Effective removal of Congo red dye using adsorbent prepared from bio-waste: isotherm, kinetic, and thermodynamic studies

This research aims to explore the potential use of carbon derived from neem bark (NBC) for the effective removal of Congo red (CR) dye from water-based solutions. A series of batch adsorption experiments were conducted to examine the impact of various factors. Subsequently, the optimal conditions were identified. The determination of the ideal operational conditions for employing NBC involved several important factors, namely agitation time: 60 min, dosage: 2 g/L, temperature: 45° C, and CR concentration: 40 mg/L. A comprehensive investigation was conducted to enhance the understanding of the composition and physical properties of the adsorbent NBC using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) analysis. The FTIR analysis detected notable changes in the spectral peaks pre- and post-adsorption. The BET analysis provided significant results regarding the surface area, total pore volume, and average pore diameter of the adsorbents. The Langmuir isotherm model was found to be more accurate in fitting the experimental data with adsorption capacity obtained as 25.84 mg/g. The kinetic investigations yielded results that conformed to the pseudo-second-order model with rate constant 1.03009 × 10⁻³ g/mg min. The thermodynamic evaluations in this study indicate that the adsorption phenomena are exothermic, thermodynamically favourable, and spontaneous. In conclusion, this research demonstrates the effectiveness of NBC as an adsorbent for removing CR dye from textile industry effluent. The findings offer new perspectives on addressing water pollution and highlight the feasibility of using sustainable adsorbents for environmental remediation. Graphical Abstract: [Figure not available: see fulltext.].