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

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.