Simultaneous adsorption of organic and inorganic micropollutants from rainwater by bentonite and bentonite‑carbon nanotubes composites

Abstract

Recently, there are numerous organic and inorganic micropollutants exist in the water environment, thus it is necessary to develop a new versatile adsorbent for simultaneous removal of different water pollutants. The aim of this study was to evaluate natural, thermally-treated bentonites (0–700 °C) and bentonite‑carbon nanotubes composites (Ben100 + SWCNT and Ben100 + SWCNT-OH) in terms of their capabilities for simultaneous adsorption of organic micropollutants and heavy metals from rainwater. Ben-CNT composites consisted of 60 wt% of bentonite (Ben100) and 40 wt% of single-walled carbon nanotubes (SWCNT) or single walled carbon nanotubes with hydroxyl groups (SWCNT-OH). The composition of the rainwater has been modified by adding lead nitrate, zinc nitrate and other organic micropollutants, including benzotriazole (BZT) and anthracene (ANT). Overall, removal of BZT and ANT varied from 4.5% to 93% and from 50% to 95.5%, respectively. Ben100 + SWCNT and Ben100 + SWCNT-OH exhibited increased removal percentage to 93% (BZT) and 95.5% (ANT), respectively. The fitting degree showed that Freundlich model was the most suitable for BZT and ANT adsorption on Ben100 and Ben100 + SWCNT, while Langmuir provided the best fit for Ben100 + SWCNT-OH. From bentonites (0–700 °C), the highest removal of both zinc and lead was observed for Ben100 and Ben300, while the lowest for Ben500 and Ben700. Ben100 + SWCNT and Ben100 + SWCNT-OH composites demonstrated over 90% removal percentage of zinc and lead. During adsorption of these compounds, the time required to reach equilibrium was very short (30 min) for both composites. The study showed that Ben-CNT composites are the effective adsorbents for removing micropollutants and heavy metals from aqueous solutions.