The efficient removal of dyes from industrial wastewater is a critical aspect of environmental protection. Direct Blue 86 (DB86), a widely used textile dye, presents a particular challenge due to its chemical stability and potential environmental impact. Understanding the dynamic process of dye adsorption onto a suitable material is key to developing effective treatment strategies. This exploration focuses on the kinetic studies of Direct Blue 86 absorption by cellulose hydrogel (CAH), a promising adsorbent material.

Kinetic studies help elucidate the rate at which an adsorbent removes a pollutant from a solution and identify the rate-limiting step in the adsorption process. Researchers have employed various kinetic models to analyze the adsorption behavior of DB86 onto CAH. Among the commonly used models are the pseudo-first-order (PFOM), pseudo-second-order (PSOM), Elovich model (EM), intraparticle diffusion model (IPDM), and film diffusion model (FDM).

The pseudo-first-order model, which assumes that the rate of adsorption is directly proportional to the concentration of the remaining adsorption sites, often describes physical adsorption processes. However, in the case of DB86 onto CAH, the experimental data did not align well with this model, with low correlation coefficients observed. This suggests that physisorption might not be the sole or dominant mechanism at play.

In contrast, the pseudo-second-order model, which is based on the assumption that the adsorption rate is governed by chemical adsorption involving valence forces or electron sharing between the adsorbent and adsorbate, showed a much stronger correlation with the experimental results. With correlation coefficients exceeding 0.990, the PSOM accurately predicted the experimental equilibrium adsorption capacity (qe). This indicates that chemical adsorption, possibly involving chemisorption or strong interactions between the dye molecules and the functional groups of the cellulose hydrogel, plays a significant role in the removal of DB86.

The Elovich model, which considers the chemisorption process on heterogeneous surfaces, was also analyzed. While it provided some insights, its correlation coefficients were less consistent, and the interpretation of its parameters was complex. The intraparticle diffusion model (IPDM) and film diffusion model (FDM) were also examined to understand mass transfer limitations. The IPDM plots indicated that intraparticle diffusion was a part of the overall process but not the sole rate-controlling step. Similarly, the FDM analysis revealed that while film diffusion influenced the rate, it did not exclusively govern the adsorption kinetics.

The strong adherence to the pseudo-second-order kinetic model for DB86 adsorption onto cellulose hydrogel is a critical finding. It implies that the process is likely driven by chemical interactions. This knowledge is invaluable for optimizing adsorption conditions, such as contact time and temperature, to maximize the efficiency of DB86 dye removal. By understanding these kinetic parameters, manufacturers and researchers can fine-tune their wastewater treatment systems to achieve superior performance and environmental compliance. The ability to predict adsorption rates allows for better design and operation of adsorption columns and batch reactors, ensuring effective and timely removal of harmful dyes from industrial effluents.