Ultrasonication and non‐ionic surfactant modification of Moringa oleifera leaf powder for methylene blue adsorption

Abstract In this study, the sonication‐mediated structural modification of Moringa oleifera leaf powder was explored in the presence of the non‐ionic surfactants Tween 60 and Tween 80 to reveal their influence on the physicochemical properties, surface topography and methylene blue (MB) adsorption capability. Three adsorbents, ultrasonicated Moringa leaf powder in water, Tween 60‐modified material and Tween 80‐modified material, were synthesised and characterised by particle size analysis, scanning electron microscopy (SEM), Fourier‐transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) analysis. The main particle size region was reduced from about 1500 nm for S1 to 500 nm for S2 and 300 nm for S3, while the distributions remained polydisperse. From S1 to S3, the specific surface area value enhanced from 6.54 to 8.72 m 2 /g and the mean pore diameter raised from 14.2 to 16.7 nm. FTIR analysis also confirmed the contents of hydroxyl, carbonyl, C–O and other oxygenated groups which are typical to Moringa biomass. The impact of adsorbent dose, pH, contact time and initial dye concentration on the adsorption of MB was studied. It was found that the maximum removal was achieved under alkaline medium at pH 9. S3 achieved the maximum adsorption performance in general; however, U‐MOLP‐W (S1), U‐MOLP‐W + T60 (S2) and U‐MOLP‐W + T80 (S3) performed very closely and the statistical analysis showed that the differences were not statistically significant ( p > 0.05). Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were used to analyse the equilibrium data, and pseudo‐first‐order and pseudo‐second‐order models were employed to analyse the kinetic data. However, the pseudo‐second‐order model gave the best fit ( R 2 ≈ 0.998–0.999), but it was not considered enough to confirm chemisorption or a particular rate‐controlling mechanism. The D–R adsorption mean energies were <8 kJ/mol, indicating that physical forces might play an important role in the process of MB uptake. Positive values of ΔH° reflected an endothermic process, positive values of ΔS° corresponded to an increase of interfacial disorder and negative values of ΔG° were evidence of a preferable process for the point of view of adsorption at the studied conditions. Collectively, the results indicate that sonication and surfactant‐modification could modify the texture and particle‐stability aspects of Moringa leaf powder with respect to MB, but the obtained enhancement in MB removal was modest.