Evaluating the Effect of Resorcin[4]Arenes Conformational Structures on the Remediation of Methylene Blue in Water

Abstract

In this study, the effects of resorcin[4]arenes/cavitand structural properties: (i) hydrophobicity, aliphatic alkyl tails elongation (methyl, propyl, hexyl, and nonyl) based on macrocycles 1–4 lower rims; (ii) H-bond and dipole–dipole importance, resorcin[4]arene 4 vs its rigid core structure cavitand 5; and (iii) cavity order/disorder, crown (C_4v) 4 vs chair (C_2h) 6 isomers on the remediation of methylene blue (MB) in water have been investigated. Additionally, the adsorption kinetics/isotherms of MB by octols 1–4 were studied, indicating that the adsorption process follows pseudo-second order and Langmuir models, respectively. Notably, the longest alkylated crown (C_4V) conformer 4 was found to be the best adsorbent among the studied macrocycle family with a remarkable adsorption capacity (Q_max = 769.230 mg/g), owing to its unique structural features and tail-to-tail aggregation behavior in water. Hence, resorcin[4]arene 4 was further used to evaluate its adsorption efficiency toward other (non)ionic dyes, and the results were considerable. Also, its recoverability/reusability toward MB removal from water was examined for five consecutive cycles, and the results revealed a promising recovering capability with excellent adsorption efficiency, leading to confidence in its effective use for manifold adsorption/desorption cycles.