The sorption of the nonsteroidal anti-inflammatory drugs diclofenac and naproxen onto UV and/or H2O2 treated MWCNT-COOH and MWCNT-OH†
The release of carbon nanotubes (CNTs) with treated wastewater is one of the major sources of CNTs in the environment. The great sorption capacity of pristine CNTs can be changed during wastewater processing. CNTs in the environment can interact with different components and pollutants. The aim of this study is the determination of the effect of treatment methods of wastewater containing functionalized CNTs on the sorption of new emerging contaminants. The process of sorption of diclofenac sodium (DCF) and naproxen (NPX) was tested using carbon nanotubes released after treatment by UV and/or H2O2. The results revealed that sorption on non-treated CNTOHs was governed by chemisorption, with chemisorption being rate limiting step (pseudo-second order regime). Treatment of the CNTOHs changed the kinetics of NPX sorption to a pseudo-first order (CNTOH-UV and CNTOH-H2O2) or an intraparticle diffusion model (CNTOH-UV + H2O2). DCF sorption was described by pseudo-first or pseudo-second order kinetics. NPX sorption onto treated CNTOHs and CNTCOOHs was ascribed to the Freundlich or Temkin models. The Freundlich and Dubinin–Radushkevich models revealed the best fitting for the description of DCF sorption onto CNTOHs and CNTCOOHs. Although treatment affected the physicochemical properties of the CNTs only slightly, it did change the sorption affinity and capacity. NPX sorption was favored over all tested CNTs, and CNTCOOHs revealed a higher sorption capacity for all tested adsorbates. The mechanism of sorption was connected with π–π interactions between the NPX and the CNTOHs, and the functional groups of the CNTCOOHs. DCF sorption onto CNTOHs was governed by electrostatic forces, with adsorption onto CNTCOOHs governed by functionalization.