Activated rice husk ash: a sustainable and high capacity adsorbent for the remediation of Carbol Fuchsin dye from aqueous effluents

Abstract The discharge of persistent synthetic dyes, such as Carbol Fuchsin (CF), from textile and related industries constitutes a significant environmental and public health concern because oftheir toxicity and resistance to natural degradation. This study presents the development and application of a low-cost, sustainable adsorbent—activated carbon derived from rice husk ash (ARHA)—for the efficient removal of CF from contaminated water. The adsorbent was characterized using FT-IR, SEM-EDX, XRD, and zeta potential analysis, revealing a mesoporous, amorphous structure with a specific surface area of 50–270 m²/g and a point of zero charge (pHpzc) at 8.3. Systematic batch adsorption studies were conducted to optimize the process parameters, achieving a maximum removal efficiency of >96% at an adsorbent dosage of 0.08 g/50 mL, contact time of 150 min, and pH 9.0. The adsorption kinetics were best described by the pseudo-second-order model, indicating that chemisorption was the rate-limiting step. The equilibrium isotherm data were well-fitted by the Langmuir model, confirming monolayer adsorption with an exceptionally high maximum capacity of 205.24 mg/g. Thermodynamic analysis (negative ΔG° and ΔH°) established the process as spontaneous and exothermic. The findings demonstrate that ARHA, an agricultural waste derivative, is a highly effective, eco-friendly, and economically viable material for the advanced treatment of dye-laden industrial wastewater, offering a promising alternative to conventional remediation methods.