ADSORPTIVE REMOVAL OF RHODAMINE B FROM AQUEOUS SOLUTION USING NITRIC ACID FUNCTIONALISED ACTIVATED CARBON.

This study investigates the adsorption performance of nitric acid-modified activated carbon (ACH) for the removal of Rhodamine B (RhB) dye from aqueous solutions. Activated carbon was modified using a solvothermal method, and the structural and surface changes were confirmed by XRD, FTIR, SEM, and EDS analyses. The modification introduced oxygen-containing functional groups, enhanced surface polarity, and lowered the point of zero charge (pHpzc) from 6.7 to 3.23, thereby improving electrostatic interactions with RhB. Batch adsorption experiments were conducted to examine the effects of initial dye concentration, adsorbent dosage, and pH. ACH achieved >99% RhB removal under optimized conditions, with adsorption capacity increasing from 2.09 to 6.42 mg/g as dye concentration increased from 1.0 to 3.0 mg/L. Removal efficiency improved with dosage, reaching 99.9% at 50 mg, while maximum adsorption occurred near neutral pH (6.5), consistent with the pHpzc. Equilibrium data fitted the Langmuir model (R2 = 0.9935) better than the Freundlich model (R2 = 0.9894), indicating monolayer adsorption on a homogeneous surface. Kinetic analysis revealed that the pseudo-second-order model (R2 > 0.99) best described the adsorption mechanism, suggesting chemisorption as the rate-limiting step. Overall, the results demonstrate that nitric acid modification significantly improves the adsorption properties of activated carbon, making ACH a highly effective and low-cost adsorbent for removing cationic dyes such as RhB from wastewater.