Adsorption of hydrocarbons from industrial wastewater onto a silica mesoporous material: Structural and thermal study

• SEM images show the superficial heterogeneity of the mesoporous silica alumina.
• Contaminants seem to adsorb in the pore through a monoclinic arrangement.
• Aromatics adsorption involves the Lewis acid sites of the MSA.
• Water is bound to the superficial silanol groups (Brǿnsted sites) of the MSA.

In this paper, the use of a mesoporous silica alumina (MSA) for the removal of hydrocarbons from water is outlined. In particular, we focused our attention on the structural modifications that occur during the adsorption process using toluene and benzene as target contaminants and two different material shapes: particle and extruded. Different characterization techniques such as SEM, powder XRD, TGA and IR absorption are used to gain a deep investigation of MSA characteristics. Indeed, morphological features of MSA, the thermal behavior of the loaded and unloaded material including its regeneration and host–guest interactions were largely examined. SEM images and EDX analysis of the two materials have confirmed their amorphous nature and their elemental composition. Powder XRD patterns of as-synthesized (unloaded) and loaded MSA displayed the appearance of some reflection peaks after the adsorption of benzene and toluene. A Le Bail refinement indicated a monoclinic structure for these molecules when adsorbed onto the MSA. FT-IR measurement on loaded and unloaded MSA highlighted the interaction of water with the free silanol groups while the aromatic hydrocarbons probably adsorbed onto different active sites (Lewis acid sites). Indeed, intrinsic acidity measurements by pyridine adsorption showed the presence of a fairly good number of these acid sites. Finally, the thermal behavior of loaded MSA samples with different contaminants has shown the strong influence of water on the desorption temperature of pollutants from MSA.

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