Selective adsorption and extraction of C70 and higher fullerenes on a reusable metal–organic framework MIL-101(Cr)

Abstract

The adsorption and extraction of fullerenes on the metal–organic framework MIL-101(Cr) were studied in detail in terms of kinetics, thermodynamics, adsorption isotherms, competitive adsorption, and breakthrough curves. The adsorption of C60 and C70 on MIL-101(Cr) follows a pseudo-second-order kinetic model. The adsorption rate constant for C70 is 3 to 5 times that for C60, showing faster and easier adsorption of C70 over C60 on MIL-101(Cr). Intraparticle diffusion model analysis reveals that the adsorption of C60 and C70 on MIL-101(Cr) proceeds by two phases, surface sorption and intraparticle/pore diffusion. The adsorption of fullerenes on MIL-101(Cr) is controlled by entropy changes. The maximum adsorption capacity for C70 at 30 °C (198.4 mg g⁻¹) is 29 times that for C60 (6.76 mg g⁻¹). MIL-101(Cr) shows much more favorable adsorption of C70 and higher fullerenes than C60 with a high selectivity (α_C70/C60 = 24). Selective extraction of C70 and higher fullerenes from crude carbon soot can be easily achieved on MIL-101(Cr) via a simple adsorption–desorption process. The used MIL-101(Cr) can be regenerated by washing with o-dichlorobenzene under ultrasonication. The high selectivity, fast adsorption, easy desorption, and excellent reusability makes MIL-101(Cr) attractive as a novel adsorbent for the enrichment and extraction of C70 and higher fullerenes.