The multiwalled carbon nanotube has been used as an efficient adsorbent for the removal of Alizarin red S (ARS) and morin from wastewater. The influence of variables including pH, temperature, concentration of the dye, amount of adsorbents and contact time, and so forth on the removal of both dyes was investigated by the batch method. Graphical correlations of various adsorption isotherm models like Langmuir, Freundlich, Tempkin, and DubininÀRadushkevich have been carried out. The adsorption of ARS and morin has been found to be endothermic and feasible in nature. Various thermodynamic parameters, such as Gibbs free energy, entropy, and enthalpy, of the ongoing adsorption process have been calculated. The kinetic studies suggest the process following pseudosecond-order kinetics and involvement of the particle-diffusion mechanism.

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In the present study, Fe 3 O 4 @SiO 2 core-shell microspheres were prepared via two steps. First, Fe 3 O 4 nanoparticles were synthesized by co-precipitation of Fe +3 and Fe +2 as reaction substrates and NaOH as precipitant. Second, the surface of Fe 3 O 4 was coated with silica by hydrolysis of tetraethylorthosilicate as the silica source. Subsequently, in order to reduce the amount of interaction and the agglomeration of Fe 3 O 4 @SiO 2 microspheres, the silica shell of these particles was modified by vinyltriethoxysilane as the silane coupling agent. The structural properties of the samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy analyses. The results indicated that the average sizes of Fe 3 O 4 and Fe 3 O 4 @SiO 2 particles were about 50 and 500 nm, respectively. Also, the surface characterization of Fe 3 O 4 @SiO 2 microspheres showed that the silane coupling agent was covalently coupled with the silica surface.

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