Kinetics, Thermodynamics, and Isothermic Evaluation in Sorption Study of Hazardous Dye Using Sodium Dodecylsulfate Physically Impregnated in Polyester‐Type Polyurethane Foam

Abstract

Use of polyester‐type polyurethane foam (PUF) is an effective adsorbent for the removal of hazardous dye: crystal violet (CV) from an aqueous solution. In this adsorption study, the formation of hydrophobic ion pair (opposite charge attraction) between the charged species, i.e., cationic (basic) dye CV and anionic surfactant sodium dodecylsulfate (SDS) sorbed onto PUF. Chemical calculations were performed using quantum simulation to understand ion‐pair formation for CV–SDS at the semiempirical PM6 level. Adsorption studies were performed using 200 mg cylindrical PUF with an overhead stirrer in solutions containing varying compositions of the dye–surfactant mixture. The equilibrium thermodynamics and kinetics of the adsorption process were studies by measuring CV dye removal as a function of time and temperature. Results show that the formation of the dye–surfactant ion pair is necessary for effective adsorption onto PUF. Various adsorption isotherms, viz., Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (DRK), Harkin‐Jura, and several kinetic models, viz., pseudo‐first order, pseudo‐second order, Elovich, and Intraparticle diffusion were used to fit the spectrophotometric result. The equilibrium adsorption data fit to the Langmuir isotherm gives the maximum adsorption of PUF as 33.39 mg g−1 from 200 mL 5.0 × 10−5 mol L−1 CV solution at 298.15 K. The kinetics study showed that the overall adsorption process follows pseudo‐second‐order kinetics. The Morris–Weber model suggests that an intraparticle diffusion process is active in controlling the adsorption rate. The Freundlich, Temkin, DRK adsorption isotherms showed that solute dye transfers from solution to the PUF adsorbent surface through physical adsorption. The Langmuir and Harkin‐Jura adsorption isotherms suggest that the adsorbent surface is homogeneous in nature. The thermodynamic data showed that the adsorption process is spontaneous and endothermic with a positive enthalpy change and a negative change in Gibb's energy.

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“…Herein, the constants of Langmuir model, that is, q max and K L represent the maximum adsorption capacity and relate to the energy of adsorption, respectively. The Freundlich isotherm constants K F and n resemble the adsorption capacity and intensity of the adsorbent 3,27,32,33 . Toth isotherm constant t is used as a measure of adsorbent's heterogeneity.…”

“…Of the Harkins‐Jura constants A and B, the former is known to be a measure external surface of the adsorbent. K R , a R , and β are Redlich–Peterson isotherm constants with β being an exponent that ranges between 0 and 1 32,33 …”

“…Toth isotherm is an empirical equation derived for heterogeneous adsorption systems and reduces to Langmuir isotherm when isotherm constant t equals to unity 33 . Harkins–Jura isotherm describes the multilayer adsorption occurring on the surface of an adsorbent with heterogeneous pore distribution 32 . Radke–Prausnitz model was initially developed for modeling the adsorption of dilute organics on activated carbon, 34 it has been applied to many adsorbent–adsorbate pairs including heavy metals 35 …”