The use of encapsulation as a proposed solution to avoid problems encountered with conventional materials in powder form: Application in methylene blue removal from aqueous solutions

Abstract

The Ziziphus jujuba stones chemically modified with orthophosphoric acid (PZJS), then encapsulated with sodium alginate (BZJS1 and BZJS2) were used for organic dye adsorption. In this context, the basic dye methylene blue (MB) was chosen as a test molecule. The characteristics of the prepared beads were examined by different characterization techniques, such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray diffraction (EDX), X-ray fluorescence (XRF), Thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller method (BET) with nitrogen adsorption-desorption isotherm at 77 °K. In a batch system, initial pH (2−12), temperature (10, 25, 30 and 40 °C), initial concentration (50–200 mg/L), contact time, salt and organic compound effects were studied. The obtained results showed that the maximum MB adsorption amounts were 737.13 mg/g and 660.12 mg/g onto BZJS1 and BZJS2 at ambient temperature respectively, showing that the prepared materials are more efficient than most of the other adsorbents. Moreover, experimental data modeling showed that the adsorption process followed the Redlich-Peterson model. Regarding kinetics modeling, pseudo-first-order (PFO), pseudo-second-order and Pseudo-nth order models were used to correlate experimental data, demonstrating that a mass transfer equation (PFO) could describe MB adsorption. Thermodynamic parameters were also evaluated, demonstrating that the MB adsorption process was achievable, spontaneous and exothermic. The regeneration study showed that both of the beads had excellent adsorption efficiency even at the sixth cycle for the two beads, 92.01 and 82.88 for BZJS1 and BZJS2, respectively. From this and in view of a future implementation at industrial scale, encapsulation by sodium alginate polymer can be therefore promisingly proposed as a solution to avoid the problems of conventional materials in powder form, such as the difficulty of regeneration, performances and mass loss during the recovery step of the powder from the medium.