EPA-97-U1U1-02-104

097

1,700 千元

2008/04/08

2008/12/31

施養信

永續發展室(停用)

吳婉怡

國立中興大學土壤環境科學系

水質保護

奈米材料,聚集,酸鹼值,陽離子,界面活性劑,腐植酸

nanoscale particle, aggregation, pH, cations, surfactant, humic acid

吳先琪,董瑞安

施養信

0930105629

wywu@sun.epa.gov.tw

奈米氧化鋅（nano-ZnO）、奈米二氧化鈦（nano-TiO2）、奈米二氧化矽（nano-SiO2）三種商業級奈米材料顆粒，經電子顯微鏡觀察確認粒徑大小在奈米等級，但一進入水溶液則迅速地團聚，形成奈米微粒之團粒，並隨時間其聚集情況顯著。由於奈米微粒在水溶液中容易聚集，經一系統分散實驗，最後使用超音波粉碎機分散奈米懸浮液，取得懸浮性良好之奈米顆粒懸浮液。 相對於奈米TiO2與SiO2，奈米ZnO粉體顆粒於水溶液中粒徑增加速率相當快。在15~35℃範圍下溫度對顆粒粒徑之影響不明顯。水溶液中TiO2顆粒粒徑隨pH之變化，pH越皆接近SiO2、TiO2之等電點可發現明顯的沉澱現象。ZnO具高pH緩衝能力，可使pH5~10之水溶液之pH趨於中性，使顆粒逐漸聚集。 當水溶液中陽離子濃度提高時，因陽離子電荷可壓縮電雙層，進而促使奈米顆粒聚集沉降，而且提高離子濃度會加快其奈米顆粒絮聚的現象。並且在相同強度下二價陽離子會較一價陽離子更強烈的影響壓縮電雙層，而使之聚集。隨著濃度的增加，離子強度增加後亦使絮聚現象更趨明顯。對SiO2而言，K+的臨界膠凝濃度（CCC）為100 meq/L，Na+的CCC為220 meq/L，Ca2+的CCC為90 meq/L。對TiO2而言，K+的CCC為10 meq/L，Na+的CCC為90 meq/L，Ca2+的CCC為20 meq/L。對ZnO而言，K+的CCC為0.25 meq/L，Na+的CCC為5 meq/L，Ca2+的CCC則小於0.2 meq/L。經由表面能量計算，DLVO理論可良好地說明陽離子種類與濃度對於奈米粒子聚集效率。另一方面，提高三種離子濃度時，使ZnO的能隙下降，隨著離子濃度越高，其下降趨勢越明顯。 介面活性劑可分散奈米顆粒，但依其濃度及性質亦可使奈米顆粒絮聚。對SiO2而言，高濃度SDS會使之有絮聚現象，而在SDS0.1倍臨界微胞濃度（CMC）時，會使SiO2略為增大並會分散存在系統中數天。在CTAB陽離子界面活性劑存在下，SiO2粒徑也會約略增加，但也可維持分散數天，然在其0.1 CMC為時有絮聚現象。TX-100也可使SiO2顆粒維持分散數天。對TiO2而言，SDS可以有效維持TiO2大小，CTAB在0.1、1、10 CMC也皆可有效地分散TiO2在原有大小，TX-100只在CMC濃度下可以分散TiO2而使之顆粒粒徑未明顯增加。對ZnO而言，相較於未有界面活性劑存在之顆粒變化，除了SDS在10 CMC時有絮聚現象，三種介面活性劑皆可使ZnO粒徑增加之速率減緩。 添加腐植酸有助於維持奈米顆粒如SiO2、TiO2與ZnO的穩定性，可能因為腐植酸可產生空間位阻與靜電排斥。在自然水體中，水中陽離子、腐植物質或介面活性劑等物質，會使奈米顆粒維持一段時間而後緩慢增大。 隨著奈米顆粒應用的增加，這些成果可以更了解水中奈米顆粒之行為，以方便評估奈米顆粒對環境的危害。並建議未來須更加強研究以製備良好之奈米懸浮液研究其在水環境中之奈米微粒轉換與其宿命。

奈米材料,聚集,酸鹼值,陽離子,界面活性劑,腐植酸

水環境介質中奈米微粒轉換及宿命研究.pdf

39MB

[期末報告]公開完整版

2009/3/1 上午 12:00:00

The application of nanoparticles is increasing in commercial products due to their special properties in electric, thermal, optical, and magnetic aspects. As the commercial usage of nanoparticles is increasing, the fate and transformation of commercial nanoparticles in environmental is of significant interest to ecosystem and human health. This research investigated the stability and morphology change of three metal oxide nanoparticles in aqueous solutions. Three commercial nanoparticles, TiO2, ZnO, SiO2, were received in powder form, and in water they were aggregated quickly into micro-sized particles due to electric double layer compression. The morphology and characteristic changes were also examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV/Vis absorption spectroscopy (UV/Vis), and transmission electron microscopy (TEM). Due to their fast aggregation behaviors, a series of separation methods are performed to disperse these three nanoparticle aggregates to their primary particle size. The direct ultrasonic probe method can well disperse these three nanoparticles. The stability of TiO2 and SiO2 can maintain one day; however, it is not for ZnO. This direct ultrasonic method is better than other physical dispersion method. As compared to nanoscale TiO2 and SiO2 particles, the aggregation rate of ZnO nanoparticles is the fastest. It could be result form the aggregation enhancement of ZnO nanoparticles through the ion bridge by zinc ions and zinc chemicals derived from the dissolution of ZnO nanoparticles in water. The temperature in the range of 15~35 oC did not affect the stability of these nanoparticles a lot. With the close of pH to the pHzpc of nanoparticles, the obvious sedimentation behaviors were found for TiO2 and SiO2 particles. Due to the high pH buffer capacity of ZnO nanoparticles, the final pH changed a lot from their initial pH to around pH7 so dissolved zinc ion species enhance the aggregation process. The ionic composition and strength can strongly affect the aggregation and sedimentation of these nanoscale materials in the aqueous environment. The nanoparticles aggregated more quickly in a higher concentration of cation. The increase in ionic strength resulted in compression of the electrical double layer (EDL), and therefore a decrease in the EDL repulsive energy such that the flocculation can be predicted. Therefore, the presence of either sodium or calcium ions can compress the EDL of these nanoparticles. Multivalent metal cations could form bridges with nanoscale particles or neutralize their surface charges to induce a quick aggregation. The critical coagulation concentration (CCC) values for nanoscale SiO2 particles were estimated as 220meq/L NaCl, 100meq/L KCl, and 90 meq/L CaCl2. The critical coagulation concentration (CCC) values for nanoscale TiO2 particles were estimated as 90meq/L NaCl, 10meq/L KCl, and 20meq/L CaCl2. The critical coagulation concentration (CCC) values for nanoscale ZnO particles were estimated as 5meq/L NaCl, 0.25meq/L KCl, and less than 0.25meq/L CaCl2. and The DLVO analysis can explain the aggregation behaviors of nanoparticles in presence due to the smaller interaction forces between particles with the increase of cation concentration. On the other hand, the energy gap of ZnO decreased with the increase of cation concentrations due to the larger particle size as the higher cation content in aqueous solutions. Surfactants can disperse and aggregate these nanoparticles, which depends on the properties of surfactant and the nature of nanoparticles. For SiO2 nanoparticles, the coagulation occurs in the presence of SDS with 10 critical micelle concentration (CMC); however, SiO2 nanoparticle size only slightly increased in presence of 0.1 CMC of SDS and then SiO2 nanoparticles keep stable for several days. In the presence of CTAB and TX-100, SiO2 nanoparticle size slightly increased and also SiO2 nanoparticles keep stable for several days. For TiO2 nanoparticles, TiO2 nanoparticles maintain stable for several days in presence of SDS and CTAB surfactants although the particle size of TiO2 nanoparticles increased a little. For TX-100, a neutral surfactant, the well dispersion of TiO2 nanoparticles only occurred when its concentration in its CMC. As compared to the aggregation of ZnO in absence of surfactants, these three surfactants can maintain the stability of ZnO nanoparticle except the 10CMC SDS, an anionic surfactant. The low pH values of 3.83 was observed for the rapid aggregation of ZnO in the presence of 10CMC SDS, indicating that could be result from the neutralization of this high concentration of SDS with dissolved zinc ion species. In presence of humic acid, the stability of these three nanoparticles can keep several days although their size may increase a little. With the increase of humic acid in aqueous solutions, the increase of these nanoparticle stability. It could result from the steric repulsion caused by humic acid molecule structure and electric repulsion of functional groups in humic acid. The fate of metal oxide nanoparticles in water would significantly depend on pH, ionic strength, ionic composition, humic substance and chemical dispersants in the aqueous environment. Our results provide important insights into the ways in which nanoparticle change under different aqueous conditions that may be generally relevant to the nanoparticle fate in diverse natural environment.

nanoscale particle, aggregation, pH, cations, surfactant, humic acid