A study of adsorption of Reactive Brilliant Red (K-2BP) by amino-modified macadamia nut shells

Macadamia nut shells (MNS), an abundant forestry residue rich in cellulose and lignin, were amino modified to adsorb reactive brilliant red (K-2BP). The raw MNS, and the ethylenediamine, diethylenetriamine and triethylenetetramine modified MNS (EMNS, DMNS, and TMNS) were characterized by scanning electron microscopy, laser particle sizer, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis. The effect of pH on the adsorption process of K-2BP was studied and combined with the zeta potential analysis. The adsorption mechanism was explained. The K-2BP dye adsorption capacity decreased as pH increased. Results showed that TMNS had the highest adsorption capacity due to a higher pH pzc which implied a more positive surface charge and more amine and secondary amine on the surface. Thermodynamic analysis verified that the adsorption process was endothermic and spontaneous. The adsorption kinetics of these modified adsorbents was well matched with pseudo-second-order equation, indicating that the adsorption process is chemical adsorption. The Langmuir and Freundlich isotherm models were used to describe the adsorption processes of K-2BP dye onto four kinds of adsorbents. The Freundlich model showed the best statistics, which meant the adsorption of K-2BP onto adsorbents from the aqueous solutions was constant with a monolayer formation.