An Investigation into the Cationic Dye Adsorption Capacity of Prickly Pear Cactus-Derived Cellulose

This research aims to investigate the potential of a plant cellulose developed from Opuntia ficus-indica (OFI) cladode as a sustainable and renewable adsorbent for the removal of neutral red (NR), a cationic dye pollutant, from aqueous environments. Analysis of raw and treated OFI using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) demonstrated the successful extraction of type cellulose. The Brunauer–Emmett–Teller (BET) analysis of the nitrogen adsorption-desorption isotherm revealed an improved specific surface area of 12.4 m2/g after treatment. A systematic study of key parameters in batch adsorption experiments revealed removal rates greater than 90% at pH = 3, an adsorbent dosage of 3 g/L and an initial dye concentration of 100 mg/L with equilibrium achieved within 2 h. The high correlation coefficient (R2 = 0.98) obtained with the Langmuir isotherm model suggests that the adsorption behavior is consistent with monolayer surface adsorption. A maximum adsorption capacity (Qm) of 357.1 mg/g for neutral red dye was achieved, demonstrating a significant adsorption capacity relative to other materials such as chitosan-modified activated carbon and halloysite nanotubes. The pseudo-second-order model effectively described the kinetics of the adsorption phenomena. Thermodynamic analysis revealed an exothermic and spontaneous adsorption process, with an enthalpy change (ΔH) of −24.886 kJ/mol, indicative of predominantly physisorption-driven interactions. Moreover, the regenerated cellulose exhibited a retention of over 70% efficiency after multiple adsorption-desorption cycles, highlighting its potential as an excellent reusable adsorbent. The outcomes of this research present an environmentally conscious alternative to synthetic adsorbents, facilitating the effective NR dye removal through renewable and sustainable means.