Untapped Sepia Shell–Based Composite for the Sorption of Cationic and Anionic Dyes

Abstract

The current research reports an efficient methodology of new sorbent (SSBC) synthesis based on neglected sepia shells for the sequestration of cationic dye (Methylene blue, MB) and an anionic dye (Reactive black 5, RB5) from aqueous solutions. The as-synthesized SSBC was produced by reaction of sepia shell powder with urea in the presence of formaldehyde. In the first part of the work, the sorbent was scrutinized by using scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform infrared spectrometry, and titration (for determining pHPZC). In the second step, the influence of several parameters including pH effect, sorbent dosage, temperature, and ionic strength on the two dyes’ sorption effectiveness was examined. The sorption isotherms and uptake kinetics were analyzed at the optimum pH. Outlined results showed that the dynamic experimental obtained data followed the Langmuir isotherm profile, while the kinetic profile fitted well to the pseudo-second-order rate equation. Maximum sorption capacities reach up to 0.794 mmol g−1 (254.05 mg g−1) for MB and 0.271 mmol g−1 (269.18 mg g−1) for RB5, at pH 10.5 and 2.3, respectively. By comparing the sorption properties at different temperatures, the endothermic nature of the sorption process was revealed. Sorption processing under microwave irradiation (microwave-enforced sorption, MES) enhanced mass transfer, and a contact time as low as 1 min is sufficient under optimized conditions (exposure time and power) reaching equilibrium, while 2–3 h was necessary for a “simple” sorption. Dye desorption was successfully tested using 0.5 M solutions of NaOH and HCl for the removal of RB5 and MB, respectively. The as-prepared sorbent can be reused for a minimum of 4 cycles of sorption/desorption. Finally, the sorbent was successfully tested on spiked tap water and real industrial wastewater.