Enhanced removal of Indigo Carmine dye from textile effluent using green cost-efficient nanomaterial: Adsorption, kinetics, thermodynamics and mechanisms

The release of Indigo Carmine in waterbodies may cause serious impact in aquatic ecosystems and human health. There is an interest in developing green, low-cost and effective adsorbents for the removal of toxic dyes from textile effluents. This study proposed the developing of an adsorbent material at the nanoscale using the waste from Moringa oleifera seeds generated after the oil extraction. Moringa oleifera seeds were grounded to obtain an adsorbent material at the nanoscale. Batch-adsorption tests were carried out to evaluate the capacity of the absorbent to retain Indigo Carmine from liquid solutions. The following variables were studied: pH, adsorbent-dye ratio, contact time, initial dye concentration and temperature. The adsorption process fitted the Langmuir isotherm in the equilibrium of adsorption and the power function in the kinetic behavior. The maximum adsorption capacity of the absorbent nanoparticles was 60.24 mg/g, which is 4.3 times higher than that of the bulk Moringa oleifera seeds. Thermodynamic results proved the adsorption process was spontaneous and exothermic. Hydrogen bonding, electrostatic interlinkage and pi-pi interactions were identified as the dominant mechanisms of Indigo Carmine adsorption on the nanoparticles. The adsorption-desorption study resulted in a slight decrease of the adsorption capacity after 4 cycles, from 94% to 88%. The removal of Indigo Carmine from a textile effluent (85%) was similar to that with pure Indigo Carmine solutions (91%). The results suggested the feasibility of Moringa oleifera seed nanoparticles as a promising, green and low cost adsorbent for textile wastewaters with dyes.