Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals

Abstract

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 Si^2-, Pu^2-, Pa^2- and Sn^2- being the best catalysts; the radioactive elements usher in new application opportunities. C₆₀^2- 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.

Keywords: Graphene; atomic metals; doubly-charged anions; electron scattering; fullerenes; tunable catalysts; water oxidation.

Figure 1

The standard total cross sections (TCSs) (a.u.) for electron elastic scattering from atomic Au (left panel) and the fullerene molecule C₆₀ (right panel) are contrasted. For atomic Au, the red, blue and green curves represent TCSs for the ground, metastable and excited states, respectively. For the C₆₀ fullerene, the red, blue and pink curves represent TCSs for the ground and the metastable states, respectively, while the brown and green curves denote TCSs for the excited states. The dramatically sharp resonances in both figures correspond to the Au⁻ and C₆₀⁻ negative ions formation during the collisions.

Figure 2

Total cross sections (a.u.) for electron elastic scattering from atomic Th(a), Pa(b), U(c) and Np(d). The red, blue, green and pink curves represent TCSs for the ground, metastable and two excited states, respectively. The dramatically sharp resonances in the figures correspond to the Th⁻, Pa⁻, U⁻ and Np⁻ negative ions formation during the collisions.

Figure 3

The total cross sections (a.u.) for electron elastic scattering from atomic Cm (left panel) and No (right panel) are contrasted. For both Cm and No, the red, blue and orange curves represent TCSs for the ground and metastable states, respectively. The brown and green curves denote TCSs for the excited states. The dramatically sharp resonances in both figures correspond to the Cm⁻ and No⁻ negative ions formation during the collisions.

Figure 4

Doubly-charged anionic transition state geometry optimization for Sn. The red, white and green spheres represent O₂, H₂ and Sn (catalyst), respectively. Note the broken bonds in the transition state.

Figure 5

Doubly-charged anionic transition state geometry optimization for Pu. The red, white, and gold spheres represent O₂, H₂ and Pu (catalyst), respectively. Note the broken bonds in the transition state.

Figure 6

Doubly-charged anionic transition state optimization for C₆₀-6. The red, white and gold spheres represent O₂, H₂ and C₆₀ (catalyst), respectively. Note that, here as well, the bonds are broken in the transition state.

Figure 7

Geometrically optimized molecules of doubly-charged graphene Gr24-6 catalyzing the water conversion to peroxide, indicated by initial, transition and final states. Carbon, oxygen and hydrogen are represented by the gray, red and white spheres, respectively. Note, here as well, that the bonds are broken in the transition state.

Figure 8

Transition state energy barrier reduction, E(eV), for selected doubly-charged anionic systems of popular catalysts in ascending order of catalytic effectiveness. The horizontal axis shows the not-to-scale catalyzing systems. The pink line represents the energy position with no catalyst present.

Figure 9

Transition state energy barrier reduction, E(eV), in ascending order of catalytic effectiveness for doubly-charged heavy systems, including C₆₀ and 24 carbon graphene (Gr24-6). The horizontal axis indicates the not-to-scale catalyzing systems, and the solid pink line represents the barrier energy position with no catalyst present.

Figure 10

Transition state energy barrier reduction, E(eV), in ascending and descending order of catalytic effectiveness for doubly-charged atomic systems. The relative effectiveness of the popular components of catalysts from Z-30 to K-19 is emphasized. For the high Zs, the radioactive atoms are the most effective, while for the small ones, Si is the best doubly-charged catalyst. The horizontal axis reflects the catalyzing systems, and the solid pink line shows the barrier energy position with no catalyst present.