Development of biobased material hydrogel from condensed tannin via anhydride esterification: A proof of concept for efficient ciprofloxacin removal

Pine bark, composed mainly of polyflavonoids, is a product widely generated by forestry industries around the world without having any significant value, being a source of waste that is disposed of for burning. Pine bark polyflavonoids, specifically condensed tannins, were subjected to esterification reactions with maleic anhydride and itaconic anhydride to promote hydrogel formation via a radical reaction with acrylic acid and potassium persulfate. The obtained materials were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning electron Microscopy (SEM), and Proton Nuclear Magnetic Resonance (¹H NMR). In water absorption tests, the modified tannin hydrogels exhibited absorption percentages of approximately ~2000 %, while the unmodified hydrogels reached percentages close to 500 %, indicating that the modification is a strong agent that promotes this increase. Rheological tests confirmed that the hydrogels displayed elastic behavior. The removal of ciprofloxacin (CIP) was close to 80 % at pH 7 and 9, while at pH 3, removal was around 50 %. The reusability of the hydrogel was determined by five adsorption/desorption cycles, with removal rates ranging from 98 to 75 %. The removal of CIP in a synthetic effluent resulted in efficiencies of 46 %. Thus, tannin-based hydrogels modified with anhydrides demonstrate potential as functional materials for environmental applications. Thus, this research seeks to provide a real value-added use for forest waste by generating materials with direct applications in pollutants removal.