dc.description.abstract | In this study the feasibility of synthesizing mesoporous molecular sieve (i.e., referred to as A-MCM41) by using sewage sludge ash (SSA) as the starting Si and Al sources ; and the enhanced adsorption of heavy metals (Pb and Cu) and organic dye (methylene blue) by the resultant A-MCM41 was investigated with surface modification by three modifiers (3-aminopropyltriethoxysilane, 3-Mercaptopropyl-trimethoxysilane, and Triethoxyvinylsilane.)
For the preparation of a precursor solution for subsequent MCM41 synthesis, Si was solubilized from sewage sludge ash (SSA) by alkali fusion process with a 1.25 NaOH (s) /SSA (by weight) ratio at 400 ℃, followed by a extraction with deionized
water at a L/S=7. It was confirmed that quartz had converted into soluble sodium silicate (Na2SiO3) and sodium aluminum (Na4Al2Si2O9) during the fusion process. The target MCM-41 was synthesized by a hydrothermal process at 105 ℃, using the precursor solution, ammonium hydroxide, and C16TAB (Cetyltrimethylammonium bromide, as surfactant). After the synthesis process, the resultant products were filtered
and calcined at 550 ℃ to remove the surfactant and the A-MCM41 was formed. However, due the presence of Al 2 O 3 derived from SSA, the extracted Al species from SSA was found to be tetrahedrally incorporated in the framework (i.e., A-MCM41), as confirmed by the 27Al NMR analysis. Moreover, the optimum A-MCM41 as synthesized from SSA in this study had a surface of 805 m
2/g and a pore volume of 0.81 cm3/g, as compared to 1025 m2/g and 1.04 cm3/g, respectively, of the control
sample synthesized from pure Na2SiO3.
Finally, the surface of A-MCM41 as synthesized was further modified with 3-aminopropyltriethoxysilane (APTES), (3-Mercaptopropyl)-trimethoxysilane (MPTMS) and Triethoxyvinylsilane (TEVS), bonding functional groups to the surface to functionalize the mesoporous materials (i.e., referred to as AA-MCM41, MA-MCM41 and TA-MCM41, respectively). The functionalized A-MCM41s were
characterized by FT-IR and EA technologies. The small angle XRD pattern indicates that the structure of AA-MCM41, MA-MCM41 and TA-MCM41 retain the characteristic peaks of A-MCM41.
Five MCM-41s, including three surface modified A-MCM41s, as well as the A-MCM41 as synthesized, and the pure Si-MCM41 were evaluated for their adsorption performance in Pb(II), Cu(II) and MB. For heavy metals adoption, the amino-functionalized AA-MCM41 was found to have a better removal efficiency for
Pb(II) and Cu(II) (i.e., 99.96 % and 58.99 %, respectively in a single component system with initial concentration 100 mg/L); whereas for organic dye adsorption, the A-MCM41 as synthesized from SSA was found to have greater removal efficiency for MB (i.e.,87.03 %.). The adsorption of Pb(II), Cu(II) and MB, in a multi-component system showed decreased adsorption quantity for the tested adsorbates, possibly due to the competition among the adsorbates. It was also found that the selectivity for the tested adsorbates in decreasing order was Cu(II)>Pb(II)>MB. In the adsorption isotherm, A-MCM41, AA-MCM41 and MA-MCM41 were found well fitted with the Langmuir model (R2=0.9959-0.9999). The maximum adsorption of MB was found to be 0.49 mmol/g for A-MCM41; and the maximum adsorption of Pb(II) and Cu(II) was 0.71mmol/g and 1.25 mmol/g, respectively for AA-MCM41.
This work demonstrated that it is feasible and beneficial to synthesize A-MCM41 with SSA as starting silicon and aluminum sources was effective in organic dye and metal ion adsorption. And for this synthesis technology suggesting that the preparation of A-MCM41 with SSA could contribute to the recycling of sewage sludge and is feasible, effective, and environmental beneficial.
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