Single- and Multicomponent Siloxane Adsorption in Al-MCM-41 (Al = 0.0, 1.3, and 4.4)

Adsorption studies in the liquid phase at 25 °C of siloxanes L5 (linear) and D4, D5, and D6 (cyclic) on silica MCM-41 (pure or Al-doped) were performed, including evaluations of siloxane removal in single- and multicomponent forms. The materials were synthesized by the sol-gel method and characterized by techniques such as XRD, SEM-EDS, ICP-OES, FT-IR, N₂ adsorption-desorption at 77 K, NH₃-TPD, and NMR. The characterization results confirmed the chemical and textural properties typical of mesoporous materials. The order of adsorption capacity was Al-MCM-41(10) ≫ Al-MCM-41(30) ≥ MCM-41 for all siloxanes (L5, D4, D5, and D6) in the different scenarios (single, binary, and ternary components), which was influenced by chemical structure, molecular geometry, and adsorbent acidity. The Al-MCM-41(10) adsorption capacities were 0.479, 0.097, 0.055, and 0.045 mmol g^-1 for L5, D4, D5, and D6, respectively. The Al-MCM-41(10) adsorption kinetics demonstrated that the siloxane adsorption process followed pseudo-first-order kinetics across all scenarios. Recovery tests showed appreciable adsorptive capacities (100-76%) of D4 on Al-MCM-41(10) at 25 °C for three consecutive uses. The results showed promising characteristics for the physical adsorption of linear and cyclic siloxanes on easy synthesis materials under less expensive operational conditions.