Behaviors and mechanism of acid dyes sorption onto diethylenetriamine-modified native and enzymatic hydrolysis starch

In this paper, different starches were modified by diethylenetriamine. The native starch reacted with diethylenetriamine giving CAS, whereas the enzymatic hydrolysis starch was modified by diethylenetriamine producing CAES. Adsorption capacities of CAES for four acid dyes, namely, Acid orange 7 (AO7), Acid orange 10 (AO10), Acid green 25 (AG25) and Acid red 18 (AR18) have been determined to be 2.521, 1.242, 1.798 and 1.570 mmol g-1, respectively. In all cases, CAES has exhibited higher sorption ability than CAS, and the increment for these dyes took the sequence of AO7 (0.944 mmol g-1) > AO10 (0.592 mmol g-1) > AR18 (0.411 mmol g-1) > AG25 (0.047 mmol g-1). Sorption kinetics and isotherms analysis showed that these sorption processes were better fitted to pseudo-second-order equation and Langmuir equation. Chemical sorption mechanisms were confirmed by studying the effects of pH, ionic strength and hydrogen bonding. Thermodynamic parameters of these dyes onto CAES and CAS were also observed and it indicated that these sorption processes were exothermic and spontaneous in nature.