Synergic binding of rhodamine-B and heavy metal ions onto polyethyleneimine grafted freeze-dried chitosan/epichlorohydrin composite beads and possible mechanism

This paper reports a synergic binding technique of dye and cadmium/lead ions onto freeze-dried modified chitosan beads (GCCS), in this work modified chitosan beads was applied in binary solution. Chitosan beads (CS) composite was produced and polyethyleneimine was grafted onto the backbone of the developed composite. The beads were analyzed utilizing different analytical techniques such as Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM). The model applied in pH equilibrium was found to justify the adsorption of pollutants onto the adsorbent. The model was established from 2 equilibrium calculations, one justifying the acid-base attributes of the modified beads, the other elucidating the adsorption of the adsorbates onto the beads, and a mass balance of the various arrangement of nitrogen in the adsorbent. The excellent fit of the Pseudo-second order and intra-particle diffusion kinetic model shows that chemical binding might be the rate-limiting step. The adsorption isotherms were well represented by the Langmuir and Temkin models at a temperature of 45 °C. The maximum binding capacities (Q_max) from the Langmuir model were observed to be 390, 315 and 278 mg/g for the adsorption of dye, lead and cadmium ions respectively`. However, it was found to be higher in the binary system with the same applicable conditions. The correlation was analyzed utilizing various models and lines of best fit were obtained. Synergic effect was observed from the experimental results acquired from the adsorption of Rhodamine B (RHB) and adsorbates. These findings show the formation of fresh binding sites during simultaneous binding process.