Regular ArticleAdsorption of reactive yellow X-RG and reactive brilliant red X-3B onto cucurbit[8]uril and cucurbit[6]uril: Effect factors, adsorption behavior and mechanism study

Cucurbit[8]uril (CB[8]) and cucurbit[6]uril (CB[6]) were applied as a high efficiency absorbent to remove reactive yellow X-RG and reactive brilliant red X-3B dyes in aqueous solution. Factors affecting adsorption such as dosage, contact time, temperature, pH value and metal cation were investigated. The adsorption isotherms for X-RG followed the Langmuir and Sips model while for X-3B followed the Freundlich model. Adsorption thermodynamic showed that X-RG and X-3B adsorption onto CB[8] and CB[6] was a spontaneous and enthalpy-driven process. Adsorption kinetics was determined to follow the pseudo-second-order model. In order to examine the adsorption mechanism, adsorbents and adsorption products of cucurbiturils were characterized further by several physicochemical techniques. FT-IR, TG analyses and DFT calculations revealed the formation of the new inclusion complexes, and Zeta potentials reveals the electrostatic interaction may be the significant driven force. UV-vis adsorption spectra were investigated by TDDFT and results showed that the main absorption bands of X-RG and X-3B mainly arisen from π → π∗ and n → π∗ transition. Encapsulated with CBn, the UV-vis absorption bands of inclusion complexes were shifted by 10-15 nm due to intermolecular charge transfer (ICT).

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