Figure 1 contains the spectrum of 100 [micro]L of 2-pyrrolidone per mL of toluene, the spectrum 100 [micro]L of 2-pyrrolidone per mL of toluene saturated with [C.sub.60], and the spectrum of 100 [micro]L of 2-pyrrolidone per mL of toluene saturated with [C.sub.70].
Complex formation, resulting from the interactions of the nanoparticles with the 2-pyrrolidone, is likely an equilibrium process involving both 2-pyrrolidone interacting and not interacting with the nanoparticles.
Concentration studies were carried out to find an optimum concentration level of 2-pyrrolidone to generate a 2-pyrrolidone-nanoparticle complex and also allow the observation of the carbonyl absorption of the complex.
Spectra collected at 5 and 2 [micro]L of 2-pyrrolidone per mL of toluene and toluene saturated with [C.sub.60] or [C.sub.70] are shown in Fig.
Figure 4 shows four spectra collected over the concentration range of 10 to 5 [micro]L of 2-pyrrolidone per mL of toluene saturated with [C.sub.60].
The infrared absorption observed near 1687 [cm.sup.-1] for the complex formed between 2-pyrrolidone and the [C.sub.60] nanoparticles at the lower concentrations (5 and 2 ([micro]L per mL) very likely exists at the higher concentrations of 2-pyrrolidone (200 and 100 [micro]L per mL); however, this infrared absorption may be buried under the intense carbonyl absorption of the excess, noninteracting 2-pyrrolidone.
Figure 5 contains again the spectrum of 100 and 5 [micro]L of 2-pyrrolidone per ml of toluene and toluene saturated with [C.sub.60]- The spectrum that results from subtracting the spectrum of 100 [micro]L of 2-pyrrolidone per mL of toluene times 0.95 (subtraction factor) from the spectrum of 100 [micro]L of 2-pyrrolidone per mL of toluene saturated with [C.sub.60] is also given in Fig.
The observed shifts to lower wavenumbers of the carbonyl absorption in 2-pyrrolidone resulting from its interactions with [C.sub.60] could suggest that its interaction with the [C.sub.60] occurs through the lone-pair electrons of the oxygen part of its amide structure.
In summary, the infrared spectra collected in this study suggest that interactions occur between 2-pyrrolidone and [C.sub.60] resulting from possible donation of the electron pairs from the oxygen part of its amide functionality into the anti-bonding MO's of the [C.sub.60] At lower concentrations of 2-pyrrolidone (5 and 2 [micro]L of 2-pyrrolidone per mL of toluene and toluene saturated with [C.sub.60]), a significant shift of its amide carbonyl absorption (~1700 [cm.sup.-1] to ~1687 [cm.sup.-1]) is observed supporting this kind of interaction.
- The spectra of 10 [micro]L of 2-pyrrolidone per [micro]L of toluene, per mL of toluene saturated with [C.sub.60], and per mL of toluene saturated with [C.sub.70] are shown.
- The spectra of 5 and 2 [micro]L of 2-pyrrolidone per mL of toluene, per [micro]L of toluene saturated with [C.sub.60], and per mL of toluene saturated with [C.sub.70] are shown.