Insights into application of novel citric acid modified Saccharum munja biosorbent for facile removal of fuchsin basic dye, crystal violet dye and copper metal ion: statistical modelling, kinetics, thermodynamics and equilibrium studies

With the recent rapid growth of the dyeing industries, extensive water contamination driven on by heavy metals and synthetic organic dyes has become more and more dangerous. Herein, we focused on adopting an adsorptive approach and designing of highly efficient and novel citric acid–modified Saccharum munja (CA-SM) with substantially dispersed adsorption sites for the adsorption of organic dyes and heavy metal. The physicochemical properties of as-synthesised biosorbent were explored by characterising with field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Further, Box-Behnken design under response surface methodology was employed to optimise the various parameters like pH, dosage and concentration. The model was found to be significant, reproducible and highly precise. The thermodynamics study revealed the adsorption process to be endothermic and spontaneous in nature. Moreover, the isotherm data was well fitted with Langmuir model for crystal violet (CV) and fuchsin basic (BF) dyes, while copper (Cu²⁺) adsorption was best fitted with Temkin model. The maximum monolayer adsorption capacity for CV, BF and Cu²⁺ was 265.95, 229.88 and 10.054 mg/g respectively. Pseudo-second-order kinetic model was found to be the best representatives for all the contaminants. Furthermore, hydrogen bonding, pi-pi interactions and electrostatic interactions governed an important role towards the adsorption mechanism. Overall, this work involves the utilisation of citric acid–modified Saccharum munja as a novel and sustainable biosorbent for removal of dyes and heavy metal.