Steric, Synergetic, Energetic Studies on the Impact of the Type of the Hybridized Polymers (Chitosan and β-Cyclodextrin) on the Adsorption Properties of Zeolite-A for Congo Red Dye

Zeolite-A was synthesized successfully from kaolinite and hybridized with two species of biopolymers (chitosan (CH/Z) and β-cyclodextrin (CD/Z)). The obtained hybridized forms were assessed as potential adsorbents of Congo red synthetic dye (CR) with enhanced affinities and elimination capacities. The synthesized CD/Z and CH/Z hybrids demonstrated uptake capacities of 223.6 and 208.7 mg/g, which are significantly higher than single-phase zeolite-A (140.3 mg/g). The integrated polymers change the surface area, surface reactivity, and number of free active receptors that are already present. The classic isotherm investigations validate Langmuir equilibrium behavior for ZA and Freundlich properties for CD/Z and CH/Z. The steric parameters validate a strong increase in the existing active receptors after the incorporation of CD (CD/Z) to be 98.1 mg/g as compared to 83 mg/g for CH/Z and 60.6 mg/g for ZA, which illustrate the detected uptake behaviors. Moreover, the CR dye was adsorbed as several molecules per single site, reflecting the vertical uptake of these molecules by multimolecular mechanisms. The energetic assessment, considering both Gaussian energies and adsorption energies (<40 kJ/mol), validates the dominant impact of the physical mechanism during the sequestration of CR (dipole binding interactions (2-29 kJ/mol) and hydrogen bonds (<30 kJ/mol)), in addition to the considerable effect of ion exchange processes. Based on the thermodynamic parameters, the CR molecules were adsorbed by exothermic and spontaneous reactions.

Steric and Energetic Studies on the Synergetic Enhancement Effect of Integrated Polyaniline on the Adsorption Properties of Toxic Basic and Acidic Dyes by Polyaniline/Zeolite-A Composite

The synergetic enhancement effect of the polyaniline (PANI) integration process on the adsorption properties of the PANI/zeolite-A composite (PANI/ZA) as an adsorbent for malachite green and Congo red synthetic dyes was evaluated based on classic equilibrium modelling in addition to the steric and energetic parameters of advanced isotherm studies. The PANI/ZA composite displays enhanced adsorption capacities for both methylene blue (270.9 mg/g) and Congo red (235.5 mg/g) as compared to ZA particles (methylene blue (179.6 mg/g) and Congo red (140.3 mg/g)). The reported enhancement was illustrated based on the steric parameters of active site density (Nm) and the number of adsorbed dyes per active site (n). The integration of PANI strongly induced the quantities of the existing active sites that have enhanced affinities towards both methylene blue (109.2 mg/g) and Congo red (92.9 mg/g) as compared to the present sites on the surface of ZA. Every site on the surface of PANI/ZA can adsorb about four methylene blue molecules and five Congo red molecules, signifying the vertical orientation of their adsorbed ions and their uptake by multi-molecular mechanisms. The energetic investigation of the methylene blue (-10.26 to -16.8 kJ/mol) and Congo red (-9.38 to -16.49 kJ/mol) adsorption reactions by PANI/ZA suggested the operation of physical mechanisms during their uptake by PANI/ZA. These mechanisms might involve van der Waals forces, dipole bonding forces, and hydrogen bonding (<30 kJ/mol). The evaluated thermodynamic functions, including enthalpy, internal energy, and entropy, validate the exothermic and spontaneous behaviours of the methylene blue and Congo red uptake processes by PANI/ZA.