Adsorption of Direct Red 23 dye from aqueous solution by means of modified montmorillonite nanoclay as a superadsorbent:
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Adsorption of Direct Red 23 dye from aqueous solution by means of modified montmorillonite nanoclay as a superadsorbent: Mechanism, kinetic and isotherm studies Seyedeh Mahtab Pormazar*,** and Arash Dalvand*,† *Environmental Science and Technology Research Center, Department of Environmental Health Engineering, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran **Student Research Committee, Shahid Sadoughi University of Medical Sciences, Yazd, Iran (Received 18 April 2020 • Revised 30 June 2020 • Accepted 7 July 2020) AbstractA novel adsorbent of modified nanoclay was synthesized by covering of alum on the montmorillonite nanoclay (Al/nanoclay). Al/nanoclay was applied as an efficient superadsorbent to remove Direct Red 23 (DR23) from colored wastewater. The adsorbent was characterized by Fourier transform infrared spectroscopy, energy-dispersive Xray spectroscopy, and zeta potential analysis. The effects of various operating parameters, such as contact time, initial dye concentration, adsorbent dose, pH and ionic strength on the performance of adsorption, have been studied. The adsorption experiments showed that pH has an obvious effect on the adsorption efficiency and the highest percentage of DR23 dye removal was observed at pH 2. Zeta potential measurement confirmed that the adsorption mechanism is ascribed to electrostatic interaction between sulfonic groups of the anionic dye and the positive surface charge of the adsorbent. The pseudo-second-order kinetic model and the Langmuir isotherm were found to best describe the DR23 adsorption and the maximum monolayer adsorption capacity at the conditions of pH 2 and the adsorbent dose of 0.05 g/L was 2,500 mg/g. The findings recommend that Al/nanoclay can be successfully used for DR23 dye removal from the colored wastewater. Keywords: Adsorption, Direct Red 23 Dye, Mechanism, Modified Montmorillonite Nanoclay
dye removal from wastewater [15]. Different adsorbents like activated carbon [16], zeolites [17], fly ash [18], and other porous materials have been prepared and used in the adsorption of dye. Clay minerals and their derivatives have also been widely used as adsorbent due to their cost-effectiveness, natural abundance, non-toxicity and environmental friendliness [19]. Montmorillonite is a type of natural clay mineral with the chemical formula of (Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2 XH2O [20]. It is classified as 2 : 1 clay which consists of alumina (Al3+) octahedral sheet sandwiched between two silica (Si4+) tetrahedral sheets [21]. However, the layers of montmorillonite carry a permanent negative charge due to isomorphous substitution of Al3+, Si4+, Mg2+, and Fe3+ ions. Some other 2 : 1 clay minerals (less than 1%) have a positive charge that is caused by broken bonds along particle edges and pH-dependence [22-24]. So, pristine montmorillonite is unsuitable for removing anionic pollutants from aqueous solutions. The changes in the molecular structure
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