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.

Insights into the Effect of Chitosan and β-Cyclodextrin Hybridization of Zeolite-A on Its Physicochemical and Cytotoxic Properties as a Bio-Carrier for 5-Fluorouracil: Equilibrium and Release Kinetics Studies

Synthetic zeolite-A (ZA) was hybridized with two different biopolymers (chitosan and β-cyclodextrin) producing biocompatible chitosan/zeolite-A (CS/ZA) and β-cyclodextrin/zeolite-A (CD/ZA) biocomposites. The synthetic composites were assessed as bio-carriers of the 5-fluorouracil drug (5-Fu) with enhanced properties, highlighting the impact of the polymer type. The hybridization by the two biopolymers resulted in notable increases in the 5-Fu loading capacities, to 218.2 mg/g (CS/ZA) and 291.3 mg/g (CD/ZA), as compared to ZA (134.2 mg/g). The loading behaviors using ZA as well as CS/ZA and CD/ZA were illustrated based on the classic kinetics properties of pseudo-first-order kinetics (R² > 0.95) and the traditional Langmuir isotherm (R² = 0.99). CD/ZA shows a significantly higher active site density (102.7 mg/g) in comparison to CS/ZA (64 mg/g) and ZA (35.8 mg/g). The number of loaded 5-Fu per site of ZA, CS/ZA, and CD/ZA (>1) validates the vertical ordering of the loaded drug ions by multi-molecular processes. These processes are mainly physical mechanisms based on the determined Gaussian energy (<8 kJ/mol) and loading energy (<40 kJ/mol). Both the CS/ZA and CD/ZA 5-Fu release activities display continuous and controlled profiles up to 80 h, with CD/ZA exhibiting much faster release. According to the release kinetics studies, the release processes contain non-Fickian transport release properties, suggesting cooperative diffusion and erosion release mechanisms. The cytotoxicity of 5-Fu is also significantly enhanced by these carriers: 5-Fu/ZA (11.72% cell viability), 5-Fu/CS/ZA (5.43% cell viability), and 5-Fu/CD/ZA (1.83% cell viability).