Electrical-Driven Transport of Endohedral Fullerene Encapsulating a Single Water Molecule

Encapsulating a single water molecule inside an endohedral fullerene provides an opportunity for manipulating the ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ through the encapsulated polar ${\mathrm{H}}_2\mathrm{O}$ molecule. Using molecular dynamic simulations, we propose a strategy of electrical-driven transport of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ inside a channel, underpinned by the unique behavior of a water molecule free from a hydrogen-bonding environment. When an external electrical field is applied along the channel’s axial direction, steady-state transport of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ can be reached. The transport direction and rate depend on the applied electrical intensity as well as the polar orientation of the encapsulated ${\mathrm{H}}_2\mathrm{O}$ molecule.

Figure 1

An electrical field is applied along the $+z$ direction of a CNT channel, with electrical intensity $E=0.02\mathrm{V}/\AA$. (a) Snapshots of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ transport along the $-z$ direction. (b) Axial position transport history of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$; note that a periodic boundary condition is applied in the axial direction, and thus the ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ transports along the $-z$ direction in an infinitely long channel at a steady rate.

Figure 2

(a) Schematic of the instantaneous inclined angle (${\theta }_t$) between the instantaneous dipolar orientation ($p_t$) of the encapsulated ${\mathrm{H}}_2\mathrm{O}$ and unit vector ($\widehat{\mu }$) along the electrical field direction. (b) The history of ${\theta }_t$ during the transport of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ under $E=0.02\mathrm{V}/\AA$.

Figure 3

Effect of the initial inclination angle upon application of the electrical field ($E=0.02\mathrm{V}/\AA$), ${\theta }_0(={\theta }_{t=t_0})$, on the (a) history of ${\theta }_t$ and (b) axial position transport history of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$.

Figure 4

Transport map of ${\mathrm{H}}_2\mathrm{O}@{\mathrm{C}}_{60}$ on a CNT channel: region I (${26.7}^{°}<|{\theta }_{ts}|<82.6°$ and $0.006\mathrm{V}/\AA <E<0.065\mathrm{V}/\AA$) where the transport is opposite to the electrical field direction ($-z$); region II ($0\le |{\theta }_{ts}|\le 26.7°$ and $E\ge 0.065\mathrm{V}/\AA$) where transport is along the direction of the electrical field ($+z$); region III ($0\le E\le 0.006\mathrm{V}/\AA$) where the transport direction is unstable.

Figure 5

Autocorrelation functions of (a) $v$-ACF and (b) $\omega$-ACF of the encapsulated ${\mathrm{H}}_2\mathrm{O}$ molecule inside ${\mathrm{C}}_{60}$ with the electrical intensity of $0.03\mathrm{V}/\AA$.