly improving the photocatalytic CO2 reduction activity. The low-temperature calcination strategy makes the heterojunction possess both abundant sulfur vacancies and strong interfacial interaction, which lead to an enhanced CO2 photoreduction activity with a CO evolution rate of 1330 μmol g–1 h–1, much higher than that of the sample without calcination treatment (639 μmol g–1 h–1). The significantly boosted photocatalytic performance can be ascribed to the improved transfer and separation of photogenerated charges resulting from the intimate heterojunction interface, as well as the strengthened visible-light absorption due to the rich sulfur vacancies. This work presents a feasible and convenient method to optimize the performance of the heterojunction photocatalysts by designing the interfaces and defects.

Citric acid-assisted in-situ synthesis of a distinctive 3D flower-like spherical Bi2MoO6 nano-film and its enhanced CO2 photoreduction activity

The photocatalytic CO2 reduction reaction for producing chemical fuels is an ideal advanced technology to effectively mitigate global warming and the energy crisis. Importantly, how to achieve excellent activity and cyclic utilization of photocatalysts has been one research hot-topic. In this work, a Bi2MoO6 (BMO) nano-film with a 3D flower-like spherical structure was fabricated on a Bi plate via a room-temperature in-situ electrochemical ion-exchange method with the assistance of citric acid (CA) (BMO (+CA)). The experimental results show that the BiOBr nano-film, as sacrificial template, plays an important role in the synthesis of the BMO nano-film. The BMO (+CA) nano-film exhibits superior photocatalytic CO2 reduction activity with a CO yield (258μmol g−1), under simulated sunlight irradiation, 3.6 times higher than the BMO (-CA) nano-film with a nanosheet-like structure. Moreover, the dominating reason and action mechanism of the enhanced photocatalytic CO2 reduction performance for the BMO (+CA) nano-film are proposed. Our outcomes provide new insights into the development and research of highly-efficient Bi-based nano-films in the CO2 reduction reaction field.

Rational design of MoS2@COF hybrid composites promoting C-C coupling for photocatalytic CO2 reduction to ethane

Photocatalytic CO2 reduction into high-value C2+ products such as ethane is quite exciting but challenging due to multielectron steps involved and sluggish C-C coupling kinetics. Herein, a well-designed MoS2@COF hybrid composite is prepared for efficient and selective CO2 photoreduction to C2H6. In-depth experimental and theoretical studies reveal that the interfacial electric field built in the heterojunction accelerates the photogenerated electrons transfer from MoS2 to COF under light irradiation, greatly facilitating charge separation and transfer and thus enhancing the activity and C2H6 selectivity for CO2 photoreduction. The optimized MoS2@COF-15 achieves C2H6 production rate up to 56.2 μmol·g−1·h−1 with 83.8% of selectivity, which is about 8.6 and 31.2 times higher than that of pristine MoS2 and COF under identical conditions. The in-situ DRIFTS and DFT calculations indicate that the structure of MoS2@COF composite can promote the adsorption of *CO and the formation of *COCO, facilitating C-C coupling to convert into C2H6 product.

Rapid charge transfer in covalent organic framework via through-bond for enhanced photocatalytic CO2 reduction

Charge transfer efficiency between discrete photosensitizers and catalytic sites is a key limiting factor in artificial photosynthesis. It is highly desirable but challenging to efficiently combine the two sections into an integration system and get insight into the kinetics and mechanisms. Here in, the photosensitizer [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) and active cobalt porphyrin (Co-Por) sites were integrated into a covalent organic framework (COF), named COF-RuBpy-Co, for efficient charge transfer and photocatalytic CO2 reduction. The catalyst COF-RuBpy-Co exhibited excellent CO2 photoreduction activity towards CO production with a rate of 547 μmol g−1h−1, which is 1.4-fold enhancement over the physical mixture of Ru(bpy)3Cl2 and COF-Bpy-Co. In situ X-ray photoelectron spectroscopy combined with theoretical calculation results revealed that COF-RuBpy-Co achieved efficient photoelectron transfer from [Ru(bpy)3]2+ to cobalt porphyrin. More importantly, transient absorption spectroscopy indicated that the covalent linking [Ru(bpy)3]2+and Co-Por units realized a faster charge transfer (44.2 ps) over the large π-conjugated system. This work provides vital insights into the charge carrier transfer process and demonstrates the potential of COFs as a platform in artificial photosynthesis.

UV light-induced oxygen doping in graphitic carbon nitride with suppressed deep trapping for enhancement in CO2 photoreduction activity

• Oxygen (O) element is introduced in the bulk graphitic carbon nitride (CN) for the first time through a precursor pretreatment by ultraviolet (UV) light irradiation. • The doped O non-metal photocatalyst of CN increased visible light absorption and enhanced carrier density. • The optimized sample has lower charge recombination and suppressed electron deep trapping. • The optimized sample shows enhanced photoreduction activity of CO2 to CH4. While photoreduction of CO 2 to CH 4 is an effective means of producing value-added fuels, common photocatalysts have poor activity and low selectivity in photocatalytic CO 2 -reduction processes. Even though creating defects is an effective photocatalyst fabrication route to improve photocatalytic activity, there are some challenges with the facile photocatalyst synthesis method. In this work, an O element is introduced into a graphitic carbon nitride (CN) skeleton through a precursory ultraviolet light irradiation pretreatment to increase the visible light absorption and enhance the carrier density of this modified non-metal CN photocatalyst; the charge transfer dynamics thereof are also studied through electrochemical tests, photoluminescence spectroscopy, and nanosecond transient absorption. We verify that the optimized sample exhibits lower charge recombination and a suppressed 84 ns electron-trapping lifetime, compared to the 103 ns electron-trapping lifetime of the CN counterpart, and thereby contributes to robust detrapping and a fast transfer of active electrons. Through density functional theory calculations, we find that the improved light absorption and increased electron density are ascribed to O-element doping, which enhances the CO 2 adsorption energy and improves the CO 2 -to-CH 4 photoreduction activity; it becomes 17 times higher than that of the bare CN, and the selectivity is 3.8 times higher than that of CN. Moreover, the optimized sample demonstrates excellent cyclic stability in a 24-hour cycle test.

Boosted charge transfer and CO2 photoreduction by construction of S-scheme heterojunctions between Cs2AgBiBr6 nanosheets and two-dimensional metal–organic frameworks

An inorganic/organic CABB/Ni-MOF hybrid photocatalyst was fabricated. Due to the efficient charge separation, high reduction potential preservation, and the improved CO2 adsorption, the CABB/Ni-MOF hybrid showed high CO2 photoreduction activity.

Hierarchical S-scheme titanium dioxide@cobalt-nickel based metal-organic framework nanotube photocatalyst for selective carbon dioxide photoreduction to methane.

Efficient photocatalysts are of great importance for the photochemical conversion of CO2 into fuels. Herein, S-scheme titanium dioxide@cobalt-nickel based metal-organic framework (TiO2@CoNi-MOF) heterojunction photocatalysts with high surface area and porosity are designed and fabricated by a multi-step controllable strategy. The photocatalytic activity of the composites can be optimized by adjusting the loading content of CoNi-MOF in TiO2@CoNi-MOF and molar ratios of Co2+ and Ni2+ in CoNi-MOF. The optimized hybrid photocatalyst showed a much higher CO2 photoreduction activity than the control single-component samples (TiO2 and CoNi-MOF) with a high CH4 yield (41.65μmolg-1h-1) and selectivity (93.2%). The accelerated charge carrier separation induced by the S-scheme heterojunction significantly promoted the photocatalytic performance of TiO2@CoNi-MOF NTs. Meanwhile, the introduction of bimetallic CoNi-MOF nanosheets significantly resulted in the increase of active sites, CO2 adsorbability, visible-light utilization, and CH4 selectivity. Moreover, the S-scheme photoinduced charge transfer model of the TiO2@CoNi-MOF NTs photocatalyst was confirmed by photoluminescence spectroscopy, free radical trapping tests, and work function calculated from Kelvin probe. The work aims to design and fabricate heterojunction photocatalysts with high efficiency for solar fuel production.

Defect engineering enhances plasmonic-hot electrons exploitation for CO2 reduction over polymeric catalysts.

Defect sites present on the surface of catalysts serve a crucial role in different catalytic processes. Herein, we have investigated defect engineering within a hybrid system composed of "soft" polymer catalysts and "hard" metal nanoparticles, employing the disparity in their thermal expansions. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and mechanistic studies together reveal the formation of new abundant defects and their synergistic integrability with plasmonic enhancement within the hybrid catalyst. These active defects, co-localized with plasmonic Ag nanoparticles, promote the utilization efficiency of hot electrons generated by local plasmons, thereby enhancing the CO2 photoreduction activity while maintaining the high catalytic selectivity.

Tailored Persistent Radical‐containing Heterotrimetal‐Organic Framework for Boosting Efficiency of Visible/NIR Light‐driven Photocatalytic CO2 Reduction

AbstractPromoting light absorption range of photocatalysts is of great significance to improve solar light‐driven photocatalytic CO2 reduction efficiency. Herein, a new viologen‐based multicomponent heterotrimetallic metal–organic framework (MOF) [Cu3Th6(µ3‐O)4(µ3‐OH)4(cpb)12][FeIII(CN)6]6 (IHEP‐14) with an unprecedented (6, 18)‐connected she‐d topology is presented. Upon UV irradiation, this MOF undergoes ligand and iron photoreduction, and a single‐crystal‐to‐single‐crystal transformation to generate persistent radical‐containing MOF [Cu3Th6(µ3‐O)4(µ3‐OH)4(cpb•)12][FeII(CN)6]6 (IHEP‐15). This radical‐containing MOF shows excellent stability without fading after at least 2 months in air. Besides extending the photoabsorption to a wider wavelength range covering from 200 to 2,500 nm, the generation of persistent radical in IHEP‐15 also largely enhances its CO2 adsorption capacity by a factor of three due to the strong affinity between π orbital of the radical and the π system of CO2. These attributes endow IHEP‐15 with excellent visible/NIR light‐driven CO2 photoreduction activity, with CO production rates under visible and NIR irradiation of 570.3 and 209.3 µmol h−1 g−1, respectively. Notably, the latter is a record high for NIR‐induced CO production among all MOFs reported so far.

Tailoring the Exciton Binding Energy of 2D Conjugated Polymers for Powering Metal-Free CO2 Photoreduction

Metal-free conjugated polymer photocatalysts have provided promising environmentally friendly options in photoreduction of CO2 to high value-added chemicals. However, due to the strong Coulombic interaction of excited electron–hole pairs, most polymer photocatalysts show moderate photocatalytic performances compared with inorganic semiconductor photocatalysts. Herein, we prepared a series of 2D porphyrin-based conjugated polymers. By simply altering the aromatic acetylene linkers, we found that the exciton binding energy (Eb) of the 2D conjugated polymers could be fine-tuned. With an increasing number of acetylene units in linkers, their Eb values were reduced by 27% accompanied by promoted charge-carrier generation (about a 4-fold increase in photocurrent) and obviously enhanced catalytic activity of CO2 photoreduction. The optimized polymer, PTPP-DA, linked with diacetylene groups, affords CO and CH4 as the carbonaceous products with rates of 465 and 237 μmol g–1 h–1, respectively, without any metal or photosensitizer. This work reveals the important implications of conjugated linkers on mediating the Eb values of 2D conjugated polymers and provides new insight for designing efficient metal-free polymeric photocatalysts for CO2 reduction.