Synthesis of sustainable iron pillared nano-composite using plant waste biomass–bentonite clay for the removal of Congo red dye

The discharge of synthetic dyes, especially from textile industries, poses significant environmental and health risks due to their toxicity, persistence, and resistance to degradation. To address this issue, a sustainable and cost-effective adsorbent, Pomelo Peel–Bentonite–Ferrous nanocomposite (PPB-Fe), was developed using a green chemistry approach that leverages agro-waste (pomelo peel), naturally abundant bentonite clay, and iron salts. Its goal is to aid in removing inorganic compounds from water solutions, making wastewater cleaner for reuse. The composite was extensively characterised using Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray analysis (SEM–EDX), Thermal Gravimetric Analysis-Differential thermal analysis (TGA-DTA), Brunauer–Emmett–Teller (BET), and Dynamic light scattering (DLS) methods, confirming its porous structure, crystalline nature, thermal stability, and large surface area. Adsorption isotherm studies using the Langmuir and the Freundlich models revealed that PPB-Fe is highly effective in removing Congo Red under favourable conditions. The Freundlich adsorption isothermal study provides better insight into the adsorption behaviour of PPB-Fe composite. The adsorption capacity (KF) of the adsorbent was calculated to be 3.67, and the adsorption intensity (n) was 1 by the Freundlich model, indicating multilayer adsorption on a heterogeneous surface. The data suggested that the Freundlich isotherm model best describes the adsorption behaviour of the composite material in the present study. The reaction kinetics show the pseudo-second-order model. The rate constant of the pseudo-second order reaction was 5.28, and the q value was 427.50 mg/g. The adsorption increases with increasing temperature, indicating that the process is endothermic and spontaneous. The current research clearly demonstrates how fruit peel waste can be transformed into functional nanocomposites, specifically highlighting the PPB-Fe material as a promising, eco-friendly adsorbent for wastewater treatment with minimal chemical discharge. Notably, this study presents the first-time integration of pomelo peel waste, bentonite clay, and iron salts into a nanocomposite designed to efficiently remove textile dyes from water.