Adsorption of iodinated trihalomethanes onto thiol functionalized ZIF-8s: Active adsorption sites, adsorptive mechanisms, and dehalogenation by-products

• Published in: The Science of the total environment 2021-02, Vol.754, p.142376-142376, Article 142376
• Main Authors: Induvesa, Phacharapol, Ratanatawanate, Chalita, Wongrueng, Aunnop, Punyapalakul, Patiparn
• Format: Article
• Language: English
• Subjects: Adsorption mechanism; Dehalogenation; Iodinated trihalomethanes; Thiol modification; Zeolite imidazolate framework
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.142376

The adsorptive mechanisms operating in, and the effect of two different thiol modification methods on, the removal of five iodinated trihalomethanes (I-THMs) by the zeolite imidazolate framework (ZIF-8) were investigated in single and mixed solutions. The direct postgrafting of dithioglycol to the zinc complex node of ZIF-8 (ZF-SH) can increase the mesopore structures that enhance inner pore accessibility; this increase is a critical property required for excellent adsorption of I-THMs. The synergetic adsorptive interactions consist of Lewis acid-base interactions via the Zn-Zn complex, ion-dipole interactions involving the protonated hydroxyl and thiol groups, and hydrophobic interactions at the imidazole ring. In contrast to ZF-SH, the (3-mercaptopropyl)-trimethoxy functionalized silica coating on ZIF-8 (ZF-Si-SH) causes a lower thiol moiety and a steric effect that is reflected in its lower adsorption capacity. In both single and mixed solutions, the small molecular size and hydrophobic nature of I-THMs can promote better adsorption capacity on all thiol-modified ZIF-8, while the minus dipole charge distribution of the I-THMs structure plays a more critical role in selective adsorption on pristine ZIF-8. Interestingly, the dehalogenation of triiodomethane to diiodomethane due to a nucleophilic substitution (SN2) reaction can be accelerated by the thiol functionalized silica layer on ZIF-8. [Display omitted] •Post-grafting of dithioglycol on ZIF-8 performs excellent I-THMs adsorption.•Si-OH, R-SH and zinc complex of ZIF-8 can accelerate dehalogenation of TIM to DIM.•Adsorption consists of Lewis acid-base, ion-dipole and hydrophobic interactions.•Dipole charge of I-THMs plays a critical role in selectivity of pristine ZIF-8.•Molecular size and hydrophobicity of I-THMs control selectivity of thiol-ZIF-8.