Removal of sulfonated azo Reactive Red 195 textile dye from liquid phase using surface-modified lychee (Litchi chinensis) peels with quaternary ammonium groups: Adsorption performance, regeneration, and mechanism

In the present work, chemically modified lychee peels were synthesized using glycidyltrimethylammo-nium chloride (GTMAC) and used to remove Reactive Red 195 (RR 195) from an aquatic environment. Lychee peel powder (LPP), GTMAC-modified LPP (G-LPP), and RR-195/G-LPP were characterized by BET/BJH, FTIR, pHPZC, XRD, and FE-SEM/EDX analyses. Adsorption tests were performed in batch mode, and various operational variables like initial dye concentration (25-250 mg/L), G-LPP mass (10-80 m g/30 mL), stirring speed (0-400 rpm), solution pH (1.0-10.0), contact time (0-480 min), and temperature (298-328 K) were studied to optimize the process. The solution pH strongly affects RR 195 removal effi-ciency. The maximal dye removal was 94.5%, achieved at pH 4.0. The non-linear assessment of isotherm and kinetics showed that the sorption system was fitted well by the Langmuir model (R2 > 0.9899) and pseudo-first-order kinetic model (R2 > 0.9918). The Langmuir maximum monolayer sorption capacities, qmax, at temperatures of 298, 308, 318, and 328 K are 144.9, 137.7, 130.1, and 124.2 mg/g, respectively, thus suggesting favorable adsorption at low temperatures. The Ea (activation energy) was computed to be 16.3 kJ/mol, which indicated that the adsorption behavior was mainly attributed to physisorption. The thermodynamic variables DHo (-46.6 kJ/mol), DSo (-133 J/mol K), and DGo (-6.8693 ti-2.9777) revealed that the sorption process was exothermic, feasible, and spontaneous. The binding of RR 195 dye onto the G-LPP surface was through hydrogen bonding and electrostatic interactions. Desorption effi-ciency follows the order NaOH (91.2%) > NaCl (69.6%) > HCl (65.2%) > methanol (58.4%) > H2SO4 (48.1% ) > acetone (45.5%) > ethanol (39.2%) > HNO3 (31.6%). After five consecutive cycles of regeneration and reusability of G-LPP adsorption performance, the adsorption efficiency was better than 77.3%. The results show that G-LPP is a promising adsorbent for removing RR 195 dye from an aqueous solution.(c) 2022 Elsevier B.V. All rights reserved.