Efficient CO2 Photoreduction Research Articles

Rational construction of MOF-on-MOF heterojunction with an array of flexible two-dimensional microsheets for efficient CO2 photoreduction

MOF-on-MOF composites are deemed promising candidates to accomplish synergistic CO2 capture and photoreduction thanks to their plentiful active sites, extended light response range, timely separation of photoexcited electron-hole pairs, and large CO2 adsorption capacities. Unfortunately, the controllable growth of the designed MOF-on-MOF heterostructure is challenging. Deficient interphase contact and the consequent mass transfer deprivation is one of the primary obstacles severely impairing the catalytic efficiency. Herein, the contact between two widely-employed MOFs of Ni-BDC and NH2-MIL-125 was significantly strengthened by exploiting a self-assembled array of Ni-BDC microsheets. In contrast to the spontaneously formed spheroidal aggregate, the loosely-packed array exhibits amplified accessible surfaces to interact with NH2-MIL-125, contributing to a radically improved interfacial built-in electric field and 7∼9 times rises in the product yields. Moreover, the preferably thin thickness of Ni-BDC microsheets prompts its macroscopic flexibility, permitting intensified deformation for enhanced interphase contact. Coupled with the additional contribution from its copious Lewis acid sites, the developed NH2-MIL-125@Ni-BDC array simultaneously converted CO2 into CO and CH4 at rates that cannot be matched by its isostructural Co counterpart with declined acidity and flexibility. This work innovatively reveals the immense importance of morphology tailoring and assembly tactic to interphase contact modulation and the upgrade of catalyst performances.

Efficient CO2 photoreduction enabled by the one-dimensional (1D) porous structured NiTiO3 nanorods

In this study, porous, and hollow nanorods of NiTiO3 (NiTiO3 NRs-p: 2–3 μm in length and 400 nm in diameter) are successfully prepared using an ethylene glycol-mediated approach at room temperature (25 °C), followed by calcination at 700 °C in air environment. Their rough surfaces and accumulated holes are advantageous for adsorption and subsequent photoreduction of carbon dioxide (CO2) under UV–vis irradiation. The NiTiO3 NRs-p exhibit superior performance in terms of photoconversion of CO2 (purity 99.999 %, 100 mL/min) into gaseous CO (57.833 μmolg−1 h−1) and CH4 (24.33 μmolg−1 h−1) with an overall CO2 selectivity (SCO2) of 89 %. In contrast, the solid NiTiO3 nanorods (NiTiO3 NRs) exhibit moderate performance in CO2 reduction, producing CO (30.33 μmolg−1 h−1) and CH4 (11.50 μmolg−1 h−1) with a CO2 selectivity of SCO2 = 60 %. NiTiO3 NRs-p exhibits superior photocatalytic activity against CO2 over other NiTiO3 morphologies with similar physical and chemical properties (such as nanoparticles (NPs) and nanofibers (NFs). This enhancement in photocatalytic activity can be attributed to the porous texture and hollow rod-like structure of NiTiO3 NRs-p, which provides a larger number of active sites to promote rapid mass transport. This unique one-dimensional (1D) structure also facilitates the separation of photogenerated electron-hole pairs, as demonstrated experimentally. This study opens a new room for a simple and facile routes for the photocatalytic conversion of CO2 into solar fuels.

Single-atom Pt–N4 active sites anchored on porous C3N4 nanosheet for boosting the photocatalytic CO2 reduction with nearly 100% CO selectivity

Photoreduction of CO2 and H2O into fuels and value-added chemicals is a promising green technology for solar-to-chemical conversion. However, improving the conversion efficiency with regulated product selectivity is a big challenge due to the sluggish dynamic transfer and insufficient active sites. Herein, we report on Pt single atoms anchored porous C3N4 nanosheet photocatalyst (Pt1@CN) with Pt–N4 coordination for stable and efficient CO2 photoreduction using H2O as reductant. The Pt1@CN exhibits an evolution rate of 84.8 μmol g−1 h−1 with nearly 100% CO selectivity, outperforming most previous C3N4-based single-atom photocatalysts. Experimental and DFT calculation results reveal that the Pt–N4 coordinated active sites promote the photogenerated electron transfer, CO2 adsorption/activation, *COOH generation, and *CO desorption, thus accounting for the significantly improved CO2 photoreduction activity with ∼100% CO selectivity. This study provides a deep insight into the significant roles of single-atom active sites in enhancing the CO2 photoreduction activity and regulating the product selectivity.

In situ irradiated XPS investigation on S-scheme TiO2/Bi2S3 photocatalyst with high interfacial charge separation for highly efficient photothermal catalytic CO2 reduction

The combination of S-scheme heterojunction and photothermal effect is a promising strategy to achieve efficient CO2 photoreduction into solar fuel due to the boosted charge carrier separation efficiency and faster surface reaction rate. Herein, unique photothermal-coupled TiO2/Bi2S3 S-scheme heterojunction nanofibers were fabricated and applied to a full-spectrum CO2 photoreduction system. Density functional theory calculation and experimental analyses have confirmed the generation of the internal electric field and the S-scheme electron transfer pathway, leading to a highly efficient charge carrier separation. Thanks to the excellent photothermal conversion capacity of Bi2S3, the photogenerated electron transfer rate, and surface reaction rate were further accelerated in hybrid photocatalysts. Under the synergistic effect of S-scheme heterojunction and photothermal effects, the optimal TiO2/Bi2S3 nanofibers achieved 7.65 μmol h–1 of CH4 production rate, which is 5.24 times higher than that of pristine TiO2. Moreover, the morphology reconstruction of Bi2S3 in hybrids facilitates the CH4 selectivity was significantly improved from 64.2% to 88.7%. Meanwhile, the CO2 photoreduction reaction route over TiO2/Bi2S3 nanofibers was investigated based on in-situ Fourier transform infrared spectra. This work provides some useful hints for designing highly efficient photothermal-coupled photocatalysts for CO2 photoreduction.

Hydrochar-Supported NiFe2O4Nanosheets with a Tailored Microstructure for Enhanced CO2Photoreduction to Syngas.

Constructing high-efficiency composite photocatalysts with enhanced charge transfer and a rapid surface catalytic reaction has recently received significant attention. Herein, a hydrochar-mediated NiFe2O4 nanosheet (C/NFO) composite was rationally constructed by a simple hydrothermal method. Intimate interface contacts and chemical interactions between hydrochar and NFO were formed. The prepared C/NFO samples exhibited remarkable visible-light-driven catalytic CO2 reduction properties under mild reaction conditions with Ru(bpy)32+ sensitization. As the optimized sample, 16%-C/NFO achieved a 4-fold enhancement of CO production (17.49 μmol/h) compared with that of pure NFO. The C/NFO samples demonstrated good activity and structural stability in the CO2 photoreduction system. The carbon source of CO derived from CO2 was verified through isotopic labeling experiments using 13CO2. In situ photoluminescence and electrochemical characterizations confirmed the role of electron transfer intermediates of C/NFO. The synergistic effect of the nanosheet-like structure of NFO, combined with the surface functional groups of hydrochar, facilitated an exceptionally high rate of charge transfer and exposed abundant active adsorption sites for CO2, thereby promoting the efficient separation of photogenerated charge carriers and enhancing photocatalytic activity for CO2 reduction. This study presents a promising strategy for the rational design of hydrochar coupled with transition metal compound catalysts for efficient CO2 photoreduction.

MOF-derived Co3O4/ZrO2 mesoporous octahedrons with optimized charge transfer and intermediate conversion for efficient CO2 photoreduction

MOF-derived Co3O4/ZrO2 mesoporous octahedrons with optimized charge transfer and intermediate conversion for efficient CO2 photoreduction

Identification of Crucial Photosensitizing Factors to Promote CO2 -to-CO Conversion.

The sensitizing ability of a catalytic system is closely related to the visible-light absorption ability, excited-state lifetime, redox potential, and electron-transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)-based PSs (Ir-1-Ir-6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible-light absorption capacity results in lower CO yields of Ir-1, Ir-2 or Ir-4. Ir-3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir-3 is ≈10 times higher than that of Ir-5, the CO yield of Ir-3 is slightly higher than that of Ir-5 due to the compensation of Ir-5's strong visible-light-absorbing ability. Ir-6 exhibits excellent photocatalytic performance due to the strong visible-light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir-6 can achieve 91.5 μmol, over 54 times higher than Ir-1, and the optimized TONC-1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction.

Identification of Crucial Photosensitizing Factors to Promote CO2‐to‐CO Conversion

AbstractThe sensitizing ability of a catalytic system is closely related to the visible‐light absorption ability, excited‐state lifetime, redox potential, and electron‐transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)‐based PSs (Ir‐1–Ir‐6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible‐light absorption capacity results in lower CO yields of Ir‐1, Ir‐2 or Ir‐4. Ir‐3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir‐3 is ≈10 times higher than that of Ir‐5, the CO yield of Ir‐3 is slightly higher than that of Ir‐5 due to the compensation of Ir‐5’s strong visible‐light‐absorbing ability. Ir‐6 exhibits excellent photocatalytic performance due to the strong visible‐light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir‐6 can achieve 91.5 μmol, over 54 times higher than Ir‐1, and the optimized TONC‐1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction.

Interfacial electron interactions governed photoactivity and selectivity evolution of carbon dioxide photoreduction with spinel cobalt oxide based hollow hetero-nanocubes

In this work, an efficient CO2 photoreduction catalyst based on Co3O4/ZnIn2S4 hollow hetero-nanocubes is precisely constructed via an in-situ transformation of cobalt-organic framework followed by a solvothermal reaction. Comprehensive in-situ spectroscopic analyses and theoretical calculations have revealed that the critical interfacial electron interactions (IEIs) effects on both photoactivity evolution and selectivity modulation in the Co3O4/ZnIn2S4 hetero-structure. As the content of ZnIn2S4 increases in the hetero-structure, the photoactivity exhibits a volcano-like evolution profile but the CH4 selectivity reduces monotonously. The improved photoactivity is attributed to the IEIs-promoted charge separation as well as the specific-surface-area effect in terms of electron unitization rate, and the electronic structure of Co3O4 is tuned and the energy barrier for the key reaction intermediate *CHO is reduced, leading to improved CH4 selection in comparison with bare Co3O4. The IEIs-mediated production selectivity is further verified by a Co3O4/CeO2 heterojunction, indicating a certain universality of the IEI effect.

Electron-enriched single-Pd-sites on g-C3N4 nanosheets achieved by in-situ anchoring twinned Pd nanoparticles for efficient CO2 photoreduction

Modulating electronic structures of single-atom metal cocatalysts is vital for highly active photoreduction of CO2, and it's especially challenging to develop a facile method to modify the dispersion of atomical photocatalytic sites. We herein report an ion-loading pyrolysis route to in-situ anchor Pd single atoms as well as twinned Pd nanoparticles on ultra-thin graphitic carbon nitride nanosheets (PdTP/PdSA-CN) for high-efficiency photoreduction of CO2. The anchored Pd twinned nanoparticles donate electrons to adjacent single Pd–N4 sites through the carbon nitride networks, and the optimized PdTP/PdSA-CN photocatalyst exhibits a CO evolution rate up to 46.5 ​μmol ​g−1 ​h−1 with nearly 100% selectivity. As revealed by spectroscopic and theoretical analyses, the superior photocatalytic activity is attributed to the lowered desorption barrier of carbonyl species at electron-enriched Pd single atoms, together with the improved efficiencies of light-harvesting and charge separation/transport. This work has demonstrated the engineering of the electron density of single active sites with twinned metal nanoparticles assisted by strong electronic interaction with the support of the atomic metal, and unveiled the underlying mechanism for expedited photocatalytic efficiency.

Efficient CO2 photoreduction using a water-soluble conjugated polyelectrolyte grafted imidazolium-functionalized side chain

Herein, we reported the delvelopment of a water-soluble conjugated polyelectrolyte (CPE) for efficient CO2 photoreduction under visible light (λ > 420 nm). Bearing a fluorene-benzothiadiazole backbone and imidazolium-functionalized side chains,...

Photosensitizing metal–organic polyhedra combined with Co catalytic sites for CO2 photoreduction

A novel photosensitizing metal–organic polyhedron combined with Co2+ catalytic sites for efficient photoreduction of CO2 to CO.

Construction of a visible light responsive dual Z-scheme NH2-MIL-101(Fe)/CdS/g-C3N4 ternary heterojunction photocatalyst for efficient CO2 photoreduction to methanol

The photocatalytic CO2 reduction reaction using various semiconductors is exceedingly difficult due to the recombination of photo-exited electron-hole (e−, h+), inefficient irradiated light utilization, and lower adsorption capacity of CO2. An efficient design of the photocatalyst system is required to address this issue. The metal–organic frameworks (MOFs), particularly NH2-MIL-101(Fe) (NML-101(Fe)), have demonstrated exceptional efficiency in CO2 adsorption, and reduction because of its large surface area, efficient charge separation capacity, and ligand-to-metal charge transfer effect (LMCT). The synergistic effect of semiconductors CdS, g-C3N4 (GCN), and metal–organic framework on efficient photocatalytic CO2 conversion to CH3OH was investigated here. The successful synthesis and design of a dual Z-scheme NML-101(Fe)/CdS/GCN (NMCG(X)) ternary hetero-nanostructured system (THS) was demonstrated, in which CdS nanoparticles and NML-101(Fe) are deposited on the surface of GCN to form a dual Z-scheme mechanism with excellent photocatalytic performance. After 8 h of visible light irradiation, NMCG8 nanocomposites containing 37.5 % GCN, 25 % CdS, and 37.5 % NML-101(Fe) exhibit 1.53 times higher methanol production (53.89 µmolg−1) than pure NML-101(Fe) (35.11 µmolg−1). The efficient reduction of CO2 was largely attributed to the systematic transportation of photo-exited e− and h+ mediated by the dual Z-scheme mechanism, as demonstrated by PL spectra, electrochemical impedance spectra (EIS) studies, and Transient photocurrent response testing.

Cobalt-tetraphenylporphyrin-based hypercrosslinked polymer for efficient CO2 photoreduction to CO

One of the main impediments during the CO2 photocatalytic reduction process is controlling a particular product’s selectivity while keeping a high conversion rate. The adsorption and affinity of the catalyst...

Constructing Cu defect band within TiO2 and supporting NiOx nanoparticles for efficient CO2 photoreduction.

Effectively harnessing solar energy for the conversion of CO2 into valuable chemical energy presents a viable solution to address energy scarcity and climate change concerns. Nonetheless, the limited light absorption and sluggish charge kinetics significantly hinder the photoreduction of CO2. In this study, we employed a facile sol-gel method combined with wetness impregnation to synthesize Cu-doped TiO2 coated with NiOx nanoparticles. Various characterizations verified the successful incorporation of Cu ions into the TiO2 crystal lattice and the formation of NiOx co-catalysts within the composites. The optimal performance attained with CTN-0.5 demonstrates an output of 11.85 μmol h-1 g-1 for CO and 9.51 μmol h-1 g-1 for CH4, which represent a 4.4-fold and 15.6-fold increase, respectively, compared to those achieved with pure TiO2. The induced Cu defect band broadens the light absorption by decreasing the conduction band edge of TiO2, while NiOx upshifts the valence band of TiO2 because of the interaction of valence orbitals. Light irradiation EPR and FTIR tests suggest that the collaboration of CuOx and NiOx promotes the formation of oxygen vacancies/defects and a rapid charge transfer pathway, thereby provides numerous active sites and electrons to enhance CO2 photoreduction performance.

Electronic structure modulation via single atom interfacial engineering for selective atmospheric CO2 photoreduction.

Single-atom iridium was interfacially engineered on CuFeS2 quantum dots (QDs) with highly efficient CO2 photoreduction performance. The electronic structure modulation yielded a remarkable CO yield rate of 32.5 μmol g-1 h-1 with 92.2% selectivity under atmospheric conditions. This work demonstrates the potential of single-atom interfacial engineering for advancing CO2 photoreduction.

Coupling doped halogen sites in copper(i)–organic frameworks with cuprous oxide for high selectivity CO2 photoreduction with H2O

Copper(i)–organic frameworks (CuX–bpy) loaded on Cu2O enable efficient CO2 photoreduction to formate, leveraging halogens (X = Cl, Br, I) and rapid electron transfer, achieving 1520 μmol g−1 in 12 hours without sacrificial agents or photosensitizers.

Step-scheme CsPbBr3/BiOBr photocatalyst with oxygen vacancies for efficient CO2 photoreduction.

Metal halide perovskites with suitable energy band structures and excellent visible-light responses have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, the efficiency of CO2 photocatalytic reduction often suffers from inefficient separation and sluggish transfer. Herein, a step-scheme (S-scheme) CsPbBr3/BiOBr photocatalyst with oxygen vacancies possessing intimate interfacial contact was fabricated by anchoring CsPbBr3 QDs on BiOBr-Ov nanosheets using a mild anti-precipitation method. The results showed that CsPbBr3/BiOBr-Ov-2 with an internal electric field (IEF) heterojunction exhibited a boosted evolution rate of 27.4 μmol g-1 h-1 (CO: 23.8 μmol g-1 h-1 and CH4: 3.6 μmol g-1 h-1) with an electron consumption rate (Relectron) of 76.4 μmol g-1 h-1, which was 5.9 and 3.2 times that of single CsPbBr3 and BiOBr-Ov, respectively. Density functional theory (DFT) calculations revealed that BiOBr with oxygen vacancies can effectively enhance the adsorption and activation of CO2 molecules. More importantly, in situ infrared Fourier transform spectroscopy (DRIFTS) spectra show the transformation process of the surface species, while the femtosecond transient absorption spectrum (fs-TA) reveals the charge transfer kinetics of the CsPbBr3/BiOBr-Ov. Overall, this work provides some guidance for the rational design of S-scheme heterojunctions and vacancy-engineered photocatalysts, which are expected to have potential applications in the fields of photocatalysis and solar energy conversion.

Intrinsic bimetallic cations regulating band centers and reactive sites for boosting CO2 photoreduction

Intrinsic bimetallic cation regulation strategy achieves precise modulation of the band center and catalytic sites of CdBiO2Br. The optimal Cd0.46Bi1.36O2Br shows strong electron reducibility and interfacial charge mobility for efficient CO2 photoreduction.

Efficient photoreduction of carbon dioxide to acetaldehyde on monatomic defective black phosphorus

Conversion of CO2 into C2 products has been challenging, largely due to the insufficient electron deliverability of catalyst. Here we proposed latent monatomic defective black phosphorus (BPV), on which the efficient photoreduction of CO2 to CH3CHO was confirmed by density functional theory (DFT) calculations. The electrostatic potential difference between the upper and lower atoms of the BPV was found responsible for the enhanced separation of electrons and holes. The COCO coupling was studied, the charge transfer from BPV to CO (0.38 |e|) was found contributes to the enhanced CO2 reduction reaction (CO2RR) activity and promoted COCO coupling process. This work provides theoretical guidelines on the design of defect catalyst for CO2 photoreduction.