Adsorption of Selected NSAIDs, Diclofenac Potassium, Piroxi-cam-beta-cyclodextrin and Paracetamol onto Activated Carbon/ Iron Oxide Nanocomposite from Wastewater: Experimental and DFT Approach

The adsorption of NSAIDs on activated carbon/ Fe2O3 nanocomposite prepared by simple coprecipitation method was investigated by batch technique. The composition of the composite was investigated by different characterization techniques, including XRD, SEM, FTIR and TGA. Subsequently, the composite was utilized to remove painkillers, namely diclofenac potassium, piroxicam-beta-cyclodextrin and paracetamol from aqueous solutions. Numerous factors affecting the adsorption process were investigated including contact time, pH, adsorbate concentration, temperature, and adsorbent dosage were systematically optimized. The optimal adsorption for piroxicam-beta-cyclodextrin (94.2%), diclofenac potassium (96.2%), and paracetamol (94.9%) were achieved at pH 2, 4 and 7 respectively. Adsorption data were analyzed, by using different adsorption isotherms. Diclofenac potassium and paracetamol obeyed more closely the Freundlich isotherm model, as compared to other models, while piroxicam-beta-cyclodextrin exhibited conformity with the Temkin isotherm model across the entire concentration spectrum. The kinetic analysis indicates that the adsorption of all three adsorbates obey pseudo-second-order kinetics. The thermodynamic analysis yielded the following parameters: ΔH = -63.04 kJ/mol, ΔS = -167.79 J mol-1 K-1 for diclofenac potassium, ΔH = -10.89 kJ/mol, ΔS = -35.11 J mol-1 K-1 for piroxicam-beta-cyclodextrin and ΔH = -68.83 kJ mol-1, ΔS = -217.22 for paracetamol. These findings suggest that the adsorption process is not only spontaneous but also exothermic, resulting in the release of heat. The DFT calculations unveiled significant interactions between the active sites of all painkillers and the AC/Fe2O3 composite, as confirmed by their negative binding energies.