Removal of Paranitrophenol from Water by Cyclodextrin Based Polymers

To date, a number of methods have been employed to remove paranitrophenol (PNP) as one of the organic pollutants and nitroaromatic compounds from water. In the present study, the PNP removal process was investigated using surface adsorption and synthesizing cyclodextrin-based adsorbents. To this end, beta-cyclodextrin polymer insoluble in water was first obtained in a green way using citric acid as a cross-linking agent with the efficiency of 81.25% at the swelling rate of 166.7 and after structural characterization, it was used in the adsorption experiments. To expand the contact surface area, some bases such as sawdust and alumina were used as the cyclodextrin supports, and the effect of different parameters on their adsorption capacity such as the contact time, pH, PNP initial concentration, temperature, and adsorbent dosage were studied. The experimental data were then fitted to the kinetics models and adsorption isotherms. It was found that for the synthesized adsorbents, the adsorption kinetics followed the pseudo-second-order equation, and the equilibrium data were more consistent with the Freundlich model. The qmax values ​​for β-cyclodextrin-citric acid, β-cyclodextrin-sawdust, and β-cyclodextrin-alumina adsorbents were obtained as 40.98 mg/g, 43.29 mg/g, and 38.46 mg/g, respectively. Finally, the adsorption thermodynamic was investigated and the standard enthalpy, entropy, and Gibbs free energy changes were calculated.