Liquid-phase adsorption of Congo red dye using modified spear grass (Imperata cylindrica) root as adsorbent

Powdered speargrass (Imperata cylindrica) (IC) root was modified by treating with orthophosphoric acid and was engaged for the trapping of Congo red (CR) dye molecule from solution. The raw and modified IC roots were characterized using Fourier transform infrared, Scanning electron microscopy, Boehm titration, and pH point of zero charge technique. Batch adsorption studies were investigated using various parameters namely contact time, initial dye concentration, and temperature respectively. The initial adsorptive uptake of the dye was observed to be rapid within 50 min of contact time while equilibrium was attained between 120 and 150 min of contact time. The high regression and closeness of experimental and calculated results of qeattested to the pseudo-second-order kinetic model being the most fitting to adsorption data. Results obtained from the adsorption of Congo red dye unto ICRAC root showed the fitting of isotherm models in the order Dubinin-Radushkevich (R2= 0.8757) < Langmuir (R2= 0.9274) < Temkin (R2= 0.9511) < Freundlich (R2= 1). Thermodynamic parameters obtained showed that the interaction was exothermic and spontaneous in nature with negative values of Gibb’s free energy (− 25.92, − 27.23, and − 28.94) kJ mol−1, and negative values for enthalpy change. The values of ∆Sfor the ICRAC root were positive, suggesting more disorderliness and randomness at the ICRAC-CR dye interface. The adsorption capacities obtained at 303 K for ICRAC root was 1666.70 mg g−1. This study showed that the prepared ICRAC effectively removed Congo red dye from the solution.