Insight into the adsorption and co-adsorption of PPCPs on Ti3C2Tx MXene: Behaviors, mechanisms and application potentials

Abstract

In this study, four pharmaceutical compounds including sulfamethoxazole (SMX), oxytetracycline (OTC), ciprofloxacin (CIP), and ibuprofen (IBU) with different functional groups and pKa, were selected as representative pollutants to systematically investigate the Pharmaceutical and Personal Care Products (PPCPs) adsorption on a nanomaterial Ti3C2Tx MXene in simulated solution and real surface water. The results show that Ti3C2Tx was an excellent PPCPs adsorbent, but the process was affected by the characteristics of pollutants pronouncedly, the obtained maximum adsorption capacity were OTC (210.97 mg/g) > IBU (185.05 mg/g) > CIP (160.60 mg/g) > SMX (68.12 mg/g). Specially, the charge screen effect caused Ti3C2Tx precipitation during CIP adsorption. The response surface methodology analysis indicates that initial solution pH (3–11) had significant effects, while the influence of humic acid (0–10 mg/L) or sodium chloride (0–10 mg/L) was limited, and the interactions between these factors was slight. In the co-adsorption process, the competitive effects reduced the adsorption of SMX and IBU, however, the enhanced positive ionization and the possible electrostatic repulsive interactions promoted that of CIP and OTC. In real surface water, although the influence of natural organic matters was negligible, the preferential adsorption of background metal ions such as aluminum and calcium ions reduced the adsorption capacity of the selected PPCPs by approximately 29.9 % to 88.4 %. Moreover, the adsorbent characterization conjoined with performance examination imply that electrostatic attraction dominated the Ti3C2Tx adsorption of PPCPs, and hydrogen bonding interactions as well as surface complexation might also contributed. These observations suggest that Ti3C2Tx MXene has the potential for use as adsorbent to eliminate aqueous PPCPs, nevertheless, the interference of co-existing metal ions and the stability of adsorbent were also noteworthy.