Photochemical Reduction Of CO2 Research Articles

Comment on “Photochemical reduction of carbon dioxide coupled with water oxidation using various soft-oxometalate (SOM) based catalytic systems” (J. Mater. Chem. A, 2016, 4, 8875–8887)

In this Comment, I propose several points of serious scientific and ethical issues in the article from Roy et al. [J. Mater. Chem. A, 2016, 4, 8875–8887].

Reply to the ‘Comment on “Photochemical reduction of carbon dioxide coupled with water oxidation using various soft-oxometalate (SOM) based catalytic systems”’ by T. Liu, J. Mater. Chem. A, 2019, 7, DOI: 10.1039/c9ta03809d

We reply to Professor Liu’s Comment on our paper (J. Mater. Chem. A, 2016, 4, 8875–8887).

Heterogeneous photocatalytic performances of CO2 reduction based on the [Emim]BF4 + TEOA + H2O system.

The photochemical reduction of CO2 was studied in a 1-ethyl-3-methylimidazolium tetrafluoroborate, triethanolamine and water ([Emim]BF4 + TEOA + H2O) system under visible light irradiation. The integration of CdS and the Co–bpy complex, which acted as a photocatalyst and cocatalyst, respectively, was employed as an efficient catalytic system for the CO2-to-CO conversion. The utilization of [Emim]BF4 and water took advantage of their green properties. The amount of CO production showed that the test medium containing 10 vol% H2O was favourable for the catalytic performance of the CO2 reduction. In order to further study the factors that influenced the current system, the physical and spectroscopy properties were characterized by altering the composition ratio of the ingredients. Relevant parameters, including the viscosity, conductivity, solubility and coordination, were adjusted using the ratio of the H2O/[Emim]BF4 addition, resulting in a different catalytic performance. All of these attempts led to an optimal reaction condition for the CO2 reduction process.

Visible-Light-Driven Conversion of CO2 to CH4 with an Organic Sensitizer and an Iron Porphyrin Catalyst.

Using a phenoxazine-based organic photosensitizer and an iron porphyrin molecular catalyst, we demonstrated photochemical reduction of CO2 to CO and CH4 with turnover numbers (TONs) of 149 and 29, respectively, under visible-light irradiation (λ > 435 nm) with a tertiary amine as sacrificial electron donor. This work is the first example of a molecular system using an earth-abundant metal catalyst and an organic dye to effect complete 8e-/8H+ reduction of CO2 to CH4, as opposed to typical 2e-/2H+ products of CO or formic acid. The catalytic system continuously produced methane even after prolonged irradiation up to 4 days. Using CO as the feedstock, the same reactive system was able to produce CH4 with 85% selectivity, 80 TON and a quantum yield of 0.47%. The redox properties of the organic photosensitizer and acidity of the proton source were shown to play a key role in driving the 8e-/8H+ processes.

Selective Photocatalytic Carbon Dioxide Reduction by a Reduced Molybdenum‐Based Polyoxometalate Catalyst

AbstractCurrently, photochemical carbon dioxide reduction is a most sought‐after process as it involves the simultaneous removal of greenhouse CO2 gas and the production of useful products. In this study, we report the selective formation of formaldehyde in photochemical carbon dioxide reduction using a reduced polyoxometalate (POM) based catalyst. By simply tuning the redox state of the metal centre in the POM, we can obtain the more reduced product formaldehyde from carbon dioxide. As a result of the high MoV/MoVI ratio in the cluster, formaldehyde is obtained as the major product as opposed to formic acid. Since the catalyst POM 1 itself readily absorbs light, no external photosensitizer is used. In the reduction process of carbon dioxide, water acts as the electron donor and is oxidized to oxygen rendering the whole process viable and green. (1=Mo16=[{(CH3)NH2}4{(MoV2O4)6(μ2‐OH)10(μ2‐O)2(μ3‐OH)2(μ3‐O)2(MoVIO3H)4}]0.94[{(MoV2O4)6(μ2‐OH)10(μ2‐O)2(MoVIO3H)4}{MoVI(μ3‐O)4}]0.06).

Selective CO2 Reduction Catalyzed by Single Cobalt Sites on Carbon Nitride under Visible-Light Irradiation

Framework nitrogen atoms of carbon nitride (C3N4) can coordinate with and activate metal sites for catalysis. In this study, C3N4 was employed to harvest visible light and activate Co2+ sites, without the use of additional ligands, in photochemical CO2 reduction. Photocatalysts containing single Co2+ sites on C3N4 were prepared by a simple deposition method and demonstrated excellent activity and product selectivity toward CO formation. A turnover number of more than 200 was obtained for CO production using the synthesized photocatalyst under visible-light irradiation. Inactive cobalt oxides formed at relatively high cobalt loadings but did not alter product selectivity. Further studies with X-ray absorption spectroscopy confirmed the presence of single Co2+ sites on C3N4 and their important role in achieving selective CO2 reduction.

Perovskite-type CsPbBr3 quantum dots/UiO-66(NH2) nanojunction as efficient visible-light-driven photocatalyst for CO2 reduction

Base-on the excellent optoelectronic properties, perovskite CsPbBr3 quantum dots (QDs) have been used on perovskite solar cells and LED devices, but little research has been focused on photochemical CO2 reduction due to their poor moisture stability. Coincidentally, metal-organic frameworks (MOFs) materials have received tremendous attention for sustainable clean energy and environmental remediation. However, the design of excellent performed MOFs is still indispensable. Therefore, the CsPbBr3 QDs/UiO-66(NH2) nanocomposites that combine the advantages of CsPbBr3 QDs and UiO-66(NH2) have been successfully designed and fabricated for the first time. Then we employ the nanocomposites as photocatalysts to convert CO2 to chemical fuels in nonaqueous media. The resultant nanocomposites exhibit significantly improved photocatalytic activity for CO2 reduction. When CsPbBr3 QDs content is 15 wt%, the amount of CO can reach 98.57 μmol·g−1. The remarkable photocatalytic performance could be ascribed to the improved electron extraction and transfer between UiO-66(NH2) and CsPbBr3 QDs, large accessible specific surface area and enhanced visible light absorption capacity. Moreover, the nanojunction shows excellent reusability for photocatalytic CO2 reduction. This work might supply new pathway to utilize halide perovskite QDs/MOF nanocomposite in energy conversion and environmental remediation.

Step-by-Step Growth of HKUST-1 on Functionalized TiO2 Surface: An Efficient Material for CO2 Capture and Solar Photoreduction

The present study reports on a simple preparation strategy of a hybrid catalyst, TiO2/HKUST-1, containing TiO2 anatase nanoparticles (NPs) with tailored morphology and photocatalytic activity coupled with a porous metal-organic framework (MOF), namely HKUST-1, as an advanced material for the CO2 photocatalytic reduction. In detail, TiO2/HKUST-1 catalyst was prepared via an easy slow-diffusion method combined with a step-by-step self-assembly at room temperature. The growth of crystalline HKUST-1 onto titania surface was achieved by functionalizing TiO2 nanocrystals, with phosphoesanoic acid (PHA), namely TiO2-PHA, which provides an intimate contact between MOF and TiO2. The presence of a crystalline and porous shell of HKUST-1 on the TiO2 surfaces was assessed by a combination of analytical and spectroscopic techniques. TiO2/HKUST-1 nanocomposite showed a significant efficiency in reducing CO2 to CH4 under solar light irradiation, much higher than those of the single components. The role of MOF to improve the photoreduction process under visible light was evidenced and attributed either to the relevant amount of CO2 captured into the HKUST-1 porous architecture or to the hybrid structure of the material, which affords enhanced visible light absorption and allows an effective electron injection from TiO2-PHA to HKUST-1, responsible for the photochemical reduction of CO2.

Highly Efficient and Selective Visible‐Light Driven CO2‐to‐CO Conversion by a Co(II) Homogeneous Catalyst in H2O/CH3CN Solution

AbstractThe photochemical reduction of CO2 to chemical resources has displayed the promise to solve energy and environmental problems. To facilitate this reaction, a considerable challenge is to design not only highly efficient and selective, but also economic catalysts. In this study, we report a homogeneous catalyst, [CoL1(CH3CN)](ClO4)2 (1, L1=Tris[2‐(iso‐propylamino)ethyl]amine) which displays high activity and selectivity for CO2 reduction to CO driven by visible light in a water‐containing system, with turnover numbers (TONCO) and turnover frequencies (TOF), and CO selectivity values of 44800, 1.24 s−1 and 97 %, respectively. The excellent performances of 1 for the photocatalytic CO2‐to‐CO conversion is confirmed by control experiments and its catalytic mechanism is corroborated by DFT calculations.

Efficient Approaches on Photochemical CO2 Reduction to Alcohol by Solar Light with Functional Multi-layered Membrane Catalysts

ABSTRACTSimple and efficient approach for artificial photosynthesis of CO2 reduction into ethanol with flexible functional multi-layered membrane catalysts is suggested. The g-C3N4 and BiVO4 particle were synthesized by self-condensation and hydrothermal method. g-C3N4 membrane catalyst and g-C3N4/BiVO4 layered membrane catalyst were fabricated by casting and shaping of Nafion polymer mixture. XRD, FT-IR and XPS analyses proved that the intrinsic properties of g-C3N4 and BiVO4 were maintained after fabricating flexible functional multi-layered membrane catalyst. The interfacial contact between g-C3N4 and BiVO4 particles in flexible membrane catalyst for efficient transport of photogenerated electron was revealed by TEM and photoelectrochemical analysis. Finally, photochemical CO2 reduction reaction was performed with flexible functional multi-layered membrane catalysts. The g-C3N4 membrane catalysts produced 147 μM of ethanol during 12 hrs of CO2 reduction reaction while the g-C3N4/BiVO4 layered membrane catalysts produced 256 μM of ethanol during 12 hrs of CO2 reduction reaction. This is due to the higher solar light harvesting and efficient hole-charge separation from functional multi-layered BiVO4 membrane catalyst leading to the higher electron transport rate to g-C3N4 membrane catalysts, promoting the CO2 reduction reaction on the surface of g-C3N4 membrane catalyst.

Cover Feature: A Copper(II) Molecular Catalyst for Efficient and Selective Photochemical Reduction of CO2 to CO in a Water‐Containing System (Chem. Eur. J. 18/2018)

Cover Feature: A Copper(II) Molecular Catalyst for Efficient and Selective Photochemical Reduction of CO₂ to CO in a Water‐Containing System (Chem. Eur. J. 18/2018)

A Copper(II) Molecular Catalyst for Efficient and Selective Photochemical Reduction of CO2 to CO in a Water-Containing System.

A catalyst developed from a CuII complex of (Et4 N)[Cu(pyN2Me2 )(HCO2 )]⋅0.5 CH3 OH⋅H2 O (1⋅0.5 CH3 OH⋅H2 O; pyN2Me2 =bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) shows a high activity to catalyze the reduction reaction of CO2 to CO driven by visible light in 4:1 acetonitrile/water (v:v) using [Ru(phen)3 ](PF6 )2 as photosensitizer and TEOA as sacrificial reductant, with a high TON of 9900 and a high CO selectivity of 98 %. The results of isotope labeling experiment, durability tests and energy dispersive spectroscopy reveal that 1 is robust during the photocatalytic process.

Unique Features of the Photocatalytic Reduction of H2O and CO2 by New Catalysts Based on the Analogues of CdS, Cd4P2X3 (X = Cl, Br, I).

Photochemical reduction of H2O and CO2 has been investigated with a new family of catalysts of the formula Cd4P2X3 (X= Cl, Br, I), obtained by the complete aliovalent substitution of the sulfide ions in CdS by P and X (Cl, Br, I). Unlike CdS, the Cd4P2X3 compounds exhibit hydrogen evolution and CO2 reduction from water even in the absence of a sacrificial agent or a cocatalyst. Use of NixPy as the cocatalyst, enhances hydrogen evolution, reaching 3870 (apparent quantum yield (AQY) = 4.11) and 9258 (AQY = 9.83) μmol h-1 g-1, respectively, under artificial and natural (sunlight) irradiation, in the case of Cd4P2Br3/NixPy. Electrochemical and spectroscopic studies have been employed to understand the photocatalytic activity of this family of compounds. Unlike most of the semiconductor-based photocatalysts, Cd4P2X3 catalysts reduce CO2 to CO and CH4 in the absence of sacrificial-agent or cocatalyst using water as the electron source. CO, CH4, and H2 have been obtained with these catalysts under artificial as well as sun-light irradiation. First-principles, calculations have been carried out to understand the electronic structure and catalytic features of these new catalysts.

Capturing the Light Fantastic

Artificial photosynthesis began as a serious research topic in the late 1970s as the oil crisis reached a critical stage. Early work focussed on the identification of photochemical systems for the evolution of either hydrogen gas or oxygen gas and usually involved precious metal catalysts and respective sacrificial electron donors or acceptors. The photochemical reduction of CO2 was soon recognised as being a highly prized goal but the experimental conditions needed for an effective system were unsuited for practical exploitation. Parallel to this rather applied research ran a theme to design and synthesize highly imaginative bio-inspired mimics that resembled the structures and functions of natural photosynthesis. This work led to massive advances in our understanding of electronic energy transfer and light-induced electron transfer between weakly coupled donor–acceptor pairs. As the price of oil stabilised and then fell, research in artificial photosynthesis took on a more fundamental nature and the synthesis of evermore complicated molecular architectures replaced the optimisation of solar fuel production. Photovoltaic cells, not normally associated with artificial photosynthesis, took centre stage in terms of realistic approaches for the harvesting of sunlight. Over the intervening years, there has been a progressive growth and diversification of photovoltaic devices. We have also witnessed the rapid rise of public concerns about climate change and global warming due to greenhouse gases. There has been a growing recognition that solar electricity production is insufficient for our needs and that there must be an avenue for the sustainable production of chemical feedstocks and fuels from readily available materials driven entirely from renewable energy sources. It is hard to imagine any sustainable photochemical cycle that does not include water as the electron and proton source, such as hydrogen evolution, or reduction of CO2 as well as N2 fixation. Options exist, however, for the complementary reductive process as long as the product can be collected, stored or utilised on-site. To be competitive with existing protocols, solar fuels production has to be transformed from the test tube to an industrial plant and from the microliter to the cubic meter scale. These are critical problems that demand urgent solutions. This special issue of ChemPhotoChem represents an opportunity to establish the current state-of-the-art in the field of Artificial Photosynthesis and to identify both barriers and promising routes for future development. Contributions address each of the key subjects, including both heterogeneous (i.e., semiconductor-based) and homogeneous (i.e., photosensitizer-based) systems. The photochemical reduction of CO2 receives well-deserved attention as an alternative to hydrogen production but we still lack ideas on how to reduce nitrogen under ambient conditions. Hybrid photosystems and the application of dedicated light-harvesting machinery are advancing quickly and could offer important benefits in terms of stability and versatility. Energy storage in the form of chemical transformations, often overlooked in the quest to design innovative strategies for solar energy conversion, makes a timely entry. Water oxidation, possibly the most important single step in the overall energy transduction cycle, gets a fresh look. These contributions are a valuable resource and offer a potential stepping stone to a future fuelled by energy from the sun. Anthony Harriman started research into bioinspired artificial photosynthesis in the late 1970s, working with Lord George Porter at the Royal Institution in London. Research centred on using metalloporphyrins to sensitise water reduction or oxidation and on the development of effective catalysts for oxygen evolution. Subsequent studies were aimed at seeking correlations between rates of light-induced electron or energy transfer and molecular topology. On-going work looks at ways to construct artificial light-harvesting arrays as universal solar concentrators. Dr. Haruo Inoue is a specially appointed full professor of Applied Chemistry at Tokyo Metropolitan University and serves also as a Director of the Center for Artificial Photosynthesis. He has been serving as the Research Supervisor of Precursory Research for Embryonic Science and Technology Project (PRSETO/JST) on “Chemical Conversion of Light Energy” and has been leading the All-Nippon Artificial Photosynthesis Project for Living Earth (AnApple: MEXT/Japan). Prof. Licheng Sun received his Ph.D. in 1990 from Dalian University of Technology (DUT), and went to Germany as a postdoc at Max-Planck-Institut für Strahlenchemie with Dr. Helmut Görner (1992–1993), and then as an Alexander von Humboldt postdoc at Freie Universität Berlin (1993–1995) with Prof. Dr. Harry Kurreck. He moved to KTH Royal Institute of Technology, Stockholm in 1995 as a postdoc with Prof. Björn Åkermark, became assistant professor in 1997, associate professor in 1999 at Stockholm University and full professor in 2004 at KTH. He is presently also a distinguished professor at DUT. His research interests cover artificial photosynthesis, including dye sensitized solar cells, perovskite solar cells, bio-inspired catalysts for water oxidation and hydrogen generation, nanomaterials and photoelectrochemical cells for water splitting and CO2 reduction.

Ir(tpy)(bpy)Cl] as a Photocatalyst for CO2 Reduction under Visible‐Light Irradiation

AbstractMononuclear iridium(III) terpyridine (tpy) 2,2′‐bipyridine (bpy) [Ir(tpy)(bpy)Cl]2+ photocatalysts (denoted [Ir(bpy)]) were developed for selective CO2 reduction to HCOOH under visible light. The CO2 reduction product could be changed dramatically by substituting a 2‐phenylpyridine (ppy) ligand with bpy, with the mononuclear Ir ppy complex ([Ir(tpy)(ppy)Cl]+) acting as a photocatalyst for selective CO2 reduction to CO. A mechanistic study showed a structural change in [Ir(bpy)] during the photocatalytic reaction. The [Ir(bpy)] complex was transformed into an iridium–hydride complex ([Ir(tpy)(bpy)H]2+) during an early stage of the photocatalytic reaction. However, [Ir(tpy)(bpy)H]2+ did not function as a key intermediate in the photochemical CO2 reduction because an additional structural change occurred. The tpy ligand of the Ir complex was reduced to piperidine‐2,6‐di‐2‐pyridine ligand during the photocatalytic reaction, resulting in the production of [Ir(piperidine‐2,6‐di‐2‐pyridine)(bpy)H]2+, which was the actual photocatalyst for HCOOH production.

Softoxometalate [{K6.5Cu(OH)8.5(H2O)7.5}0.5@{K3PW12O40}]n (n = 1348-2024) as an Efficient Inorganic Material for CO2 Reduction with Concomitant Water Oxidation.

An immediate challenge for chemists is to devise different methods to trap chemical energy using light by reduction of carbon dioxide to a transportable fuel. To reach this goal the major obstacle lies in finding a suitable material that is abundant and possesses catalytic power to effect such reduction reaction and perform this reduction reaction without using any external photosensitizer. Here we report for the first time a softoxometalate based on a {[K6.5Cu(OH)8.5(H2O)7.5]0.5[K3PW12O40]} metal oxide framework which is stable in reaction conditions that effectively performs photochemical CO2 reduction reaction in water with a very high turnover number of 613 and TOF of 47.15 h-1. We observe that during this reaction water gets oxidized to oxygen, while the electrons released directly go to CO2 reducing it to formic acid. A detailed account of the characterization of the catalyst along with that of products of this reaction is reported.

Design and Synthesis of Tunable Ligands with 4,4′-Bipyridyl as an Electron-Accepting Unit and Their Rhenium Complexes

We have designed and prepared a series of rhenium complexes with 4,4′-bipyridyl as an electron-accepting unit. Electrochemical studies revealed that oxidation and reduction of these complexes occurred on the rhenium center and the 4,4′-bipyridyl skeleton, respectively. The redox potentials of the rhenium complexes are controllable by tuning the substituents on the 4,4′-bipyridyl skeleton and the coordinating groups to the rhenium center. We have also examined the reactivity of the rhenium complexes in electrochemical and photochemical CO2 reduction.

Photocatalytic reduction of CO2 to CO by diamond nanoparticles

Recent studies have shown that optically excited diamond can act as a solid-state source of solvated electrons in aqueous media, leading to novel reduction reactions such as the one-electron activation pathway (CO2+e−→−CO2−, E°=−1.9V vs SHE) for reduction of CO2 to CO. However, an understanding of the valence band reactions is also essential, especially since CO can also be produced in the absence of CO2 by oxidation of diamond via C+H2O→CO+2H++2e− (E°=0.52V). Here, we demonstrate that H-terminated diamond nanoparticles with a median diameter of 125nm can initiate selective photochemical reduction of CO2 to CO, and that argon-purged control samples show no production of CO production in the absence of intentional CO2 reactant as long as a sacrificial electron donor (here, Na2SO3) is present. However, in the absence of an electron donor clear signs of diamond oxidation and aggregation are observed. In contrast, experiments with detonation nanodiamond show rapid changes upon illumination consistent with oxidation of the samples. Our results indicate that crystallinity and absence of high-energy defect sites is important to stability of nanodiamond-based photocatalysts.

Recent Progress in the Photocatalytic Reduction of Carbon Dioxide.

Elimination or reduction of CO2 in the atmosphere is a serious problem faced by humankind, and it has become imperative for chemists to find ways of transforming undesirable CO2 to useful chemicals. One of the best means is the use of solar energy for the photochemical reduction of CO2. In spite of considerable efforts, discovery of stable photocatalysts which work in the absence of scavengers has remained a challenge although encouraging results have been obtained in the photocatalytic reduction of CO2 in both gas and liquid phases. Semiconductor-based catalysts, multicomponent semiconductors, metal–organic frameworks (MOFs), and dyes as well as composites involving novel composite materials containing C3N4 and MoS2 have been employed for the photoreduction process. Semiconductor heterostructures, especially those containing bimetallic alloys as well as chemical modification of oxides and other materials with aliovalent anion substitution (N3– and F– in place of O2–), remain worthwhile efforts. In this article, we provide a brief perspective of the present status of photocatalytic reduction of CO2 in both liquid and gas phases.

Photocatalytic CO2 Reduction by Periodic Mesoporous Organosilica (PMO) Containing Two Different Ruthenium Complexes as Photosensitizing and Catalytic Sites

A periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) has great potential for designing novel catalysts by modifying metal complexes. A photosensitizing site (Ru(PS)) was introduced by treating cis-[Ru(bpy)2 (dimethylsulfoxide)Cl]Cl with BPy-PMO. Then a catalytic site (Ru(Cat)) was brought in Ru(PS)x -BPy-PMO by reaction with a ruthenium polymer [Ru(CO)2 Cl2 ]n . The stepwise modification of BPy-PMO successfully affords a novel photocatalyst Ru(PS)x -Ru(Cat)y -BPy-PMO. The molar fractions (x, y) of Ru(PS) and Ru(Cat) were determined by energy dispersive X-ray (EDX) measurement and quantification of the amount of CO emitted in the photo-decarbonylation of Ru(Cat), respectively. Photochemical CO2 reduction (λex >430 nm) by Ru(PS)x -Ru(Cat)y -BPy-PMO in a CO2 -saturated N,N-dimethylacetamide/water solution containing 1-benzyl-1,4-dihydronicotinamide catalytically produced CO and formate. The total turnover frequency of CO and formate reached more than 162 h-1 on x=0.11 and y=0.0055. The product selectivity (CO/formate) became large when the ratio of Ru(PS)-to-Ru(Cat) (x/y) was increased. The photocatalysts can be recycled at least three times without losing their catalytic activity, demonstrating that the Ru(PS) and Ru(Cat) units were strongly immobilized on the BPy-PMO framework.