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標題: | 疏水塗層對球狀活性碳於潮濕環境中吸附揮發性有機物之影響 Impacts of Hydrophobic Modification on Beaded Activated Carbon for the Adsorption of Volatile Organic Compounds in Humid Environment |
作者: | 黃宥瑋 You-Wei Huang |
指導教授: | 席行正 Hsing-Cheng Hsi |
關鍵字: | 球狀活性碳,揮發性有機物,甲苯,疏水塗層,高濕度環境, beaded activated carbon,volatile organic compounds,toluene,hydrophobic coating,humid environment, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 揮發性有機物(volatile organic compounds, VOCs)為重點控制、監測之空氣污染物種,其不僅對環境和人體健康直接產生影響,並會在大氣中進行光化學反應後生成二次污染物。在眾多污染去除技術中,吸附法因在低濃度下對VOCs具有高去除率與可回收性而備受注目。值得注意的是,一般環境下存在濕度,而水分子會與VOCs相互競爭吸附位點,導致VOCs在高濕度條件下較難以去除。因此,吸附劑表面之親水性與疏水性於真實環境條件下對VOCs的吸附行為至關重要。
為了探究吸附劑表面之疏水性與在高濕度環境下對VOCs的吸附表現,本研究採用商用球狀活性碳(beaded activated carbon, BAC),一種具有高比表面積、高機械強度及高流動性等特點之材料作為主要吸附劑,並選擇甲苯做為目標污染物。此外,應用疏水塗層及水熱法技術改質並合成一系列高疏水性球狀活性碳,並與改質前之BAC進行比較。 由氮氣吸脫附實驗得知隨改質劑濃度增高,其比表面積與孔體積會隨之降低,並且四乙氧基矽烷(tetraethyl orthosilicate, TEOS)的引入可以改善比表面積與孔體積的下降。由FT-IR與XPS的數據能得出其改質劑之主要官能基Si-O-Si成功合成於材料表面。 吸附實驗結果顯示於等溫吸附試驗中,兩種材料對於D-R等溫模型多具有高度擬合結果,而改質後的材料展現出對甲苯更高的等容吸附熱;於動力學分析得知兩種材料對Y-N模型顯示最高的擬合度。 根據與水分子競爭吸附的實驗結果,整體而言,無論在任何溼度條件下,改質前的BAC仍然表現出最高的吸附容量。而對吸附量進行標準化,即將吸附量除上比表面積後,發現在高濕度條件下隨著改質劑量的提升,其每單位面積所吸附甲苯量也隨之提升(相對濕度80%條件下,BAC之吸附容量為0.377 mg m-2,而T-H_1之吸附容量為0.401 mg m-2),證明此疏水塗層於高濕度條件下的應用是可行的。另一方面,隨著環境濕度的增加,改質後的吸附劑所表現的吸附容量下降率也趨於減緩。這結果表明,疏水塗層的引入有助於改善在濕度條件下吸附量下降的情況。 於循環吸脫附實驗中,每個樣品的吸附容量均隨著吸脫附次數的增加而降低,但仍保持不低的吸附能力。於15次循環吸脫附實驗中能觀察到在相對濕度為80%的條件下,BAC的吸附容量下降百分比為32.29%,T-H_0.5則為21.48%;而在乾燥條件BAC與T-H_0.5所下降的吸附容量百分比各為28.9%與8.84%,即於高濕度條件下,樣品的吸附量下降百分比較為顯著。而循環再生後,樣品的比表面積與吸附前幾乎保持相等,表示在再生過程中,可能使材料表面變得更具親水性;此外,在任何濕度下T-H_0.5吸附量所下降的百分比皆低於BAC,表明使用疏水塗層法改質後之樣品能夠減緩親水性增加之幅度。 整體而言,BAC在改質之前已具有一定程度的疏水性。但改質後的BAC在高濕度條件下每單位面積所吸附的甲苯量優於原本的BAC,證明在真實條件下應用此技術的潛力與可行性。 Volatile organic compounds (VOCs) pose a significant challenge in the atmospheric environment. Adsorption is widely recognized as an effective method for VOC removal, but the presence of humidity hinders its efficiency, as water molecules compete with VOCs for adsorption sites. This study investigates the hydrophobicity of the adsorbent surface and its impact on VOC adsorption under actual atmospheric conditions. Commercial beaded activated carbon (BAC) is utilized as the adsorbent, with toluene chosen as the adsorbate. Hydrophobic coatings and hydrothermal modification techniques are employed to enhance the hydrophobic properties of BAC, and the modified BAC is compared to the unmodified BAC in terms of adsorption capacity. The physical and chemical analyses reveal that increasing the dosage of the modifier decreases the specific surface area and pore volume while introducing tetraethyl orthosilicate (TEOS) helps mitigate this decline. Successful grafting of the Si-O-Si functional group onto the material surface is confirmed. Adsorption experiments demonstrate an excellent fit to the D-R isotherm model for both materials, with the modified BAC exhibiting higher heat of adsorption for toluene. Kinetic analysis indicates the highest fitting degree to the Y-N model for both materials. While the unmodified BAC exhibits the highest overall adsorption capacity for water molecules regardless of relative humidity (RH) conditions, the modified BAC shows increased toluene adsorption per unit surface area with higher modifier dosage under high RH conditions. Specifically, the adsorption ability of BAC is 0.377 mg m-2, and that of T-H_1 is 0.401 mg m-2. The decrease in adsorption capacity of the modified BAC is less pronounced as RH increases, suggesting the effectiveness of the hydrophobic coating in mitigating the decline in adsorption capacity under humid conditions. Cyclic experiments reveal decreased adsorption capacity with increasing cycles, particularly under high humidity conditions. In 15-cycle experiments, at RH 80%, the percentage of decrease in adsorption capacity for BAC is 32.29%, while that for T-H_0.5 is 21.48%, suggesting its feasibility under humid conditions. On the other hand, under a dry condition, the decrease percentages for BAC and T-H_0.5 are 28.9% and 8.84%, respectively. Nevertheless, after regeneration, the surface area of the samples remains similar, indicating a potential increase in surface hydrophilicity. The application of a hydrophobic coating can help alleviate this effect. To summarize, while BAC exhibits inherent hydrophobicity, the modified BAC demonstrates improved toluene adsorption per unit area under high RH conditions. This study highlights the potential and feasibility of applying this technology in real-world situations. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/90565 |
DOI: | 10.6342/NTU202302159 |
全文授權: | 同意授權(限校園內公開) |
顯示於系所單位: | 環境工程學研究所 |
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