Okra-psyllium based green synthesis of eco-friendly bio-adsorbent for efficient removal of uranium and crystal violet dye from aqueous media: statistical optimization using response surface methodology

Abstract

Abstract The prime objective of this study is to synthesize eco-friendly okra-psyllium based hydrogel through free radical crosslinking method by using citric acid-ammonium persulfate as a crosslinker-initiator system. Various techniques were used to explore the morphology, structure and thermal behaviour of the synthesized hydrogel via. Powdered X-ray diffraction studies, SEM and TGA techniques. Response surface methodology was performed to maximize the grafting percentage of the synthesized hydrogel up to 244 % and swelling percentage of 598 %. The physicochemical properties like salt-resistance behaviour and the impact of ionic strength on the swelling percentage of synthesized hydrogel were investigated and thus observed with the following trend as K+ > Ca2+ > Fe3+. Furthermore, the synthesized sample showed an excellent bio-adsorbent behaviour for the removal of uranium with 97.75 % removal in 60 min and crystal violet dye removal up to 85.32 % in 24 h from contaminated water. Various kinetic and isotherm adsorption modelling were implied to probe the mechanism of adsorption with displayed interactions between the absorbate and the absorbent. The Langmuir isotherm model was well-fitted in dye adsorption case with regression co-efficient value of 0.99. In case of uranium, tempkin isotherm model was best fitted with regression co-efficient value as 0.92. Crystal violet dye adsorption favoured second-order kinetic model whereas the adsorption mechanism of uranium followed first-order kinetics. Hence, the revealed results depicted that the synthesized hydrogel served as a potential candidate for the effective removal of toxic dye (crystal violet) and metal ion (uranium) from aqueous media with a sustainable approach towards environment.