Succinylated Starches for Dye Removal

Abstract Succinylated bitter cassava starches are evaluated for the removal of cationic, methylene blue (MB) and anionic, methyl orange (MO) dyes present in water. The native starch (NS) extracted from bitter cassava by the dry method, is modified using succinic anhydride (SA) as esterifying agent and sodium hydroxide, sodium carbonate, sodium sulfate, and sodium chloride as non‐toxic and environmentally friendly catalysts. The effect of the type and concentration of catalyst on the modification is evaluated. Starch replacement with SA is confirmed by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The degree of substitution in the resulting succinylated starches is determined by volumetric analysis, presenting high values (0.5–0.9). These materials act as superabsorbent gels, sensitive to changes in pH and ionic strength, and mostly with anti‐polyelectrolytic behavior. MB dye has a higher affinity for succinylated starches than the MO dye. The removal capacity of MB is also influenced by the pH and the ionic strength of the solution. The kinetics and adsorption isotherms are satisfactorily adjusted to the pseudo‐second order and Freundlich models, respectively. The esters functionalities of the starch prove to be reusable adsorbents, completing successfully five cycles of adsorption‐desorption.