Estudo de diferentes sínteses de materiais mesoporosos à base de sílica para sorção de gadolínio

Abstract

The use of magnetic resonance imaging (MRI) exams in clinics and hospitals frequently requires intravenous gadolinium (Gd)-based contrast agents, which are bioaccumulative and potentially toxic substances. These compounds, when discharged into wastewater, tend to accumulate in aquatic environments. Considering the low efficiency of wastewater treatment processes in removing Gd³⁺ ions, this study aimed to evaluate the retention of this ion using mesoporous molecular sieves. For this purpose, two types of silica-based materials were synthesized: MCM-41 and SBA-15. MCM-41 was synthesized under basic conditions using tetraethyl orthosilicate (TEOS) as the silica source and cetyltrimethylammonium bromide (CTABr) as the structuredirecting agent. SBA-15 was synthesized under acidic conditions, employing the same silica source and the block copolymer polyethylene glycol-polypropylene glycolpolyethylene glycol (EO20PO70EO20) as the structure-directing agent. After synthesis and calcination, both materials were functionalized with di(2-ethylhexyl)phosphoric acid (D2EHPA) to enable gadolinium sorption from aqueous solutions. Preliminary experiments employed standard Gd³⁺ solutions, while subsequent tests were conducted with the contrast agents Dotarem and Magnevistan. Additionally, experiments involving the addition of these contrast agents to real wastewater samples from a sewage treatment plant in Rio de Janeiro were performed. The synthesized materials were characterized using Thermogravimetric Analysis (TGA), N₂ Adsorption, and Fourier Transform Infrared Spectroscopy (FTIR). The results demonstrated a high retention capacity for Gd³⁺ by the mesoporous materials, which was confirmed through tests using the contrast agents. Two experimental strategies were employed: retention from samples pre-digested using microwave radiation and retention from untreated samples. Microwave-assisted digestion was applied to decompose the contrast agents and evaluate the capacity of MCM-41 and SBA-15 to retain Gd³⁺ ions in digested and non-digested samples. For digested solutions, retention exceeded 99%. For nondigested solutions, the results varied: Dotarem showed no significant retention, whereas Magnevistan exhibited retention above 90%. This difference is attributed to Magnevistan’s linear structure, as opposed to the macrocyclic structure of Dotarem, and its shorter half-life, making it less stable. Similar results were obtained when using wastewater samples spiked with the contrast agents. The findings indicate that an analytical method can be proposed to enable quality control of water effluents contaminated with gadolinium.