Nanocomposite HKUST-1@polysulfone membrane for the adsorptive removal of tetracyclines in waters

Abstract

To mitigate the presence of tetracyclines in water, it is essential to implement proper wastewater treatment processes that can effectively remove these compounds. In this work we develop a polymeric filtration membrane functionalized with nanocrystals of a metallic organic framework, designated by HKUST-1. The membrane was evaluated for the remotion of oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) in water samples. The membrane was fabricated using polysulfone (PSU), polyethyleneglycol (PEG), MOF (HKUST-1), and N-methyl-2-pyrrolidone (NMP) through the nonsolvent induced phase separation (NIPS) method. The membrane that presents the best antibiotic rejection characteristics was prepared with 15 % (w/w) PSU, 3 % (w/w) PEG, 1 % (w/w) HKUST-1, and 81 % (w/w) N-methyl-2-pyrrolidone (NMP). This membrane exhibited a pure water flux of up to 76.2 L.m−2.h−1, approximately 40 times more than the one achieved for pristine membranes. Once determined the best membrane composition, a physical–chemical characterization of membrane was done. A high antibiotic rejection rate was obtained for OTC, TC, and CTC, around 91 %, 91 %, and 99 % respectively. The pH of solutions has a strong influence on membrane rejection. The results suggest that intermolecular forces such as π-π type interactions and hydrogen bonds exist between the neutral molecules of tetracyclines (pH > pKa1 and < pKa2) and HKUST-1@PSU MMM, which are greater than the electrostatic forces at pH < pKa1 or pH > pKa2. Furthermore, FTIR spectra demonstrate the formation of a Cu-tetracycline complex as another adsorption mechanism. Finally, the interaction of the tetracyclines in the mixture on the removal performance was evaluated. The study revealed that chlortetracycline (CTC) exhibited superior removal performance, even over extended periods of time, despite having a lower initial concentration in the mixture. This innovative membrane represents a new generation of highly efficient filter systems specifically designed for water purification purposes.