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.

Automated summary

In this study, chemically modified lychee peels were used as an adsorbent to remove Reactive Red 195 dye from water. The results showed that the solution pH had a significant effect on the removal efficiency, with the highest removal efficiency of 94.5% achieved at pH 4.0. The adsorption process followed the Langmuir model and pseudo-first-order kinetic model, indicating favorable adsorption at low temperatures. The desorption efficiency was also evaluated, and the regenerated adsorbent showed a retention of over 77.3% efficiency after five cycles.