氨基修飾二氧化矽之製備與銨離子吸附研究

Abstract

本研究將針對NH4+去除，首度開發以鹼基為基礎的吸附材料，製備氨基修飾二氧化矽(NH2-SiO2)，研究中以四乙氧基矽烷(tetraethyl orthosilicate，TEOS)與(3-氨基丙基)三乙氧基矽烷((3-Aminopropyl)triethoxysilane，APTES)作為SiO2與-NH2來源，從FTIR圖譜中可以看到單純SiO2樣品中波數為798 cm-1的訊號代表Si-O-Si之鍵結，而不同APTES：TEOS比例之NH2-SiO2中，除SiO2的特徵峰外，在694cm-1多出N-H鍵結的訊號，表示-NH2成功地修飾在SiO2顆粒上。隨著APTES：TEOS比例從0：5增加至20：5，NH4+吸附量從無法量測增加至9.85 mg/g，表示-NH2為一有效吸附活性位址。再以動力吸附模式、等溫吸附模式、FTIR圖譜瞭解NH4+吸附行為與機制，結果顯示動力吸附模式較符合擬二階動力模式，其相關係數R2高達0.997，等溫吸附模式較符合Langmuir model，其相關係數為0.984且最大吸附量為11.53 mg/g，表示其速率決定步驟為NH4+與NH2-SiO2表面上的-NH2形成化學作用力，-NH2在溶液中以質子化的-NH3+形式存在，而-NH3+中的H+與NH4+進行離子交換達吸附效果，而再生方面，相較於酸基為基礎吸附材再生容易造成二次污染，本研究以簡單的100℃加熱方式使NH4+脫附達到再生效果，再生率為74.5%。

In this study, amino-functionalized silica (NH2-SiO2) was prepared as the adsorbent for NH4+ removal for the first time. Tetraethyl orthosilicate (TEOS) and 3-Aminopropyltriethoxysilane (APTES) were used as the precursor for SiO2 and the source of -NH2 functional groups, respectively. From the FTIR spectra, the wavenumber of 798 cm-1 in the pure SiO2 sample represented the Si-O-Si bonding, while in the NH2-SiO2 powders with different APTES：TEOS ratios, additional N-H bonds at 694cm-1 indicates that -NH2 was successfully modified on the SiO2 particles. When the APTES：TEOS ratio increased from 0：5 to 20：5, the NH4 + adsorption amount increased from an undetectable value to 9.85 mg/g, implying that -NH2 is an active adsorption site for NH4+ ions. The adsorption behavior and mechanism of NH2-SiO2 were investigated through kinetic adsorptions, isothermal adsorptions, and FTIR characterization. The kinetics was better fitted by the pseudo-second-order model with R2= 0.997. Adsorption isotherm was better fitted by the Langmuir model with R2= 0.984 and the maximum adsorption capacity of 11.53 mg/g. These results reveal that the rate-limiting step is the chemical reaction between NH4+ and -NH2. Most of -NH2 are in the form of -NH3+ in the solution, and the H+ ions on the -NH3+ groups were exchangeable with NH¬4+ ions. In the aspect of regeneration, the NH4+ desorption can be achieved by simple heating at 100℃ and the regeneration efficiency was 74.5%.