Abstract
In this study, an unsaturated Cu-based MOF, HKUST (Cu3(BTC)2), was fabricated and modified with sulfonate groups in two steps, leading to the construction of a novel sulfo-functionalized MOF. The prepared framework was utilized in the adsorption and separation of various organic dyes (MB, Er, FS, and MV). The adsorption process represented intriguing features due to the introduction of the SO3H functional groups into the framework. Such an attractive feature has rarely been depicted in previous works. In addition to the substantially increased adsorption capacity of the modified framework compared with that of pristine MOF, a reverse and selective phenomenon was perceived in the cases of FS and MV. The sulfo-functionalized MOF could adsorb MV with high adsorption capacity but barely adsorbed FS, and the opposite condition was observed for pristine MOF. In addition, the prepared framework showed high selectivity in a mixed solution of dyes. On the other hand, the modified framework had no role in the first step of the adsorption and separation process and showed the same behavior as pristine MOF. Furthermore, the sulfonate functional groups could not be directly incorporated into HKUST. The experimental data followed the pseudo-second-order kinetics and the Langmuir isotherm model. Thermodynamic studies demonstrated an exothermic spontaneous mechanism for the dye adsorption process. The prepared adsorbents were capable of being recycled for four sequential cycles. Hereupon, this study presents a notably efficacious approach for the reverse performance of frameworks for the dye adsorption and separation process.
Highlights
Nowadays, dyes are applied in various industries, such as leather, paper, pharmaceutical, textiles, cosmetics and food.[1,2,3] Despite the great applications of these compounds in the industry, they have some disadvantages: they are highly stable, non-degradable, toxic and carcinogenic.[4]
The FT-IR spectrum of HKUST-AMP is shown in Fig. S1b.† The band related to the stretching vibration of the Scheme 1 Synthesis of HKUST-AMP-SO3H
The XRD patterns of the synthesized compounds can be observed in Fig. S2.† According to the main diffraction peaks, it could be seen that the XRD patterns of stimulated (Fig. S2a†) and as-synthesized HKUST (Fig. S2b†) were thoroughly identical and in agreement with previous reports, con rming the purity and crystallinity of the framework.[36]
Summary
Dyes are applied in various industries, such as leather, paper, pharmaceutical, textiles, cosmetics and food.[1,2,3] Despite the great applications of these compounds in the industry, they have some disadvantages: they are highly stable, non-degradable, toxic and carcinogenic.[4]. MOFs have gained signi cant attention in recent years owing to their unique characteristics.[22] MOFs are a new class of porous crystalline structures, which constitute metal clusters and multifunctional organic ligands They have attracted much attention among other porous structures due to their intriguing and unique properties, including high porosity and surface area, diverse accessible sites, high thermal stability, and tunable pore size.[23,24,25] These features make MOFs good candidates for various applications, such as adsorption,[26,27] catalysis,[28,29] drug delivery,[30,31] separation,[32] and sensing.[33] various methods have been applied to enhance the dye adsorption capacity of MOFs, the effect of functional groups on the reverse and selective adsorption and separation of dyes has rarely been investigated.[34,35] Post-synthetic modi cation (PSM) is one of the impressive methods to increase the performance of the
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