Design and evaluation of a polyaniline-Azadirachta indica composite for efficient dye removal: Insights from experimental and theoretical simulations

In this study, a novel composite of polyaniline and Azadirachta indica sawdust (PAIS) was synthesized to explore its potential in the adsorptive removal of methylene blue (MB) and crystal violet (CV) dyes from aqueous solution. PAIS was characterized using various instrumental techniques, including FTIR, SEM/EDXS, XRD, TEM/SAED, BET, and TGA-DTG/DTA analyses. Batch adsorption tests revealed that pH, medium temperature, initial adsorbate concentration, adsorbent dose, and contact duration significantly influence adsorption efficiency. Adsorption equilibrium was reached at 30 min for MB and 90 min for CV in an acidic medium (up to pH 7), with minimal changes observed beyond these times. The Langmuir isotherm provided the best validation, with a maximum monolayer adsorption capacity of 454.54 mg/g for MB and 370.37 mg/g for CV, showcasing superior performance compared to most reported materials. The adsorption process adhered to a pseudo-second-order approach for both dyes, with a high coefficient of determination value. The adsorption of MB and CV by this innovative adsorbent was spontaneous, endothermic, and accompanied by entropy enhancement. The adsorbent loaded with dyes was subjected to different desorbing agents (HCl, NaOH, NaCl, CH3COOH, and H2O), and HCl was the most effective. Computational studies using Density Functional Theory supported the experimental results, confirming the higher efficiency of PAIS for MB removal over CV. It is submitted that PAIS uniquely exhibits highly adaptable, recyclable, and potent low-cost adsorbent properties for eliminating both dyes from aqueous systems, representing a significant advancement in the field of dye removal. [Display omitted] •Synthesis of polyaniline/Azadirachta indica sawdust composite as a novel adsorbent.•Adsorbent efficiently removed methylene blue and crystal violet from water.•Langmuir isotherm obeyed with qm values of 454.54 and 370.37 mg/g for MB and CV.•The adsorbent was efficient, recyclable, cost-effective, and validated by DFT.