奈米氧化鋅於水環境介質之宿命研究

Abstract

本研究為探討不同pH值、陽離子種類及腐植酸濃度下奈米氧化鋅分散性，以分析奈米氧化鋅懸浮液的上層總鋅濃度及表面電位，進而探討奈米氧化鋅之分散效率。 結果顯示，於表面電位分析說明氧化鋅的pHIEP~8，在pH值靠近等電點越容易聚集，故pH值為9時，奈米氧化鋅懸浮效果差。在陽離子種類分析方面，於奈米氧化鋅懸浮液中分別添加KCl及CaCl2，以DLVO理論計算懸浮液顆粒間之能量變化，結果顯示鉀離子之懸浮液產生的能障較鈣離子高，故添加鉀離子之奈米氧化鋅懸浮液之顆粒分散效果較佳，相較於含鈣離子之穩定性約可提升20%。 最後，探討腐植酸(Humic acid)存在對奈米氧化鋅懸浮液之影響。添加低腐植酸濃度時奈米氧化鋅懸浮液的表面電位由30.7±1.13mV降至-3.93±3.32mV，顆粒間靜電排斥力降低，容易碰撞形成大顆粒，使沉降速率增加，故奈米氧化鋅懸浮性僅為20%。高腐植酸濃度下，帶負電荷的腐植酸包覆於奈米氧化鋅顆粒表面，使顆粒表面轉為帶負電荷，靜電排斥力也增加，顆粒懸浮性較低腐植酸濃度增高60%。 關鍵字:奈米氧化鋅; 腐植酸; DLVO 理論;凡得瓦爾力

This study was mainly focused on the behavior of aqueous nano-zinc-oxide under different pH, concentration of cations and humic acid. The amount of the stably dispersed nano-zinc-oxide was determined by measuring the total particle concentration in the supernatant (detected by atomic absorption spectrometry) and zeta potential of the particle surface. The results showed that the nano-zinc-oxide existed mainly in dissolved form, at lower pH(<8),and the amount of zinc particles in the supernatant could not be determined. On the contrary, under higher pH the nano-zinc-oxide particles formed aggregated easily when the pH of the solution equaled approximately to 8, the isoelectric point (IEP). The effects of the concentration of cations on nano-zinc-oxide aggregation and dispersion were investigated by adding 0.1mM KCl or CaCl2 to the nano-zinc-oxide suspensions. The variations of the energy barrier between supernatant nano-zinc-oxide particles were calculated by using Derjaguin Landau Verwey Overbeek (DLVO) theory. The results revealed that the energy barrier between particles in the presence of K+ was higher than that of Ca2+, and the efficiency of nano-zinc-oxide dispersion by adding K+ was higher than that with Ca2+ by 20%. Besides, the nano-zinc-oxide dispersion was also affected by the presence of humic acid ( a naturally occuringe organic matter in the aquatic environment). Under lower humic acid concentrations(0.5 to 50 mg/L), due to that the zeta potential of the nano-zinc-oxide decreased from 30.7 ± 1.13 mV from without humic acid to -3.93 ± 3.32 mV and the static-electric repulsion between particles diminished, there were dramatic particle collision and sedimentation. The stably dispersed nano-zinc-oxide in the supernatant was only 20%. However, with higher humic acid concentration(2.0 to 50 mg/L), the concentration of the stably dispersed nano-zinc-oxide was higher than that with lower humic aicd concentration by 60% due to that the surface of nano-zinc-oxide particles were thoroughly covered with negatively charged humic acid, and the static-electric repulsion increased significantly. Keywords: nano zinc oxidep; humic acid; DLVO theory; Van der Waals forces