Effect of Water during the Quantitation of Formate in Photocatalytic Studies on CO2 Reduction in Dimethylformamide

Recent Trends in Plasmon-Assisted Photocatalytic CO2 Reduction

Direct photocatalytic reduction of CO₂ has become an highly active field of research. It is thus of utmost importance to maintain an overview of the various materials used to sustain this process, find common trends, and, in this way, eventually improve the current conversions and selectivities. In particular, CO₂ photoreduction using plasmonic photocatalysts under solar light has gained tremendous attention, and a wide variety of materials has been developed to reduce CO₂ towards more practical gases or liquid fuels (CH₄ , CO, CH₃ OH/CH₃ CH₂ OH) in this manner. This Review therefore aims at providing insights in current developments of photocatalysts consisting of only plasmonic nanoparticles and semiconductor materials. By classifying recent studies based on product selectivity, this Review aims to unravel common trends that can provide effective information on ways to improve the photoreduction yield or possible means to shift the selectivity towards desired products, thus generating new ideas for the way forward.

Strategies for induced defects in metal-organic frameworks for enhancing adsorption and catalytic performance

Metal-organic frameworks (MOFs) have emerged among porous materials. The designable structure and specific functionality make them stand out for diverse applications. In conceptual MOF, the metal ions/clusters and organic ligands...

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

The Coordination Chemistry of Bio-Relevant Ligands and Their Magnesium Complexes

The coordination chemistry of magnesium (Mg²⁺) was extensively explored. More recently; magnesium; which plays a role in over 80% of metabolic functions and governs over 350 enzymatic processes; is becoming increasingly linked to chronic disease—predominantly due to magnesium deficiency (hypomagnesemia). Supplemental dietary magnesium utilizing biorelevant chelate ligands is a proven method for counteracting hypomagnesemia. However, the coordination chemistry of such bio-relevant magnesium complexes is yet to be extensively explored or elucidated. It is the aim of this review to comprehensively describe what is currently known about common bio-relevant magnesium complexes from the perspective of coordination chemistry.

A Heterometallic Three-Dimensional Metal-Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit

A heterometallic metal−organic framework (MOF) of [Cd₆Ca₄(BTB)₆(HCOO)₂(DEF)₂(H₂O)₁₂]∙DEF∙xSol (1, H₃BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N′-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO₃)₂·4H₂O, CaO and H₃BTB in a mixed solvent of DEF/H₂O/HNO₃. The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd₂Ca]₂Ca′ and an infinite one-dimensional (1D) chain of [Cd₂CaCa′]_n that are orthogonally linked via a corner-shared Ca²⁺ ion (denoted as Ca′), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P4₁ helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.

Improving Photocatalysis for the Reduction of CO2 through Non-covalent Supramolecular Assembly

We report the enhancement of photocatalytic performance by introduction of hydrogen-bonding interactions to a Re bipyridine catalyst and Ru photosensitizer system (ReDAC/RuDAC) by the addition of amide substituents, with carbon monoxide (CO) and carbonate/bicarbonate as products. This system demonstrates a more-than-3-fold increase in turnover number (TON_CO = 100 ± 4) and quantum yield (Φ_CO = 23.3 ± 0.8%) for CO formation compared to the control system using unsubstituted Ru photosensitizer (RuBPY) and ReDAC (TON_CO = 28 ± 4 and Φ_CO = 7 ± 1%) in acetonitrile (MeCN) with 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as sacrificial reductant. In dimethylformamide (DMF), a solvent that disrupts hydrogen bonds, the ReDAC/RuDAC system showed a decrease in catalytic performance while the control system exhibited an increase, indicating the role of hydrogen bonding in enhancing the photocatalysis for CO₂ reduction through supramolecular assembly. The similar properties of RuDAC and RuBPY demonstrated in lifetime measurements, spectroscopic analysis, and electrochemical and spectroelectrochemical studies revealed that the enhancement in photocatalysis is due not to differences in intrinsic properties of the catalyst or photosensitizer, but to hydrogen-bonding interactions between them.

CO2 capture by Mn(i) and Re(i) complexes with a deprotonated triethanolamine ligand

CO₂ capture at low concentration by catalysts is potentially useful for developing photocatalytic and electrocatalytic CO₂ reduction systems.

CO₂ capture at low concentration by catalysts is potentially useful for developing photocatalytic and electrocatalytic CO₂ reduction systems. We investigated the CO₂-capturing abilities of two complexes, fac-Mn(X₂bpy)(CO)₃(OCH₂CH₂NR₂) and fac-Re(X₂bpy)(CO)₃(OCH₂CH₂NR₂) (X₂bpy = 4,4′-X₂-2,2-bipyridine and R = –CH₂CH₂OH), which work as efficient catalysts for CO₂ reduction. Both complexes could efficiently capture CO₂ even from Ar gas containing only low concentration of CO₂ such as 1% to be converted into fac-M(X₂bpy)(CO)₃(OC(O)OCH₂CH₂NR₂) (M = Mn and Re). These CO₂-capturing reactions proceeded reversibly and their equilibrium constants were >1000. The substituents of X₂bpy strongly affected the CO₂-capturing abilities of both Mn and Re complexes. The density functional theory (DFT) calculation could be used to estimate the CO₂-capturing abilities of the metal complexes in the presence of triethanolamine.

Molecular polypyridine-based metal complexes as catalysts for the reduction of CO2

Polypyridyl transition metal complexes represent one of the more thoroughly studied classes of molecular catalysts towards CO₂ reduction to date. Initial reports in the 1980s began with an emphasis on 2nd and 3rd row late transition metals, but more recently the focus has shifted towards earlier metals and base metals. Polypyridyl platforms have proven quite versatile and amenable to studying various parameters that govern product distribution for CO₂ reduction. However, open questions remain regarding the key mechanistic steps that govern product selectivity and efficiency. Polypyridyl complexes have also been immobilized through a variety of methods to afford active catalytic materials for CO₂ reductions. While still an emerging field, materials incorporating molecular catalysts represent a promising strategy for electrochemical and photoelectrochemical devices capable of CO₂ reduction. In general, this class of compounds remains the most promising for the continued development of molecular systems for CO₂ reduction and an inspiration for the design of related non-polypyridyl catalysts.

High-efficiency photocatalytic CO2 reduction in organic–aqueous system: a new insight into the role of water

We have first identified a new promotional mechanism of water in the photocatalytic conversion of CO₂ into CO, which is different from the traditional role of proton source. High efficiency (44.5 μmol h⁻¹) achieved through construction of a binary liquid system was determined by systematic research.

A high efficiency photocatalytic conversion of CO₂ into CO has been achieved by construction of a binary liquid system.

Activation of the Carbon Nitride Surface by Silica in a CO-Evolving Hybrid Photocatalyst

Photocatalytic reduction of CO₂ to CO proceeded by visible light (λ>400 nm) using mesoporous graphitic carbon nitride (C₃ N₄ ) coupled with a Ru^II -Re^I binuclear complex (RuRe) containing a photosensitizer and catalytic units. The selectivity to CO exceeded 90 % during the initial stage. Photocatalytic reactions (including isotope tracer experiments) and electrochemical measurements revealed that the reaction proceeded according to a two-step photoexcitation of C₃ N₄ and the Ru^II photosensitizer unit, that is, it followed the Z-Scheme mechanism. Modification of C₃ N₄ with highly dispersed silica was found to improve the ability of C₃ N₄ to accommodate RuRe, which enhanced the photocatalytic activity for CO production.

Temperature dependence of photocatalytic CO2reduction by trans(Cl)–Ru(bpy)(CO)2Cl2: activation energy difference between CO and formate production

The temperature dependence of photocatalytic CO₂reduction bytrans(Cl)–Ru(bpy)(CO)₂Cl₂(bpy: 2,2′-bipyridine) has been researched in ethanol (EtOH)/N,N-dimethylacetamide (DMA) solutions containing [Ru(bpy)₃]²⁺(a photosensitizer) and 1-benzyl-1,4-dihydronicotinamide (BNAH, an electron donor). The catalytic system efficiently reduces CO₂to carbon monoxide (CO) with formate (HCOO⁻) as a minor product. The mechanism of the catalysis consists of the electron-relay cycle and the catalytic cycle: in the former cycle the photochemically generated reduced species of the photosensitizer injects an electron to the catalyst, and in the latter the catalyst reduces CO₂. At a low concentration of the catalyst (5.0 μM), where the catalytic cycle is rate-determining, the temperature dependence of CO/HCOO⁻is also dependent on the EtOH contents: the selectivity of CO/HCOO⁻decreases in 20% and 40%-EtOH/DMA with increasing temperature, while it increases in 60%-EtOH/DMA. The temperature dependence of the CO/HCOO⁻selectivity indicates that the difference in activation energy (ΔΔG^‡) between CO and HCOO⁻production is estimated asca.3.06 kJ mol⁻¹in 40%-EtOH/DMA at 298 K.

Highly efficient, selective, and durable photocatalytic system for CO2 reduction to formic acid

We discovered an extremely suitable sacrificial electron donor, 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole, for the selective photocatalytic reduction of CO₂ to formic acid using a Ru(ii)-Ru(ii) supramolecular photocatalyst. The efficiency, durability, and rate of photocatalysis are significantly increased (Φ_HCOOH = 0.46, TON_HCOOH = 2766, TOF_HCOOH = 44.9 min^-1) in comparison with those using 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole or 1-benzyl-1,4-dihydronicotinamide.

Unexpected effect of catalyst concentration on photochemical CO2 reduction by trans(Cl)-Ru(bpy)(CO)2Cl2: new mechanistic insight into the CO/HCOO- selectivity

Photochemical CO₂ reduction catalysed by trans(Cl)-Ru(bpy)(CO)₂Cl₂ (bpy = 2,2'-bipyridine) efficiently produces carbon monoxide (CO) and formate (HCOO^-) in N,N-dimethylacetamide (DMA)/water containing [Ru(bpy)₃]²⁺ as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor. We have unexpectedly found catalyst concentration dependence of the product ratio (CO/HCOO^-) in the photochemical CO₂ reduction: the ratio of CO/HCOO^- decreases with increasing catalyst concentration. The result has led us to propose a new mechanism in which HCOO^- is selectively produced by the formation of a Ru(i)-Ru(i) dimer as the catalyst intermediate. This reaction mechanism predicts that the Ru-Ru bond dissociates in the reaction of the dimer with CO₂, and that the insufficient electron supply to the catalyst results in the dominant formation of HCOO^-. The proposed mechanism is supported by the result that the time-course profiles of CO and HCOO^- in the photochemical CO₂ reduction catalysed by [Ru(bpy)(CO)₂Cl]₂ (0.05 mM) are very similar to those of the reduction catalysed by trans(Cl)-Ru(bpy)(CO)₂Cl₂ (0.10 mM), and that HCOO^- formation becomes dominant under low-intensity light. The kinetic analyses based on the proposed mechanism could excellently reproduce the unusual catalyst concentration effect on the product ratio. The catalyst concentration effect observed in the photochemical CO₂ reduction using [Ru(4dmbpy)₃]²⁺ (4dmbpy = 4,4'-dimethyl-2,2'-bipyridine) instead of [Ru(bpy)₃]²⁺ as the photosensitizer is also explained with the kinetic analyses, reflecting the smaller quenching rate constant of excited [Ru(4dmbpy)₃]²⁺ by BNAH than that of excited [Ru(bpy)₃]²⁺. We have further synthesized trans(Cl)-Ru(6Mes-bpy)(CO)₂Cl₂ (6Mes-bpy = 6,6'-dimesityl-2,2'-bipyridine), which bears bulky substituents at the 6,6'-positions in the 2,2'-bipyridyl ligand, so that the ruthenium complex cannot form the dimer due to the steric hindrance. We have found that this ruthenium complex selectively produces CO, which strongly supports the catalytic mechanism proposed in this work.

Terpyridine complexes of first row transition metals and electrochemical reduction of CO2 to CO

Homoleptic terpyridine complexes of 3d transition metals are found to electrocatalytically reduce CO₂ to either CO or tuneable CO–H₂ mixtures.

Red-light-driven photocatalytic reduction of CO2 using Os(II)-Re(I) supramolecular complexes

The novel supramolecular complexes, which are composed of an [Os(5dmb)2(BL)](2+)-type complex (5dmb = 5,5'-dimethyl-2,2'-bipyridine; BL = 1,2-bis(4'-methyl-[2,2'-bipyridin]-4-yl)ethane) as a photosensitizer and cis,trans-[Re(BL)(CO)2{P(p-X-C6H4)3}2](+)-type complexes (X = F, Cl) as a catalyst, have been synthesized. They photocatalyzed selective reduction of CO2 to CO under red-light irradiation (λ > 620 nm). The photocatalytic abilities were affected by the phosphine ligands on the Re unit, and the supramolecule with P(p-Cl-C6H4)3 ligands exhibited better photocatalysis (ΦCO = 0.12, TONCO = 1138, TOFCO = 3.3 min(-1)). The detailed studies clarified the electron balance and material balance; i.e., one molecule of the sacrificial electron donor (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH)) donated two electrons, one molecule of CO2 accepted the two electrons, and another CO2 molecule served as an "O(2-)" acceptor to give each molecule of the two-electron oxidized compound of BIH, CO, and HCO3(-).

Photocatalytic reduction of CO2 on TiO2 and other semiconductors

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.