Selective adsorption of single and binary dyestuffs by citrus peel: Characterization, and adsorption performance

The powdered citrus peel, which has been replaced with sodium hydroxide, was used in this study to test how well methylene blue and reactive black 5 dyestuff absorbed one or both. To find out about the texture and surface chemistry of modified citrus peel, Fourier transform infrared spectroscopy and scanning electron microscope analyses were carried out. Fourier transform infrared spectroscopy data revealed the presence of amphoteric radicals on the modified citrus peel surface, indicating the effective adsorption of methylene blue and reactive black 5. Many parameters affecting the batch adsorption process, such as modified citrus peel dose (0.1-0.5 g), pH (2-10), time (20-80 min), stirring speed (60-180 rpm), and temperature (20-45 °C), were studied. It is seen that the physical effect is at the forefront, homogeneous monolayer adsorption occurs, and the process fits the Langmuir and pseudo first order models for dyestuffs. Thermodynamic modeling showed that the adsorption of methylene blue and reactive black 5 was spontaneous and endothermic. At pH 2, an adsorption capacity of 0.67 mg/g and a removal efficiency of 66.86% were achieved for reactive black 5. For methylene blue at pH 6, the adsorption capacity was 4.34 mg/g, and the decolorization rate was 87%. The decreases in the removal rates of dyestuffs in the binary system indicate that they are affected by their simultaneous presence in the solution. The results proved that modified citrus peel can be useful for dyestuff removal in single or binary systems, although the removal capacity of modified citrus peel is highly dependent on methylene blue and reactive black 5.