Highly efficient adsorption of direct Scarlet dye using guanidinium-based covalent organic polymer
Narges Abdolhossein Rejali, Mohammad Dinari
Abstract
Ionic covalent organic polymers are promising water pollutant adsorbents with enhanced adsorption potential compared to their neutral counterparts benefiting from both electrostatic attractions and the ion-exchange process. This work deals with the construction of a cationic COP through a facile direct approach and assessment of its performance for the scavenging of Direct Scarlet 4BS (DS-4BS) anionic dye. Many analytical techniques including FT-IR, TGA, BET, XRD, zeta potential, and FE-SEM/EDS were conducted to validate this cationic polymer formation. As results revealed the maximum adsorption capacity (q max ) was obtained 236.4 mg/g under pH = 2, adsorbent quantity = 0.005 g, dye concentration = 250 ppm, and time = 3.5 h. Based on the regression coefficient (R 2 ) values, experimental data were suitably matched with the Langmuir model, indicating monolayer adsorption and the best-fitted kinetics model was pseudo-second-order. Also, according to the calculated adsorption energy (Ea = 4.5 kJ/mol), the dye adsorption mechanism was mainly governed by the physisorption process. Additionally, thermodynamic investigations revealed that according to the negative values of the standard free Gibb’s energy (∆G 0 ), the adsorption process is spontaneous. Also, the positive value of the standard enthalpy (∆H 0 = 38.5 kJ/mol) indicated the endothermic nature of this adsorption, which means adsorption capacity increases with the increase in temperature.