Adsorption of Dyes, Pharmaceuticals, and Humic Acids onto Chitosan Biomaterials Doped with Activated Carbon: Colloidal Approaches and Interaction Explanations

Various pollutants affect the hazardousness of wastewater, with organic pollutants playing a main role. Thus, among others, wastewater contains natural organic matter (NOM), pharmaceutical compounds, and various toxic and nonbiodegradable dyes. Removing these hazardous compounds from water is essential since they are harmful to both human health and water quality. Therefore, in this study, we evaluated the removal of humic acids (HA), Diclofenac (DCF), and Reactive Red 120 (RR120) by using chitosan/activated carbon and chitosan/activated carbon/curcumin derivatives as adsorbents. Several derivatives with different composition ratios, such as CS/AC@1:1, CS/AC@1:2, and CS/AC@2:1, were initially synthesized and examined. Furthermore, the addition of curcumin (Cur), which is a natural polyphenolic substance, to the CS/AC@ derivative, i.e., CS/AC@Cur5% and CS/AC@Cur10%, was also examined, in order to scrutinize the possibility of additional enhancement of organic contaminants removal. It was found that at pH 2.0, more than 93% of HA was removed by applying CS/AC2:1 (109 mg/g). In the case of DCF at pH 6.0, 97% was removed by CS/AC@Cur5% (148 mg/g), but CS/AC@Cur10% (112 mg/g) was optimum for RR120 removal (94%) at pH 3.0 and 293 K. The adsorption data were more consistent with the Langmuir isotherm model, whereas the adsorption kinetics followed the pseudo-second-order model in all cases. Thermodynamic analysis confirmed that the adsorption was endothermic and spontaneous for all of the organic pollutants. Adsorption-desorption experiments confirmed that these adsorbents can be used effectively for up to six cycles of regeneration.