Adsorption of linear and cyclic pentasiloxanes onto MCM-41: Experimental and computational studies

Abstract

In this work MCM-41 solid was evaluated for the adsorption of dodecamethylpentasiloxane (L5) and decamethylcyclopentasiloxane (D5) siloxanes. The adsorbent was synthesized at room temperature using the sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and N2 adsorption-desorption at 77 K. Adsorption equilibrium and kinetic studies were performed in isooctane at 25 °C in single and binary modes. The equilibrium data by Langmuir isotherm showed maximum adsorption capacity (qmax) of 0.058 mmol g−1 (22.3 mg g−1) and 0.019 mmol g−1 (7.05 mg g−1) for single mode of L5 and D5, respectively, while in binary mode these values were 0.054 (20.8 mg g−1) and 0.032 mmol g−1 (11.9 mg g−1) for L5 and D5, respectively. The adsorption kinetics in both contact modes were typically of pseudo-first order. DFT simulations to calculate the adsorption energies between the ligands (siloxanes) and the receptor (MCM-41) showed a value of −0.76 eV for the MCM-L5 system, which is much higher than that found for MCM-D5 (−0.50 eV). This base research is important from an environmental and technological perspective, in which researchers will use the initial values obtained in this research to optimize the adsorbent matrix with an infinite number of modifications that can be made.

Keywords

• Siloxanes
• Adsorption
• MCM-41
• DFT simulations