Photocatalytic CO2 Reduction Performance Research Articles

Synergetic effect of oxygen vacancies coupled with in-situ Bi clusters in Bi2WO6 for enhancing photocatalytic CO2 reduction

In order to improve photocatalytic performance, Bi2WO6 (BWO) with oxygen vacancies (Vo) and in-situ loaded Bi clusters was prepared by using mild aluminothermic reduction. From morphological and structural characterization, it can be seen that Bi clusters gradually precipitates from the surface of BWO owing to oxygen vacancies as annealing temperature increases. The photocatalyst annealed at 450 ℃ (Bi-Vo-BWO-450) demonstrates the best photocatalytic CO2 reduction performance with CO and CH4 production rate reaching 5.94 and 1.18 µmol·g−1·h−1, respectively. From experimental analyses and first principles calculation, in-situ Bi clusters exhibit the unique surface plasma resonance (SPR) effect and induce the formation of internal electric field by Schottky barrier between Bi and BWO, which enhance the light absorption of photocatalyst and improve charge separation and transfer efficiency. Meanwhile, Bi clusters act as the surface active sites to activate CO2 adsorption for reducing the rate-limiting potential barrier in photocatalytic CO2 reduction, and improve the activity of oxygen vacancies by preventing the oxygen-containing groups from being adsorbed at the oxygen defect site. This work has a clear understanding of the synergetic effect between Bi clusters and oxygen vacancies, and provides a new enlightenment into high-efficiency catalyst.

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.

Facet-Dependent Photocatalytic Behavior of Fe-soc-MOF for Carbon Dioxide Reduction.

Exposing different facets on metal-organic frameworks (MOFs) is an efficient approach to regulate their photocatalytic performance for CO2 reduction. Herein, Fe-soc-MOFs exposed with different facets were successfully synthesized, and the morphologies of Fe-soc-MOF exposed with eight {111} facets (Fe-soc-O) and that exposed with eight {111} and six {100} crystal facets (Fe-soc-M) are first reported. Fe-soc-MOFs have facet-dependent active sites on their surface and correspondingly different catalytic performance for photocatalytic CO2 reduction. Fe-soc-O has the highest CO production of 1804 μmol g-1 h-1, while the Fe-soc-MOF exposed with six {100} facets (Fe-soc-C) has the best CO selectivity of 94.7%. Density functional theory (DFT) calculations demonstrate that the (111) facet has more favorable thermodynamic potential for CO2 reduction and H2 evolution compared with the (100) one, deriving from its facet-dependent active sites. This work shows that utilizing the facet-engineering strategy to regulate the active sites exposed on the surface of MOFs is feasible. The results display the relation between the facet of MOFs and the photocatalytic behavior for CO2 reduction.

Recent developments in metal nanocluster-based catalysts for improving photocatalytic CO2 reduction performance

Photocatalytic reduction of carbon dioxide (CO2) is a promising technology for carbon recycling that offers both environmental and economic benefits. Among the potential photocatalysts, metal nanoclusters (MNCs) stand out as a class of materials with remarkable photophysical and photochemical properties. Despite the growing number of studies on MNCs-based photocatalytic reduction of CO2 in recent years, a systematic and comparative overview of these studies is still lacking. This review provides a concise and comprehensive summary of the latest research on MNCs-based catalysts for enhancing photocatalytic CO2 reduction performance. Moreover, this review highlights the challenges and opportunities in this field based on the current development trends.

Recent developments in lead-free bismuth-based halide perovskite nanomaterials for heterogeneous photocatalysis under visible light.

Halide perovskite materials, especially lead-based perovskites, have been widely used for optoelectronic and catalytic applications. However, the high toxicity of the lead element is a major concern that directs the research work toward lead-free halide perovskites, which could utilize bismuth as a promising candidate. Until now, the replacement of lead by bismuth in perovskites has been well studied by designing bismuth-based halide perovskite (BHP) nanomaterials with versatile physical-chemical properties, which are emerging in various application fields, especially heterogeneous photocatalysis. In this mini-review, we present a brief overview of recent progress in BHP nanomaterials for photocatalysis under visible light. The synthesis and physical-chemical properties of BHP nanomaterials have been comprehensively summarized, including zero-dimensional, two-dimensional nanostructures and hetero-architectures. Later, we introduce the photocatalytic applications of these novel BHP nanomaterials with visible-light response, improved charge separation/transport and unique catalytic sites. Due to advanced nano-morphologies, a well-designed electronic structure and an engineered surface chemical micro-environment, BHP nanomaterials demonstrate enhanced photocatalytic performance for hydrogen generation, CO2 reduction, organic synthesis and pollutant removal. Finally, the challenges and future research directions of BHP nanomaterials for photocatalysis are discussed.

Cu-doped SnS2 nanosheets with superior visible-light photocatalytic CO2 reduction performance.

Photocatalytic CO2 reduction utilizing solar energy is a clean, environment-friendly strategy converting CO2 into hydrocarbon fuels to solve the energy crisis and climate issues. Herein, we report the synthesis of Cu-doped SnS2 nanosheets via a simple hydrothermal method. The prepared Cu-doped SnS2 composite displays superior photocatalytic CO2 reduction activity. The optimized CH3OH yield of the composite is two times higher than that of pure SnS2. The enhanced photocatalytic performance is attributed to effective charge separation resulting from the thinner nanosheets and delocalization of electrons from SnS2 to Cu, high visible light utilization efficiency, enlarged SBET, negative shift of the flat-band potential and reduced charge transfer resistance with the introduction of Cu atoms. This work suggests the potential application of Cu-doped SnS2 in photocatalytic CO2 reduction.

Highly dispersed Co-modified covalent organic frameworks as bridging cocatalysts for boosting CO2photoreduction over defective carbon nitride

TpTta COF with efficient electron mobility traps electrons from the photosensitizer, and efficiently transfers them to the Co center to improve the photocatalytic CO2reduction performance.

Dioxygen-enhanced CO2 photoreduction on TiO2 supported Cu single-atom sites

Supported Cu single-atom (Cu-SA) catalysts have exhibited unique activity and selectivity in CO2 reduction, but they generally suffer from the easy transformation of active Cuδ+ into inactive Cu0. Herein, porous TiO2 supported Cu single atoms (Cu-SAs/TiO2) photocatalyst was fabricated and dioxygen (O2) enhanced photocatalytic CO2 reduction performance of Cu-SAs/TiO2 was investigated by in-situ characterizations and theoretical calculations. The results showed that both activity and stability of Cu-SAs/TiO2 photocatalyst could be improved by feeding a small amount of O2 (117.6 ppm) in the reaction system. The competitive electron transfer to O2 on Cu-SAs/TiO2 maintained dynamic stability of Cuδ+ active sites, and O2-derived *OOH species lowered the formation energy barrier of key intermediate *COOH as well as delivered *H species for accelerating intermediates protonation process. Total yield rate of CH4 and CO reached 34.64 μmol·gcat·h−1 for CO2 photoreduction over Cu-SAs/TiO2 after introducing 117.6 ppm O2, accompanied by enhanced durability.

Dual interfacial build-in electric field effect induced by sandwich-type heterojunction for propelling photocatalytic fuel extraction from CO2 in water

Photocatalytic fuel extraction from CO2 in water driven by solar energy is a sustainable technology with potential applications, but the developing high-efficient photocatalysts is still a challenging issue. Herein, a new sandwich-type polymeric carbon nitride (PCN)-based heterojunction is exploited by embedding Bi12O17Cl2 nanoplates in PCN nanosheet interlayers through a complex series of Bi12O17Cl2 dissolution, ions diffusion and in situ growth on the exfoliated PCN nanosheets, and subsequent self-assembly procedure in a facile hydrothermal process. The fabricated sandwich-type PCN/Bi12O17Cl2/PCN heterojunction significantly enhances the photocatalytic CO2 reduction performance in comparison with Bi12O17Cl2 and PCN. The CO and CH4 yields of the optimal PCN/Bi12O17Cl2/PCN-3 sample within 4 h are 3.74 and 2.62 times as high as that of PCN, and 8.95 and 6.65 times as high as that of Bi12O17Cl2, respectively. The unique sandwich-type structure of PCN/Bi12O17Cl2/PCN induces dual interfacial build-in electric field effect to effectively impel the spatial charge separation at the interface inside heterojunction, thus boosting photocatalytic performance. This work develops an innovative structure design philosophy of PCN-based heterojunctions applied in photocatalytic CO2 reduction.

ZIF-8 derived hierarchical ZnO@ZnFe2O4 hollow polyhedrons anchored with CdS for efficient photocatalytic CO2 reduction

Converting CO2 into chemical energy by efficient photocatalysts is a promising strategy to meet the increasing energy demand and decrease greenhouse gases. In this work, hierarchical ZnO@ZnFe2O4 hollow polyhedrons decorated with CdS quantum dots were designed and prepared to improve photocatalytic CO2 reduction performance. The facile strategy for the synthesis of hierarchical ZnO@ZnFe2O4 hollow polyhedrons involves the synthesis of ZnO hollow polyhedrons derived from the thermal decomposition of 2-Methylimidazole zinc salt (ZIF-8) precursor and in situ generating Zn-Fe layer double hydroxide nanosheets on the surface of ZnO hollow polyhedrons and subsequent thermal treatment. More importantly, the in situ formation of ZnFe2O4 nanosheets can form strong interaction between ZnO hollow polyhedrons and ZnFe2O4 nanosheets. The hierarchical hollow polyhedral structure of the ZnO@ZnFe2O4 sample possesses more preferable active sites to promote CO2 adsorption and reduction process. The prepared hierarchical ZnO@ZnFe2O4 hollow polyhedron sample shows a significantly enhanced performance for photocatalytic CO2 reduction compared with single-component catalysts (ZnO, ZnFe2O4, and CdS) with a CO evolution rate of 95.84 μmol g−1h−1. The decoration of CdS quantum dots makes the ternary heterostructure hybrid form multichannel charge transfer path, which further accelerate charge separation and enhance electrons utilization, resulting in a significant improvement of photocatalytic activity. Noticeably, the CO evolution rate reaches 197.66 μmol g−1h−1, 3 and 2 times higher than that of the bare ZnO and binary ZnO@ZnFe2O4 hollow polyhedrons, respectively. This work gives a promising direction to prepare high-active photocatalysts for solar fuel production.

Ag-Doped CuV2O6 Nanowires for Enhanced Visible-Light Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction into chemical fuels is a promising strategy to realize the CO2 conversion and solar energy utilization, yet there remains a great challenge in conversion efficiency. Herein, Ag-ion-doped CuV2O6 nanowires (NWs) with abundant oxygen vacancies were prepared by a simple hydrothermal method and utilized as catalysts for CO2 photoreduction with H2O vapor. It was demonstrated that Ag-ion doping in CuV2O6 resulted in a narrow band gap, enhanced visible-light absorption ability, elevated conduction band, abundant oxygen vacancies, strong CO2 surface-absorption capacity, superior hydrophilicity, and high separation/transfer efficiency of the photoinduced electron–hole pairs. Consequently, the Ag-doped CuV2O6 NWs exhibit excellent photocatalytic performance for CO2 reduction as compared to the pristine CuV2O6 NWs. Remarkably, the optimized Ag-doped CuV2O6 NWs exhibited a significantly enhanced photocatalytic activity with a CO evolution rate of 6.95 μmol g–1 h–1 under visible-light irradiation, which is 8.9 times higher than those of pure CuV2O6 NWs. The present work may provide a valid strategy to engineer CuV2O6 NWs for boosting visible-light photocatalytic CO2 reduction.

Novel 2D/2D BiOBr/Zn(OH)2 photocatalysts for efficient photoreduction CO2

For the sake of enhancing the photocatalytic performance of BiOBr, 2D Zn(OH)2 nanosheets were introduced on 2D BiOBr nanosheets to construct a 2D heterosturcture in BiOBr/Zn(OH)2 composites by direct precipitation polymerization. After depositing Zn(OH)2, the specific surface areas of BiOBr/Zn(OH)2 composites were improved, which resulted in more active sites. Meanwhile, the synergistic action between Zn(OH)2 and BiOBr can adjust the band-gap, enhancing the light absorption and reducing the charge transfer resistance. BiOBr/Zn(OH)2 composites possessed the better separation efficiency of photogenerated carriers. Meanwhile, the results showed that the ability of photocatalytic CO2 reduction was improved. Under 3 h simulated sunlight irradiation, BiOBr/Zn(OH)2–10% showed the highest performance of photocatalytic CO2 reduction, and the total output of photocatalytic reduction product CO was 16.21 μmol g−1, which is 2.2 times than that of BiOBr.

Effect of point defect-induced surface active sites of MoSi2N4 on performance of photocatalytic CO2 reduction

The selectivity of photocatalytic CO 2 reduction is often limited by the surface active sites of the catalyst. To overcome this limitation, the point defects are applied to the structural design of MoSi 2 N 4. Three different point defect structures (N Mo _Si, N Si _Si and N Abs _N) are screened out. The selectivity of photocatalytic products is closely related to the type of active sites, the N Abs _N with N active sites reduce CO 2 to CO, however, the N Mo _Si and N Si _Si with Si active sites reduce CO 2 to HCOOH. Furthermore, the coordination environment of active sites has an important effect on the catalytic performance. The N Mo _Si and N Si _Si with the same Si active sites have different photocatalytic capabilities. This study provides theoretical guidance for the catalysts design to improve product selectivity by controlling point defects.

Surface Electron Localization in Cu-MOF-Bonded Double-Heterojunction Cu2O Induces Highly Efficient Photocatalytic CO2 Reduction.

Truncated octahedron Cu2O (TOC) has attracted more attention for its suitable band gap and high carrier separation efficiency due to introduction of the facet heterojunction, but its practical drawback is still the instability caused by the irreversible disproportionation reaction (Cu2O → Cu + CuO). Here, we design and fabricate the TOC/Cu-MOF (MOF: metal-organic framework) double-heterojunction structures with different Cu-MOF loadings. The introduced heterojunction between TOC and Cu-MOF not only produces a stable interface Cux+ bonding structure with the electronic states localized within the average collisional diameter of electrons 1.72 nm for TOC/2.1 wt %Cu-MOF as the active sites, but also promotes the surface energy level difference between the (100) and (111) facet heterojunctions. Meanwhile, the bonded Cu-MOF with a narrow bandgap effectively consumes holes by recombination with the photoexcited electrons from Cu-MOF itself. In our experiments, the TOC/Cu-MOF double heterostructure with a loading amount of 2.1 wt % Cu-MOF shows an optimal photocatalytic CO2 reduction performance. The CO evolution rate reaches 23.01 μmol g-1 h-1, which is about 2.01 and 4.47 times larger than those of octahedral and hexahedral Cu2O/Cu-MOF, respectively, and an excellent photostability is shown for four cycles with each cycle lasting for 4 h. Such a double heterostructure provides insight into highly efficient electron transfer and photostability in Cu2O-related composite materials.

Enhanced CO2 Photoreduction through Spontaneous Charge Separation in End-Capping Assembly of Heterostructured Covalent-Organic Frameworks.

It is well known that charge separation is crucial for efficient photocatalytic solar conversion. Although some covalent-organic frameworks (COFs) exhibit visible-light harvest, the large exciton binding energies reduce their photocatalytic efficiencies. Herein, we developed a novel method to post-treat the olefin-linked COFs with end-capping polycyclic aromatic hydrocarbons (PAHs) for spontaneous charge separation. Interestingly, a type-II heterostructure is constructed in our perylene-modified COFs which displays drastically enhanced performance for photocatalytic CO2 reduction, with an efficiency of 8-fold higher than that of unmodified COF. A combination of electrochemical, steady-state, and time-resolved spectroscopic measurements indicates that such drastically enhanced performance should be attributed to photoinduced spontaneous charge separation in the heterostructure. These results illustrate the feasibility of engineering the charge-separation properties of crystalline porous frameworks at a molecular level for artificial photosynthesis.

Enhanced CO2 Photoreduction through Spontaneous Charge Separation in End‐Capping Assembly of Heterostructured Covalent‐Organic Frameworks

AbstractIt is well known that charge separation is crucial for efficient photocatalytic solar conversion. Although some covalent‐organic frameworks (COFs) exhibit visible‐light harvest, the large exciton binding energies reduce their photocatalytic efficiencies. Herein, we developed a novel method to post‐treat the olefin‐linked COFs with end‐capping polycyclic aromatic hydrocarbons (PAHs) for spontaneous charge separation. Interestingly, a type‐II heterostructure is constructed in our perylene‐modified COFs which displays drastically enhanced performance for photocatalytic CO2 reduction, with an efficiency of 8‐fold higher than that of unmodified COF. A combination of electrochemical, steady‐state, and time‐resolved spectroscopic measurements indicates that such drastically enhanced performance should be attributed to photoinduced spontaneous charge separation in the heterostructure. These results illustrate the feasibility of engineering the charge‐separation properties of crystalline porous frameworks at a molecular level for artificial photosynthesis.

Surface-iodination-induced efficient charge separation in bismuth oxysulfide crystals for enhanced photocatalytic CO2 conversion

Solar-energy-driven CO2 conversion to green fuels has great potential to alleviate energy crises and environmental issues. However, the low separation efficiency of charge carriers and the weak adsorption ability towards CO2 still hamper the efficiency of photocatalytic CO2 reduction. Herein, surface iodinated Bi2O2S materials (IBOS) were demonstrated to be efficient [Bi2O2]2+-containing photocatalysts, which could be prepared through facile hydrothermal process. The surface iodide ions are grafted onto the Bi atoms of Bi2O2S by replacing surface adsorbed OH, which slightly changes the electronic structure and then facilitates the separation of photo-generated electrons and holes in IBOS. Meanwhile, surface iodination also exhibits an enhanced adsorption and activation ability towards CO2, which contributes to photocatalytic CO2 conversion to CH4. The vital role of surface iodination was evidenced by the experimental analyses and theoretical calculations in detail. The optimized 2.0%IBOS shows marked photocatalytic CO2 reduction performance with a CH4 yield of 80.03 μmol g−1 under 90 min of visible light irradiation, which is ∼25-folds higher than pristine Bi2O2S. The mechanism of green transformation of CO2 to CH4 on 2.0%IBOS was finally proposed by the analyses of in situ FT-IR patterns. This work offers inspiration in designing and modifying [Bi2O2]2+-containing photocatalysts for highly efficient photocatalytic CO2 conversion.

Bicomponent Cocatalyst Decoration on Flux-assisted CaTaO2 N Single Crystals for Photocatalytic CO2 Reduction under Visible Light.

Cubic-like CaTaO2 N photocatalysts with high crystallinity and uniform particle size were successfully prepared by the flux-assisted nitridation method. The growth of CaTaO2 N single crystals under different synthesis conditions was systematically investigated to understand the effects of the crystallinity and optical property on photocatalytic performance of CO2 reduction. Moreover, the modification of CaTaO2 N single crystals with core-shell Ni-Ag bicomponent cocatalyst by two-step decoration process gave a 2.4 times higher amount of CO evolution than the deposition of sole Ag cocatalyst, because of the synergistic effects of bicomponent cocatalyst on the interfacial electron transfer and surface catalytic process. This study provides a valuable way to construct high-crystalline photocatalysts with effective bicomponent cocatalyst for visible-light-driven CO2 reduction with H2 O.

Design of Pyrene-Based Small Molecules Constructed Organic Photocatalyst with Tunable Energy Level and Adjustable Electron Transfer for Efficient Photocatalytic CO2 Reduction

Organic semiconductor materials recently have been widely used in photocatalytic CO2 reduction due to their diverse synthesis methods, good light absorption, and tunable band structure, while their uncontrollable synthesis processes and exact structures have hindered the study for the relationships of structure–property over these organic photocatalysts. Herein, a series of pyrene-based conjugated small molecules were synthesized via the strategy of precise design. The conjugation of these pyrene-based molecules was modified by the introduction of unsaturated acetylene bonds and the benzene rings through classic cross-coupling reactions, which induces the different localization of photogenerated carriers on themselves and achieves an enhanced intermolecular electron transfer to the catalytic center of metal complexes. Based on this strategy, 1,3,6,8-tetraphenylpyrene (TPPy) exhibits a remarkable performance of 0.96 mmol g–1 h–1 with a selectivity of 79% in photocatalytic CO2 reduction, while 1,6-diphenylpyrene (BPPy) possesses an enhanced selectivity of 94% but a halved performance in photocatalytic CO2 reduction (0.44 mmol g–1 h–1) compared to the TPPy. The further characterizations and in situ studies reveal that the performance and selectivity of photocatalytic CO2 reduction are highly dependent on the optimized electron transfer and the modified energy levels, respectively. The purpose of this work is to not only promote the development of organic photocatalysts to reduce CO2 emissions but also provide new vision for the design of pyrene-based photocatalysts with tunable energy band levels and tunable electron transfer.

Ultra-Fast Construction of Novel S-Scheme CuBi2O4/CuO Heterojunction for Selectively Photocatalytic CO2 Conversion to CO.

Herein, step-scheme (S-scheme) CuBi2O4/CuO (CBO/CuO) composite films were successfully synthesized on glass substrates by the ultra-fast spraying-calcination method. The photocatalytic activities of the obtained materials for CO2 reduction in the presence of H2O vapor were evaluated under visible light irradiation (λ > 400 nm). Benefiting from the construction of S-scheme heterojunction, the CO, CH4 and O2 yields of the optimal CBO/CuO composite reached 1599.1, 5.1 and 682.2 μmol/m2 after irradiation for 9 h, and the selectivity of the CO product was notably enhanced from below 18.5% to above 98.5% compared with those of the bare samples. In the sixth cycling experiment, the yields of main products decreased by less than 15%, and a high CO selectivity was still kept. The enhanced photocatalytic performance of CO2 reduction was attributed to the efficient separation of photogenerated charge carriers. Based on the photocatalytic activity, band structure and in situ-XPS results, the S-scheme charge transfer mechanism was conformed. The study provides an insight into the design of S-scheme photocatalysts for selective CO2 conversion.