Clays-based geopolymers: a sustainable application as adsorbent of cytostatic drugs for water purification

The administration of cytostatic drugs in chemotherapy is steadily increasing, triggering thus a risk to the environment. Identifying powerful ways to effectively remove these hazardous pollutants from hospital and effluent wastewater before they discharge into the aquatic environment remains a critical and challenging task. Adsorption is among the most effective ways to treat contaminated water due to the wide availability and selectivity of the adsorbents besides the simplicity and the low start-up costs of the technique. In this work, a geopolymer, elaborated from an illito-kaolinitic clay (Douiret region of Tunisia) and industrial waste (silica fume and phosphogypsum), has been tested as promising decontamination of the cytostatic drugs paclitaxel (PCX) and irinotecan (IRI) from water samples. The foamed geopolymer was characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy and thermogravimetric analysis before and after adsorption. Adsorption batch assays were performed using different concentrations of PCX and IRI, contact times and environmental conditions. The geopolymer had an excellent removal efficiency (almost 100% for PCX and 89% for IRI) using 20 mg of adsorbent and 2.5 mg/L of each drug concentration. The characterization results showed that cytostatic drugs were adsorbed to the geopolymer through physical interactions, pore filling, electrostatic attraction and hydrogen bonding. The specific surface area and pore volume of the geopolymer were 82.23 m²/g and 0.19 cm³/g, respectively. In addition to its cost-effective properties, the geopolymer demonstrated excellent efficiency in contaminated natural samples (including influent, effluent wastewater and surface water) denoting a great application for water purification.