Adsorption kinetics, equilibrium and thermodynamics of a textile dye V5BN by a natural nanocomplex material: Clinoptilolite

Dyes are considered as a major pollutant released in industrial (leather, textile, and paper) effluents. In this study, the ability of Clinoptilolite in adsorbing an industrial dye (Violet 5BN) was assessed. Clinoptilolite was characterized by Scanning Electron Microscopy, Energy Dispersive analysis using X-ray and Brunauer, Emmett and Teller analysis. Batch studies at varying adsorbent dosage, pH, temperature, and time revealed that 96% of the dye was adsorbed with an adsorbent mass of 1.5 g at 30 °C, pH 5 and reaction time of 90 min. Both Langmuir and Freundlich isotherms were found to be fit, which proves the process to be heterogeneous. The experimental and calculated values of adsorption capacity were almost similar, with correlation coefficients greater than 0.9, thus implying pseudo-second order and intraparticle diffusion as the favorable models. Negative values of ΔG° indicate strong binding energy between the adsorbent and adsorbate, while negative ΔS° values prove less randomness of the process and higher adsorbate concentration on the adsorbent surface due to ion-exchange interaction. The exothermic nature of adsorption is evident from the negative ΔH° recorded. Thermodynamic studies showed the system was a spontaneous and enthalpy driven process, with chemisorption as the predominant mode of adsorption at 30 °C and physisorption at elevated temperatures. The study demonstrates the significance of natural clinoptilolite in environmental protection, as an adsorbent for remediation of dyes.