Investigation the Efficiency of Activated Carbon Coated with ZnO Nanoparticles Prepared by Green Synthesis Method in Removing Humic Acid from Aqueous Solutions: Kinetics and Isotherm Study

Background & objective: The presence of natural organic matter in water sources creates various problems, especially in common water treatment process. These compounds cause unfavorable taste and odor in water and are among the most important precursors of water disinfection by-products. This study was carried out to evaluate the efficiency of activated carbon (AC) and activated carbon modified with ZnO nanoparticles (AC-ZnO) in removal of humic acid (HA) from aqueous solutions. Methods: In the present experimental study, the removal of HA with AC or AC-ZnO was discontinuously studied as a function of pH, contact time, HA concentration, and absorbent dose. The structure of absorbents and their morphology were investigated by FTIR, SEM, XRD and pHpzc techniques. The HA was measured using spectrophotometer at the wavelength of 245 nm. Absorption isotherm was determined by using Langmuir and Froundlich models and absorption kinetics by pseudo-first and pseudo second-order models. Results: The efficiency of removing HA had a direct relationship with absorbent dose and inverse relationship with pH and HA concentrations. The optimal removal rate of HA for 1.6 g/L dose of AC or AC-ZnO were reached to 82.44 % and 96/26%, respectively, in HA concentration of 50 mg/L and contact time of 40 minutes Conclusion: The removal rate was considerably higher for AC-ZnO than AC, which indicates the effective role of nanoparticulate stabilization on activated carbon. As a result, the method of nanoparticulate stabilization on activated carbon can provide an effective and very efficient adsorbent and appropriate alternative to remove humic acid from aqueous media.