Abstract
Moringa oleifera (MO) seed coat, a postharvest waste of MO seed, was mercerized and used as eco-friendly adsorbent for removal of Congo red (CR) dye from aqueous solution at different time and temperature. Mercerized M. oleifera seed coat (MSC) was characterized through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) before and after adsorption process. Data obtained from effect of contact time on CR dye-uptake were applied on Elovich, pseudo-first- and second-order kinetic models, as well as on intraparticle diffusion and Boyd models. SEM and FTIR showed adsorption of CR dye on MSC through filled holes (SEM), appearance of new and shifting existing of functional groups (FTIR) on the surface of MSC after adsorption process. Adsorption kinetics was seen to be best fitted with pseudo-second-order model with the highest value of correlation coefficient at all temperatures. Film diffusion mechanism controlled the adsorption process, where external mass transfer was higher than internal mass transfer. Adsorption kinetics parameters confirmed removal of CR dye from aqueous solution through chemical and physical adsorption on MSC.
Highlights
Congo red (CR) dye is a disazo synthetic dye, characterized by large molecular structure with two azo group (N=N) that are bond to aromatic rings having linear and planar molecular structure (Dhaif-Allah et al 2020; Christie 2015; Rong et al 2015)
The scanning electron microscopy (SEM) image of M. oleifera seed coat (MSC) before adsorption (Fig. 1) shows the presence of holes on its surface. These holes are the available pores at the surface of adsorbent, where CR dye molecules are to be captured from aqueous solution
MSC adsorbent was prepared through mercerization of M. oleifera seed coat
Summary
Congo red (CR) dye is a disazo synthetic dye, characterized by large molecular structure with two azo group (N=N) that are bond to aromatic rings having linear and planar molecular structure (Dhaif-Allah et al 2020; Christie 2015; Rong et al 2015). (due to its intense color, high affinity and fastness properties), (Chen and Zhao 2009) as pH indicator in chemical laboratory and for microbial staining (Chukki et al 2018). Its effluent from these industries, if not properly treated before being discharged into the water bodies, can cause. Mercerization of MO seed coat as adsorbent in removal of dye from industrial or simulated effluent has not been reported to the best of our knowledge
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