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The Adsorption of Reactive Blue 19 Dye onto Cucurbit[8]uril and Cucurbit[6]uril: An Experimental and Theoretical Study
The adsorption behavior and mechanism
of Reactive Blue 19 (RB19)
on cucurbit[6]Âuril (CB[6]) and cucurbit[8]Âuril (CB[8]) were investigated.
The adsorption isotherm data obtained at different temperatures were
fitted well to the Langmuir isotherm, and according to this model,
CB[8] and CB[6] exhibited maximum monolayer adsorption capacities
of 714.29 and 100.5 mg/g, respectively, at 298.15 K. The adsorption
thermodynamic functions Δ<i>G</i>, Δ<i>H</i>, and Δ<i>S</i> were evaluated and revealed
that RB19 adsorption onto CB[8] and CB[6] is a spontaneous and enthalpy-driven
process. The adsorption process was determined to follow pseudo-second-order
kinetics, indicating that chemisorption dominates the adsorption process.
Fourier tranform IR spectroscopy, thermogravimetric analysis, and
density functional theory (DFT) calculations revealed that the formation
of an inclusion complex is the main driving force of adsorption. The
phenyl and sulfone moieties of RB19 reside inside the cavity of CB[8],
but because of the small cavity, only the sulfone of RB19 resides
inside the cavity of CB[6]. Time-dependent DFT calculations revealed
that all of the absorption bands of RB19 derive from π →
Ï€* transitions, while for the adsorption product of CB[8], the
bands located at 590 and 287 nm derive from π → π*
transitions and the bands located at 254 and 202 nm mainly derive
from intermolecular charge transfer (ICT)