CO2 Photoreduction Research Articles

Highly efficient photoreduction of CO2 to CO: Synergistic optimisation of progressive electron transfer via Fe2+ and oxygen vacancies

The electron transfer in photocatalytic reaction, including electron transfer between the components in the catalyst, electron transfer between reactant molecules and catalysts. Fe2+/Fe3+ and oxygen vacancies (VOs) were simultaneously introduced in Fe-In2O3, the 5 wt% Fe-In2O3 exhibited a 13.7-fold increase in activity (4.80 mmol·g−1·h−1) compared to the In2O3 and a CO selectivity of approximately 84.32 %. Multiple in-situ techniques indicated that the doping of FeOX serves to effectively modulate the concentration of VOs, FeOX and In2O3 form a p-n heterojunction interfacial structure and match energy bands, promoting carrier separation. More importantly, Fe2+, In2+, and VOs serve as electron-donating adsorption sites, increasing the number of electrons received by CO2 and H2O, which causing pre-reduction activation of the reactant molecules. Eventually the dual-reduction reaction of CO2 and H2O were realized, subsequently, CO2 was selectively converted into CO through intermediate species such as formate. This study employs Fe2+ and VOs to synergistic optimize the progressive transfer of photogenerated electrons, and presents a novel approach for elucidating the catalytic mechanism.

Large-Scale Synthesis of High-Loading Single Metallic Atom Catalysts by a Metal Coordination Route.

Single atom catalyst (SAC) is one of the most efficient and versatile catalysts with well-defined active sites. However, its facile and large-scale preparation, the prerequisite of industrial applications, has been very challenging. This dilemma originatesfrom the Gibbs-Thomson effect, which renders it rather difficult to achieve high single atom loading (< 3 mol%). Further, most synthesizing procedures are quitecomplex, resulting in significant mass loss and thus low yields. Herein, a novel metal coordination route is developed to address these issues simultaneously, which is realized owing to the rapid complexation between ligands (e.g., biuret) and metal ions in aqueous solutions and subsequent in situ polymerization of the formed complexes to yield SACs. The whole preparation process involves only one heating step operated in air without any special protecting atmospheres, showing general applicability for diverse transition metals. Take Cu SAC for an example, a record yield of up to 3.565kg in one pot and an ultrahigh metal loading 16.03 mol% on carbon nitride (Cu/CN) are approached. The as-prepared SACs are demonstrated to possess high activity, outstanding selectivity, and robust cyclicity for CO2 photoreduction to HCOOH. This research explores a robust route toward cost-effective, massive production of SACs for potential industrial applications.

Dimensionally Intact Construction of Ultrathin S-Scheme CuFe2O4/ZnIn2S4 Heterojunctional Photocatalysts for CO2 Photoreduction.

The conversion of CO2 into carbon-neutral fuels such as methane (CH4) through selective photoreduction is highly sought after yet remains challenging due to the slow multistep proton-electron transfer processes and the formation of various C1 intermediates. This research highlights the cooperative interaction between Fe3+ and Cu2+ ions transitioning to Fe2+ and Cu+ ions, enhancing the photocatalytic conversion of CO2 to methane. We introduce an S-scheme heterojunction photocatalyst, CuFe2O4/ZnIn2S4, which demonstrates significant efficiency in CO2 methanation under light irradiation. The CuFe2O4/ZnIn2S4 heterojunction forms an internal electric field that aids in the mobility and separation of exciton carriers under a wide solar spectrum for exceptional photocatalytic performance. Remarkably, the optimal CuFe2O4/ZnIn2S4 heterojunction system achieved an approximately 68-time increase in CO2 conversion compared with ZnIn2S4 and CuFe2O4 nanoparticles using only pure water, with nearly complete CO selectivity and yields of CH4 and CO reaching 172.5 and 202.4 μmol g-1 h-1, respectively, via a 2-electron oxygen reduction reaction (ORR) process. The optimally designed CuFe2O4/ZnIn2S4 heterojunctional system achieved approximately 96% conversion of BA and 98.5% selectivity toward benzaldehyde (BAD). Additionally, this photocatalytic system demonstrated excellent cyclic stability and practical applicability. The photogenerated electrons in the CuFe2O4 conduction band enhance the reduction of Fe3+/Cu2+ to Fe2+/Cu+, creating a microenvironment conducive to CO2 reduction to CO and CH4. Simultaneously, the appearance of holes in the ZnIn2S4 valence band facilitates water oxidation to O2. The synergistic function within the CuFe2O4/ZnIn2S4 heterojunction plays a pivotal role in facilitating charge transfer, accelerating water oxidation, and thereby enhancing CO2 reduction kinetics. This study offers valuable insights and a strategic framework for designing efficient S-scheme heterojunctions aimed at achieving carbon neutrality through solar fuel production.

Enhanced CO2 photoreduction to CH4 via *COOH and *CHO intermediates stabilization by synergistic effect of implanted P and S vacancy in thin-film SnS2

Reduction of CO2 to value-added hydrocarbons through artificial photosynthesis is one of the way to address the energy crisis and climate change issues. It is known that lowering the activation energy of CO2 molecules on the photocatalyst surface and key intermediates is crucial in photocatalytic CO2 reduction. Herein, we present phosphorus-implanted 20-nm SnS2 continuous thin film with sulfur vacancies (i.e., SV-SnS2:P where P substitutes on S sites). The fabrication process involves thermal evaporation, post-sulfurization, and ion implantation. Our gas-phase photocatalytic experiments show an enhanced and selective CO2 photoreduction to CH4 with a yield of 0.13 µmol cm−2 and selectivity of 92 % under solar-light irradiation for 4 h over an optimal ∼4.5 % P and ∼16 % SV. Experimental observations, conducted through X-ray absorption near edge, in situ near ambient pressure X-ray photoelectron, and in situ Fourier transform infrared spectroscopies, along with first-principle density functional theory calculations. Results reveal that P dopant is significantly affected by nearby SV via local charge density transfer from P to the nearest Sn and next-nearest S neighbor atoms, consequently, leads to the stabilization of *COOH and *CHO intermediates, where asterisks stand for P as the active site. Our results demonstrate how active site modulation, without using precious co-catalysts, plays a crucial role in intermediate stabilization in a wireless photocatalysis process.

Optimized CO2 photoreduction using cuprous oxide (Cu2O) nanoparticles synthesized using Psidium guajava extract

Optimized CO2 photoreduction using cuprous oxide (Cu2O) nanoparticles synthesized using Psidium guajava extract

Ultrafast electron transfer at the In2O3/Nb2O5 S-scheme interface for CO2 photoreduction

Constructing S-scheme heterojunctions proves proficient in achieving the spatial separation of potent photogenerated charge carriers for their participation in photoreactions. Nonetheless, the restricted contact areas between two phases within S-scheme heterostructures lead to inefficient interfacial charge transport, resulting in low photocatalytic efficiency from a kinetic perspective. Here, In2O3/Nb2O5 S-scheme heterojunctions are fabricated through a straightforward one-step electrospinning technique, enabling intimate contact between the two phases and thereby fostering ultrafast interfacial electron transfer (<10 ps), as analyzed via femtosecond transient absorption spectroscopy. As a result, powerful photo-electrons and holes accumulate in the Nb2O5 conduction band and In2O3 valence band, respectively, exhibiting extended long lifetimes and facilitating their involvement in subsequent photoreactions. Combined with the efficient chemisorption and activation of stable CO2 on the Nb2O5, the resulting In2O3/Nb2O5 hybrid nanofibers demonstrate improved photocatalytic performance for CO2 conversion.

Optimizing Adsorption‐Redox Sites and Charge Transfer of Ternary Polymer Photocatalyst with P─N Linkage for CO2 Conversion Coupled with Antibiotics Removal

AbstractThe rational design of bifunctional photocatalysts with high adsorption and enrichment characteristics and excellent photocatalytic redox activity is an effective way to address environmental pollution and energy shortage crisis. In this study, cyclophosphazene‐derived porous organic polymer (PCPD) microspheres with P─N linkage are coated with graphene oxide (GO) and loaded with Ag0 nanoparticles (NPs) to prepare covalently bonded xAg‐rGO/PCPD composites. The catalyst with the highest specific surface area (denoted as 2.5Ag‐rGO/PCPD) shows excellent adsorption capacity for fluoroquinolone antibiotics, removing 96.2% of ciprofloxacin (CIP) through adsorption. By applying the catalyst with the best photocatalytic redox activity (denoted as 5Ag‐rGO/PCPD), 82.97% of refractory sulfonamide antibiotics are removed through adsorption‐degradation, and 635.3 µmol g−1 of CO and 162.3 µmol g−1 of CH4 are generated as products of CO2 photoreduction alone. Among the co‐catalytic systems, the highest CO yield of 9.16 µmol g−1 is obtained by coupling CO2 reduction with levofloxacin (LVX) degradation to harness the electron‐donating power of the pollutant molecule. This study is expected to provide useful guidance for the rational design of bifunctional photocatalysts.

Single-cluster Functionalized TiO2 Nanotube Array for Boosting Water Oxidation and CO2 Photoreduction to CH3OH.

Solar-driven CO2 reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH3OH and CH3CH2OH dominated by multi-electron transfer. Single-cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells-Dawson- and Keggin-type polyoxometalates on TiO2 nanotube arrays, resulting in a series of single-cluster functionalized catalysts P2M18O62@TiO2 and PM12O40@TiO2 (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO2 for enhancing surface-hole concentration and promote water oxidation. Among these samples, P2Mo18O62@TiO2-1 exhibits the highest electron consumption rate of 1260 μmol g-1 for CO2-to-CH3OH conversion with H2O as the electron source, which is 11 times higher than that of isolated TiO2 nanotube arrays. This work supplied a simple synthesis method to realize the single-dispersion of molecular cluster to enrich surface-reaching holes on TiO2, thereby facilitating water oxidation and CO2 reduction.

Au-Cu dual-single-atom sites on Bi2WO6 with oxygen vacancy for CO2 photoreduction towards multicarbon products

CO2 photoreduction into high-value-added C2+ products struggles with energetic challenges in forming critical intermediates and multiple C−C bonds. Herein, an effectively synthesized photocatalyst, Bi2WO6 nanosheets with oxygen vacancies anchoring Au and Cu dual single atoms on the surface, can convert CO2 and H2O vapour into C3H6 and C2H4. The high product selectivity of 18.2 % for C3H6 and 65.4 % for total C2+ hydrocarbons are achieved under concentrated light irradiation (2.4 W·cm−2). Au-Cu dual-single-atom sites and defect engineering strategies exhibit synergistic effects on optimizing the reaction thermodynamics and charge kinetics for CO2 conversion. Theoretical calculations provide reference values for reaction pathways of C3H6 and C2H4 formation, with the C−C couplings being potential determining steps of multicarbon product formation. Our work offers a promising strategy with a combination of concentrated light irradiation technology and catalyst modification to achieve high selectivity of C2+ products.

Engineering MXene-based photocatalyst for efficient NADH regeneration and photoenzymatic CO2 reduction without electron mediator

In this study, an MXene-based photocatalyst, ARTM to regenerate NADH without electron mediator is reported. The ARTM was able to achieve a regenerated NADH yield of 65 % within 50 min in the absence of electron mediator, with a 1,4-NADH selectivity of 90.8 %. The turnover frequency (TOF) of 1,4-NADH was as high as 0.148 h−1, which was 74 and 148 times higher than that of A-TiO2 and R-TiO2, respectively. The synergetic effect between anatase/rutile TiO2 phase junction (ART-PJ) and TiO2@Ti3C2Tx heterojunction (TM-HJ) facilitates the efficient carriers separation and NADH regeneration. Enzymatic assay and HNMR revealed that the incorporation of Ti3C2Tx promoted the highly selective generation of 1,4-NADH. DFT calculation elucidated that this could be attributed to the end-on adsorption of the nicotinamide ring of NAD+. Subsequently, an electron mediator free photoenzyme cascade catalysis system was constructed, which could effectively promote CO2 photoreduction to formate (594 μmol g−1 h−1).

Regulated reaction pathway of CO2 photoreduction into CH4 by metal atom pair sites

Regulated reaction pathway of CO2 photoreduction into CH4 by metal atom pair sites

Effect of hydrogen sources toward the CO2 photoreduction on boron decorated crystalline carbon nitride

Photocatalytic CO2 conversion to industrial fuels is considered an effective measure to solve energy and environmental problems. Presently, Catalysts for CO2 reduction reaction (CO2RR) are mostly confined to metal-based materials, but non-metal materials are less explored. We decorate the highly crystalline carbon nitride, i.e., poly(triazine) imides (PTI), with non-metallic boron (B) to obtain two B/PTI catalysts: Bi/PTI with B being deposited into the six-fold cavity of the PTI, and Bs/PTI with B substituting for C in PTI. For CO2RR, Bi/PTI follows a quasi Mars-van Krevelen process, but the high exposure of Bi results in an overly strong interaction with intermediates, inhibiting the reactivity. In contrast, Bs/PTI enhances the binding with intermediates by introducing Lewis acid-base pairs (B-N), which reduce the ring conjugation effect and induce the enrichment of electrons at the pyridine N. Hence, CO2 reduction with the adsorbed H* (Ha) hydrogenation mechanism in Bs/PTI has a significant reactivity.

Synergistic effect between ohmic contacts and localized surface plasmon resonance for enhancing CO2 photoreduction of BiOBr

The fast recombination rate of photogenerated carrier and short electron lifetime are the main factors affecting the CO2 reduction performance of BiOBr (BOB). The utilization of ohmic contacts and the localised surface plasmon resonance (LSPR) effect of metals can effectively solve the above problems. However, one mean alone is not ideal for improving the photocatalytic performance of BOB. Therefore, in this work, we reduced the metal Bi to the surface of BOB in an attempt to form a synergistic effect of ohmic contact and LSPR effect. DFT calculations confirm the ohmic contact between Bi and BOB. Meanwhile, electrochemical tests show that Bi/BOB-2 has a higher photocurrent density (1.1 μA/cm2), suggesting that the ohmic contact achieves ultrafast electron transfer from BOB to Bi under light. While the UV–Vis diffuse reflectance spectroscopy results show resonance absorption peaks from the LSPR effect of Bi, the TRPL results show that Bi/BOB-2 has a longer τave (3.05 ns), implying that longer-lived hot electrons are generated on the Bi surface. The synergistic effect of the two contributes to the efficient CO2 to CO transition on the catalyst surface. As a result, Bi/BOB-2 exhibites a 4.37-fold higher CO generation rate (11.45 μmolg-1 h−1) than that of pure BOB (2.62 μmolg-1 h−1) under light. This study provides a new blueprint for the design of BiOBr-based materials for efficient photocatalytic reduction of CO2.

Step-by-step transfer of photoexcited electron in donor-acceptor-catalyst configuration covalent triazine framework for efficient photoreduction CO2 to formic acid

Covalent triazine frameworks (CTFs) have great potential for photocatalysis. However, the electron-hole recombination and the lack of efficient catalytic sites constrain the activity and selectivity. Herein, a novel design strategy of donor–acceptor-catalyst (D-A-C) configuration is proposed. This configuration enables the photoexcited electron undergoes stepwise transfer from donor unit to acceptor unit and ultimately reaches catalytic center, effectively inhibiting electron-hole recombination. The proof-of-concept model CTF-TT-Ir, in which thieno[3,2-b]thiophene (TT) serves as the donor unit, triazine as the acceptor unit, and Cp*Ir(bpy) (Ir) as the built-in catalytic site, was prepared for the photocatalytic reduction of CO2 to HCOOH. The stepwise transfer of photoexcited electrons in the ternary structure has been demonstrated through the in-situ XPS measurements and the theoretical calculations. Photoluminescence and photocurrent tests have indicated CTF-TT-Ir exhibits superior charge separation efficiency. Without additional photosensitizer and co-catalyst, the photocatalytic HCOOH yield rate of CTF-TT-Ir reached 245 μmol g−1h−1 (selectivity of 97 %).

Recent Advances in Carbon Nitride Supported Single‐Atom Catalysts: Synthesis, Characterization, and Applications for CO2 Photoreduction

AbstractPhotoreduction of CO2 into value‐added chemicals and fuels is a promising green technology for solar‐to‐chemical conversion. Owing to the atomic utilization, unique metal‐support interaction, and unsaturated coordination active sites, single‐atom catalysts (SACs) have been attracting great attention in achieving high activity and selectivity of CO2 photoreduction reactions. On the other hand, carbon nitride (C3N4) with abundant periodically unsaturated coordination of nitrogen atoms can serve as an excellent support for anchoring metal single atoms. In this context, extensive research efforts have been paid in C3N4‐based SACs for CO2 photoreduction in recent years. In this review, we report the recent advances in C3N4 supported SACs for CO2 photoreduction. We start from the introduction of synthetic strategies of various C3N4 supported metal SACs. Secondly, the main advanced characterization techniques and calculation methods for identifying the single‐atoms and their coordination environments of C3N4‐based SACs are summarized. Thirdly, some state‐of‐the‐art works on the rational design of C3N4‐based SACs and their applications in CO2 photoreduction are introduced. Lastly, we briefly summarize the main challenges and propose important perspectives of C3N4‐based SACs in CO2 photoreduction. This review is expected to provide some useful guidelines for the development of efficient and stable C3N4‐based SACs for CO2 photoreduction.

In Situ Construction of CuTCPP/Bi4O5Br2 Hybrids for Improved Photocatalytic CO2 and Cr(VI) Reduction.

Global warming and heavy metal pollution pose tremendous challenges to human development, and photocatalysis is considered to be an effective strategy to solve these problems. Herein, copper(II) tetra (4-carboxyphenyl) porphyrin (CuTCPP) molecules were successfully in situ loaded onto Bi4O5Br2 by a hydrothermal approach. A series of experimental results show that the light absorption capacity and photogenerated carrier separation efficiency were synchronously enhanced after the construction of CuTCPP/Bi4O5Br2 composites. Hence, the as-prepared composites possess significantly improved photocatalytic ability for both CO2 and Cr(VI) reduction. Specifically, CuTCPP/Bi4O5Br2-2 achieves a CO generation rate of 17.14 μmol g-1 under 5 h irradiation, which is twice as high as that of Bi4O5Br2 (8.57 μmol g-1). Besides, the optimized CuTCPP/Bi4O5Br2-2 also exhibits a removal rate of 61.87% for Cr(VI) within 100 min under irradiation. Furthermore, the mechanism of CO2 and Cr(VI) photoreduction was explored by in situ Fourier transform infrared spectroscopy and capture experiments, respectively. This work can be a reference toward the construction of photocatalysts with high activity for solar energy conversion.

Pt-N catalytic centres concisely enhance interfacial charge transfer in amines functionalized Pt@MOFs for selective conversion of CO2 to CH4

Improving ligand-to-active metal charge transfer (LAMCT) by finely tuning the organic ligand is a decisive strategy to enhance charge transfer in metal organic frameworks (MOFs)-based catalysts. However, in most MOFs loaded with active metal catalysts, electron transmission encounters massive obstacle at the interface between the two constituents owing to poor LAMCT. Herein, amines (–NH2) functionalized MOFs (NH2-MIL-101(Cr)) encapsulated active metal Pt nanoclusters (NCs) catalysts are synthesized by the polyol reduction method and utilized for the photoreduction of CO2. Surprisingly, the introduction of –NH2 (electron donating) groups within the matrix of MIL-101(Cr) improved the electron migration through the LAMCT process, fostering a synergistic interaction with Pt. The combined experimental analysis exposed the high number of metallic Pt (Pt0) in Pt@NH2-MIL-101(Cr) catalyst through seamless electron shuttling from N of –NH2 group to excited Pt generating versatile hybrid Pt-N catalytic centres. Consequently, these versatile hybrid catalytic centres act as electro-nucleophilic centres, which enable the efficient and selective conversion of CO bond in CO2 to harvest CH4 (131.0 µmol.g−1) and maintain excellent stability and selectivity for consecutive five rounds, superior to Pt@MIL-101(Cr) and most reported catalysts. Our study verified that the precise tuning of organic ligands in MOFs immensely improves the surface-active centres, electron migration, and catalytic selectivity of the excited Pt NCs catalysts encaged inside MOFs through an improved LAMCT pathway.

Modeling and simulation of reactors for methanol production by CO2 reduction: A comparative study

The extensive utilization of fossil fuel energy has caused severe degradation to our environment, therefore the search for new clean efficient energy is the need of the hour. Photocatalytic conversion of CO2 to solar fuels, and artificial photosynthesis, offer a promising solution for the energy crisis and global warming. Improving efficiency in the photo-reduction of CO2 to fuels involves developing highly efficient catalysts and optimizing photoreactor configuration. Photocatalysis is a process in which light radiations having energy equal to or greater than the band gap energy (Ebg) of a semiconductor strikes on its surface and generates electron (e−) hole(h+) pairs. The photogenerated electrons and holes participate in various oxidation and reduction processes to produce final products. This field focuses on harnessing solar energy to drive the conversion of carbon dioxide into hydrocarbon fuels, showcasing significant potential for sustainable energy solutions. The global methanol market was valued at $30.9 billion in 2023 and is projected to reach $38 billion by 2028, growing at 4.2 % CAGR during the forecast period. For determining the feasibility of reactions on a larger scale, simulations must be performed at different conditions for obtaining higher conversion and cost-effective management of the process at the industrial level. So, a simulation of methanol photoreactors using different software was done to examine the kinetics of methanol reactors by employing ASPEN, DWSIM, and MATLAB software for simulating experimental data.

Enhanced room temperature CO2 photoreduction on gas-solid interfaces using nanocrystals integrated with ZIF-8 wrapping design

Composites derived from metal-organic frameworks (MOFs) show promise as catalysts for the photocatalytic reduction of CO2. However, their potential is hindered by constraints such as limited light absorption and sluggish electron transfer and separation, impacting the overall efficiency of the photocatalytic process. In this study, TiO2 nanocrystals, modified with Ptx+, underwent laser etching were encapsulated within the traditional MOF-ZIF-8 framework. This enhanced the adsorption capabilities for CO2 reactants and solar light, while also facilitating directed electron transfer and the separation of photogenerated charges. The finely-tuned catalyst demonstrates impressive CH4 selectivity at 9.5 %, with yields of 250. 24 μmol g-1 h-1 for CO and 25.43 μmol g-1 h-1 for CH4, utilizing water as a hole trap and H+ source. This study demonstrates the viability of achieving characteristics related to the separation of photogenerated charges in TiO2 nanocrystals through laser etching and MOF composite catalysts. It offers novel perspectives for designing MOF-based catalysts with enhanced performance in artificial photosynthesis.

Asymmetric aggregation enables red-light CO2 reduction with tunable activity and selectivity by intermolecular electronic coupling

Photocatalytic CO2 reduction to value-added chemicals is a promising way to simultaneously mitigate environmental and energy issues. Integrating low-energy red light harvesting, fast charge separation, and robust CO2 activation in a photosystem is a crucial prerequisite for highly efficient CO2 photoreduction but remains a huge challenge. Herein, we constructed an aggregated [Ru(2, 2'-bipyridine)3]Cl2 (denoted as Ru(bpy)3Cl2) photosystem. Various characterizations combining molecular dynamic simulations and theoretical calculations confirm that the electronic coupling between adjacent Ru(bpy)3Cl2 molecules can induce orbital hybridization, thus broadening the light absorption edge to the red light region. Meanwhile, the asymmetric aggregation of Ru(bpy)3Cl2 enables exciton dissociation and charge transfer through a dipole polarization effect. Significantly, this dipole polarization can also upshift the d-orbital of Ni catalytic centers, greatly strengthening the activation of CO2 and lowering the formation energy barrier of COOH* intermediates. Consequently, the apparent quantum yield (AQY) of aggregates for CO2-to-CO reduction reaches 4.2% at 610 nm, significantly higher than the AQYs of other reported photosystems at wavelengths ≥ 600 nm. More importantly, the catalytic efficiency and selectivity of CO2 reduction can be rationally tuned by controlling the aggregated degrees of Ru(bpy)3Cl2. This work highlights the key role of Ru(bpy)3Cl2 aggregation in prompting red-light harvesting and CO2 activation, which may help boost CO2 photoreduction efficiency from a fresh perspective.