Dye effluent causes serious pollution and damage to the environment and needs a series of treatments before it can be discharged. Among the numerous effluent treatment methods, adsorption is the simplest and does not cause secondary pollution. Bio-adsorbents are especially advantageous in the treatment of low-concentration dye effluent. In this study, the adsorption and removal capacities of unmodified α- and β-chitosan and modified β-chitosan (β-chitosan cross-linked with triethylenetetramine, BCCT) on C.I. Reactive Blue 221 (RB221) dye were compared. The experiments were performed on the adsorption of the RB221 dye by unmodified α- and β-chitosan and cross-linkage–modified BCCT at different temperatures and for different durations, which are presented along with the relevant adsorption kinetics calculations. According to the results, as the temperature increased from 303 to 333 K, the initial adsorption rates of the adsorbents, α-chitosan, β-chitosan, and BCCT, for the RB221 dye, changed from 1.01 × 10², 4.74 × 10², and 1.48 × 10⁶ mg/g min to 5.98 × 10⁴, 4.23 × 10⁸, and 1.52 × 10¹³ mg/g min, respectively. BCCT thus showed the best adsorption for the dye at all temperatures from the Elovich model. These results confirmed the successful introduction of a polyaminated and cross-linked extended structure as a modification for the BCCT adsorbent, which makes it resistant to acid hydrolysis and gives it the functional amine group for dye adsorption, thereby promoting the ability of BCCT to adsorb dyes under strongly acidic conditions. The compound synthesized in this study is expected to be a good choice in the future for purifying strongly acidic effluent containing anionic organic dyes.

A hybrid material obtained by blending β-chitosan (CS) with triethylenetetramine-functionalized graphene oxide (TFGO) (CSGO), was used as an adsorbent for a reactive dye (C.I. Reactive Blue 221 Dye, RB221), and the adsorption and removal performances of unmodified CS and mix-modified CSGO were investigated and compared systematically at different pH values (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12). The adsorption capacities of CS and CSGO were 45.5 and 56.1 mg/g, respectively, at a pH of 2 and 5.4 and 37.2 mg/g, respectively, at a pH of 12. This indicates that TFGO was successfully introduced into CSGO, enabling π–π interactions and electrostatic attraction with the dye molecules. Additionally, benzene ring-shaped GO exhibited a high surface chemical stability, which was conducive to maintaining the stability of the acid and alkali resistance of the CSGO adsorbent. The RB221 adsorption performance of CS and CSGO at acidic condition (pH 3) and alkaline condition (pH 12) and different temperatures was investigated by calculating the adsorption kinetics and isotherms of adsorbents. Overall, the adsorption efficiency of CSGO was superior to that of CS; thus, CSGO is promising for the treatment of dye effluents in a wide pH range.