Polyaniline-modified halloysite nanotubes as high-efficiency adsorbents for removing of naproxen in the presence of different heavy metals.

In this work, novel adsorbent polyaniline-modified halloysite nanotubes (HNT@PA-2) were synthesized successfully by polymerization to increase active adsorption sites. With the increase of the amount of aniline, the adsorption capacity of naproxen becomes higher. The optimal ratio of halloysite nanotubes to aniline was 1 : 2. The effects of adsorption conditions such as pH, mass of HNT@PA-2, time and initial concentration of naproxen were systematically researched. The optimum adsorption for naproxen was pH 9, mass 10 mg and contact time 4 h. The adsorption of naproxen conformed to the pseudo-first-order kinetic model, and the maximum adsorption capacity was 242.58 mg g at 318 K. In addition, the effects of ionic strength and different heavy metals also were studied. Higher ionic strength of the system could influence the adsorption of naproxen. The effects of Al, Pb, Zn and Co ions on the adsorption of naproxen could be ignored, while Cu and Fe ions inhibited the process. The mechanisms for naproxen adsorbed by the HNT@PA-2 were π-π interaction, hydrogen bonding and hydrophobic reaction. Therefore, the HNT@PA-2 could be used for the treatment of medical wastewater for removing naproxen.