New insights on the adsorption of CI-Reactive Red 141 dye using activated carbon prepared from the ZnCl2-treated waste cotton fibers: Statistical physics, DFT, COSMO-RS, and AIM studies

Abstract

This study aims to develop and apply new adsorbents derived from cotton fiber waste. ZnCl2 was used to activate the activated carbon chemically. The textile industry's waste is readily available and economical to remove the CI dye Reactive Red 141 (RR141). The activated carbon was characterized by TGA, Fourier Transform Infrared (FTIR), and Scanning Electron Microscopy (SEM) to determine the adsorbents' physical and chemical characteristics. Working conditions such as contact time, pH, initial concentration of CI Reactive Red 141 (RR141), and batch biosorption tests were optimized for a given temperature. Kinetics and thermodynamics were determined to investigate the adsorption mechanism. The removal rate of the new adsorbent (adsorption efficiency) ranged from 69.99 to 98.61%. The results show that the adsorption kinetics is fast, with an equilibrium time of 70 min. The optimal conditions were an initial dye concentration of 10 mg/L, a temperature of 20 °C, an adsorbent concentration of 0.25 g/L, and a pH of = 3. The adsorption follows a pseudo-second-order kinetic. The adsorption isotherms study was calculated by statistical physics models with a maximum adsorption capacity of Nasat = 970.34 mg/g at T = 20 °C. According to the thermodynamic results, intraparticle diffusion governs the adsorption process. The thermodynamic parameters determine that the adsorption is chemisorption (-ΔH° = 50.182 kJ/mol). The statistical physics provides a value of 11.495 kJ/mol (physisorption) and reveals that the adsorption process was both exothermic and spontaneous.