An Anthracene-Based Metal-Organic Framework for Selective Photo-Reduction of Carbon Dioxide to Formic Acid Coupled with Water Oxidation.

Currently, 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).

THE non-biological reduction of carbon dioxide to organic compounds is of interest, as an alternative to natural photosynthesis, for the production of organic raw materials or fuel. In one approach, the required energy was supplied by irradiation with UV light, in the presence of ferrous salts, and resulted in the production of formic acid and of formaldehyde1. In another approach, the energy was supplied from an external power source by electrochemical reduction of aqueous carbon dioxide. The reduction of carbon dioxide and production of formic acid during the electrolysis of sodium bicarbonate in aqueous solutions has also been reported2, and a study of the reduction of carbon dioxide on a mercury cathode reviews earlier work3. Polarographic measurements on mercury electrodes showed that carbon dioxide, rather than the bicarbonate ion, is the electroactive species, with a half-wave reduction potential of −2.1 V (relative to SCE), and that formic acid is the only product4. We report here the photoassisted electrolytic reduction of aqueous carbon dioxide, achieved using p-type gallium phosphide as a photocathode, with part or all of the energy being supplied by light. The products were formic acid, formaldehyde and methanol.

ConspectusUtilizing light to enable chemical conversions presents a green and sustainable approach to produce fuels and chemicals, and photocatalysis is one of the key chemical technologies that needs to be well developed in this century. Despite continuous progress in the advancement of various photocatalysts based on small inorganic and organic compounds, polymers, and networks, designing and constructing photocatalysts that combine activity, selectivity, and reusability remains a challenging goal. For catalytic activity, the difficulty originates from the complexity of photochemical reactions, where the light-harvesting system, multielectron and multihole-involving processes, and pinpoint mass delivery simultaneously need to be established in the system. For selectivity, the difficulty stems from the elaborate design of catalytic sites and space, especially their orbital energy levels, spatial arrangement, and environment; developing a molecular strategy that enables an overall design and control of these factors of different aspects is necessary yet arduous. For reusability, the difficulty arises from the stability and recyclability of the photocatalysts upon continuous operation under photoredox reaction conditions. How to recover photocatalysts in an energy-saving way to enable their cyclic use while retaining activity and selectivity is at the core of this problem. These bottleneck issues reflect that molecular design of a photocatalyst is not a simple summation of the above requirements, but a systematic scheme that can organically interlock various aspects is needed.To enable such an elaborate design and precise control, a basic requirement of the scaffold for constructing a promising photocatalyst is that its primary and high-order structures should be molecularly predesignable and synthetically controllable. Such a molecular regime has successfully evolved in natural photosynthesis, where light-harvesting chlorophyll antennae and photocatalytic centers are spatially well-organized and energetically well-defined to build ways for exciton migration, photoinduced electron transfer and charge separation, electron and hole flows, and oxidation of water and reduction of carbon dioxide, thereby converting water into oxygen to release ATP and NADPH via the light reaction and carbon dioxide into glucose with ATP and NADPH through the dark reaction. Similarly, a predesignable polymeric scaffold would be promising for integrating these complex photochemical processes to construct photocatalysts.Covalent organic frameworks (COFs) are a class of extended yet polymeric materials that enable the organization of organic units or metallo-organic moieties into well-defined architectures. In principle, COFs are molecularly designable with topology diagrams and synthetically controllable through polymerization reactions, offering an irreplaceable platform for designing and synthesizing photocatalysts. This feature enticed researchers to develop various photocatalysts based on COFs and drove the rapid progress in this field over the past decade. In this Account, we summarize the recent advances in the molecular design and synthetic control of COF photocatalysts, by highlighting the key achievements in developing ways to enable light harvesting, trigger photoinduced electron transfer and charge separation, allow charge carrier transport and mass delivery, control energy level, catalytic space, and environmental engineering, and develop stability and recyclability with an aim to reveal a full picture of this field. By scrutinizing typical photocatalytic reactions, we show the key problems to be addressed for COFs and predict future directions.

Inspired by natural enzymes, this study presents a nickel-based molecular catalyst, [Ni‖(N2S2)]Cl2 (NiN2S2, N2S2=2,11-dithia[3,3](2,6)pyridinophane), for the photochemical catalytic reduction of CO2 under visible light. The catalyst was synthesized and characterized using various techniques, including liquid chromatography-high resolution mass spectrometry (LC-HRMS), UV-Visible spectroscopy, and X-ray crystallography. The crystallographic analysis revealed a slightly distorted octahedral coordination geometry with a mononuclear Ni2+ cation, two nitrogen atoms and two sulfur atoms. Photocatalytic CO2 reduction experiments were performed in homogeneous conditions using the catalyst in combination with [Ru(bpy)3]Cl2 (bpy=2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a sacrificial electron donor. The catalyst achieved a high selectivity of 89 % towards CO and a remarkable turnover number (TON) of 7991 during 8 h of visible light irradiation under CO2 in the presence of phenol as a co-substrate. The turnover frequency (TOF) in the initial 6 h was 1079 h-1, with an apparent quantum yield (AQY) of 1.08 %. Controlled experiments confirmed the dependency on the catalyst, light, and sacrificial electron donor for the CO2 reduction process. These findings demonstrate this bioinspired nickel molecular catalyst could be effective for fast and efficient photochemical catalytic reduction of CO2 to CO.

The photocatalytic reduction of CO2 using copper-loaded silicate rocks has been reported. The Cu-silicate rock powders suspended in the solution were illuminated with sunlight. Amphibolite, gneiss, granite, granodiorite, phyllite, quartzdiorite, and shale, which are quite ordinary rocks, were tested as substrates (silicate rock) of the catalyst. These catalysts were specific for the formation of formic acid. The effects of amounts of copper, illumination time, and temperature were investigated on photoreduction of CO2. The 30% Cu-loaded quartzdiorite (0.3 g/g) in these Cu rocks was the best catalyst. The formation of formic acid on the Cu-silicate rock increased with time up to 10 h after which the formation decreased, and then became constant. The formic acid formation decreased with temperature for 10 h sunlight illumination. For the photochemical reduction of CO2, a relatively low temperature was suitable. With photochemical reduction, the maximum yield of formic acid was 54 nmol/g under optimum experimental conditions. The carbon dioxide reduction system developed might well become of practical interest for the photochemical production of raw materials for the photochemical industry.Key words: photocatalytic reduction of carbon dioxide, formic acid, copper-loaded silicate rocks, temperature effect, illumination time.

Catalyst: Chemistry’s Role in Providing Clean and Affordable Energy for All

Photochemical reduction of CO₂ (to produce formic acid) can be seen both as a method to produce a transportable hydrogen-based fuel and also to reduce levels of CO₂ in the atmosphere. However, an often overlooked necessity for photochemical CO₂ reduction is the need for a sacrificial electron donor, usually a tertiary amine. Here, we describe a new strategy for coupling the photochemical reduction of CO₂ to photochemical water splitting, and illustrate this with a prototype example. Instead of seeking to eliminate the use of an external reducing agent altogether, our alternative strategy makes the reducing agent recyclable. This has two potential advantages over the direct coupling of CO₂ reduction and water oxidation. First, it allows the two redox reactions to be carried out with existing chemistry, and second, it permits these reactions to be conducted under mutually incompatible conditions.

An in-situ spectroscopic study on the photochemical CO2 reduction on CsPbBr3 perovskite catalysts embedded in a porous copper scaffold

Metal-organic frameworks are an excellent platform for photochemical CO2 reduction into valuable chemicals. Herein, we report the synthesis and photocatalytic behavior of Ru@MOF-808, a Zr-based MOF, modified with a Ru-polypyridyl complex. The postsynthetic modification was achieved using solvent-assisted incorporation of bipyridine-carboxylate ligands onto the nodes of the MOF-808, followed by the coordination of Ru(II)-terpyridine moiety. A thorough characterization including 1H NMR, diffuse reflectance UV/vis, X-ray absorption spectroscopy and gas adsorption studies, combined with DFT calculations, provides strong support for efficient incorporation of the molecular Ru-complex at the loading of one Ru center per node. In the presence of a strong sacrificial reductant BIH, Ru@MOF-808 was found to catalyze the photochemical reduction of CO2 into a mixture of CO and formate ion. When compared to the homogeneous model catalyst Ru(tpy)(bpy)2+, Ru@MOF-808 was found to exhibit higher formate yields. To explain these formate enhancements, we propose a mechanism that involves CO2 capture at the MOF nodes to form Zr-bicarbonate species, which further react in a hydride transfer reaction with photogenerated Ru-H donor, thereby outperforming molecular catalysts in HCOO- production. Overall, the results presented in this work indicate the potential of Zr-based MOFs in integrating CO2 capture with its photochemical conversion to desired products.

Photochemical reduction of carbon dioxide by trichlorobis(2,2′:6′,2″-terpyridyl)vanadium(III) and methyl viologen

Photosynthesis as represented by the reaction stoichiometry $$ \begin{array}{*{20}{c}} {visible{\text{ }}light} \\ {\begin{array}{*{20}{c}} {C{{O}_{2}} + {{H}_{2}}O} & { - - - - - - - - > } & {(1/n){{{(C{{H}_{2}}O)}}_{n}}} \\ \end{array} + {{O}_{2}}} \\ {CHl{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{a}}} \\ \end{array} $$ is of great importance in carbon dioxide chemistry. In green plants the oxygen evolution from water oxidation and carbon dioxide reduction evidently involve the participation of two Ch1 a photosystems respectively known as PSII and PSI. In nonbiological applications the observed effects of reaction 1 are attributed to a single Ch1 a light reaction. An important problem in photosynthesis research is a description of the intrinsic properties of Ch1 a in the photocatalysis of reaction 1. The goal is to find the optimized parameters for the reduction of carbon dioxide by water outside of the living plant.1 This chapter deals with the current progress in the use of Ch1 a model systems towards the attainment of that goal.

Photoinduced reduction of formate to methanol has been achieved using microcrystalline colloid which contained formate, methanol dehydrogenase (MDH), pyrroloquinoline quinone (PQQ) as an electron mediator for MDH, and 2‐propanol. This reaction was combined with photoreduction of carbon dioxide to formate on the microcrystallite which had already been reported to provide a new photosynthetic route for production of methanol from carbon dioxide. The production of methanol showed a saturation tendency when it was accumulated to 0.25 mmol dm−3, probably due to oxidation of the produced methanol at MDH or on the photocatalyst or both. The concentration of PQQ influenced the amount of formate production but not the methanol production. The quantum efficiency obtained at 280 nm for the reduction of carbon dioxide to methanol was 5.9%, which is the highest value that has ever been reported for the photochemical reduction of carbon dioxide to methanol.

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.

Hi Reddit! I am a Professor of Chemistry at Virginia Tech. I was hired as an Energy chemist and my research focuses of solar energy harvesting and storage. At Virginia Tech, I am affiliated with the Center for Energy Harvesting Materials (link), the Sustainable Energy Thrust of the Institute for Critical Technology and Applied Science (link), and the Macromolecules and Interfaces Institute (link). With the American Chemical Society, I serve as an ACS Expert in the field of sustainable energy. In one and a half hours enough solar energy hits the earth surface to power human civilization for an entire year. Remaining challenges that limit the wide-spread use of solar energy are the development of economical solar harvesting materials and advances in energy storage. Along those lines, my research group focuses on two next generation solar cell architectures – quantum dot sensitized solar cells and hybrid bulk heterojunction solar cells. Both of these architectures use inexpensive, nanocrystalline titanium dioxide as the bulk of the solar cell. Therefore, these cells can theoretically be made for a fraction of the cost of a silicon solar cell. Even if the cost of the solar module is reduced, there is still the issue of the intermittent nature of the sun. So in addition to research on photovoltaics, my research group explores methods to store solar energy in chemical bonds. Nature’s photosynthetic system — a complex assembly of light harvesting arrays, electron transfer relays, and catalytic centers — achieves just that using energy from the sun to convert water and carbon dioxide into sugars (our stored fuel!). In our lab, we try to mimic the photosynthetic system with metal organic framework arrays. Metal organic frameworks are porous networks of inorganic clusters and organic ligands. The function of the framework (light harvesting, catalytic, etc) can be tuned by the type of clusters and organic molecules incorporated. We are interested in the guiding principles behind efficient light harvesting, energy transfer, electron transport, and catalysis in these arrays. Check out our recent publications in the areas discussed above: http://pubs.acs.org/doi/abs/10.1021/ja410684q http://pubs.acs.org/doi/abs/10.1021/jacs.5b03071 http://pubs.acs.org/doi/abs/10.1021/am500101u So feel free to ask me anything about next generation solar cells including dye-sensitized solar cells, quantum dot sensitized solar cells, bulk heterojunction solar cells, and hybrid bulk heterojunctions solar cells, artificial photosynthesis, water oxidation, carbon dioxide reduction, metal organic frameworks, and chemistry. I would welcome discuss around the economic outlook for solar energy. Additionally, I would be happy to answer steps we all can take to reduce our carbon footprint and the role solar energy can play in our own households. Lastly, I am open to discussions around academic career paths and diversity in science. I will return at 11 am ET to answer your questions. [EDIT] I am here with members of my team (Dr. William Maza, Spencer Ahrenholtz (PhD Candidate), Andrew Haring (PhD Candidate). We are ready to answer your questions! AMA! [EDIT] Signing off now (12:15 PM ET). I will try to return to continue the discussions that have started. Thank you for participating! [EDIT] Back on (3:30 PM ET) to try to answer some more questions! Glad to see the discussions kept going! [EDIT] Signing off again (5:18 PM ET). I hope to come back again to answer the remaining questions! [EDIT] I will keep returning to answer any more questions that pop up! Thank you for a stimulating discussion! Signing off (11:30 PM ET)

Recent advances of Zr based metal organic frameworks photocatalysis: Energy production and environmental remediation