Activated Rice Husk Ash: A Sustainable and High-Capacity Adsorbent for the Remediation of Carbol Fuchsin Dye from Aqueous Effluents

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.