Regeneration of the ciprofloxacin-loaded clinoptilolite by non-thermal atmospheric plasma

Natural clinoptilolite (CLI) exhibited a high efficacy in ciprofloxacin (CIP) removal from aqueous solution by adsorption. However, the regeneration of the spent adsorbent was a challenge since the adsorption occurred via electrostatic interactions and ion-exchange reaction. Herein, the feasibility of non-thermal plasma (NTP) was studied for the regeneration of ciprofloxacin-containing clinoptilolite (CIP-CLI) in five successive adsorption/NTP regeneration cycles. The NTP treatments were performed using a surface dielectric barrier discharge (SDBD) operating at atmospheric pressure in air. Plasma discharge gap, sample mass, and electrode surfaces were varied to find optimal regeneration parameters. For the plasma source with an electrode surface of 37.2 cm2, the 2 mm electrode gap and 20 min of plasma treatment were found as optimal parameters (sample mass of 0.2 g). The plasma treatment did not affect clinoptilolite features which were concluded from a study of textural properties and powder X-ray diffraction (PXRD) analysis. X-ray photoelectron spectroscopy (XPS) showed a decrease of total carbon content with around 10% of carbon residual left on the surface. The CLI adsorption capacity can be regenerated to at least 90% of its initial capacity during the five successive cycles, showing the involvement of plasma reactive species in decomposition of adsorbed CIP.