Tragacanth gum grafted polyaniline hydrogel as a biodegradable adsorbent for the removal of uranyl ions from water samples

Natural gum polysaccharides have poor mechanical and physical properties and need to be modified with synthetic monomers. In this study, one-step in situ synthesis of Tragacanth gum grafted polyaniline hydrogel (TG-g-PANI) was used to prepare a new biodegradable and an inexpensive adsorbent for the removal of uranyl ions from aqueous solutions followed by the determination using UV-Vis spectrophotometry. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The FTIR spectrum identified functional groups in TG-g-PANI. SEM micrographs of Tragacanth gum revealed smooth surface, whereas TG-g-PANI present nanoparticles with rough surface and spherical shape that were compactly accumulated on the surface of hydrogel. The effective experimental parameters on the removal of uranyl ions such as sample pH, adsorbent dosage, contact time, and initial uranyl concentration were investigated. The results of optimization showed that one gram of hydrogel adsorbed 26 mg uranyl ions from aqueous solutions. The Langmuir and Freundlich models were examined to evaluate the adsorption isotherm. The data of sorption process were fitted well with the Freundlich isotherm. The adsorption rates of uranyl ions onto the adsorbent followed pseudo-second-order kinetic model and efficient removal of uranyl ions have occurred within 4 h. The thermodynamic investigation revealed that the adsorption process was exothermic and spontaneous. The adsorbent could be recycled for two times usage with removal efficiency of 90% after acid wash treatment. Finally, the adsorbent was successfully employed for removal of uranyl ions from bio-aggressive media such as seawater and ground water.