Comparison of the adsorption efficiency of cationic (Crystal Violet) and anionic (Congo Red) dyes on Valeriana officinalis roots: Isotherms, kinetics, thermodynamic studies, and error functions

Abstract

In this study, the removal of basic violet 3 (CV) and direct red 28 (CR) dyes, which are commonly used in textile and hazardous for environmental health, from wastewater by adsorption, using Valeriana officinalis roots was investigated. Characterization of Valeriana officinalis roots was performed by FTIR, SEM, BET-BJH, XRD, and pHpzc analyzes. The pores in the Valeriana officinalis roots have a BET surface area of 2.007 m2/g and an average pore size of 2.76 nm, indicating that they were mesoporous. The average pore size of BJH is 1.90 nm, which is ideal for adsorption. The pHpzc of Valeriana officinalis was calculated as 4.5. Firstly, the optimum conditions including contact time, initial pH, adsorbent dosage, and concentration were determined. Afterward, the raw data obtained as a result of equilibrium experiments were applied to Freundlich, Langmuir, and D-R isotherms, and the adsorption efficiency was evaluated by determining the most suitable model. The qm values at 25 degrees C for CV and CR dyes from the Langmuir model were calculated as 476.2 and 166.7 mg/g. The data obtained from adsorption studies performed depending on the contact time were applied to the kinetics. From the kinetic parameters, it was determined that the adsorption followed the pseudo-second-order and the adsorption process occurred in three steps. Thermodynamic parameters were calculated by performing the experiments at 25-55 degrees C. Besides, error functions were calculated using the obtained theoretical and experimental adsorption capacities, and the accuracy and reproducibility of the adsorption were evaluated. Considering all the results, Valeriana officinalis roots were found to be a suitable adsorbent for the adsorption of cationic and anionic dyes from wastewater.