Functionalization of Powdered Walnut Shell with Acid Activation for Congo Red Dye Removal

Abstract

Activated carbon was prepared from walnut shells (WS-AC) to study the adsorption mechanism of Congo red (CR) dye in an aqueous solution. The adsorbent was characterized using a Fourier transform infrared spectrophotometer (FT-IR), a scanning electron microscope (SEM), and X-ray diffraction (XRD). The effect of experimental factors, including pH, CR initial concentration, adsorbent dosage, and adsorption time were investigated. 98% of CR dye removal was achieved at pH 2 for 25 mg/L of CR concentration at a 1 g adsorbent dosage at 25°C. The Langmuir and Freundlich models were employed to analyze the data and find the most suitable isothermal model for achieving CR adsorption over WS-AC. The pseudo-first-order (PFO) and pseudo-second-order (PSO) models were used to characterize the CR adsorption kinetics onto the WS-AC adsorbent surfaces. The Langmuir equilibrium model was the most accurate representation of the experimental data. The maximum Langmuir adsorption capacity of WS-AC was determined to be 61.6 mg/g. The kinetic analyses demonstrated that the adsorption of CR over WS-AC followed a pseudo-second-order kinetic model, as evidenced by the high R² values (0.999) found. This work has shown that walnut shell activated carbon is an effective and economical adsorbent for removing Congo red anionic dyes from wastewater.