Functionalizing the recently developed porous materials such as porous organic frameworks and coordination polymer networks with active homogeneous catalytic sites would offer new opportunities in the field of heterogeneous catalysis. In this regard, a novel covalent triazine framework functionalized with an Ir(III)-N-heterocyclic carbene complex was synthesized and characterized to have a coordination environment similar to that of its structurally related molecular Ir complex. Because of the strong σ-donating and poor π-accepting characters of the Nheterocyclic carbene (NHC) ligand, the heterogenized Ir-NHC complex efficiently catalyzes the hydrogenation of CO 2 to formate with a turnover frequency of up to 16 000 h −1 and a turnover number of up to 24 300; these are the highest values reported to date in heterogeneous catalysis for the hydrogenation of CO 2 to formate.
A series of water-soluble half-sandwich [Cp*Rh(N^N)Cl] (Cp* = pentamethylcyclopentadiene, N^N-substituted 2,2'-bipyridine) complexes containing electron-donating substituents around the 2,2'-bipyridyl ligand were synthesized and fully characterized for the regioselective reduction of nicotinamide coenzyme (NAD). The influence of the positional effect of the substituents on the structural, electrochemical, and catalytic properties of the catalyst was systematically studied in detail. The catalytic efficiency of the substituted bipyridine Cp*Rh complexes are inversely correlated with their redox potentials. The 5,5'-substituted bipyridine Cp*Rh complex, which had the lowest reduction potential, most effectively regenerated NADH with a turnover frequency of 1100 h. Detailed kinetic studies on the generation of intermediate(s) provide valuable mechanistic insight into this catalytic cycle and help to direct the future design strategy of corresponding catalysts.
Zinc oxide (ZnO) thin films were electrodeposited from an aqueous zinc acetate solution onto fluorine-doped thin oxide (FTO) coated conducting glass substrates. The effect of organic surfactants like polyvinyl pyrrolidone (PVP), sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), ethylene glycol (EG) and polyvinyl alcohol (PVA) on their structural, morphological, optical and photoelectrochemical properties was studied. The x-ray diffraction patterns revealed the formation of phase-pure ZnO thin films. The films deposited using organic surfactants exhibit different surface morphologies. It was observed that the organic surfactants play important roles in modifying the surface morphology and size of the crystallites. A compact granular morphology was observed for the ZnO samples grown without organic surfactants. The films exhibit nanoparticles of size 100-150 nm for PVP, EG and PVA mediated growth. The vertically aligned thin and compact hexagonal crystallites stem from the SDS, whereas microporous corrugated morphology is observed for PEG-mediated growth. All the samples exhibit room temperature photoluminescence (PL). Oxygen vacancies contribute to the active luminescent centers for the emission of green light in ZnO thin films. PL gets quenched for the SDS surfactant. All the samples were post-treated with ethanol to remove stray surfactant molecules. FTIR study was used to confirm the removal of adsorbed surfactant molecules from the samples. Moreover the samples are photoelectrochemically (PEC) active and exhibit the highest photocurrent of 231 µA, a photovoltage of 492 mV and 0.42 fill factor for the ZnO:SDS films.
Development of an
industrially viable catalyst for the ring-expansion
carbonylation of epoxides remains challenging in the view of facile
product separation and recyclability. Herein, we report a heterogenized
porous porphyrin Al(III) tetracarbonylcobaltate bimetallic catalyst
for the ring-expansion carbonylation of epoxides. The catalyst was
synthesized using a hyper-cross-linking strategy involving methylene
bridges introduced by the Friedel–Crafts reaction and incorporated
with cobaltate anions. The catalyst effectively converts epoxides
into the corresponding β-lactones with an excellent site time
yield of 360 h–1, which is comparable to that of
the corresponding homogeneous catalysts and is the highest of any
heterogeneous catalyst reported so far for this reaction.
Functionalized covalent triazine frameworks (CTFs) realized by rational design of the monomer have been recognized as a promising candidate to achieve improvements in various applications.
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