Nickel Nanoparticles for Enhancing Carbon Capture

Hydration reaction of CO2 is one of the rate limiting steps for CO2 absorption (in aqueous solutions) and aqueous CO2 mineralization. The catalytic activity of nickel nanoparticles (NiNPs) for CO2 hydration is studied at different temperatures, pH, and low CO2 partial pressures to mimic the true flue gas conditions. Results show that NiNPs can work as active catalyst for hydration of CO2 in applications such as CO2 separation and CO2 mineralization. The NiNPs display optimum activity within 20–30°C and at pH value <8. NiNPs show catalytic activity even at low CO2 partial pressures (12 vol%). In 50 wt% K2CO3 solution, an enhancement of 77% is observed in the rate of CO2 absorption with NiNPs. Commercially, CO2 saturated K2CO3 solutions are usually regenerated at 150°C; at these conditions, NiNPs show no considerable surface oxidation. They still exhibit catalytic activity for hydration reaction of CO2. CO2 absorption and mineralization (as CaCO3) in DI water are three times higher in presence of NiNPs. Calcite (CaCO3) particles precipitated in presence of NiNPs are spherical in morphology

Effect of Pressure on the Solubilization of a Fluorescent Merocyanine Dye by a Nonionic Surfactant

The target dye, which is a derivative of Merocyanine 540 bearing a naphthoxazole headgroup, persists as a monomer in ethanol solution but dimerizes in water under ambient conditions. Analysis of the absorption spectrum indicates that the dimer has an oblique geometry with the two molecules being held at an angle of ca. 55°. Applying high pressure to the system forces the two molecules into closer contact, resulting in a decreased partial molar volume of 3.1 cm³. One molecule of the monomeric dye enters a neutral micelle formed from Triton X-100, where it is highly fluorescent and free of exciton coupling. The result of applied pressure on these latter systems depends on the concentration of surfactant. Above the critical micelle concentration (CMC), applied pressure has little effect other than to increase the viscosity inside the micelle. At very low surfactant concentration, applied pressure forces monomeric dye into the dimeric form, as observed in the absence of Triton X-100. It is notable, however, that the pressure effect on the dimerization constant is exaggerated in the presence of surfactant. At intermediate surfactant concentrations, applied pressure leads to a marked change in the CMC. In particular, applied pressure reduces the partial molar volume of the micelle by ca. 7.9 cm³ and induces micelle formation at relatively low concentration of surfactant. For example, the CMC falls from ca. 250 μM at atmospheric pressure to only 50 μM at 460 MPa

CCDC 633724: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 633721: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 633723: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 633722: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Unusually slow photodissociation of CO from (η6-C 6H6)Cr(CO)3 (M= Cr or Mo): a time-resolved Infrared, Matrix Isolation, and DFT investigation

The photochemistry of (η6-C6H6)M(CO)3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λexc. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm−1) that decays over 150 ps to (η6-C6H6)Cr(CO)2(n-heptane) (70%) and (η6-C6H6)Cr(CO)3 (30%). Pulsed photolysis (λexc. = 266 nm) of (η6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H6)Cr(CO)2(n-heptane) (1930 and 1870 cm−1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of (η6-C6H6)Cr(CO)3. Photolysis of (η6-C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm−1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy

Anthracene as a sensitiser for near-infrared luminescence in complexes of Nd(III) Er(III) and Yb(III) : an unexpected sensitisation mechanism based on electron transfer

The ligand L1, which contains a chelating 2-(2-pyridyl)benzimidazole (PB) unit with a pendant anthacenyl group An connected via a methylene spacer, (L1 = PB-An), was used to prepare the 8-coordinate lanthanide(III) complexes [Ln(hfac)3(L1)] (Ln = Nd, Gd, Er, Yb) which have been structurally characterised and all have a square antiprismatic N2O6 coordination geometry. Whereas free L1 displays typical anthracene-based fluorescence, this fluorescence is completely quenched in its complexes. The An group in L1 acts as an antenna unit: in the complexes [Ln(hfac)3(L1)] (Ln = Nd, Er, Yb) selective excitation of the anthracene results in sensitised near-infrared luminescence from the lanthanide centres with concomitant quenching of An fluorescence. Surprisingly, the anthracene fluorescence is also quenched even in the Gd(III) complex and in its Zn(II) adduct in which quenching via energy transfer to the metal centre is not possible. It is proposed that the quenching of anthracene fluorescence in coordinated L1 arises due to intra-ligand photoinduced electron-transfer from the excited anthracene chromophore 1An* to the coordinated PB unit generating a short-lived charge-separated state [An˙+–PB˙−] which collapses by back electron-transfer to give 3An*. This electron-transfer step is only possible upon coordination of L1 to the metal centre, which strongly increases the electron acceptor capability of the PB unit, such that 1An* → PB PET is endoergonic in free L1 but exergonic in its complexes. Thus, rather than a conventional set of steps (1An* → 3An* → Ln), the sensitization mechanism now includes 1An* → PB photoinduced electron transfer to generate charge-separated [An˙+–PB˙−], then back electron-transfer to generate 3An* which finally sensitises the Ln(III) centre via energy transfer. The presence of 3An* in L1 and its complexes is confirmed by nanosecond transient absorption studies, which have also shown that the 3An* lifetime in the Nd(III) complex matches the rise time of Nd-centred near-infrared emission, confirming that the final step of the sequence is 3An* → Ln(III) energy-transfer