光催化降解管制藥物—甲基安非他命與可待因之研究

Abstract

管制藥物甲基安非他命(methamphetamine)與可待因(codeine)合法地使用在醫療用途與非法地經常濫用在其他用途上，在許多地區的廢污水處理廠進、出流水與環境水體中皆可偵測到此兩種藥物分布於其中，因此其對於環境的潛在衝擊逐漸備受重視。甲基安非他命與可待因無法藉由傳統的民生污水處理程序有效去除，故考慮高級處理研究利用紫外光照射二氧化鈦的光催化技術降解甲基安非他命與可待因，探討利用低瓦數的紫外光（9 W且最大波長在365 nm）照射二氧化鈦降解兩種管制藥物的反應動力學和機制，研究在不同操作參數(二氧化鈦添加量、管制藥物初始濃度與pH值)的處理效率和影響，處理過程中利用高效能液相層析串聯式質譜儀(HPLC-MS/MS)監測和分析兩種管制藥物與其中間產物，並利用總有機碳分析儀(TOC)與離子層析儀(IC)測定其礦化程度。 在溶液pH值為7、添加0.1 g/L的二氧化鈦情況下進行光催化反應，分別為100 μg/L的甲基安非他命與可待因皆可在3分鐘內達完全去除，兩管制藥物的降解反應動力學呈一階反應。在溶液pH值為5、添加0.1 g/L的二氧化鈦情況下進行光催化反應，10 mg/L的甲基安非他命經180分鐘反應後近乎完全礦化，其有機氮成分轉化為NH4+ (76%)和NO3- (21%)；10 mg/L的可待因經90分鐘反應後亦近乎完全礦化，其有機氮成分轉化為NH4+ (74%)和NO3- (22%)。 甲基安非他命的中間產物包括經標準品確認過的對位氫氧基甲基安非他命(p-OHMAT)，與其他八種經實驗性鑑定的物質；可待因的中間產物包括經標準品確認過的嗎啡，與其他五種經實驗性鑑定的物質。藉由中間產物的鑑定分析，可提出甲基安非他命的兩種主要降解途徑，其一為甲基安非他命的邊鏈裂解，另一為甲基安非他命產生氫氧化反應；而可待因的兩種主要降解途徑則包括同位取代反應導致其芳香環裂解，以及可待因發生重複的氫氧化反應導致含氫氧基的中間產物生成。此兩種管制藥物的主要降解途徑皆來自於光催化照射二氧化鈦產生氫氧自由基的非選擇性攻擊，導致有機物持續的斷鍵裂解，最終達到完全礦化。紫外光照射二氧化鈦的光催化程序為防止此兩種管制藥物與處理不完全的中間產物流入環境水體的可應用處理技術。

Methamphetamine (MAT) and codeine which belong controlled drugs are legally used in prescription and often illegally abused for other purpose. They are found in domestic wastewater treatment plants (WWTPs) influents and effluents as well as surface waters in many regions, elevating concerns about their potential impact. These two drugs are not effectively removed by conventional processes of WWTPs. To contemplate advanced treatment, this study investigates the photocatalytic degradation of MAT and codeine by UV-illuminated TiO2. The degradation kinetics and mechanism of these two different drugs by TiO2 under low-wattage UV illumination (9 W with maximum output at 365 nm) were studied. Experimental parameters were varied including the TiO2 loading, initial substance concentration, and pH. During treatment, these two controlled drugs and their intermediates were identified and tracked by HPLC-MS/MS, along with TOC and IC measurements to determine the mineralization extent. In contact with 0.1 g/L of TiO2 under illumination at pH 7, an entire spike amount of 100 μg/L of MAT was completely removed in 3 min and the same initial concentration of codeine was also eliminated in 3 min. The degradation of MAT and codeine followed an apparent first-order kinetics. Near complete mineralization of MAT and codeine from 10 mg/L were achieved in 180 min and in 90 min, respectively, with 0.1 g/L of TiO2 at pH 5, by which the organic nitrogen was converted to NH4+ and NO3-. 76% and 21% of organic nitrogen in MAT was converted to NH4+ and NO3-, respectively. 74% of codeine nitrogen constituent was converted to NH4+ and 22% to NO3-. MAT intermediates include authenticated p-hydroxymethamphetamine (p-OHMAT) and eight tentatively identified compounds. Codeine intermediates include authenticated morphine and five tentatively identified compounds. Based on identified intermediates, two degradation pathways of MAT were deduced that involved cleavage of the side chain as well as hydroxylation of the MAT compound. Also, two degradation pathways of codeine were proposed including one involving ipso-substitution followed by cleavage of the aromatic ring and another involving repeated hydroxylation of the codeine molecule followed by fragmentation of the hydroxylated intermediates. These all degradation pathways occurred via non-selective attacks by hydroxyl radicals generated by irradiated TiO2 that led to continual fragmentation and eventual mineralization. The photocatalytic UV/TiO2 process shows promise in arresting the release of these two controlled drugs and their intermediate derivatives into the water environment.