Water-based room-temperature synthesis of Ce-BDC-MOFs using different additives: a comprehensive investigation on properties and tetracycline adsorption performance

Abstract

The water-based room-temperature synthesis of cerium (Ce(IV))-based metal–organic frameworks (Ce-MOFs) has gained significant attention in recent years. However, due to the low solubility of most organic linkers, especially 1,4-benzene dicarboxylic acid (BDC), in water, it is essential to use different additives and organic co-solvents for the synthesis of such MOFs. Hence, in this work, the role of additives in the synthesis of Ce-BDC-MOFs is systematically investigated by synthesizing a series of Ce-BDC-MOFs in the presence of different additives, including sodium perchlorate monohydrate (SPM), acetic acid (HAc), triethylamine (TEA), sodium acetate (NaAc), formic acid (FA), and potassium hydroxide (KOH). It is found that the additives are not only essential for the synthesis of Ce-BDC-MOFs but also play a critical role in the crystallization, porosity, and adsorption performance of the resulting MOFs towards tetracycline (TC) antibiotics. Owing to the dual-functional nature of NaAc, which at first significantly increases the solubility of BDC in water and then acts as a modulator and accelerates the generation of Ce-based clusters, the resulting sample synthesized in the presence of this additive exhibited the highest crystallinity and porosity among all synthesized samples. This sample not only exhibited good structural stability during activation at high temperatures, after the adsorption of TC, and cyclic adsorption/desorption experiments but also showed good water stability, because of which its surface area reduced from 821 ± 28 to 706 ± 77 m² g⁻¹ after being stored in water for 30 days. This sample also exhibited low toxicity, further indicating the potential of this strategy in the synthesis of green MOFs that are suitable for water treatment applications. Adsorption results showed that this green adsorbent reached a maximum adsorption capacity of 2128.77 mg g⁻¹ within 16 min, which is much higher than the values reported previously. Accordingly, it can be concluded that this optimized synthesis strategy offers superior performance compared with the solvothermal and conventional room-temperature synthesis methods, and it does not need any pre-treatment, activation energy, or organic solvents, thereby simplifying the large-scale synthesis of Ce-MOFs, reducing their production costs, and extending their practical applications.