Abstract
Adsorption of direct red 80 (DR 80) and methylene blue (MB) from aqueous solutions on potato peels (PP) has been compared. The use of peels in decontamination technology is very promising given the near zero-cost for the synthesis of those adsorbents. The selected potato peels were first analyzed by scanning using electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR). Then the adsorption behavior was studied in a batch system. The adsorption process is affected by various parameters such as the solution pH (2-11), the initial concentration of the dye (20, 50, 100, 150 and 200 mg L-1), the adsorbent dose (0.1-3%), the temperature (303.16 K, 313.16 K, and 323.16 K), agitation (up to 250 rpm), as well as the contact time. Adsorption isotherms of the studied dye on the adsorbent were determined and compared with the Langmiur, Freundlich and Temkin adsorption models. The results show that the data was most similar to the Freundlich isotherm (R2 = 0.99). The maximum adsorption capacities (Qmax) of MB and DR 80 by the PP at temperatures 303.16 K, 313.16 K and 323.16 K were found to be approximately 97.08 mg g-1; 45.87 mg g-1; 61.35 mg g-1 and 27.778 mg g-1; 45.45 mg g-1; and 32.258 mg g-1. The kinetic data was compared to the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. This revealed that adsorption of methylene blue onto PP abided mostly to the pseudo-second-order kinetic model. Calculations of various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and free energy change (ΔG) display the endothermic and spontaneous nature of the adsorption process.
Highlights
Water pollution has become a major issue in modern times
The peaks detected at 3,434 cmÀ1 and 3,435 cmÀ1, were found in both potato peels (PP) spectra before and after dye adsorption, and could be assigned to O-H stretching vibration of hydroxyl groups (Davila-Jimenez et al ; Mohanty et al )
The results show that the adsorption equilibrium was reached after a contact time of 10 and 60 min, respectively, for methylene blue (MB) and direct red 80 (DR 80), and this is whatever the size of the particles
Summary
Water pollution has become a major issue in modern times. Increased industrial and agricultural activities have resulted in the increase of various types of toxic pollutants. Numerous types of dyes have shown to be toxic and carcinogenic, even affecting aquaticbiota and human health (Ferreira et al ; Kyzas & Kostoglou ) Amongst these dyes, direct red are water-soluble anionic dyes, generally the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines and oxazines (Gupta & Suhas ). Direct red are water-soluble anionic dyes, generally the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines and oxazines (Gupta & Suhas ) Their discharge into the hydrosphere possesses a significant source of pollution due to their visibility even at very low concentrations and due to their recalcitrance nature, giving undesirable color to the water, reducing sunlight penetration, resisting photochemical and biological attack, and their degradation products being toxic or even mutagenic and carcinogenic (Van der Zee & Villaverde ). Research has largely yielded bio-adsorbents as substitutes or complements to commercially activated carbon for wastewater treatment, which is affordable and preferable to economies of developing countries
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