The Role of Zeolite Structure in Its β-cyclodextrin Modification and Tetracycline Adsorption from Aqueous Solution: Characteristics and Sorption Mechanism

Abstract

Modification of zeolites with organic compounds is of increasing interest due to their significant potential in removing emerging pollutants from water. In this work, zeolites from fly ash with three different structure types, NaX (faujasite), NaA (Linde A) and NaP1 (gismondine), were modified with β-cyclodextrin (β-CD), and their adsorption efficacy towards tetracycline (TC) antibiotic in aqueous solutions have been studied. To assess the effect of modification on the zeolites, they were subjected to chemical, mineralogical and surface analyses using X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscope (SEM), N2 adsorption/desorption isotherm, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The maximum adsorption capacity for NaX-CD, NaA-CD and NaP1-CD was around 48, 60, and 38 mg/g, respectively. The fastest adsorption rate was observed for NaP1-CD, which achieved adsorption equilibria after 200 min, while for NaX-CD and NaA-CD it was established after around 24 h. The kinetic data were best described by the Elovich model, followed by pseudo-second order, while the Sips and Redlich–Peterson models were the most suitable to describe the adsorption isotherms. Based on the adsorption data as well as FTIR and XPS results, TC adsorption efficacy is strongly related to the amount of CD attached to the mineral, and hydrogen bonding formation probably plays the major role between CDs and adsorbate.

Zeolite Properties, Methods of Synthesis, and Selected Applications

“…These off-grid cations, together with water molecules, are located in the free spaces of the aluminosilicate skeleton, moving freely inside the mineral and easily exchanging with other ions present in the environment [ 6 ]. The peculiar internal structure of zeolites is the result of a diverse distribution of tetrahedra, forming a network of structural chambers and channels of different sizes that, under normal temperature conditions, are filled with water molecules, the so-called zeolitic water [ 7 ]. By means of thermal treatment, this water can be easily removed without disturbing the crystal structure of the zeolite ( Figure 1 ).…”

Pickering Emulsion Stabilized by β-Cyclodextrin and Cinnamaldehyde/β-Cyclodextrin Composite

“…Generally, substances embedded in β-CD are not only more stable when exposed to light, heat, and oxygen but also improve color, fragrance, and flavor [ 43 , 44 , 45 ]. Therefore, it has wide applications in the food [ 46 ], cosmetic [ 47 ], and pharmaceutical [ 48 , 49 ] industries. Its amphiphilicity makes it useful for stabilizing Pickering emulsions by adsorbing at the oil–water interface [ 50 ].…”