Adsorption equilibrium and kinetics of maxilon blue GRL on cotton fiber

<title>Abstract</title> The adsorption interaction between cotton fibers and dye maxilon blue GRL was systematically investigated under varying contact times, initial dye concentrations, agitation speeds and temperatures; and the adsorption capacity of dyes increases with the increase of those four parameters. Analysis of adsorption isotherms revealed superior fit with the Langmuir model compared to the Freundlich model, and both the saturated adsorption capacity <italic>q</italic>_m and adsorption capacity <italic>K</italic>_F exhibited temperature-dependent enhancement. The adsorption of dye onto cotton fibers could be described satisfactorily by the pseudo-second-order rate model, where both the equilibrium adsorption amount <italic>q</italic>_e and the apparent rate constant <italic>k</italic>₂ increase with elevated agitation speeds and temperatures. Thermodynamic analysis yielded an enthalpy change Δ<italic>H</italic>* of 63.5 kJ·mol⁻¹ and Gibbs energy change Δ<italic>G</italic>* of 8.7 kJ·mol⁻¹, collectively indicating a non-spontaneous endothermic process. The negative entropy change (Δ<italic>S</italic>* = ⎼209.3 J·mol^{− 1}·K^{− 1}) suggested reduced molecular randomness at the solid-liquid interface during adsorption. The low activation energy (<italic>E</italic>ₐ = 11.34 kJ·mol⁻¹) and adsorption enthalpy change confirmed physical adsorption mechanisms dominated by hydrogen bonding. Understanding the interaction between fiber and dye is helpful for optimizing dye utilization in industrial processes and engineering modified cotton fibers for wastewater decolorization.