| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 100 === This study investigated the feasibility of synthesizing Al-MCM-41 with silicon and aluminum sources that were extracted by alkaline fusion process from sewage sludge ash (SSA). The synthesized and the further surface-modified Al-MCM-41s were characterized, and the adsorption performance was evaluated.
Two types of sewage sludge ash (SSA) as received, and SSA treated with acid, were tested in this study. The results indicate that starting with an alkaline fusion treatment of the SSA (mixed with NaOH by 1:1.25 weight ratio) at 400℃, it rendered the quartz soluble for extraction by forming sodium silicate (Na2SiO3) and sodium aluminum silicate (Na4Al2Si2O9).
After this fusion treatment, silica and aluminum were extracted from the fused solid with deionized water at various tested L/S ratios (i.e., liquid to solid ratio), ranging from 3,7,15 to 50. It was noted that acid-treated SSA showed increased efficiency in Al and Si extraction as compared to the SSA as received. Both the tested SSAs showed the greatest extraction efficiency at L/S=3, and then the extraction efficiencies decreased with increasing L/S ratios. Maximum extraction efficiencies for Si and Al were found to be 34.81 wt% and 7.78 wt%, respectively, for SSA without acid treatment, as compared to those of 79.17 wt% and 37.59 wt% for acid-treated SSA.
The Al-MCM-41 was synthesized by hydrothermal process at 105℃, in the presence of the precursor solution (i.e., as prepared by the above extraction process), ammonium hydroxide, and C16TAB (Cetyltrimethylammonium bromide, as surfactant). After the completion of hydrothermal process, the target products were filtered from the solution and then calcined at 550℃ to remove the surfactant, this resulting in Al-MCM-41 products. However, due to the presence of SSA-derived Al2O3, the Al-MCM-41 thus synthesized incorporated Al into its structure (i.e., referred to as Al-MCM-41), and was reported to have
enhanced the stability of the Al-MCM-41 structure. The composition of Al-MCM-41 as prepared from original SSA was found to contain 86.89-93.21% Si, 3.86-9.58% Al, and trace of other elements, with a 761.65 m2/g surface area, and 0.85 cm3/g pore volume. In contrast, the Al-MCM-41 as prepared from the acid-treated SSA showed a greater surface area of 1057.95 m2/g, and a pore volume of 1.02 cm3/g. For the acid-treated SSA, the extraction efficiencies of Si and Al varied with L/S ratio. This resulted in a wide range of Si/Al ratio in the precursor solutions (i.e.,11.89-62.88) and in the resultant Al-MCM-41
products (i.e., 16.89-39.36). The Al-MCM-41 prepared at higher Si/Al ratio seemed to have better sieve properties (i.e., larger surface area and pore volume.)
Finally, the surface of Al-MCM-41 as synthesized was further modified with 3-aminopropyltriethoxysilane(APTES) to bond ammoniums-functional groups. The surface-modified Al-MCM-41, referred to as ammonium-functionalized mesoporous materials (AFMM), were proved to enhance the adsorption capability of mesoporous sieves.The AFMM was characterized by FT-IR, XRD, TEM and SEM techniques, and BET analysis. The XRD pattern indicated that the structure of AFMM retained the characteristic peaks of MCM-41; and further the FT-IR confirmed the functional groups of -NH2 and N-H around 714 and 1560 cm-1.
This study demonstrated that it is feasible to synthesize Al-MCM-41 using silicon and aluminum sources extracted from sewage sludge ash. An acid-pretreatment of the SSA
would enhance the extraction efficiencies of Si and Al, this resulting in the synthesis of Al-MCM-41, with larger surface area and pore volume. The results may contribute to the recycling of sewage sludge and the production of a green functionalized mesoporous material.
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