Polyester waste activated carbon assisted micropollutant methylene blue and Congo red dyes removal from wastewater: RSM modeling, kinetics, mechanism, and reusability study

Abstract

This study explores the synthesis of activated carbon (AC) from polyester waste using zinc chloride (ZnCl2) as a chemical activator, designed to efficiently remove both positive methylene blue (MB) and negatively charged Congo red (CR) dyes from wastewater. Response Surface Methodology integrated with Central Composite Design was employed to optimize critical parameters, including adsorbent dosage, solution pH, dye concentration, and temperature, for enhanced dye removal. The results showed remarkable removal efficiencies of 100 % for MB and 99 % for CR under optimal conditions. The kinetic analysis showed that the pseudo-second-order model best described the adsorption process because of chemisorption, which includes ion exchange, complexation, π–π stacking, electrostatic interaction, and hydrogen bonding, while intra-particle diffusion was a key factor in the rate-limiting step. The results suggest MB followed the Langmuir isotherm, while the CR adsorption favored both Langmuir and Freundlich models. Thermodynamic studies revealed distinct adsorption behaviors: MB adsorption was exothermic, while CR adsorption was endothermic. Additionally, reusability tests confirmed the material's ability to maintain high performance over five adsorption–desorption cycles with no significant structural changes. These findings underscore the potential of polyester waste-derived AC as a sustainable and effective material for wastewater treatment.The authors are thankful to the Higher Education Commission (HEC) Government of Pakistan for funding this study under the NRPU program through Project No. 15188. We are thankful to Fiber Craft Industries (FCI) in Lahore, Pakistan, for supplying composite waste material. The authors (M.Y and V.S) gratefully acknowledge the support from the European Just Transition Fund within the Operational Programme: Just Transition under the aegis of the Ministry of the Environment of the Czech Republic, project CirkArena number CZ.10.03.01/00/22_003/0000045 and the Ministry of Education Youth and Sports of the Czech Republic, Operational Programme Johannes Amos Comenius OP JAC \u201CApplication potential development in the field of polymer materials in the context of circular economy compliance (POCEK)\u201D, number CZ.02.01.01/00/23_021/0009004. The authors are further grateful for co-funding from the development process of the Centre of Polymer Systems, Tomas Bata University in Zlin, program DKRVO (RP/CPS/2024-28/002) supported by the Ministry of Education Youth and Sports of the Czech Republic. M.Y also expresses his gratitude for support within the \u201CCreativity, Intelligence & Talent for the Zlin Region\u201D (CIT - ZK) program