Batch Adsorption of Orange II Dye on a New Green Hydrogel-Study on Working Parameters and Process Enhancement

Abstract

A new green hydrogel consisting of cherry stone (CS) powder and sodium alginate (SA) was synthesized through physical crosslinking. The product had a mean diameter of 3.95 mm, a moisture content of 92.28%, a bulk density of 0.58 g/cm³, and a swelling ratio of 45.10%. The analyses of its morphological structure and functional groups by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) showed the successful entrapping of the CS in the SA polymeric matrix. The viability of the prepared hydrogel as adsorbent was tested towards Orange II (OII) anionic dye. The influence of the pH, adsorbent amount, contact time, and initial dye concentration was evaluated. Then, the impact of three accelerating factors (stirring speed, ultrasound exposure duration, and temperature) on the OII retention was investigated. The highest recorded removal efficiency and adsorption capacity were 82.20% and 6.84 mg/g, respectively. The adsorption followed Elovich and pseudo-second-order kinetics, was adequately described by Freundlich and Khan isotherms, and can be defined as spontaneous, endothermic, and random. The experiments confirmed that the obtained hydrogel can be used acceptably for at least two consecutive cycles, sustaining its effectiveness in water decontamination.

Keywords: Orange II; adsorption; cherry stones; desorption; equilibrium isotherm; hydrogel; kinetic study; sodium alginate; thermodynamic study; ultrasound.

Figure 1

SEM images of the CSSA hydrogel before (A) and after (B) OII adsorption.

Figure 2

FTIR spectra of CSSA hydrogel before (A) and after (B) OII adsorption.

Figure 3

pH_PZC of CSSA hydrogel.

Figure 4

Influence of pH (A), adsorbent dose (B), time (C), and initial dye concentration (D) on the removal of OII from aqueous solution through adsorption on CSSA hydrogel (the experiments were carried out with 10 mL of OII, at room temperature, without stirring, the working conditions being as follows A: OII concentration—20 mg/L, pH—variable, adsorbent dose—0.038 g/L, contact time—300 min; B: OII concentration—20 mg/L, pH—3, adsorbent dose—variable, contact time—300 min; C: OII concentration—20 mg/L, pH—3, adsorbent dose—0.058 g/L, contact time—variable; D: OII concentration—variable, pH—3, adsorbent dose—0.058 g/L, contact time—300 min).

Figure 5

Kinetic models of the OII adsorption on CSSA hydrogel (initial OII concentration: (A) 10 mg/L, (B) 15 mg/L, (C) 20 mg/L, (D) 25 mg/L, (E) 30 mg/L, (F) 35 mg/L, (G) 40 mg/L, (H) 45 mg/L, (I) 50 mg/L) (the experiments were carried out with 10 mL of OII, at room temperature, without stirring, the working conditions being as follows: pH—3, adsorbent dose—0.058 g/L, contact time—variable).

Figure 6

Equilibrium isotherms for the OII adsorption on CSSA hydrogel (the experiments were carried out with 10 mL of OII, at room temperature, without stirring, the working conditions being as follows: OII concentration—variable, pH—3, adsorbent dose—0.058 g/L, contact time—1440 min).

Figure 7

Influence of stirring speed (A), ultrasound exposure (B), and temperature (C) on the removal of OII from aqueous solution through adsorption on CSSA hydrogel (the experiments were carried out with 10 mL of OII, having pH 3 and a concentration of 20 mg/L, with an adsorbent dose of 0.058 g/L, for 300 min).

Figure 8

Van ’t Hoff plot for the adsorption of OII on CSSA hydrogel.

Figure 9

Adsorption–desorption cycles for OII–CSSA hydrogel system (the adsorption experiments were carried out with 10 mL of OII having a concentration of 20 mg/L, and pH 3, at room temperature under stirring at 150 rpm, for 300 min; the desorption experiments were carried out for 240 min, with 50 mL of eluent, under stirring at 150 rpm).