Photocatalytic CO2 Reduction Performance Research Articles

Porphyrin-based Bi-MOFs with Enriched Surface Bi Active Sites for Boosting Photocatalytic CO2 Reduction.

The inherent challenges in using metal-organic frameworks (MOFs) for photocatalytic CO2 reduction are the combination of wide-range light harvesting, efficient charge separation and transfer as well as highly exposed catalytic active sites for CO2 activation and reduction. We present here a promising solution to satisfy these requirements together by modulating the crystal facet and surface atomic structure of a porphyrin-based bismuth-MOF (Bi-PMOF). The series of structural and photo-electronic characterizations together with photocatalytic CO2 reduction experiment collectively establish that the enriched Bi active sites on the (010) surface prefer to promote efficient charge separation and transfer as well as the activation and reduction of CO2 . Specifically, the Bi-PMOFs-120-F with enriched surface Bi active sites exhibits optimal photocatalytic CO2 reduction performance to CO (28.61 μmol h-1 g-1 ) and CH4 (8.81 μmol h-1 g-1 ). This work provides new insights to synthesize highly efficient main group p-block metal Bi-MOF photocatalysts for CO2 reduction through a facet-regulation strategy and sheds light on the surface structure-activity relationships of the MOFs.

Ternary nanocomposite of NH2-MIL-125(Ti) MOF-modified TiO2 nanotube arrays (TNTs) with GO electron mediator for enhanced photocatalytic conversion of CO2 to solar fuels under visible light

Facile fabrication of highly efficient NH2-MIL-125(Ti)-GO-TNTs ternary nanocomposite was achieved through a simple drying-deposition approach. The newly developed photocatalyst exhibited efficient performance in CO2 photoreduction owing to hierarchically structured TiO2 nanotubes with porous MOF nanoparticles and GO nanosheets, which acted as the electron mediator. The experimental investigations revealed the superiority of the MOF-modified TNTs over pure TNTs, indicating the significant role of MOF in improving the optoelectronic properties and thus increasing the photocatalytic activity. The highest photocatalytic performance for CO2 reduction was obtained using ternary nanocomposite with CO production of 29782 μmol m−2. However, when compared to pure TNTs, CH4 production was reduced, indicating that the NH2-MIL-125(Ti) MOF preferentially produces CO rather than CH4. The effect of pressure displayed a direct relationship with the photocatalytic production of both products. Furthermore, the nanocomposite's recyclability and stability studies revealed continuous CO and CH4 production in multiple cyclic runs with no significant photocatalyst deactivation. This study gives new ideas for making and developing cheap Ti metal and other low-cost, effective materials that can be used to recycle CO2 gas emissions into useful solar fuels.

Atomically dispersed Au confined by oxygen vacancies in Au-θ-Al2O3/Au/PCN hybrid for boosting photocatalytic CO2 reduction driven by multiple built-in electric fields

A new Au-θ-Al2O3/Au/PCN hybrid is fabricated by the collaborative design strategy of active site and assembled structure, which achieves highly efficient photocatalytic CO2 reduction (CO2R) performance. The energy band structure of PCN is adjusted significantly owing to the strong coupling effect of Au-θ-Al2O3/Au nanosheets intercalated in PCN nanosheets. The result brings about up-shift of CB, VB and Fermi energy level overall and decrease of bandgap, which is in favor of harvesting visible light, exciting VB electrons and increasing reduction ability. In addition, the multiple built-in electric fields are induced by electron diffusion effect between structural units, due to the tight interface contact in the Au-θ-Al2O3/Au/PCN hybrid, which can effectively promote the separation of photoinduced charge carriers. Furthermore, the atomically dispersed Au atoms confined by the oxygen vacancies in Au-θ-Al2O3/Au can provide the plenty of effective active sites for CO2R reaction, and meanwhile, the localized surface plasmon resonance (LSPR) effect induced by Au nanoparticles on Au-θ-Al2O3/Au can improve the visible light response and produce abundant hot electrons to contribute to CO2R reaction. As a consequence, the average CO evolution rate of over the optimizing 10 %-Au-θ-Al2O3/Au/PCN hybrid (7.76 μmol g-1h−1) reaches up to 3.53 times than that of PCN (2.20 μmol g-1h−1) in the CO2R reaction, and maintains basically stable operation within 7 cycles of running, suggesting the superior activity and recyclability.

Noble metals-deposited TiO2 photocatalysts for photoreduction of CO2: Exploration of surface chemistry and a reflection on the importance of wavelength dependence

We report the enhanced photocatalytic performance of CO2 reduction by introducing noble metal-deposited TiO2 photocatalysts (NMD/TiO2) under both visible light irradiation (VLI) and UV. It was found that NMD-TiO2 samples demonstrated an expanded ability for light absorption, resulting in an improved photoefficiency for CO2 reduction and selectivity towards carbon monoxide (CO). The conversion yields of CO2 to CO followed the order: Rh >Ru >Pt and with Rh/TiO2 reached 10.65 μmol/gcat (under visible light) and 7.84 μmol/gcat (under UV), which are ∼3 and 10 times more as compared to pristine anatase TiO2 (0, and 2.43 μmol/gcat). Various factors were addressed including theoretical studies via DFT revealed that the formation of new impurity energy state levels in NMD/TiO2, which act as acceptor levels. Moreover, DRIFTS studies showed that the H-O-C-O and formyl (H2CO) species were the important intermediates towards the hydrogenation of CO2 to CO. Also, a charge transfer mechanism toward CO2 reduction was elucidated.

Adjusting Surface Oxidized Layer of CoTe on PCN via In Situ N-Doping Strategy to Promote Charge Separation of Z-Scheme Heterojunction for Propelling Photocatalytic CO2 Reduction.

It has been a challenging issue to profoundly actuate the transfer and separation of photoinduced charge carriers by controlling the interface structure inside the heterojunction, owing to the molecular/subnanometric level interface region. Herein, a unique one-dimensional/two-dimensional (1D/2D) CoTe/PCN Z-scheme heterojunction is fabricated through the self-assembly of CoTe nanorods on the surface of polymeric carbon nitride (PCN) nanosheets. Significantly, in situ N-doping in the molecular/subnanometric surface oxidized layer of CoTe nanorods is achieved, effectively adjusting its chemical structure and element chemical states. Moreover, this N-doped surface oxidized layer can serve as a recombination region of photogenerated electrons from PCN and photogenerated holes from CoTe to increase the overall carrier separation efficiency in the Z-scheme heterojunction actuated by the built-in electric field. As a result, the photocatalytic CO2 reduction (CO2R) performance is enhanced dramatically, in which the yield of CO generated over the optimal 1D/2D CoTe/PCN heterojunction reaches up to triple than that over PCN. This unique contribution provides an emblematic paradigm for adjusting the interfacial structure of heterojunction and has a profound insight into the interfacial adjusting mechanism to improve the charge separation efficiency in the photocatalytic reaction.

Exploring a Ni-N4 Active Site-Based Conjugated Microporous Polymer Z-Scheme Heterojunction Through Covalent Bonding for Visible Light-Driven Photocatalytic CO2 Conversion in Pure Water.

Designing photocatalysts with efficient charge transport and abundant active sites for photocatalytic CO2 reduction in pure water is considered a potential approach. Herein, a nickel-phthalocyanine containing Ni-N4 active sites-based conjugated microporous polymer (NiPc-CMP), offering highly dispersed metal active sites, satisfactory CO2 adsorption capability, and excellent light harvesting properties, is engineered as a photocatalyst. By virtue of the covalently bonded bridge, an atomic-scale interface between the NiPc-CMP/Bi2 WO6 Z-scheme heterojunction withstrong chemical interactions is obtained. The interface creates directional charge transport highways and retains a high redox potential, thereby enhancing the photoexcited charge carrier separation and photocatalytic efficiency. Consequently, the optimal NiPc-CMP/Bi2 WO6 (NCB-3) achieves efficient photocatalytic CO2 reduction performance in pure water under visible-light irradiation without any sacrificial agent or photosensitizer, affording a CO generation rate of 325.9µmol g-1 with CO selectivity of 93% in 8h, outperforming those of Bi2 WO6 and NiPc-CMP, individually. Experimental and theoretical calculations reveal the promotion of interfacial photoinduced electron separation and the role of Ni-N4 active sites in photocatalytic reactions. This study presents a high-performance CMP-based Z-scheme heterojunction with an effective interfacial charge-transfer route and rich metal active sites for photocatalytic CO2 conversion.

Interface engineering of hollow CsPbBr3/Co3O4 p-n heterojunction with rich oxygen vacancy for highly enhanced photocatalytic CO2 reduction

Surface defect or p-n heterojunction is considered as an efficient strategy to fabricate intrinsic built-in electric field and facilitate the charge separation and transfer. Herein, a novel p-n heterojunction photocatalyst CsPbBr3/Co3O4 was constructed by a facile microwave-assisted method, in which CsPbBr3 QDs anchored on ZIF-67 derived Co3O4 nanocage can simultaneously introduce oxygen vacancies and strengthen the interfacial interaction. As a result, the as-prepared CsPbBr3/Co3O4 displays the satisfactory photocatalytic CO2 reduction performance without photosensitizer and sacrificial agent, and the optimal catalyst exhibits that the average electron consumption rate (Relectron) is 158.80 μmol‧g−1‧h−1, which is 12.41 times higher than that of pure CsPbBr3. Photoassisted Kelvin probe force microscopy (KPFM) and experimental characterizations exhibit the formation of strong built-in electric fields probably due to the rich oxygen vacancies in this p-n heterojunction. Besides, DFT calculations confirm that the charge transfer pathway, where the electrons are quickly migrated to the catalytic active sites through the formed Cs-O bonds, thus accelerating the charge separation. This work could establish an effective strategy for the rational design of p-n heterojunctionto achieve high-performance CO2 conversion.

Construction of graphene supported dual-phase perovskite quantum dots for efficient photocatalytic CO2 reduction

Lead halide perovskites (LHPs) quantum dots (QDs) has been deemed as a promising material for photocatalytic conversion (e.g., CO2 reduction or water splitting) due to their remarkable photoelectrical properties. However, the severe carrier recombination and low charge transfer efficiency largely restrain their photocatalytic performance. Herein, a series of graphene supported dual-phase perovskite QDs photocatalysts were designed by a facile hot-injection strategy for highly efficient photocatalytic CO2 reduction. Catalytic results showed that under a 5 W white LED irradiation, the CsPbBr3/Cs4PbBr6@G5% composite with 5 wt% graphene loading exhibited an optimum CO yield of 18.76 μmol g−1 with a selectivity of 52.99% towards the product of CO for photocatalytic CO2 reduction. The enhanced photocatalytic CO2 reduction performance over the composites compared with that of CsPbBr3, Cs4PbBr6 and CsPbBr3/Cs4PbBr6 QDs could be ascribed to the type-I heterojunction structure and graphene support as the electron acceptor in the composite, which could stepwise accelerate the charge separation, suppresses recombination process, and provide more active sites for CO2 adsorption and reaction. This work would bring new insight in designing novel efficient perovskite-based catalysts for photocatalytic CO2 transformation.

In-situ construction of Bi2WO6/BiOCl p-n heterojunction film for photocatalytic CO2 reduction

Heterojunction composite construction has been considered as a viable method to improve photocatalytic performance. In this study, a kind of highly efficient 2D/0D Bi2WO6/BiOCl p-n heterojunction film with boosted photocatalytic CO2 reduction performance was synthesized on Bi plate via in-situ electrochemical ion-exchange hydrothermal method. Furthermore, the XRD, XPS, SEM, TEM and other techniques were carried out to evaluate as-synthesized films. Our findings indicate that Bi2WO6/BiOCl composite film, with close border contact between Bi2WO6 and BiOCl surfaces, should be conducive to achieve excellent separation and migration of photogenerated charge carriers. Finally, the formation mechanism of p-n heterostructure is demonstrated using XPS core-level alignment method. This work should offer new perspectives into the immobilization method of efficient powder catalysts and the photocatalytic CO2 reduction mechanism of p-n heterojunction films.

Unraveling the impact of Cu-doping in lead free halide perovskites for markedly enhancing photocatalytic CO2 reduction performance

Excessive CO2 emissions from the consumption of fossil fuels contribute to both global warming and the energy crisis. To address these pressing issues, it is essential to capture and convert CO2 into chemical feedstock using renewable energy such as solar energy. Solar-powered photocatalytic fuel production is widely acknowledged as a viable solution for a sustainable energy future. However, the development of high-performance photocatalysts remains a significant challenge to overcome in this endeavor. Recently, lead-free perovskites have emerged as a promising category of materials for CO2 photoreduction, thanks to their remarkable optoelectronic properties, cost-effective solution processing, and non-toxic nature. Nonetheless, their inherent photocatalytic CO2 reduction activity remains low due to the insufficient separation of photogenerated charges and the lack of active sites. Here, we demonstrate that Cu doping in lead-free double perovskites can lead to markedly enhanced CO2 reduction performance. The interstitial Cu dopants modulate the fermi level and introduce the active energy sites near the conduction band, which significantly enhances light absorption and separation of charge carriers. The Cu-Cs2AgBiCl6 shows the activity of 88 and 48 µmol/gcat for CH4 and CO products which are both higher than those of the pristine Cs2AgBiCl6 (27 and 10 µmol/gcat). The total yield of Cu-Cs2AgBiCl6 perovskite for CO2 photoreduction is superior to those reported under similar conditions. Transient absorption results show that hot carrier relaxation is slower and carrier decay lifetime is extended in Cu-Cs2AgBiCl6, which can enhance the charge migration efficiency and boost the CO2 reduction performance. These findings provide valuable insight into the mechanism of CO2 reduction in Cu-doped Cs2AgBiCl6 perovskite crystals and suggest that Cu-doping is a promising strategy for developing highly efficient and selective CO2 reduction photocatalysts.

Heterophase junction engineering: Enhanced photo-thermal synergistic catalytic performance of CO2 reduction over 1T/2H-MoS2

Photocatalytic CO2 reduction technology has been proposed as a promising solution to the greenhouse effect and energy crisis. However, the lower quantum efficiency limits its practical applications. Here, we have significantly improved the photocatalytic CO2 reduction performance of MoS2 by coupling the heterophase junction (1T/2H-MoS2) construction and photo-thermal synergy strategies. At 200 °C and 42 mW·cm−2 of 420 nm LED irradiation, the CO production rate of 1T/2H-MoS2 reached 35.3 μmol·g−1·h−1, which was 3.5 and 2.8 times that of 1T-MoS2 and 2H-MoS2, respectively. In addition, only faint CO was detected under sole photo- or sole thermal catalysis conditions. Mechanism studies showed that COOH* was the key intermediate in the photo-thermal synergistic catalytic CO2 reduction over 1T/2H-MoS2. The heterophase junction engineering significantly facilitated the separation of photogenerated carriers, and the introduction of heat accelerated the charge migration and surface reaction rates. Our work provides innovative insights into the catalyst design and mechanism studies for photo-thermal synergistic catalytic CO2 reduction.

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.

Variously calcined potassium hexatitanate photocatalysts with silver cocatalyst for photocatalytic CO2 reduction with water

Photocatalytic CO2 reduction to CO with water can be promoted over potassium hexatitanate (K2Ti6O13, KTO) photocatalyst decorated with Ag cocatalyst. In the present study, a sol-gel method was employed to know the effect of the calcination temperature for preparation of KTO samples. The KTO samples calcined at temperatures above 773 K show X-ray diffraction pattern assignable to K2Ti6O13 crystal phase while the crystallite size increases with increasing the calcination temperature. After photodeposition (PD) of Ag cocatalyst on these KTO samples, their photocatalytic performance for CO2 reduction was evaluated. The photocatalytic activity of the Ag/KTO photocatalysts increases with the calcination temperature and a clear positive relationship is found between the KTO crystallite size and the photocatalytic activity. Some spectroscopic investigations reveal that the state of the Ag cocatalyst is also influenced by the calcination temperature of the KTO samples, i.e., the KTO sample calcined at low temperature provides oxidized Ag species by the PD method while the ones calcined at high temperature gives the metallic Ag nanoparticles, meaning that the KTO photocatalytic property varied with the calcination temperature controls the oxidation state of the photodeposited Ag species. It is demonstrated that the property of the resulting Ag cocatalyst is another contributing factor for the photocatalytic activity of the Ag/KTO photocatalysts. Thus, it is concluded that the photocatalytic activity is determined by both the KTO properties and the property of the photodeposited Ag cocatalyst depending on the KTO photocatalytic activity, where both originally come from the calcination temperature of the KTO sample.

Highly selective photocatalytic CO2 reduction and hydrogen evolution facilitated by oxidation induced nitrogen vacancies on g-C3N4

The introduction of nitrogen vacancies into polymeric carbon nitride (PCN) has been attested to be a reliable strategy to enhance photocatalytic performance. Nitrogen vacancies were considered as active sites to promote the adsorption of target molecules and capture photoexcited electrons to inhibit the recombination of charge pairs, accelerate photoinduced electrons to participate in photocatalytic reaction. In this paper, a series of PCN with rich nitrogen vacancies were prepared by etching of chromic acid solution. Sample 20KCSCN had the highest photocatalytic performance whose evolution efficiency of CO2 to CO and CH4 can reach 3.9 and 0.5 μmol·g−1·h−1, respectively. These evolution efficiencies are 2.9 and 4 times higher than that of the PCN. Meanwhile, 20KCSCN demonstrates high CO conversion selectivity and stability. The successful introduction of nitrogen vacancies not only increases the active sites of PCN surface, but also optimizes the optical structure, which dramatically boosts the separation of photoexcited charge pairs and the reduction capacity of photogenerated electrons. The enhancement mechanism for photocatalytic CO2 reduction performance of PCN was proposed. Besides, photocatalytic H2 evolution experiments were performed on all samples to confirm the universality of PCN photocatalytic activity enhancement etched by chromic acid solution. H2 evolution rate on 20KCSCN can reach 652 μmol·g−1·h−1, which is 1.6-fold higher than that on PCN (254 μmol·g−1·h−1) after 4 h irradiation under a 300 W Xe lamp. This work offers new venue for introducing nitrogen vacancies in PCN to regulate photoexcited charge pairs transfer. The photocatalytic enhancement of CO2 reduction could be used to alleviate the serious issue of excessive CO2 emission and energy crisis.

Thermally Induced Orderly Alignment of Porphyrin Photoactive Motifs in Metal-Organic Frameworks for Boosting Photocatalytic CO2 Reduction.

Efficient transfer of charge carriers through a fast transport pathway is crucial to excellent photocatalytic reduction performance in solar-driven CO2 reduction, but it is still challenging to effectively modulate the electronic transport pathway between photoactive motifs by feasible chemical means. In this work, we propose a thermally induced strategy to precisely modulate the fast electron transport pathway formed between the photoactive motifs of a porphyrin metal-organic framework using thorium ion with large ionic radius and high coordination number as the coordination-labile metal node. As a result, the stacking pattern of porphyrin molecules in the framework before and after the crystal transformations has changed dramatically, which leads to significant differences in the separation efficiency of photogenerated carriers in MOFs. The rate of photocatalytic reduction of CO2 to CO by IHEP-22(Co) reaches 350.9 μmol·h-1·g-1, which is 3.60 times that of IHEP-21(Co) and 1.46 times that of IHEP-23(Co). Photoelectrochemical characterizations and theoretical calculations suggest that the electron transport channels formed between porphyrin molecules inhibit the recombination of photogenerated carriers, resulting in high performance for photocatalytic CO2 reduction. The interaction mechanism of CO2 with IHEP-22(Co) was clarified by using in-situ electron paramagnetic resonance, in-situ diffuse reflectance infrared Fourier transform spectroscopy, in-situ extended X-ray absorption fine structure spectroscopy, and theoretical calculations. These results provide a new method to regulate the efficient separation and migration of charge carriers in CO2 reduction photocatalysts and will be helpful to guide the design and synthesis of photocatalysts with superior performance for the production of solar fuels.

Recent Advances on Single-Atom Catalysts for Photocatalytic CO2 Reduction.

The present energy crisis and environmental challenges may be efficiently resolved by converting carbon dioxide (CO2 ) into various useful carbon products. The development of more effective catalysts has been the main focus of current research on photocatalytic CO2 reduction. Due to their high atomic efficiency and superior catalytic activity, single-atom catalysts (SACs) have attracted considerable interest in catalytic CO2 conversion. This review discusses the current research developments, obstacles, and potential of SACs for photocatalytic CO2 reduction. And further, discusses the principle of photocatalytic carbon dioxide reduction. This work has compared and analyzed the effects of support materials and active site types in SACs on photocatalytic CO2 reduction performance. This work believes that by sharing these developments, some inspiration for the rational design and development of stable and effective photocatalytic CO2 reduction catalysts based on SACs can be provided.

Enhancing photocatalytic CO2 reduction activity of ZnIn2S4/MOF-808 microsphere with S-scheme heterojunction by in situ synthesis method

The design of a heterogeneous structure for photocatalysts has attracted significant attention. In this study, a step-scheme (S-scheme) heterojunction was designed using an in-situ synthesis method. The resulting heterojunction comprised 3D microspheres of ZnIn2S4 and octahedral MOF-808 (ZnIn2S4/MOF-808). During this process, we investigated the impact of the scale of the ZnIn2S4 microspheres on performance by controlling the growth of the ZnIn2S4 microspheres with various scales. The maximum catalytic activity was discovered to be achieved with ZnIn2S4 microspheres of 6 µm when coupled with MOF-808. Compared to pure ZnIn2S4 and MOF-808, the fabricated S-scheme ZnIn2S4/MOF-808 heterojunction exhibited notably improved photocatalytic CO2 reduction performance. The performance of the CO yield of the optimized sample could reach 8.21 μmol g−1 h−1, which was approximately 10 and 8 times higher than those of ZnIn2S4 (0.84 μmol g−1 h−1) and MOF-808 (1.03 μmol g−1 h−1), respectively. Moreover, ultraviolet photoelectron spectroscopy, ESR, in situ X-ray photoelectron spectroscopy, and density functional theory calculations were used to study the charge transfer mechanism of the S-scheme heterojunction. In-situ FT-IR investigation established the Carbene pathway as the source of CO production (CO2 → CO2* → COOH* → CO* → CO). This study provides an efficient method for designing an S-scheme heterojunction for photocatalytic CO2 reduction.

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction.

Photoconversion of CO2 and H2O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton coupled electron transfer (PCET), slow C-C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi2WO6 (BP/BWO) was constructed for photocatalytic CO2 reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO2 reduction, with a yield of 61.3 μmol g-1 h-1 for ethanol (selectivity of 91%).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi-O-P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C-C coupling. In addition, the substitution of BA oxidation for H2O oxidation can further enhance the photocatalytic performance of CO2 reduction to C2H5OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO2 photoconversion to C2H5OH based on cooperative photoredox systems.

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S‐Scheme Heterojunction

AbstractPhotoconversion of CO2 and H2O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half‐reaction involving multi‐step proton‐coupled electron transfer (PCET), a slow C−C coupling process, and sluggish water oxidation half‐reaction. Herein, a two‐dimensional/two‐dimensional (2D/2D) S‐scheme heterojunction consisting of black phosphorus and Bi2WO6 (BP/BWO) was constructed for photocatalytic CO2 reduction coupling with benzylamine (BA) oxidation. The as‐prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO2 reduction, with a yield of 61.3 μmol g−1 h−1 for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S‐scheme heterojunction can effectively promote photogenerated carrier separation via the Bi−O−P bridge to accelerate the PCET process. Meanwhile, electron‐rich BP acts as the active site and plays a vital role in the process of C−C coupling. In addition, the substitution of BA oxidation for H2O oxidation can further enhance the photocatalytic performance of CO2 reduction to C2H5OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO2 photoconversion to C2H5OH based on cooperative photoredox systems.

Control of charge transfer direction by spatial engineering of redox active centers for boosting photocatalytic CO2 reduction

Photocatalytic CO2 reduction with H2O to value-added fuels is an advanced strategy to solve the energy crisis and realize carbon neutralization. Herein, the spatial engineering of redox-active sites on different facets of TiO2 was achieved by stepwise selective photo-deposition, which controls the transfer direction of photogenerated electrons and holes. The 2Cu/TiO2/2Co3O4 sample exhibited high photocatalytic CO2 reduction performance with the production of CO, CH4, CH3CH3, and CH2CH2 reached 9.41, 43.52, 5.39, and 1.41 μmol∙gcat-1∙h-1, respectively. Notably, the C2 products was generated over the 2Cu/TiO2/2Co3O4 composite in comparison with pure TiO2 under same reaction condition. The in-situ DRIFTS spectra identify the formation of critical intermediates (*CHO, *CH4, and CHO*CHO*) and reveal the reaction kinetics of H2O oxidation. Moreover, the DFT calculations combined with the in-situ spectral technique are applied to investigate the reaction pathways of photocatalytic CO2 reduction and C–C coupling. This work demonstrated that the spatial engineering of Cu and Co3O4 on TiO2 provides appropriate redox reaction sites to synergistically boost the photocatalytic CO2 reduction and C–C coupling.