Adsorption behaviors of methylene blue onto tubular cadmium sulfide polycrystals

Abstract

The temporal evolution of methylene blue’s adsorption onto tubularly mesoporous CdS synthesized by templating the fibrous precursor of cadmium oleates is investigated using the batch experiment method. UV–visible measurements on the supernatants at λ = 665 nm reveal the adsorption of methylene blue at 25 and 5 °C exhibits the type IV isotherms, having the typical features of mesoporous materials, and the isotherm can be fitted by Freundlich and Langmuir equation for low and high c_e, respectively. The adsorption enthalpy change H, which is estimated − 12 kJ/mol, reveals the H-bond existing between CdS and MB molecules. The first hour of contact has proved to be a quite rapid dynamics, and subsequently, the dye molecules go through a tardy process in 30–36 h to reach the equilibrium. The uptake of methylene blue by tubular CdS is interpreted by pseudo-second-order model better than by pseudo-first-order model, and the experimental data over the whole adsorption process can be described based on the intraparticle diffusion model.