Aristolochic Acid I Adsorption onto Activated Carbon: Kinetics, Equilibrium, and Thermodynamic Studies

The removal of phytotoxins from herbal preparations is important due to evidence linking exposure to aristolochic acid I (AAI), a toxin found in Aristolochiaceae species, with certain kidney diseases. This study evaluates the effectiveness of activated carbon (AC) in removing AAI from aqueous solutions and determines the optimal conditions for the process, which are necessary for accurate kinetic, thermodynamic, and equilibrium analyses. After establishing the best conditions for the adsorption reaction (pH > 6; solid/liquid ratio (S:L) = 0.1 g adsorbent: 25 mL AAI solution; contact time 120 min; temperature = 298 K, AAI initial concentration (Ci) = 150 mg/L), a maximum adsorption capacity of 10.67 mg/g was obtained. Quantitative analysis of AAI was performed using UV-VIS spectrophotometry. Experiments on kinetics, thermodynamics, and adsorption isotherms were carried out. The findings showed that the process adheres to pseudo-second-order kinetics and is spontaneous and endothermic and takes place at the interface between the adsorbent and adsorbate. The equilibrium data fits the Sips isotherm model with a regression coefficient close to 1. The findings indicate that AC is an effective material for the removal of AAI by adsorption from an aqueous solution.