CO2 Photoconversion Research Articles

Enhancing d/p-2π* Orbitals Hybridization via Strain Engineering for Efficient CO2 Photoreduction.

The photoconversion of CO2 into valuable chemical products using solar energy is a promising strategy to address both energy and environmental challenges. However, the strongly adsorbed CO2 frequently impedes the seamless advancement of the subsequent reaction by significantly increasing the reaction activation energy. Here, we present a BiFeO3 material with lattice strain that collaboratively regulates the d/p-2π* orbitals hybridization between metal sites and *CO2 as well as *COOH intermediates to achieve rapid conversion of solidly adsorbed CO2 to critical *COOH intermediates, accelerating the overall CO2 reduction kinetics. Quasi in situ X-ray photoelectron spectroscopy and in situ Fourier Transform infrared spectroscopy combined with theoretical calculation reveals that the optimized Fe sites enhance the adsorption and activation effect of CO2, and continuous internal electrons are rapidly transferred to the reaction sites and injected into the surface *CO2 and *COOH under the condition of illumination, which promotes the rapid formation and stability of *COOH. Certainly, the performance of CO2 photoreduction to CO is improved by 12.81-fold compared with the base material. This work offers a new perspective for the rapid photoreduction process of strongly adsorbed CO2.

Enhancing d/p‐2π* Orbitals Hybridization via Strain Engineering for Efficient CO2 Photoreduction

AbstractThe photoconversion of CO2 into valuable chemical products using solar energy is a promising strategy to address both energy and environmental challenges. However, the strongly adsorbed CO2 frequently impedes the seamless advancement of the subsequent reaction by significantly increasing the reaction activation energy. Here, we present a BiFeO3 material with lattice strain that collaboratively regulates the d/p‐2π* orbitals hybridization between metal sites and *CO2 as well as *COOH intermediates to achieve rapid conversion of solidly adsorbed CO2 to critical *COOH intermediates, accelerating the overall CO2 reduction kinetics. Quasi in situ X‐ray photoelectron spectroscopy and in situ Fourier Transform infrared spectroscopy combined with theoretical calculation reveals that the optimized Fe sites enhance the adsorption and activation effect of CO2, and continuous internal electrons are rapidly transferred to the reaction sites and injected into the surface *CO2 and *COOH under the condition of illumination, which promotes the rapid formation and stability of *COOH. Certainly, the performance of CO2 photoreduction to CO is improved by 12.81‐fold compared with the base material. This work offers a new perspective for the rapid photoreduction process of strongly adsorbed CO2.

Rapid Charge Transfer Endowed by Hollow‐structured Z‐Scheme Heterojunction for Coupling Benzylamine Oxidation With CO2 Reduction

AbstractIn the field of photocatalysis, ultrafast electron transfer at the interface is the key factor affecting photocatalytic activity. Herein, ultrafast carrier transport is achieved through constructing a Z‐scheme heterojunction of CoSe@Zn0.5Cd0.5S (CoSe@ZCS), which is prepared by in situ growth of ZCS on the ZIF‐67‐derived hollow CoSe. The ultrafast charge transfer at the Z‐scheme heterojunction interface is verified by advanced fs‐transient absorption, which provides vital evidence for the specific mechanism of photocatalytic charge transfer. In addition, the presence of key intermediates (*COOH and C═N) is detected by in‐situ FTIR spectroscopy, which further clarified the mechanism of coupling benzylamine oxidation with CO2 photoconversion. DFT calculations also confirm that the Z‐scheme heterojunction effectively reduces the energy barrier of the rate‐limiting step of *COOH formation, facilitating the photocatalytic CO2 reduction process of ZCS. Benefiting from the ultrafast electron transfer at the interface of the Z‐scheme heterojunction, CoSe@ZCS exhibits excellent bifunctional photocatalytic performance. This work lays the foundation for further exploration of the charge transfer mode at the heterojunction interface to facilitate solar‐driven energy conversion.

Snowflake-like In2S3/Cu2S heterojunction for simultaneous photocatalytic persulfate oxidation of tetracycline hydrochloride and CO2 photoreduction

To achieve tetracycline hydrochloride (TCH) elimination and CO2 photoconversion to CH4 and CO, snowflake-like In2S3/Cu2S heterojunctions were fabricated through the hydrothermal approach. Z-scheme junction generated between In2S3 and Cu2S was likely to separate and migrate the photoactivated e-/h+ pairs, boosting the photocatalytic-persulfate (photo-PS) activity and CO2 photoconversion capacity. The single photo-PS oxidation of TCH and CO2 photoreduction as well as their simultaneous photocatalytic behaviors over snowflake-like In2S3/Cu2S composites were comparatively investigated. For optimal 3-In2S3/Cu2S with a nominal In2S3 content of 5.0 wt%, the removal efficiency of unary photo-PS oxidation system was 99.90 %, CH4 and CO yield rates of single CO2 photoreduction process were respectively 177.67 and 94.42 μmol g-1h−1. In dual photo-PS oxidation and CO2 photoreduction system, the addition of CO2 leaded to the lower photo-PS activity, while the higher CH4 and CO yield rates of 3-In2S3/Cu2S. When added CO2 to dual photocatalytic system, the removal efficiency of TCH, CH4 and CO yield rates reached to 78.38 %, 106.80, and 73.84μmol g-1h−1, which were 0.94, 1.34, and 1.39 folds than those without CO2. This work provided the possibility of simultaneous photo-PS oxidation of pollutants and CO2 photoconversion to C1 compounds.

Facilitating Charge Separation of Donor–Acceptor Conjugated Microporous Polymers via Position Isomerism Strategy for Efficient CO2 Photoconversion

Photoreduction of CO2 into the chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Nevertheless, undesirable charge separation and migration, as well as rapid reverse charge recombination results in the unsatisfactory photocatalytic activity of most conjugated microporous polymers (CMPs). Herein, a pair of donor–acceptor (D-A) CMPs for CO2 photoconversion was developed through position isomerism by altering linkage sites. The results show that Py-D27F with 2,7-site linkage exhibits a completely conjugated structure and a large molecular dipole moment, thus significantly accelerating charge separation and transfer. As a result, Py-D27F achieves a higher yield of 320.9 μmol g−1 h−1 for CO2-to-CO photoreduction (without the addition of any photosensitizers and precious metals), which is about three-fold greater than that of Py-D36F (3,6-site linkage). This study provides a valuable idea for exploring outstanding CMP photocatalysts for the efficient processing of photocatalysis.

Recent progress in solar-driven CO2 reduction to multicarbon products.

Currently, most catalysts used for photoconverting carbon dioxide (CO2) typically produce C1 products. Achieving multicarbon (C2+) products, which are highly desirable due to their greater energy density and economic potential, still remains a significant challenge. This difficulty is primarily due to the kinetic hurdles associated with the C-C coupling step in the process. Given this, devising diverse strategies to accelerate C-C coupling for generating multicarbon products is requisite. Herein, we first give a classification of catalysts involved in the photoconversion of CO2 to C2+ fuels. We summarize metallic oxides, metallic sulfides, MXenes, and metal-organic frameworks as catalysts for CO2 photoreduction to C2+ products, attributing their efficacy to the inherent dual active sites facilitating C-C coupling. In addition, we survey covalent organic frameworks, carbon nitrides, metal phosphides, and graphene as cocatalysts for CO2 photoreduction to C2+ products, owing to the incorporated dual active sites that induce C-C coupling. In the end, we provide a brief conclusion and an outlook on designing new photocatalysts, understanding the catalytic mechanisms, and considering the practical application requirements for photoconverting CO2 into multicarbon products.

Coupling monoclinic Pb2(CrO4)O with Mn3O4 quantum dots as oxygen vacancies-rich S-scheme photocatalysts for visible-light-driven photocatalytic CO2 reduction with H2O

Simulating natural photosynthesis to convert CO2 and H2O into fuels achieving overall reaction is a promising solution for addressing environmental problems and energy crises. Constructing an S-scheme catalyst of two or more catalytic sites with rapid electron transfer and strong redox capability may be an effective strategy for coupling photocatalytic CO2 reduction and H2O oxidation. Here, an oxygen vacancies-rich S-scheme semiconductor photocatalyst composed of monoclinic lead chromate oxide (Pb2(CrO4)O) coupled with Mn3O4 quantum dots (QDs) (Pb2(CrO4)O@Mn3O4QDs) are synthesized and tested for photoconversion of CO2 with H2O under visible light. Through the integration of Pb2(CrO4)O with Mn3O4QDs, the photocatalytic C1-evolution rate on Pb2(CrO4)O@Mn3O4QDs is radically increased by 6.0 and 8.1 times, which is much faster than that of pristine Pb2(CrO4)O and Mn3O4. The origin of the greatly raised activity is revealed by advanced characterizations, and in situ X-ray photoelectron spectroscopy (XPS) confirms the electron transport pathway in Pb2(CrO4)O@Mn3O4QDs with light illumination, unveiling the efficient spatial separation/transfer of charge carriers in oxygen vacancies-rich Pb2(CrO4)O@Mn3O4QDs S-scheme heterojunction. Consequently, powerful photoelectrons and holes accumulate in the Mn3O4 conduction band and Pb2(CrO4)O valence band, respectively, exhibiting prolonged long lifetimes and facilitating their involvement in CO2 photoreduction and H2O photooxidation through altering the interfacial charge dynamics.

Meeting the Industrial Challenges of CO2 Photocatalytic Reduction: Moving From Molybdenum Disulfides to Oxysulfides Based Materials?

Reducing CO2 emissions is one of the greatest challenges of the century. Among the means employed to tackle CO2 emissions, the photocatalytic conversion of CO2 is an appealing way to valorize CO2 since it uses the sun energy, which is abundant. However, nowadays, the best photocatalytic systems still report too low efficiencies, and use expensive materials, so they cannot be readily industrialized for use at large scale. In this report, we first highlight general industrial and process challenges (including operating conditions). Then, focusing on MoS2/TiO2 heterojunction systems, we analyze advantages and limitations of such systems and open perspectives on Mo oxysulfides supported on TiO2 discussing their potential to reach higher efficiency for CO2 photoconversion.

Correction: Visible light active SrZrO3/PbS nanocomposite for photoconversion of CO2 into methane and methanol

Correction: Visible light active SrZrO3/PbS nanocomposite for photoconversion of CO2 into methane and methanol

Clustering-Resistant Cu Single Atoms on Porous Au Nanoparticles Supported by TiO2 for Sustainable Photoconversion of CO2 into CH4.

Photocatalysts based on single atoms (SAs) modification can lead to unprecedented reactivity with recent advances. However, the deactivation of SAs-modified photocatalysts remains a critical challenge in the field of photocatalytic CO2 reduction. In this study, we unveil the detrimental effect of CO intermediates on Cu single atoms (Cu-SAs) during photocatalytic CO2 reduction, leading to clustering and deactivation on TiO2. To address this, we developed a novel Cu-SAs anchored on Au porous nanoparticles (CuAu-SAPNPs-TiO2) via a vectored etching approach. This system not only enhances CH4 production with a rate of 748.8 μmol ⋅ g-1 ⋅ h-1 and 93.1 % selectivity but also mitigates Cu-SAs clustering, maintaining stability over 7 days. This sustained high performance, despite the exceptionally high efficiency and selectivity in CH4 production, highlights the CuAu-SAPNPs-TiO2 overarching superior photocatalytic properties. Consequently, this work underscores the potential of tailored SAs-based systems for efficient and durable CO2 reduction by reshaping surface adsorption dynamics and optimizing the thermodynamic behavior of the SAs.

Regulating the Oxygen Vacancy on Bi2MoO6/Co3O4 Core‐Shell Nanocage Enables Highly Selective CO2 Photoreduction to CH4

AbstractPhotocatalytic CO2 reduction reaction (CO2RR) into high‐value‐added fuels has received significant attention, yet multiple electron and proton processes involved in CO2RR result in low selectivity. Herein, a strategy involving oxygen vacancies (Ovs)‐enriched Bi2MoO6 coated on ZIF‐67‐derived Co3O4 to construct well‐defined core‐shell nanocage is developed, which drives effective CO2 photoconversion to CH4 with nearly 100% selectivity and high apparent quantum efficiency of 2.5% at 420 nm in pure water under simulated irradiation. Theoretical calculations and experiments exhibit that the potential difference stemming from the built‐in electric field provides guarantee for CO2 reduction occurring on Bi2MoO6 and H2O oxidation set in Co3O4. Numerous exposed Bi2MoO6 with Ovs formed in Bi─O bond by ethylene glycol mediated approach promotes the CO2 adsorption and charge separation efficiency, which can optimize the reaction kinetics and thermodynamics, facilitating the hydrogenation of key intermediate *CO to generate CH4. This work provides a new strategy for controlled oxygen vacancy generation on photocatalysts to achieve high‐performance CO2 methanation.

Cu(II)-doped flower-like TiO2 nano-catalyst for enhanced photoconversion of CO2 to CH4

Cu(II)-doped flower-like TiO2 nano-catalyst for enhanced photoconversion of CO2 to CH4

Enhanced CO2 photoreduction by constructing BiOCl/NiS Schottky heterojunction with a giant internal electric field

Constructing Schottky junctions is a potent strategy for enhancing charge separation and charge dynamics, essential for optimizing the kinetics of efficient CO2 photoreduction reactions (CO2 RR). Yet, developing highly efficient Schottky heterojunction photocatalyst continues to be a formidable challenge. Here, we utilize two-step hydrothermal technology to prepare a BiOCl/NiS Schottky heterojunction with a powerful internal electric field (IEF) to accelerate the photo-conversion of CO2 to CO. Experimental results show that the charge separation efficiency and IEF strength of the BiOCl/NiS composite photocatalyst are 1.26 and 5.63 times those of BiOCl, respectively. In addition, the BiOCl/NiS composite sample has excellent light absorption ability. Under Uv–vis light irradiation, the BiOCl/NiS sample exhibits superior CO2 to CO photoreduction activity without any sacrificial agents, and a CO yield reaching 7.97 μmol⋅g−1⋅h−1, which is 2.97 times higher than that of BiOCl (2.68 μmol⋅g−1⋅h−1). This work provides a viable solution for designing efficient and stable Schottky junction composite materials.

Modification of TNF@UiO-66 composite by amine functionalized (TEPA) to improve photoconversion of CO2 using visible light: Investigation of intrinsic kinetic study and optimization

In this work, 25 % weight percentages of UiO-66 in TiO2 nanoflower composite was treated with varying quantities of Tetraethylenepentamine (TEPA) to improve photoconversion of CO2 into fuel using visible light (VL). The results revealed that maximum production rates of CH4 and CH3OH on TNF@25 %U-TEPA(2) sample were 64.59 and 2.47 µmol gcat−1 h−1, respectively, at the optimum conditions of V-LP=150 W, PCO2 =73 KPa, PH2O =15 KPa and T=332.15 K. 15 LHHW models were evaluated based on different assumptions of rate determining step and the most abundant surface intermediate to obtain kinetics of the CO2 photoconversion. The chosen model was the one that was closest to the experimental data. Furthermore, the kinetic rate and adsorption coefficients at T= 298.15–338.15 K and V-LP=150 W were obtained for the best-selected model. Finally, at T= 298.15–338.15 K, the activity energy of the produced CH4 was determined as 3.6 kJ mol−1.

Healable multilayered photocatalysts promote durability and productivity of solar-driven CO2 conversion

Numerous studies have focused on efficient CO2 photoreduction on short notice. However, more hours of efficient and selective CO2 and pure water photoconversion without precious metals or sacrificing reagents should be emphasized. Herein, a multilayer (SrTiO3/Ce:CaF2/CuNi/Ce:CaF2/TiN) is utilized with a high selectivity of 87 % for healable photocatalytic CO2 and pure water conversion without sacrificial reagents and the longest service life for the Cu nanolayers, to the best of our knowledge. Meanwhile, the photocatalytic activity, optical absorption, and charge separation ability of SrTiO3/Ce:CaF2/CuNi/Ce:CaF2/TiN can be recovered after regeneration. The deactivation and healable mechanism are illuminated that the adsorption of CO2 molecules at the photocatalyst surface is changed from M-CO2 to MO-CO2, due to the oxidation of active sites, resulting in the deactivation of CO2 reduction. The Ce:CaF2 nanolayers can accommodate oxygen atoms effectively to heal the photocatalyst. The article proposes a feasible way for commercial CO2 and pure water photoconversion.

Engineering Single Cu Atoms Anchored via N‐Heterocyclic Carbene in COF Mesopores for Modulating Electron Kinetics of CO2 Photoconversion

AbstractCharge transfer and carbon dioxide (CO2) adsorption/activation are critical factors for the electron kinetics during CO2 photoconversion. Herein, high‐loading and robust single Cu atoms (7.8 wt.%) are anchored via N‐heterocyclic carbene ligands derived from imidazolium ionic liquid motifs, precisely bonding to the acceptors of mesoporous donor‐acceptor pyridine‐covalent organic framework (pCOF) nanosheets. By engineering the valance and coordination structure, atomic Cu(I)‐CO2 sites, superior to Cu(II)‐CN2OCl ones, enable a 22‐fold increase of CO2 conversion rate compared to pCOF in pure water, ≈100% selectivity toward CO, and an apparent quantum yield of 1.7% (420 nm). The photoactivity outperforms analogous COF‐based photocatalysts under similar conditions. Experimental results prove single Cu(I) atoms possess more improved electron capture and CO2 adsorption/activation capacities than single Cu(II) ones. Combining fs‐ and µs‐transient absorption spectroscopy, the electron kinetics mechanism is investigated on the single‐atom pCOF photocatalyst model. The fs‐transient absorption spectra confirm single Cu(I) atoms can rapidly and precisely extract electrons from the electron‐rich region of pCOF along N‐heterocyclic carbene, exhibiting an electron transfer rate of 3 × 109 s−1. Using in situ µs‐transient absorption spectroscopy, the electron transfer efficiency is quantified to reach 60.4% under photocatalytic reaction conditions. This work provides a rational design strategy for advanced single‐atom photocatalysts.

Engineering Spatially Adjacent Redox Sites with Synergistic Spin Polarization Effect to Boost Photocatalytic CO2 Methanation.

The integration of oxidation and reduction half-reactions to amplify their synergy presents a considerable challenge in CO2 photoconversion. Addressing this challenge requires the construction of spatially adjacent redox sites while suppressing charge recombination at these sites. This study introduces an innovative approach that utilizes spatial synergy to enable synergistic redox reactions within atomic proximity and employs spin polarization to inhibit charge recombination. We incorporate Mn into Co3O4 as a catalyst, in which Mn sites tend to enrich holes as water activation sites, while adjacent Co sites preferentially capture electrons to activate CO2, forming a spatial synergy. The direct H transfer from H2O at Mn sites facilitates the formation of *COOH on adjacent Co sites with remarkably favorable thermodynamic energy. Notably, the incorporation of Mn induces spin polarization in the system, significantly suppressing the recombination of photogenerated charges at redox sites. This effect is further enhanced by applying an external magnetic field. By synergizing spatial synergy and spin polarization, Mn/Co3O4 exhibits a CH4 production rate of 23.4 μmol g-1 h-1 from CO2 photoreduction, showcasing a 28.8 times enhancement over Co3O4. This study first introduces spin polarization to address charge recombination issues at spatially adjacent redox sites, offering novel insights for synergistic redox photocatalytic systems.

Modified-TiO2 Nanotube Arrays as a Proficient Photo-Catalyst Nanomaterial for Energy and Environmental Applications

Recently, TiO2 nanotube arrays (TNTAs) have attracted researcher’s attention in the fields of energy production and environmental remediation applications; this is mainly due to their unique optoelectronic characteristics, corrosion resistance, chemical and mechanical stability. In this study, the ability of employing of TiO2 nanotube arrays-based catalysts in the field of photocatalytic CO2 reduction has been investigated. Possible modification strategies have been presented for improving the TNTAs performance by using different types of nanomaterials including graphitic carbon nitrides (g-C3N4), metal-organic frame work (MOF), reduced graphene oxide (RGO) and gold nanoparticles (Au NPs). The TNTAs composites were characterized using XRD and FESEM analyses and the results revealed the successful synthesis of these composites. The TNTAs and their composites exhibited good results for the photo-conversion of CO2 into CH4 gas product. This study gives new ideas for making and developing low-cost Ti metal-based nanomaterials which can be used in the future for recycling the CO2 gas emissions into useful solar fuels.

Effect of copper and silver modification of NH2-MIL-125(Ti) on the photoreduction of carbon dioxide to formic acid over this framework under visible-light irradiation

Cu and Ag enhance the photocatalytic activities of metal–organic frameworks (MOFs) toward CO2 conversion because of their CO2 adsorption capacities and effects on the lowest unoccupied molecular orbital (LUMO) overpotentials of MOFs. However, to date, targeted introduction of metals into MOFs to achieve visible (Vis)-light-active photocatalysts for CO2 photoconversion has not been realized. Herein, a series of amine-functionalized Ti MOF (NH2-MIL-125(Ti))-based photocatalysts were successfully synthesized using metalation, incorporation, and photodeposition, allowing Cu and Ag incorporation into NH2-MIL-125(Ti) and attainment of ultraviolet- and Vis-light-active photocatalysts. Notably, the most active photocatalyst obtained by post-synthetic metalation of NH2-MIL-125(Ti) by Cu2+ (MOF_met_0.5%Cu) demonstrated excellent performance in photoreducing CO2 to HCOOH: a conversion rate of 30.1 umolg−1h−1 and quantum yield of 1.18% at 380 nm. Photoconversion of CO2 to HCOOH was further confirmed using 13CO2. The novel approach proposed herein is a significant step toward clean energy production and environmental pollutant elimination.

Purposefully construction of ZnIn2S4/CdIn2S4/Co3O4 synergistic mix-heterojunction for enhanced CO2 photoconversion and H2 evolution reaction via cascade charge transfer

The high-dispersed nano complex ZnO/Co3O4 was first prepared by calcining the ZIF-8@ZIF-67 in Air. Then, the ternary mix-heterojunction ZnIn2S4/CdIn2S4/Co3O4 (CdIn2S4/Z/C) was first in situ constructed by introducing nano complex ZnO/Co3O4 into the CdIn2S4 precursor solution via a solvent thermal reaction. Overall, the CdIn2S4/Z/C photocatalyst exhibits excellent performance in the photoconversion of CO2 and H2O, which increased by 18.1%∼34.1% for CO, 36.8%∼73.9% for H2, and 21.1%∼40.6% for syngas (CO+H2), respectively, compared with CdIn2S4. The CdIn2S4/Z/C-40 shows the highest H2-evolution rate of 1661.8 μmolg−1h−1, which is 87.5% higher than that of CdIn2S4 (886.3 μmolg−1h−1). The CdIn2S4/Z/C exhibits higher surface S-vacancy concentration, larger specific surface area, stronger light absorption, and photocurrent density than that of CdIn2S4. The band structure reveals that the ZnIn2S4/CdIn2S4/Co3O4 forms a tandem internal electric field at the double heterojunction interface, which is beneficial to improve the migration of photocarrier. This work provides a feasible strategy for constructing synergistic mix-heterojunction photocatalyst for photoconversion of CO2 and H2O.