Kinetics, Thermodynamics, and Mechanistic Understanding of Adsorptive Removal of Congo Red Using Oxidized Carbon Nanoplatelets

Abstract

ABSTRACT The illicit use of synthetic dyes, which are harmful to humankind's health and aquatic ecosystems, highlights the urgent need for efficient adsorbents in wastewater treatment. This work investigates the adsorption performance, kinetics, and thermodynamics of anionic Congo red (CR) dye removal, using oxidized carbon nanoplatelets (OCNPs). Optimal adsorption was achieved at pH 2.25, 25°C, initial CR concentration of 30 mg L −1 , adsorbent dose of 10 g L −1 , after 1 h. Fourier transformation infra‐red spectroscopy (FTIR) analysis before and after adsorption suggested a predominantly physisorption mechanism, and this trait enhances reusability, thus indirectly supporting the practical applicability of OCNPs. The adsorption data follow the pseudo‐second‐order kinetic model ( R 2 = 0.9998), suggesting adsorption rates governed by adsorption capacity. The negative Gibbs energy at all temperatures and enthalpy changes confirm spontaneous and exothermic processes, respectively, whereas a positive entropy change indicates increased energy dispersal at the solid–liquid interface. Notably, OCNPs achieved high decontamination efficiency under both acidic and basic conditions, demonstrating strong affinity toward CR molecules. These findings position oxidation‐tailored OCNPs as effective and low‐cost adsorbents with oxidation‐induced surface chemistry for the remediation of anionic dye‐contaminated wastewater at low adsorbent doses and operational at room temperature. The material demonstrated high adsorption performance without the need for composite formation across a wide pH range or additional functionalization. Furthermore, its surface properties can be systematically controlled with oxygen content/species, providing a straightforward route to tailor adsorption behavior. This approach also reduces production complexity and cost, particularly given the potential derivation of the precursor from renewable biomass sources.