奈米二氧化鈦在水環境中之穩定度研究

The stability of Titanium Dioxide Nano-particles in Aquatic Environment

邱意婷(Yi-Tin CHIU)

指導教授 ： 吳先琪

國立臺灣大學/工學院/環境工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00755

摘要

在奈米科技蓬勃發展之下，奈米微粒可能會在環境中大量流佈，而造成健康上的危害。為掌握奈米顆粒在水環境中的行為和宿命，首先要釐清在不同水質條件下奈米顆粒間的交互作用。本研究主要藉由分析不同水質條件之懸浮奈米顆粒濃度，探討不同pH值、離子強度、天然有機物(腐植酸和黃酸)濃度之下，奈米二氧化鈦顆粒的穩定性。
研究結果發現，自製之奈米二氧化鈦pHzpc=5.5，當奈米懸浮液pH值趨近5.5時，顆粒粒徑迅速增大至微米級，上層液之殘留濃度也僅剩7.8 %，此現象可以DLVO理論計算不同介達電位與離子強度下能量變化情形來驗證。
吸附試驗發現對於奈米二氧化鈦吸附黃酸及腐植酸之吸附試驗結果分別可依Freundlich和B. E. T. 吸附模式模擬之，二氧化鈦對於腐植酸之吸附量大於黃酸，且在實驗濃度範圍內等溫吸附曲線未能達平衡。由沉降試驗結果可發現腐植物質初始濃度為0.1 mg/ L 時，會使奈米二氧化鈦顆粒較不穩定。添加腐植物質對於顆粒介達電位的影響不顯著，但腐植物質平衡濃度增加，上層液之殘留濃度逐漸提升，似乎顆粒間立體屏障效應趨於明顯。唯腐植酸平衡濃度過高(14.1 mg/L)時，則因吸附量大發生架橋作用，顆粒聚集沉澱。
利用三類真實水體試驗比對上述實驗結果，可找出水質參數與奈米顆粒穩定度之相關性。科學園區放流水離子強度偏高，使奈米顆粒極易團聚而沉澱；而影響奈米顆粒在水庫水中之穩定度的主要因子為總有機碳濃度，適量的腐植物質可增加顆粒間的立體屏障，達穩定懸浮。而自來水其水質較佳，使奈米二氧化鈦可長時間穩定懸浮。

關鍵字

奈米二氧化鈦 ； 穩定度 ； 腐植酸 ； 黃酸 ； 膠凝 ； 立體屏障

並列摘要

The increasing use of nano-materials in consumer products has led to much concerns about their release to the environment and the subsequent health impacts. To better predict the fate and behavior of nano-particles in aquatic systems, it is essential to understand their interactions with different components of natural waters including natural organic matter (NOM), such as humic acid and fulvic acid.
The objective of this study is to investigate the stability of nano- titanium- dioxide (nano-TiO2) under different pH, ionic strength and concentration of NOM in aqueous phase. The stability was determined by measuring the concentration of Ti in supernatant of the suspension.
In this study, the surface charge of nano-TiO2 particles changed from positive to negative at pH 5.5. When the pH of the solution approaching 5.5, the average particle size increased rapidly to the micrometer level, and residual supernatant concentration was only 7.8% of the original concentration after three days. The effects of the ionic strength on the stability of nano-TiO2 particle were investigated. The result showed that when ionic strength was greater than 30 mM, the supernatant residual concentration of Ti would not influenced by pH value. The residual concentration decreased as ionic strength increased. Theses results were validated by the value of the estimated energy barrier between nano-TiO2 particles, which is calculated by following Derjaguin Landau Verwey Overbeek (DLVO) theory.
The results from the settling experiments revealed that initial concentration of humic substances lower than 1 mg/L would cause nano-scale titanium dioxide particles unstable. Zeta potential for particles had no significant influence when humic substances were added under different concentrations. But the residual concentration of Ti in the supernatant would increase when the equilibrium concentration of humic substances increased. It seemed that the static-electric repulsion become more apparent. Under high equilibrium concentration of humic acid (14.1 mg/L) the surfaces of nano-TiO2 particles were covered with humic acid, the amount of adsorbate caused bridging between particles, and the particles easily aggregated and settled.

並列關鍵字

nano-scale titanium dioxide ； stability ； humic acid ； fulvic acid ； steric repulsion

參考文獻

陳麗華，2009，奈米氧化鋅於水環境介質之宿命研究，碩士論文，國立台灣大學環境工程學研究所。

Bischoff, B. L. and Anderson, M. A. (1995) Peptization Process in the Sol-Gel Preparation of Porous Anatase (TiO2), Chem. Mater., 7, 1772-1778

Brown, D.M., Wilson, M.R., MacNee, W., Stone, V. and Donaldson, K. (2001) Size-dependent proinflammatory effects of ultrafine polystyrene particles: A role for surface area and oxidative stress in the enhanced activity of ultrafines. Toxicol. Appl. Pharmacol. 175(3), 191-199.

Carey, J.H., Lawrence, J., and Tosine, H.M. (1976) Photodechlorination of PCB's in the presence of titanium dioxide in aqueous suspensions. Bull. Environ. Contam. Toxicol. 16(6) , 697-701

Christian, P., Von der Kammer, F., Baalousha, M. and Hofmann, T. (2008) Nanoparticles: structure, properties, preparation and behaviour in environmental media. Ecotoxicology 17(5), 326-343.