Integrated experimental, thermodynamic and molecular-level investigation of anionic and cationic dye removal by raw Moringa oleifera seed powder: mechanistic and structural insights
摘要
The present study examines how well raw Moringa oleifera seeds can perform with regard to their capacity for removing both methyl red (MR) and methylene blue (MB) from water solution at the same time, using a comprehensive combination of experimental and molecular-level methods. In batch adsorption tests both of the dye adsorbents showed that most of the dye was adsorbed into the adsorbent within 20 to 25 min of contact time between adsorbent and adsorbate. The removal efficiencies of both MR and MB were 89.4 and 81.9% when using raw Moringa oleifera seeds. The kinetic data for both the adsorbates followed a pseudo-second order model indicating the use of surface interactions as an important mechanism for adsorption to occur. The equilibrium data for both adsorbates was best represented by the Langmuir and the Freundlich isotherm models, while the mean energy of adsorption calculated using the Dubinin-Radushkevich isotherm model indicate that physisorption was the main type of interaction, since the mean energy value was less than 8 kJ mol−1. The results of the thermodynamic studies indicated that the adsorption of both adsorbates onto raw Moringa oleifera seeds is spontaneous and endothermic in nature. The results of Fourier transform infrared (FTIR) and molecular docking studies indicate that the mechanisms of dye adsorption onto raw Moringa oleifera were attributed to electrostatic attraction, hydrogen bonding and π-π interactions. A comparative analysis of the performance of non-modified raw Moringa oleifera seeds with performance data from the literature suggests that RMOSP shows competitive performance characteristics and has the potential to be a low-cost and environmentally friendly solution for biosorption of wastewater effluents.