Congo red dye removal using highly porous sulfuric acid activated papaya petiole biochar: Experimental, characterization, optimization and isotherm study

The article focuses on the performance of sulfuric acid activated papaya petiole (PP) biochar on Congo red (CR) dye removal for the first time. Papaya petiole biochar (PPC) was produced from dried PP, placed in the muffle furnace at 300°C for 1 h. PPC was treated with 1 M sulfuric acid solution at 25°C for 24 h followed by neutralization and carbonized in the muffle furnace at 500°C for 1 h and called activated papaya petiole char (APPC). The PPC and APPC were characterized using TGA (thermo gravimetric analysis), FTIR (Fourier transform infrared), XRD (X-ray diffraction), FESEM (field emission electron microscopy) and EDS (Energy Dispersive X-ray Spectroscopy) techniques. Under present study, a 3-level, 3-factor Box-Behnken statistical design in response surface methodology (RSM) was used to determine the optimum condition for the removal of CR dye from aqueous solution with variable parameters namely pH, time and dosage of char. Under present investigation, Langmuir and Freundlich adsorption isotherm models were studied. In the present investigation, it was observed that the CR removal efficiency of APPC was higher than PPC due to more porous nature. At optimum condition (pH 3.2, time 105.3 min and 126.7 mg char/ 100 mL solution) using 100 mg/L dye concentration at 30°C, the CR removal efficiency was achieved as 90.7%. Under present investigation, the mechanism of CR dye adsorption using APPC was also proposed. It is expected that the outcomes of the present study will add some value for waste water treatment research area.