下水污泥灰合成中孔徑分子篩及表面改質吸附重金屬之研究

Synthesis of mesoporous molecular sieve using sewage sludge ash and surface modification applications of heavy metal adsorption

黃子光(Tzu-kuang Huang)

指導教授 ： 王鯤生

國立中央大學/工學院/環境工程研究所/碩士(2010年)

摘要

本研究利用下水污泥灰作為取代合成中孔徑分子篩(Al-MCM-41)之矽、鋁源，使用三種不同液固比(L/S=3、5、7)之前驅液，探討合成Al-MCM-41時所造成的影響，並與偏矽酸鈉合成之MCM-41作比較，之後將下水污泥灰與偏矽酸鈉所合成之MCM-41進行胺基官能基的表面改質，探討不同條件下官能基的修飾量，以及對重金屬離子的吸附能力；另外將萃取SiO2後的污泥灰合成微孔沸石吸附劑，以達到全資源化的效果。研究結果顯示，當液固比=7時，前驅液的Si/Al比最高，所合成出Al-MCM-41的鋁含量最少，其XRD的特徵峰強度為最高，在結構特性方面，其比表面積為932 m2/g、孔體積為0.93 cm3/g，是三種液固比所合成Al-MCM-41中最高的，相較於偏矽酸鈉所合成的MCM-41，比表面積為1047 m2/g、孔體積為1.05 cm3/g，其差異性不大。由27Al NMR圖譜可發現在54ppm時皆有波峰(Peak)的產生，表示鋁原子為鋁氧四面體，證實鋁原子有進入到MCM-41的骨架當中，而鋁含量會影響特徵峰強度與結構特性。萃取SiO2後的污泥灰二次回收結果顯示，可合成出鈣霞石(Cancrinite)微孔沸石，使得下水污泥灰在本研究中確實達到全資源化的目標。在表面改質的結果顯示，低液固比(L/S=3、5)所合成的MCM-41，因含鋁量較高，使得比表面積降低，會讓官能基修飾量降低。不同迴流時間下，可知迴流時間越長，官能基修飾量會越高。利用下水污泥灰所合成含鋁之MCM-41，官能基修飾量最高為液固比=7、迴流12小時此組(FM7-12H)，其氮含量為2.55 mmole/g，偏矽酸鈉所合成純矽MCM-41中，官能基修飾量最高為24小時此組(FMS-24H)，氮含量為2.56 mmole/g。重金屬離子吸附方面，FM7-12H與FMS-24H皆屬於Langmuir 等溫吸附模式，FM7-12H對Pb2+、Cu2+、Cd2+的最大吸附量分別為204.08 mg/g、80 mg/g及80 mg/g，FMS-24H對Pb2+的最大吸附量為200 mg/g、Cd2+為84.03 mg/g、Cu2+為78.74 mg/g。

關鍵字

鈣霞石 ； 中孔徑分子篩 ； 下水污泥灰 ； 重金屬離子 ； 表面改質

並列摘要

This study investigated the feasibility of synthesizing mesoporous molecular sieve (i.e., referred to as MCM-41), using sewage sludge ash (SSA) as the starting SiO2 sources. Furthermore, the MCM-41 as synthesized was modified, and its performance was evaluated.
Firstly, to prepare the precursor solution for MCM-41 synthesis, the target SiO2 component was extracted from SSA by heating the ash with NaOH (i.e., alkaline fusion). This reaction resulted in the formation of Quartz, Al2O3, Fe2O3, and ash residue. And then, after the ash residue was removed, deionized water was added to the filtered solution at a proper L/S ratio to prepare the precursor solution. As the Al2O3 concentration in the precursor solution may affect the synthesis of MCM-41, the L/S ratio was so determined that resulted in both the highest SiO2 concentration and the lowest Al2O3 concentration (i.e., the highest Si/Al ratio) in a resultant precursor solution. The results indicate that a NaOH/SSA (by weight) of 1.25 and heating a temperature at 400 oC were found to be optimal conditions for alkaline fusion; and a L/S=7 for deionized water and the filtered solid would generated a precursor solution with a highest Si/Al ratio (i.e., 51 in this study).
Secondly, the MCM-41 was synthesized by hydrothermal method at 100 oC, 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 oC to remove the surfactant and the MCM-41was formed. However, due the presence of Al2O3 derived form sewage sludge ash, the MCM-41 as synthesized contained alumiuoxide (referred to as Al-MCM-41). The composition of Al-MCM-41 as synthesized using SSA as starting SiO2 source was found close to that using sodium metasilicate as starting SiO2 source, the former containing 98.2 %(by weight) of SiO2, and the latter 94.7% SiO2, 3.2% Al2O3, 1.6% Na2O, and trace percent of other oxides. The Al-MCM-41 synthesized from SSA in this study had a surface of 932 cm2/g and a pore volume of 0.93 cm3/g, as compared to 1047 cm2/g and 1.05 cm3/g, respectively, of control sample synthesized from Na2SiO3. 27Al MAS NMR analysis of Al-MCM-41 synthesized from the precursor solution revealed that the extracted Al species from SSA was tetrahedrally incorporated in the framework effectively. On the other hand, the ash residual filtered from the extraction process was also successfully synthesized into zeolite (Cancrinite) by alkali hydrothermal reaction, showing a beneficial recycling of the SSA.
Finally, in this study, the surface of MCM-41 as synthesized was further modified with 3-aminopropyltriethoxysilane (APTES) to bonding ammoniums-functional groups to the surface, forming ammonium-functionalized mesoporous materials (AFMM). The resulted showed that the coverage of functional group on MCM-41 surface were increased with increasing surface area of MCM-41 and longer reaction time of refluxing.
A FM7-12H sample (i.e., sample generated at L/S=7 and fluxing time=12 hours) had the largest number of functional groups (N content=2.55 mmole/g), as compared to that of the control sample (N content=2.56 mmole/g). The efficiency to remove heavy metal ions in aqueous solution by the modified MCM-41 were evaluated. It was proved that the adsorption behavior of AFMM on heavy metals ions was best fitted by the Langmuir model. It was noted that the maximum adsorption capacities of FM7-12H sample for Pb(II), Cu(II), Cd(II) were 204.08 mg/g, 80 mg/g, and 80 mg/g, as compared to 200 mg/g, 84.04 mg/g, and 78.74 mg/g, of control sample (FMS-24H), respectively. It is demonstrated that the AFMM synthesized using SSA as SiO2 source was equal-effective in metal adsorption as that prepared using pure SiO2 source (Na2SiO3), suggesting that the preparation of AFMM using SSA as SiO2 source is feasible, effective, and environmental beneficial.

並列關鍵字

heavy metal ion ； function group ； sewage sludge ash ； cancrinite ； Al-MCM-41

參考文獻

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