Exploration of Reactive Black 5 Dye Desorption from Composite Hydrogel Beads-Adsorbent Reusability, Kinetic and Equilibrium Isotherms

Abstract

A low-cost adsorbent was prepared by using cherry stones powder and chitosan and used to retain Reactive Black 5 dye from aqueous solution. Then, the spent material was submitted to a regeneration process. Five different eluents (water, sodium hydroxide, hydrochloric acid, sodium chloride and ethanol) were tested. Among them, sodium hydroxide was selected for an advanced investigation. Values of three working conditions, namely the eluent volume, its concentration and the desorption temperature, were optimized by Response Surface Methodology-Box-Behnken Design. In the established settings (NaOH volume: 30 mL, NaOH concentration: 1.5 M, working temperature: 40 °C), three successive cycles of adsorption/desorption were conducted. The analysis performed by Scanning Electron Microscopy and by Fourier Transform Infrared Spectroscopy revealed the evolution of the adsorbent throughout the dye elution from the material. Pseudo-second-order kinetic model and Freundlich equilibrium isotherm were able to accurately describe the desorption process. Based on the acquired results, our outcomes sustain the suitability of the synthesized material as dye adsorbent and the possibility of efficaciously recycling and reusing it.

Keywords: Box–Behnken Design; Reactive Black 5; cherry stones; chitosan; desorption; equilibrium isotherms; hydrogel beads; kinetics.

Figure 1

Impact of eluent type on the desorption efficiency of Reactive Black 5 dye from the prepared adsorbent (RB volume: 30 mL, RB initial concentration: 30 mg/L, eluent volume: 30 mL, eluent concentration: 1 M, adsorbent amount: 3 g, contact time: 6 h, temperature: 30 °C).

Figure 2

3D response surface plots of Box–Behnken Design.

Figure 3

The Normal probability plot of residuals obtained for RB desorption efficiency.

Figure 4

Experimental versus predicted values of RB desorption efficiency.

Figure 5

Impact of the parameters affecting the desorption of Reactive Black 5 dye from the prepared adsorbent.

Figure 6

Adsorption/desorption efficiency of Reactive Black 5 dye on/from the prepared adsorbent (Adsorption conditions: RB volume: 30 mL, RB initial concentration: 30 mg/L, adsorbent amount: 3 g, contact time: 6 h, temperature: 30 °C; Desorption conditions: eluent volume: 30 mL, eluent concentration: 1 M, adsorbent amount: 3 g, contact time: 6 h, temperature: 40 °C).

Figure 7

SEM images for the prepared adsorbent before RB adsorption (A), after 1st, 2nd and 3rd cycle of RB adsorption (B,D,F) and after 1st, 2nd and 3rd cycle of RB desorption (C,E,G) (Device: TESCAN MIRA (TESCAN Orsay Holding, Brno, Czech Republic); Detection mode: Normal secondary electron in high vacuum; Detector: large field detector; Accelerating voltage: 20 keV; Beam current: 300 pA; Magnification: 320×; Field of view: 873 µm; Working distance: 5 mm; Scan speed: 6).

Figure 8

FTIR spectra for CSCH adsorbent before RB adsorption (A), after 1st, 2nd and 3rd cycle of RB adsorption (B,D,F) and after 1st, 2nd and 3rd cycle of RB desorption (C,E,G) (Device: IRSpirit FT-IR spectrometer (Shimadzu, Bucharest, Romania); Accessory: QATR; Wavenumber range: 4000 cm⁻¹–400 cm⁻¹; Scans: 45 scans/min.; Resolution: 4 cm⁻¹; Background spectrum reference: air; Cleaning solution: ethanol).

Figure 9

Desorption kinetics of Reactive Black 5 dye from the prepared adsorbent during the first cycle (A), second cycle (B) and third cycle (C) (RB volume: 30 mL, RB initial concentration: 30 mg/L, eluent volume: 30 mL, eluent concentration: 1 M, adsorbent amount: 3 g, contact time: 6 h, temperature: 40 °C).

Figure 10

Equilibrium isotherms for Reactive Black 5 dye desorption from the prepared adsorbent in first cycle (A), second cycle (B) and third cycle (C) (RB volume: 30 mL, RB initial concentration: 30 mg/L, eluent volume: 30 mL, eluent concentration: 1 M, adsorbent amount: 3 g, contact time: 6 h, temperature: 40 °C).