Tryptophan-Based Organoclay for Aqueous Naphthol Blue Black Removal – Preparation, Characterization, and Batch Adsorption Studies

To prevent the serious threat of textile wastewater, researchers have developed adsorption-based wastewater treatment using cheap, yet effective, adsorbent materials. Of which is natural bentonite, that has the advantages for adsorption due to its porous structure and functional groups but still suffers from its low affinity against anionic and hydrophilic azo dyes. Herein, we aimed of improving the affinity by amino acid tryptophan embedment into the locally isolated natural bentonite collected from Aceh Province, Indonesia. The prepared bentonite samples were characterized using Fourier transform infrared, X-ray diffraction, and scanning electron microscopy. Adsorptive removal was performed on naphthol blue black (NBB) in a batch system with variations of contact time, pH, and adsorbent dosage. The isotherm studies were carried out at optimum conditions (contact time=15 minutes; pH 1; adsorbent dosage=0.2 g) with several models including Langmuir, Freundlich, Sips, and Redlich-Peterson isotherm models. The characterization results revealed that the modification altered its functional group, crystallinity, and micro-surface morphology that add more benefits for adsorption. At optimum conditions, 99.2% NBB has been successfully removed from the aqueous solution. The isotherm studies suggested that the NBB adsorption onto the tryptophane-modified natural bentonite was dependent on Sips isotherm model (R2=0.999; root-mean-square-errors=1.11×10-4 mg/g).