Sustainable Dye Removal Using Date Stones and Adsorption Process Optimization: Factorial Design, Kinetics, and Isotherm Analysis

This study aims to present the preparation of date stone activated carbon (DSAC) through physical activation with carbon dioxide. The Brunauer–Emmett–Teller (BET) technique, Boehm titrations, elemental analysis, Raman and Fourier-transform infrared (FTIR) spectroscopy have been used to characterize the raw material (date stone), date stone activated carbon (DSAC) produced, Congo Red (CR) and to investigate the adsorption phenomena. The study of the DSAC porous material revealed the dominance of micropores with a specific surface area greater than 535.9 m2 g−1 and an approximate volume value equal to 0.208 cm3 g−1. The Langmuir model predicted an adsorption capacity of approximately 27.77 mg g−1, while a 90% removal efficiency for CR dye was achieved under neutral pH conditions. Thermodynamic analysis confirmed that the adsorption of CR on DSAC has a spontaneous (ΔG° < 0) and exothermic (ΔH° < 0) character. The adsorption mechanism of CR on DSAC was proposed and discussed, based on the determination of electrostatic interactions being identified as a critical factor that controls the adsorption phenomenon of CR on DSAC. A 23 full factorial design was implemented to systematically investigate the effects of three critical parameters (temperature, adsorbent dosage, and pH) on the adsorption performance. Statistical analysis indicated that all three primary factors significantly influenced the results. The square correlation coefficient of the model (R2-sq of 97.26%) was in good agreement with the statistical model. The variable is considered statistically significant when the p-value is lower than 0.05. These findings, supported by experimental data, strongly indicate that DSAC possesses remarkable potential as a sustainable and effective bio-adsorbent for wastewater remediation applications capable of removing diverse contaminants with high efficiency.