Electrocatalytic Isoxazoline–Nanocarbon Metal Complexes

Abstract

We report the synthesis of new carbon-nanomaterial-based metal chelates that enable effective electronic coupling to electrocatalytic transition metals. In particular, multiwalled carbon nanotubes (MWCNTs) and few-layered graphene (FLG) were covalently functionalized by a microwave-assisted cycloaddition with nitrile oxides to form metal-binding isoxazoline functional groups with high densities. The covalent attachment was evidenced by Raman spectroscopy, and the chemical identity of the surface functional groups was confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The functional carbon nanomaterials effectively chelate precious metals Ir(III), Pt(II), and Ru(III), as well as earth-abundant metals such as Ni(II), to afford materials with metal contents as high as 3.0 atom %. The molecularly dispersed nature of the catalysts was confirmed by X-ray absorption spectroscopy (XAS) and energy-dispersive X-ray spectroscopy (STEM-EDS) elemental mapping. The interplay between the chelate structure on the graphene surface and its metal binding ability has also been investigated by a combination of experimental and computational studies. The defined ligands on the graphene surfaces enable the formation of structurally precise heterogeneous molecular catalysts. The direct attachment of the isoxazoline functional group on the graphene surfaces provides strong electronic coupling between the chelated metal species and the conductive carbon nanomaterial support. We demonstrate that the metal-chelated carbon nanomaterials are effective heterogeneous catalysts in the oxygen evolution reaction with low overpotentials and tunable catalytic activity.

Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode

“…The catalysis of the multielectron, multiproton oxygen evolution reaction (OER) is especially challenging. A typical molecular catalyst for OER is a reversible redox mediator whose standard potential is sufficiently positive to oxidize water. − Typically based on transition-metal complexes, such catalysts are either homogeneous (i.e., dispersed in electrolyte solution) − or heterogeneous (i.e., immobilized on the electrode surface). − In addition to a very low load and ease of recycling, surface attachment of some molecular catalysts has improved their activities. − Despite potential advantages of metal-free, fully organic OER catalysts, only a few of them have been reported to date. − A high standard potential required for water oxidation limits the choice of suitable organic molecular catalysts. Another problem is the decomposition of organic and organometallic water oxidation catalysts at high anodic potentials …”

Synchrotron-based X-ray absorption spectroscopy of Pd nanoparticles decorated on multi-walled carbon nanotubes during successive cycles of He/H2 exposure

“…9 On the other hand, synchrotron radiation in general and X-ray absorption spectroscopy (XAS) in particular can be beneficial to understanding the local structures and chemical compositions of the metal and metal oxide anchoring on the MWCNTs' surface. [39][40][41][42][43][44][45][46] Bugaev et al have studied the hydrogen interaction with Pd nanoparticles using in situ XAS, in both the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions at Pd K-edge, as well as X-ray diffraction (XRD) as a function of temperature and hydrogen pressure. The effect of hydrogen concentration has been reported on the electronic palladium structure to increase Pd-Pd interatomic distance.…”

2-((3-(4-Methoxyphenyl)-4,5-dihydroisoxazol-5-yl)methyl)benzo[d]isothiazol-3(2H)-one1,1-dioxide

“…In addition, isoxazoline derivatives have attracted much attention due to their various pharmacological activities such as antimicrobial [8], anticancer [9], antidiabetic [10], anti-inflammatory [11][12][13], antistress [14], antibacterial [15,16], anti-Alzheimer [17], analgesic [18], insecticidal [19,20], and acaricidal activities [21]. Besides its biological significance, isoxazolines play an important role in coordination chemistry as ligands in the synthesis of metal complexes with broad biological applications [22][23][24].…”