Abstract
Natural adsorbents as low-cost materials have been proved efficient for water remediation and have significant capacity for the removal of certain chemicals from wastewater. The present investigation aimed to use Citrullus colocynthis seeds (CCSs) and peels (CCPs) as an efficient natural adsorbent for methylene blue (MB) dye in an aqueous solution. The examined biosorbents were characterized using surface area analyzer (BET), scanning electron microscope (SEM), thermogravimetric analyzer (TGA) and Fourier transform infra-red (FT-IR) spectroscopy. Batch adsorption experiments were conducted to optimize the main factors influencing the biosorption process. The equilibrium data for the adsorption of MB by CCSs were best described by the Langmuir isotherm followed by the Freundlich adsorption isotherms, while the equilibrium data for MB adsorption by CCPs were well fitted by the Langmuir isotherm followed by the Temkin isotherm. Under optimum conditions, the maximum biosorption capacity and removal efficiency were 18.832 mg g−1 and 98.00% for MB-CCSs and 4.480 mg g−1 and 91.43% for MB-CCPs. Kinetic studies revealed that MB adsorption onto CCSs obeys pseudo-first order kinetic model (K1 = 0.0274 min−1), while MB adsorption onto CCPs follows the pseudo-second order kinetic model (K2 = 0.0177 g mg−1 min−1). Thermodynamic studies revealed that the MB biosorption by CCSs was endothermic and a spontaneous process in nature associated with a rise in randomness, but the MB adsorption by CCPs was exothermic and a spontaneous process only at room temperature with a decline in disorder. Based on the obtained results, CCSs and CCPSs can be utilized as efficient, natural biosorbents, and CCSs is promising since it showed the highest removal percentage and adsorption capacity of MB dye.
Highlights
Dyes are considered one of the most concerning industrial contaminants that are discharged into the environment in large amounts
Infrared spectra of the biosorbents and methylene blue (MB)-loaded biosorbents were recorded over 4000–400 cm−1, using Thermo Scientific Nicolet iS50 Fourier transform infra-red (FT-IR) spectrophotometer in the attenuated total reflectance (ATR) mode
An adverse trend was detected for the uptake of MB by CCPs, which was decreased from 91.43% to 82.52%, suggesting the exothermic nature of the adsorption process
Summary
Dyes are considered one of the most concerning industrial contaminants that are discharged into the environment in large amounts. There are increasing research efforts, as it is vitally important to develop suitable and efficient techniques for the treatment of dye pollutants and their effective removal from wastewater to guarantee the safe discharge of treated liquid wastes into watercourses and water bodies [2]. Adsorption is considered an efficient and prevalent process used for wastewater remediation, as it is capable of eliminating hazardous pollutants and color [5]. It has been reported as an attractive method, due to its multiple benefits, such as the operation facileness, the design simplicity and the high-quality treated water production [6,7]. The biosorption kinetics, isotherms and thermodynamic properties were analyzed
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