Microwave Energy Drives "On-Off-On" Spin-Switch Behavior in Nitrogen-Doped Graphene

Emerging graphene derivatives as active 2D coordination platforms for single-atom catalysts

Single-atom catalysts (SACs) based on graphene derivatives are an emerging and growing class of materials functioning as two-dimensional (2D) metal-coordination scaffolds with intriguing properties. Recently, owing to the rich chemistry of fluorographene, new avenues have opened toward graphene derivatives with selective, spacer-free, and dense functionalization, acting as in-plane or out-of-plane metal coordination ligands. The particular structural features give rise to intriguing phenomena occurring between the coordinated metals and the graphene backbone. These include redox processes, charge transfer, emergence, and stabilization of rare or otherwise unstable metal valence states, as well as metal-support and metal-metal synergism. The vast potential of such systems has been demonstrated as enzyme mimics for cooperative mixed-valence SACs, ethanol fuel cells, and CO2 fixation; however, it is anticipated that their impact will further expand toward diverse fields, e.g., advanced organic transformations, electrochemical energy storage, and energy harvesting.

Singly and Triply Linked Magnetic Porphyrin Lanthanide Arrays

The introduction of paramagnetic metal centers into a conjugated π-system is a promising approach toward engineering spintronic materials. Here, we report an investigation of two types of spin-bearing dysprosium(III) and gadolinium(III) porphyrin dimers: singly meso-meso-linked dimers with twisted conformations and planar edge-fused β,meso,β-linked tapes. The rare-earth spin centers sit out of the plane of the porphyrin, so that the singly linked dimers are chiral, and their enantiomers can be resolved, whereas the edge-fused tape complexes can be separated into syn and anti stereoisomers. We compare the crystal structures, UV-vis-NIR absorption spectra, electrochemistry, EPR spectroscopy, and magnetic behavior of these complexes. Low-temperature SQUID magnetometry measurements reveal intramolecular antiferromagnetic exchange coupling between the GdIII centers in the edge-fused dimers (syn isomer: J = -51 ± 2 MHz; anti isomer: J = -19 ± 3 MHz), whereas no exchange coupling is detected in the singly linked twisted complex. The phase-memory times, Tm, are in the range of 8-10 μs at 3 K, which is long enough to test quantum computational schemes using microwave pulses. Both the syn and anti Dy2 edge-fused tapes exhibit single-molecule magnetic hysteresis cycles at temperatures below 0.5 K with slow magnetization dynamics.

Influence of Defects and Heteroatoms on the Chemical Properties of Supported Graphene Layers

A large and growing number of theoretical papers report the possible role of defects and heteroatoms on the chemical properties of single-layer graphene. Indeed, they are expected to modify the electronic structure of the graphene film, allow for chemisorption of different species, and enable more effective functionalisation. Therefore, from theoretical studies, we get the suggestion that single and double vacancies, Stone–Wales defects and heteroatoms are suitable candidates to turn nearly chemically inert graphene into an active player in chemistry, catalysis, and sensoristics. Despite these encouraging premises, experimental proofs of an enhanced reactivity of defected/doped graphene are limited because experimental studies addressing adsorption on well-defined defects and heteroatoms in graphene layers are much less abundant than theoretical ones. In this paper, we review the state of the art of experimental findings on adsorption on graphene defects and heteroatoms, covering different topics such as the role of vacancies on adsorption of oxygen and carbon monoxide, the effect of the presence of N heteroatoms on adsorption and intercalation underneath graphene monolayers, and the role of defects in covalent functionalisation and defect-induced gas adsorption on graphene transistors.

Nitrogen doped graphene with diamond-like bonds achieves unprecedented energy density at high power in a symmetric sustainable supercapacitor

Supercapacitors have attracted great interest because of their fast, reversible operation and sustainability. However, their energy densities remain lower than those of batteries. In the last decade, supercapacitors with an energy content of ∼110 W h L^-1 at a power of ∼1 kW L^-1 were developed by leveraging the open framework structure of graphene-related architectures. Here, we report that the reaction of fluorographene with azide anions enables the preparation of a material combining graphene-type sp² layers with tetrahedral carbon-carbon bonds and nitrogen (pyridinic and pyrrolic) superdoping (16%). Theoretical investigations showed that the C-C bonds develop between carbon-centered radicals, which emerge in the vicinity of the nitrogen dopants. This material, with diamond-like bonds and an ultra-high mass density of 2.8 g cm^-3, is an excellent host for the ions, delivering unprecedented energy densities of 200 W h L^-1 at a power of 2.6 kW L^-1 and 143 W h L^-1 at 52 kW L^-1. These findings open a route to materials whose properties may enable a transformative improvement in the performance of supercapacitor components.

sp3-Functionalization of Single-Walled Carbon Nanotubes Creates Localized Spins

Chemical functionalization-introduced sp³ quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature- and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of sp³ quantum defects. Signatures of isolated spins that are highly localized at the sp³ defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin-lattice relaxation time T₁ and spin dephasing time T₂ to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the sp³ quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.

Tailoring Electronic and Magnetic Properties of Graphene by Phosphorus Doping

The electronic and magnetic properties of graphene can be modulated by doping it with other elements, especially those with a different number of valence electrons. In this article, we first provide a three-dimensional reconstruction of the atomic structure of a phosphorus substitution in graphene using aberration-corrected scanning transmission electron microscopy. Turning then to theoretical calculations based on the density functional theory (DFT), we show that doping phosphorus in various bonding configurations can induce magnetism in graphene. Our simulations reveal that the electronic and magnetic properties of P-doped (Gr-P) and/or phosphono-functionalized graphene (Gr-PO₃H₂) can be controlled by both the phosphorus concentration and configurations, ultimately leading to ferromagnetic (FM) and/or antiferromagnetic (AFM) features with the transition temperature up to room temperature. We also calculate core-level binding energies of variously bonded P to facilitate X-ray photoelectron spectroscopy-based identification of its chemical form present in P-doped graphene-based structures. These results may enable the design of graphene-based organic magnets with tailored properties for future magnetic or spintronic applications.