Kinetic and thermodynamic investigation of the removal of alizarin red dye using silica-supported nanoscale zero-valent iron particles

Abstract

Alizarin red (ARS) dye is a persistent and toxic pollutant in aquatic environments, posing a significant environmental threat. Among various treatment technologies, adsorption offers a practical and highly efficient method for dye removal. This study investigates the application of silica-supported nanoscale zero-valent iron (nZVI) particles as adsorbents for the removal of ARS dye, with a focus on evaluating the adsorption kinetics and thermodynamic behavior of the process. Two nanocomposites were synthesized using iron precursors with different counter ions: chloride (nZVI/Cl⁻) and nitrate (nZVI/NO₃⁻). The choice of counter ion influenced the physicochemical characteristics of the materials, thereby affecting their adsorption efficiency. The effects of key operational parameters, including solution pH, temperature, contact time, and adsorbent dosage, were systematically examined. Optimal adsorption was observed at pH 3, achieving removal efficiencies of 94.9% for nZVI/Cl⁻ and 85.0% for nZVI/NO₃⁻. Adsorption isotherm analysis revealed that the data fit well to the Langmuir model, indicating monolayer adsorption onto a homogeneous surface. Thermodynamic parameters confirmed that the adsorption process is spontaneous and endothermic in nature. These results underscore the potential of silica-supported nZVI nanocomposites as effective, sustainable, and environmentally friendly adsorbents for the remediation of dye-contaminated wastewater.