Search Results (5)

Gas-phase studies of fullerenes and metallofullerenes, though less well explored compared to condensed-phase research in recent years, offer critical insights into the mechanisms governing their formation and behavior. In this study, we re-examined the coalescence reactions of fullerenes using a high-resolution Fourier transform ion cyclotron resonance (FT ICR) mass spectrometer, especially the effect of electric fields in the source region on the formation of large-sized fullerenes. By varying the voltages on the metal plate where the C₆₀ was deposited, we achieved enhanced control over the coalescence process, revealing distinct distributions of fullerene products that differ from those reported in earlier studies. What is the most attractive is that a negative voltage applied on the metal plate is actually more conducive to the production of large-sized fullerene cations. Notably, we identified previously unobserved species, including doubly charged fullerene cations (e.g., C₁₆₀²⁺) and metallofullerene ions (e.g., Y_1–2C_94–124⁺), providing new evidence for the complexity of gas-phase fullerene chemistry. These findings underscore the importance of source region electric fields in shaping coalescence outcomes and highlight the potential of gas-phase approaches for synthesizing novel metallofullerenes. Full article

Graphene oxide (GO) is considered as a promising adsorbent material for the removal of metal from aqueous environments. Here, we have used the density functional theory (DFT) approach and a combination of parameters to characterise the interactions of GO with lead (Pb) and cadmium (Cd), i.e., typical harmful metals often found in water. Our model systems consist of a singly and doubly adsorbed neutral (${\mathrm{Pb}}^0$, ${\mathrm{Cd}}^0$) and charged (${\mathrm{Pb}}^{2+}$, ${\mathrm{Cd}}^{2+}$) atoms adsorbed on the GO nanoparticle of the chemical formula ${\mathrm{C}}_{30}$${\mathrm{H}}_{14}$${\mathrm{O}}_{15}$. We show that a single charged metal ion binds more strongly than a neutral atom of the same type. Moreover, to determine the possibility of multiple adsorptions of the GO nanoparticle, two metal atoms of the same species were co-adsorbed on its surface. We found a site-dependent adsorption energy such that when two atoms of the same specie are adsorbed at sites ${\mathrm{S}}_i$ and ${\mathrm{S}}_j$, the binding energy per atom depends on whether one of the two atoms is adsorbed firstly on the ${\mathrm{S}}_i$ or ${\mathrm{S}}_j$ sites. Furthermore, the binding energy per atom for the two co-adsorbed atoms of the same specie (i.e., neutral or charged) is less than the binding energy of a singly adsorbed atom. This suggests that atoms may become less likely to be adsorbed on the GO nanoparticle when their concentration increases. We adduce the origin of this observation to be interplay between the metal–metal interaction on the one hand and GO–metal on the other, with the former resulting in less binding for the charged adsorbed metals in particular, due to repulsive interaction between two positively charged ions. The frontier molecular orbitals analysis and the calculated global reactivity descriptors of the respective GO–metal complexes revealed that all the GO–metal complexes have a smaller HOMO–LUMO gap (HLG) relative to that of pristine metal-free GO nanoparticle. This may indicate that although the GO–metal complexes are stable, they are less stable compared to metal-free GO nanoparticles. The negative values of the chemical potentials obtained for all the GO–metal complexes further confirm their stability. Our work differs from previous experimental studies in that those lacked details of the interaction mechanisms between GO, Pb and Cd, as well as previous theoretical studies which used limited numbers of parameters to characterise the GO–metal interactions. Rather, we present a set of parameters or descriptors which provide comprehensive physical and electronic characterisation of GO–metal systems as obtained via the DFT calculations. These parameters, along with those reported in previous studies, may find applications in rational design and high-throughput screening of graphene-based materials for water purification, as an example. Full article

The sulfur dioxide (SO₂) compound is a primary environmental pollutant worldwide, whereas elemental sulfur (S) is a global commodity possessing a variety of industrial as well as commercial functions. The chemical relationship between poisonous SO₂ and commercially viable elemental S has motivated this investigation using the Density Functional Theory calculation of the relative transition state barriers for the two-step dehydro-sulfurization oxidation–reduction reaction. Additionally, doubly-charged nanoscale platelet molybdenum disulfide (MoS₂), armchair (6,6) carbon nanotube, 28-atom graphene nanoflake (GR-28), and fullerene C-60 are utilized as catalysts. The optimal heterogeneous and homogeneous catalysis pathways of the two-step oxidation–reduction from SO₂ to elemental S are further inspired by the biomimicry of the honeybee species’ multi-step bio-catalysis of pollen conversion to organic honey. Potential applications include environmental depollution, the mining of elemental sulfur, and the functionalization of novel technologies such as the recently patented aerial and amphibious Lynchpin^TM drones. Full article

We show that carboxyl-functionalized ionic liquids (ILs) form doubly hydrogen-bonded cationic dimers (c⁺=c⁺) despite the repulsive forces between ions of like charge and competing hydrogen bonds between cation and anion (c⁺–a⁻). This structural motif as known for formic acid, the archetype of double hydrogen bridges, is present in the solid state of the IL 1−(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC−CH₂−py][NTf₂]. By means of quantum chemical calculations, we explored different hydrogen-bonded isomers of neutral (HOOC–(CH₂)_n–py⁺)₂(NTf₂⁻)₂, single-charged (HOOC–(CH₂)_n–py⁺)₂(NTf₂⁻), and double-charged (HOOC– (CH₂)_n−py⁺)₂ complexes for demonstrating the paradoxical case of “anti-electrostatic” hydrogen bonding (AEHB) between ions of like charge. For the pure doubly hydrogen-bonded cationic dimers (HOOC– (CH₂)_n−py⁺)₂, we report robust kinetic stability for n = 1–4. At n = 5, hydrogen bonding and dispersion fully compensate for the repulsive Coulomb forces between the cations, allowing for the quantification of the two equivalent hydrogen bonds and dispersion interaction in the order of 58.5 and 11 kJmol⁻¹, respectively. For n = 6–8, we calculated negative free energies for temperatures below 47, 80, and 114 K, respectively. Quantum cluster equilibrium (QCE) theory predicts the equilibria between cationic monomers and dimers by considering the intermolecular interaction between the species, leading to thermodynamic stability at even higher temperatures. We rationalize the H-bond characteristics of the cationic dimers by the natural bond orbital (NBO) approach, emphasizing the strong correlation between NBO-based and spectroscopic descriptors, such as NMR chemical shifts and vibrational frequencies. Full article

The fundamental mechanism underlying negative-ion catalysis involves bond-strength breaking in the transition state (TS). Doubly-charged atomic/molecular anions are proposed as novel dynamic tunable catalysts, as demonstrated in water oxidation into peroxide. Density Functional Theory TS calculations have found a tunable energy activation barrier reduction ranging from 0.030 eV to 2.070 eV, with Si²⁻, Pu²⁻, Pa²⁻ and Sn²⁻ being the best catalysts; the radioactive elements usher in new application opportunities. C₆₀²⁻ significantly reduces the standard C₆₀⁻ TS energy barrier, while graphene increases it, behaving like cationic systems. According to their reaction barrier reduction efficiency, variation across charge states and systems, rank-ordered catalysts reveal their tunable and wide applications, ranging from water purification to biocompatible antiviral and antibacterial sanitation systems. Full article