Application of statistical physical, DFT computation and molecular dynamics simulation for enhanced removal of crystal violet and basic fuchsin dyes utilizing biosorbent derived from residual watermelon seeds (Citrullus lanatus)

Abstract

This study investigates the use of watermelon seeds (Citrullus lanatus), a plentiful and cost-effective biosorbent, for the removal of basic fuchsin (BF) and crystal violet (CV) dyes from aqueous solutions. Characterization of the biosorbent was conducted using Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), while Brunauer–Emmett–Teller (BET) analysis revealed a specific surface area (SBET) of 54.50 m² g−1, highlighting its mesoporous structure advantageous for adsorption. Adsorption isotherms were best described by the Langmuir model, indicating monolayer adsorption with high correlation coefficients (R² values of 0.9959 for CV and 0.9978 for BF) and notable adsorption capacities of 139.2493 mg g−1 for CV and 238.80501 mg g−1 for BF. Thermodynamic analysis confirmed the spontaneous and exothermic nature of the adsorption, driven by molecular interactions. To elucidate the adsorption mechanism at the molecular level, we employed Density Functional Theory (DFT) calculations, Molecular Dynamics (MD) simulations, and Non-Covalent Interaction (NCI) analysis. These computational methods provided insights that closely aligned with experimental data, establishing a robust theoretical-experimental framework for understanding dye adsorption by watermelon seed biosorbent. The practical implications of our findings are significant, suggesting that watermelon seed biosorbent can be effectively scaled up for industrial effluent treatment in continuous systems. The study underscores the potential of utilizing this sustainable and economically viable biosorbent for environmental remediation, offering a promising alternative to conventional adsorbents with its high efficiency and lower sensitivity to environmental conditions such as pH and temperature.