New hydrogels based on symmetrical aromatic anhydrides: Synthesis, characterization and metal ion adsorption...

Unsatisfactory mechanical properties, poor heat resistance, dissolution in acidic media and high swelling ratios limit using chitosan as an adsorbent in industry. In this study, we used dianhydride derivatives famous for their exceptional mechanical and thermal characteristics and low water absorption. In this study, pyromellitic dianhydride (PMDA), benzophenone-3,3',4,4'-tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA) and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (FDA) were utilised as crosslinking agents. Use of common crosslinking agents usually decreases the metal uptake capacity of chitosan. These novel crosslinking agents increased the metal uptake from 1.8 (ODPA/Cu²⁺) to 7.8 (PMDA/Zn²⁺) times. Langmuir and Freundlich adsorption models were applied to analyse the isotherms and isotherm constants. Kinetic, X-ray diffraction, pH, FTIR studies were also carried out.