Sacrificial Donor Research Articles

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH.

Optimized photocatalytic conversion of CO2 requires new potent catalysts that can absorb visible light. The photocatalytic reduction of CO2 using rhenium(i) has been demonstrated but suffers from low turnover. Herein, we describe a [Re(CO)3(1-(1,10)phenanthroline-5-(4-nitro-naphthalimide))Cl] photocatalyst, which when combined with the sacrificial donor 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, results in selective production of formic acid and a high turnover number of 533 and turnover frequency of 356 h−1. Single-crystal X-ray diffraction and DFT studies are also discussed.

Post-synthetic particle size reduction of a layered cesium titanate (Cs2Ti5O11) for the improvement of photocatalytic H2 production

Layered cesium titanate (Cs2Ti5O11) having an elongated rectangular particle shape of size a few hundreds of nanometers has been prepared by size reduction of a macroscopic sample prepared by a previously reported solid-state reaction procedure. The as-prepared material had a particle size of 3 μm (length) and 0.5 μm (width). The described size reduction was accomplished by first pelletizing the Cs2Ti5O11 by pressing it in a mold, and then crushing it in a mortar. The Cs2Ti5O11 samples before and after size reduction were proton-exchanged to obtain H2Ti5O11, which proved to be active for photocatalytic H2 production in the presence of methanol as a sacrificial donor under UV irradiation. In this process, H2Ti5O11 derived from size-reduced Cs2Ti5O11 exhibited higher activity than that derived from the pristine Cs2Ti5O11.

Do Sacrificial Donors Donate H2 in Photocatalysis?

Do <i>Sacrificial Donors</i> Donate H₂ in Photocatalysis?

Hydrogen Goes Green - Model Experiments for Artificial Photosynthesis

Photocatalytic hydrogen production without the bypass via photovoltaics and electrolysis has been realized using a versatile photocatalytic system with only three components: the redox mediator ethyl viologen, the photocatalyst proflavin and the sacrificial donor EDTA. By adding a reduction catalyst made of nano-platinum on alumina to the aqueous solution of these three chemicals, hydrogen can be produced by irradiation with sunlight.

Light assisted nickel(II) grafted-g-carbon nitride molecular hybrid promoted hydrocarboxylation of olefins with CO2 at atmospheric pressure condition

An efficient photocatalytic method was developed for the hydrocarboxylation of olefins to corresponding acids using carbon dioxide assisted by a molecular hybrid photocatalyst consisting of nickel phthalocyanine complex grafted to graphitic carbon nitride support (NiPc/g-C3N4) under ambient temperature and pressure conditions. The reaction is found to be regioselective in nature as aromatic olefins i.e. styrenes and its derivatives afforded α-carboxylated products; whereas aliphatic olefins yielded terminal acids selectively in moderate-to-good yields. The DFT calculations suggested the higher efficiency of the hybrid photocatalyst as compared to its individual components. Based on the electrochemical measurements and adsorption behaviour of the CO2 on the catalyst and corresponding bond distances calculated by DFT, a possible mechanism is proposed. Furthermore, triethylamine was used as a sacrificial donor that provided the required electrons to complete the redox cycle of the reaction.

Mixed-metal MOFs as efficient catalysts for transfer hydrogenation of furfural, levulinic acid and other carbonyl compounds

Crystalline, porous Fe-Ni mixed-metal metal-organic frameworks (MOFs), namely MIL-88B(Fe2Ni) and NH2-MIL-88B(Fe2Ni), were synthesized and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, atomic absorption spectrophotometry (AAS) and nitrogen physisorption measurements. The MOFs were then employed as catalysts for transfer hydrogenation (TH) of biomass derivatives such as furfural and levulinic acid, and various other carbonyl compounds using 2-propanol as a sacrificial hydrogen donor. These heterogeneous catalysts are deemed to be environmentally benign, efficient and recyclable. NH2-MIL-88B(Fe2Ni) showcased good catalytic activity with low catalyst loading in short reaction time. The catalysts were recovered and reused several times without significant degradation in catalytic activity. A mechanism for the TH reaction was also proposed. As far as we are aware, this is the first report on the synthesis of furfuryl alcohol and γ-valerolactone (GVL) via TH reaction in just 60 min using a MOF catalyst.

Time-Resolved Spectroscopy and High-Efficiency Light-Driven Hydrogen Evolution of a {Mo3 S4 }-Containing Polyoxometalate-Based System.

Polyoxothiometalate ions (ThioPOM) are active hydrogen-evolution reaction (HER) catalysts based on modular assembly built from electrophilic clusters {MoSx } and vacant polyoxotungstates. Herein, the dumbbell-like anion [{(PW11 O39 )Mo3 S4 (H2 O)3 (OH)}2 ]8- exhibits very high light-driven HER activity, while the active cores {Mo3 S4 } do not contain any exposed disulfido ligands, which were suspected to be the origin of the HER activity. Moreover, in the catalyst architecture, the two central {Mo3 S4 } cores are sandwiched by two {PW11 O39 }7- subunits that act as oxidant-resistant protecting groups and behave as electron-collecting units. A detailed photophysical study was carried out confirming the reductive quenching mechanism of the photosensitizer [Ir(ppy)2 (dtbbpy)]+ by the sacrificial donor triethanolamine (TEOA) and highlighting the very high rate constant of the electron transfer from the reduced photosensitizer to the ThioPOM catalyst. Such results provide new insights into the field of molecular catalytic systems able to promote high HER activity.

Hard template synthesis and photocatalytic activity of graphitic carbon nitride in the hydrogen evolution reaction using organic acids as electron donors

Porous graphitic carbon nitride obtained by pyrolysis of melamine in the presence of silica (TEOS in the reaction mixture) has been found to be more active in photocatalytic hydrogen evolution from the aqueous solutions of electron donors (organic acids) under visible light irradiation compared to the bulk analogue. The use of the optimal melamine/TEOS molar ratio in the initial reaction mixtures allows to obtain g-C3N4 characterized by increased mesoporosity due to the formation of smaller particles. It has been shown for the first time that oxalic acid can be used as an environmentally friendly sacrificial donor allowing to reach significantly higher rates of the photocatalytic reaction (up to 300 μmol H2/h*gphotocat.).

Effect of energy bandgap and sacrificial agents of cyclopentadithiophene-based polymers for enhanced photocatalytic hydrogen evolution

A library of donor-acceptor system consisting of cyclopentadithiophene-based polymer photocatalysts have been designed and synthesized. Among all photocatalysts, the active PCPDTBSO achieved hydrogen evolution rates of 24.6 mmol h–1 g–1 with apparent quantum yields of 8.7 % at 500 nm. More importantly, combined the results of photocatalytic efficiency, apparent quantum yield, the time-resolved fluorescence decay spectra, the steady-state photoluminescence spectra, and the transient absorption spectroscopy, and the oxidation potentials of sacrificial donors and protons reduction potentials in different pH values, we confirmed the concept that ascorbic acid is a suitable sacrificial donor for narrow bandgap polymers and triethylamine is a suitable sacrificial donor for wide bandgap polymers owing to the existence of the optimal thermodynamic driving force. We believed this study would be advantageous for the selection of photocatalysts and sacrificial donors for hydrogen production.

Efficient and region-selective conversion of octanes to epoxides under ambient conditions: Performance of tri-copper catalyst, [Cu3I(L)]+1 (L=7-N-Etppz)

In this paper, is described the conversion of the octane group of hydrocarbons into industrially important epoxides using tri-copper catalyst, [Cu 3 I (L)] +1 (L=7-N-Etppz). The role of hydrogen peroxide as a sacrificial oxygen donor during catalytic conversion to epoxides has been investigated. The performance of the catalyst has been evaluated in terms of turnover numbers (TON) and turnover frequencies (TOF) reported in this article.

The Role of Computational Chemistry in Discovering and Understanding Organic Photocatalysts for Renewable Fuel Synthesis

In this review the role computational chemistry plays in helping to rationalize the ability of organic materials, such as conjugated polymers, to drive photocatalytic water splitting and CO2 reduction, and the discovery of new organic photocatalysts, is reviewed. The ways in which organic photocatalysts differ from their inorganic counterparts, the mechanism by which such materials, when illuminated, reduce protons or CO2 and oxidize water or sacrificial donors, and how this can be studied using computational methods, as well as the high‐throughput virtual screening of organic materials as photocatalysts, are discussed. Finally, the current opportunities and challenges associated with studying photocatalysts computationally, are examined.

Polymer Chromophore–Catalyst Assembly for Photocatalytic CO2 Reduction

A polystyrene-based chromophore–catalyst assembly (PS-RuC/RuCat) was synthesized and applied for photocatalytic CO2 reduction in an organic solution in the presence of a sacrificial donor. The polymer assembly contains Ru(bpy)32+ (RuC, bpy = 2,2′-bipyridine) as the chromophore and a derivative of [Ru(tpy)(6-mbpy)(CH3CN)]2+ (RuCat, tpy = 4′-phenyl-2,2′:6′,2″-terpyridine and 6-mbpy = 6-methyl-2,2′-dipyridyl) as the CO2 reduction catalyst. The photophysical and electrochemical properties of the polymer assembly were investigated. Picosecond transient absorption and time-resolved emission reveal that the RuC chromophores are quenched by energy transfer to the RuCat units in the polymer assembly. Cyclic voltammetry shows that PS-RuC/RuCat effects electrocatalytic reduction of CO2 with an onset of approximately −1.25 V versus Ag/AgCl. Photocatalytic studies were conducted separately for the PS-RuC/RuCat polymer assembly and a mixture of monomers RuC and RuCat in a mixture of dimethylformamide and triethanolamine with 1-benzyl-1,4-dihydronicotinamide as a sacrificial reductant. The primary CO2 reduction products CO and H2 were detected in both photocatalytic systems. Formic acid was detected at low levels by nuclear magnetic resonance and is a very minor product. The polymer assembly system shows a lower photocatalytic CO2 reduction quantum yield (6.7%) but exhibits improved stability compared with a mixed molecular chromophore/catalyst system.

Visible-light assisted photoreduction of CO2 using CdS-decorated Bi24O31Br10

CdS-based heterojunctions are highly active for the production of hydrocarbon fuels from the photoreduction of CO2. In the present study, we have synthesized CdS decorated bismuth oxyhalide (Bi24O31Br10) heterojunction as an efficient nanocomposite material for producing methanol from CO2 using water and TEA as the proton source and sacrificial donor, respectively, under visible-light irradiation. The nanocomposite material exhibited the highest 1739 μmol-g−1 yield of methanol in 24 h than the CdS and Bi24O31Br10 with significant recyclability. The improved yield of methanol was observed due to the confinement of CdS nanoparticles into the bulk of Bi24O31Br10, making a Z-scheme heterojunction. Also, the charge separation was improved with the doping of CdS on Bi24O31Br10 semiconductor support. The synthesized semiconductors and nanocomposite materials have been characterized using XRD, FTIR, HR-TEM, XPS, PL, TGA-DTA, PEC analysis, N2 adsorption-desorption analysis, UV–vis, and Raman spectroscopy.

Synergetic Electrocatalytic Effects of Cu2O-TiO2 Heterostructures in a Solar Driven PEC Device for CO2 Reduction to >C1 Chemicals

A solar driven photo-electro-catalytic (PEC) device for CO2 reduction/water oxidation is here presented. The electrodes are engineered to be used in the n-type configuration, without using precious metals or rare/expensive raw materials. Specifically, the photoanode for water oxidation is made of TiO2 nanotube arrays prepared via controlled anodic oxidation, while Cu2O-TiO2 heterostructures, synthesised by ultra-sonicated assisted co-precipitation and then spray-coated over a carbon-based gas diffusion layer (GDL), are used as electrocathode materials for CO2 reduction. All the tests are performed without applying external bias or adding sacrificial donors, in a compact homemade PEC reactor in comparison with a conventional slurry photoreactor. The catalytic performances are evaluated in terms of formic acid and acetic acid production, the latter involving the formation of C-C bond. The effect of the presence of TiO2 is investigated in comparison with a bare cuprous oxide (Cu2O) film. Results for the bare Cu2O/GDL electrode (no TiO2) show 31.8 and 80.6 µmol h-1 gCu-1 as formic acid and acetic acid production rates, respectively. Cu2O-TiO2/GDL electrode, instead, shows more than one order of magnitude higher productivity (0.69 and 2.59 mmol h-1 gCu-1, respectively). The Faradaic efficiency (FE) to acetic acid is much higher for Cu2O-TiO2/GDL electrodes (61.9 %) considering the higher number of electrons involved for acetic acid with respect to formic acid (8 vs. 2). This behaviour can be ascribed to the synergetic electrocatalytic effects of the as-formed Cu2O-TiO2 heterostructures, favouring the formation of C-C bond for the sustainable production of >C1 chemicals and fuels.

Synthesis of Ni2P/CdS and Pt/TiO2 nanocomposite for photoreduction of CO2 into methanol

It is a great challenge to convert thermochemically stable CO2 into value-added products such as CH4, CH3OH, CO via utilizing solar energy. It is also a difficult task to develop an efficient catalyst for the reduction of CO2. We have designed and synthesized noble metal-free photocatalytic nanostructure Ni2P/CdS and Pt/TiO2 for conversion of CO2 to methanol in the presence of sacrificial donor triethylamine (TEA) and hydrogen peroxide. The synthesised catalysts physicochemical properties were studied by using several spectroscopic techniques like; XRD, UV-DRS, XPS, TEM, SEM and PL. Quantification of methanol by GC–MS showed encouraging results of 1424.8 and 2843 μmol g−1 of catalyst for Pt/TiO2 and 5 wt% Ni2P/CdS composites, respectively. Thus, Ni2P/CdS is a promising catalyst with higher productivity and significant selectivity than in-vogue catalysts.

Amine–Boranes as Transfer Hydrogenation and Hydrogenation Reagents: A Mechanistic Perspective

AbstractTransfer hydrogenation (TH) has historically been dominated by Meerwein–Ponndorf–Verley (MPV) reactions. However, with growing interest in amine–boranes, not least ammonia–borane (H3N⋅BH3), as potential hydrogen storage materials, these compounds have also started to emerge as an alternative reagent in TH reactions. In this Review we discuss TH chemistry using H3N⋅BH3 and their analogues (amine–boranes and metal amidoboranes) as sacrificial hydrogen donors. Three distinct pathways were considered: 1) classical TH, 2) nonclassical TH, and 3) hydrogenation. Simple experimental mechanistic probes can be employed to distinguish which pathway is operating and computational analysis can corroborate or discount mechanisms. We find that the pathway in operation can be perturbed by changing the temperature, solvent, amine–borane, or even the substrate used in the system, and subsequently assignment of the mechanism can become nontrivial.

Amine-Boranes as Transfer Hydrogenation and Hydrogenation Reagents: A Mechanistic Perspective.

Transfer hydrogenation (TH) has historically been dominated by Meerwein–Ponndorf–Verley (MPV) reactions. However, with growing interest in amine–boranes, not least ammonia–borane (H3N⋅BH3), as potential hydrogen storage materials, these compounds have also started to emerge as an alternative reagent in TH reactions. In this Review we discuss TH chemistry using H3N⋅BH3 and their analogues (amine–boranes and metal amidoboranes) as sacrificial hydrogen donors. Three distinct pathways were considered: 1) classical TH, 2) nonclassical TH, and 3) hydrogenation. Simple experimental mechanistic probes can be employed to distinguish which pathway is operating and computational analysis can corroborate or discount mechanisms. We find that the pathway in operation can be perturbed by changing the temperature, solvent, amine–borane, or even the substrate used in the system, and subsequently assignment of the mechanism can become nontrivial.

Controlling Spin-Correlated Radical Pairs with Donor-Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis.

One‐electron reduced metal complexes derived from photoactive ruthenium or iridium complexes are important intermediates for substrate activation steps in photoredox catalysis and for the photocatalytic generation of solar fuels. However, owing to the heavy atom effect, direct photochemical pathways to these key intermediates suffer from intrinsic efficiency problems resulting from rapid geminate recombination of radical pairs within the so‐called solvent cage. In this study, we prepared and investigated molecular dyads capable of producing reduced metal complexes via an indirect pathway relying on a sequence of energy and electron transfer processes between a Ru complex and a covalently connected anthracene moiety. Our test reaction to establish the proof‐of‐concept is the photochemical reduction of ruthenium(tris)bipyridine by the ascorbate dianion as sacrificial donor in aqueous solution. The photochemical key step in the Ru‐anthracene dyads is the reduction of a purely organic (anthracene) triplet excited state by the ascorbate dianion, yielding a spin‐correlated radical pair whose (unproductive) recombination is strongly spin‐forbidden. By carrying out detailed laser flash photolysis investigations, we provide clear evidence for the indirect reduced metal complex generation mechanism and show that this pathway can outperform the conventional direct metal complex photoreduction. The further optimization of our approach involving relatively simple molecular dyads might result in novel photocatalysts that convert substrates with unprecedented quantum yields.

Dye-sensitized H2 evolution from water facilitated by photoinduced electron transfer between molecules on the inside and the outside of a carbon nanotube

Dye-encapsulated single-walled carbon nanotubes (dye@SWCNTs) were physically modified to fabricate a water-dispersible dye@SWCNT/dendrimer hybrid. A photocatalytic H2 evolution reaction that uses this dye@SWCNT hybrid as a particulate photocatalyst was conducted in the presence of an electron-relay molecule [methyl viologen (MV2+)], a co-catalyst [PVP–Pt; poly(vinylpyrrolidone)], and a sacrificial donor [1-benzyl-1,4-dihydronicotinamide]. Photoinduced electron transfer occurs between the encapsulated dye molecule inside the SWCNT and the MV2+ ion outside the SWCNT. This is followed by the relay of the electron to the co-catalyst, which reduces H+ to generate H2. The external quantum yield of the H2 evolution reached a maximum of 8.5% under irradiation with light at 510 nm. Notably, the photoinduced electron transfer between the molecules on the inside and the outside of the SWCNT proceeded smoothly despite the possibility of energy migration from the encapsulated dye to the SWCNT or the possibility of charge recombination.

Dehalogenation reaction photocatalyzed by homoleptic copper(i) complexes associated with strongly reductive sacrificial donors

To perform challenging reduction reactions with light at low cost and low toxicity, we use for the first time a reductive quenching cycle with a simple, strongly colored homoleptic copper(i) complex [Cu(dipp)2]+(dipp = 2,9-diisopropyl-1,10-phen).