Abstract
摘要:延續前三年計畫,97年使用商用奈米粉末,其容易在水中聚集,對水體環境衝擊較小。98年利用自行合成奈米顆粒,進行水質參數探討,發現其聚集所需要之鹽濃度較高。99年採用商用奈米懸浮液,研究發現奈米懸浮液的穩定性相當高。由於商用二氧化鈦 (TiO2) 與商用氧化鋅 (ZnO) 奈米材料已廣泛地在使用,所以今年針對此兩商用奈米懸浮液作沉降特性之探討,並嘗試探討建立分析水體中奈米顆粒之方法。商用二氧化鈦 (TiO2) 與商用氧化鋅 (ZnO) 奈米懸浮液,皆經電子顯微鏡與動態光散射技術 (dynamic light scattering, DLS) 確認為奈米等級。本研究採用動態光散射儀,探討過濾、離心及沉降三種前處理流程,去除大顆粒影響DLS偵測奈米顆粒強度的效應,並搭配濃度分析儀器,嘗試探討建立分析水體中奈米顆粒之方法。三種前處理在奈米顆粒與微米級的顆粒分離上,過濾效果不佳。而以奈米Polystyrene (PS)與微米SiO2混合液的分離,在沉降方面,最佳條件為沉降2小時,可有效將微米SiO2大顆粒移除,並可有87% PS的回收率。在離心方面,最佳條件為轉速4060 g,時間2分鐘,可有效將大顆粒移除,並得到74% PS的回收率。就奈米TiO2與微米SiO2混合液的分離,在沉降2小時,可有效將大顆粒移除,並有88%的奈米TiO2回收率。在離心4060 g 2分鐘,也可有效將大顆粒移除,得81%的奈米TiO2回收率。然而在奈米ZnO與微米SiO2混合液的分離方面,以離心4060 g 2分鐘,可有效將大顆粒移除,但僅得到27%的奈米ZnO回收率,可能因其表面電荷相異,奈米ZnO與微米SiO2易聚集。另外,對於會溶解之氧化鋅而言,在測總濃度後,可再利用超過濾離心法,檢測溶解濃度後扣除,則可定量氧化鋅奈米顆粒濃度。在檢驗水體中奈米顆粒之方法方面,建議結合離心分離後,以DLS量測並搭配電子顯微鏡作確認。在不同水質下之聚集與沉降實驗方面,在15~35℃範圍下,溫度對1000 mg/L TiO2 (pH 3~4) 及ZnO (pH 7~8) 顆粒粒徑與沉降之影響不明顯。500 mg/L商用TiO2奈米懸浮液於25℃水溶液中,顆粒粒徑在其等電點 (pHpzc 6.5) ±1.2,可發現明顯的顆粒粒徑變大與沉澱現象。500 mg/L商用ZnO奈米懸浮液於25℃水溶液中,顆粒粒徑在其等電點 (pHpzc 10.5) ±0.6,亦可發現明顯的顆粒粒徑變大與沉澱現象。
Abstract: We have studied the aggregation behaviors of commercial nanopowders in 2008, self-synthesized suspension nanoparticles in 2009 and two commercial nanoparticle suspensions in 2010. In this year, TiO2 and ZnO nanoparticles have been widely used so these two commercial nanoparticle suspensions were chosen as model nanoparticles to develop the analytical methodology and study the sedimentation behaviors under different aquatic conditions. The two commercial nanoparticles, TiO2 and ZnO, in aqueous suspensions were identified as nanoscale particles by a transmission electron microscopy (TEM) and dynamic light scattering (DLS). Zero point of charges (pHpzc) for TiO2 nanoparticles are 6.5 and 10.5, respectively. The DLS technology is cooperated with a pretreatment process including filtration, centrifugation, and settling to develop a methodology for the analysis of nanoparticles in the aquatic environment. Microscale SiO2 (micro-SiO2) particles were used to mimic general particles in the environment. The filtration pretreatment does not work well. For settling pretreatments, the mixture of micro-SiO2 and nanoscale polystyrene (nano-PS) can be settled for 2 h to removal the interference effect of large particles on DLS analysis and the recovery of nano-PS was 87%. By centrifugation, the mixture of micro-SiO2 and nano-PS was centrifuged with an angular speed of 4060 g for 2 min to removal SiO2 microparticles and the recovery of nano-PS was 74%. For nano-TiO2, the mixture of micro-SiO2 and nano-TiO2 was settled for 2 h to remove large particles and the recovery of nano-TiO2 was 88%. For the centrifugation of the mixture of micro-SiO2 and TiO2 (4060 g, 2 min), SiO2 particles can be removed and the recovery of nano-TiO2 was 81%. For the mixture of micro-SiO2 and nano-ZnO, the settling pretreatment cannot work. It can be centrifuged (4060 g, 2 min) to remove large particles on DLS analysis and the recovery of ZnO was 27%. All these results are confirmed by TEM. In addition, because the ZnO could be dissolved in water, the pretreated solution can be filtered with a centrifugal ultrafilter containing a membrane for 3kDa cutoff and then to calculate the real concentration of ZnO nanoparticles by the difference of total ZnO concentration. The combination of the centrifugation pretreatment before the DLS analysis and then confirmation by SEM or TEM is suggested to detect nanoparticles in the environment. For various aquatic parameters, the temperature in the range of 15~35℃did not significantly affect the stability of 1000 mg/L TiO2 (pH 3-4) and ZnO (pH 7-8). When the pH value in the range of pHpzc±1.2 for nano-TiO2 and pHpzc±0.6 for nano-ZnO at 25oC, obvious aggregation and sedimentation behaviors were found for these two nanoparticles in aqueous suspensions.
Keyword(s)
奈米懸浮液
聚集
沉降
酸鹼值
陽離子
陰離子
腐植酸nanoscale particle suspension
sedimentation
aggregation
pH
cations
anions