以石墨烯衍生物催化臭氧去除水中微污染物之研究

Abstract

微污染物(micropollutants, MPs)已廣泛地在天然水體中被監測到，而對環境乃至於人類健康造成影響。臭氧(ozone, O3)是一強氧化劑，其在水中會和氫氧根反應產生氫氧自由基(hydroxyl radical, OH•)。自1970年代開始，臭氧逐漸被運用在水處理系統中。然而，臭氧具選擇性，對臭氧難降解(ozone-recalcitrant)物質的去除效果有限。本研究利用氧化石墨烯(graphene oxide, GO)及還原氧化石墨烯(reduced graphene oxide, rGO)作為臭氧處理程序的催化劑來產生更多無選擇性的氫氧自由基，以利去除臭氧難降解物質。GO係利用改良後之Hummers 法來製備，而rGO則利用不同溫度的熱還原處理來合成。本研究對GO及rGO在臭氧與氫氧自由基的鏈反應中的直接臭氧反應(direct ozone reaction)、起始反應(initiation)、促進反應(promotion)以及抑制反應(inhibition)的速率常數加以測定，來研究GO及rGO在催化臭氧系統中的動力評估。本研究中發現，rGO-600(在攝氏600度熱還原處理的還原氧化石墨烯)同時具有最高的起始反應和抑制反應速率常數，顯示rGO-600最能促進氫氧自由基的產生，但同時也是消耗氫氧自由基終止鏈反應的最強抑制劑。當GO及rGO在臭氧系統中作為催化劑時，臭氧難降解微污染物，包括酮洛芬、布洛芬及草脫淨的去除率可有效提升。污染物在催化臭氧處理程序的模擬降解可透過上述四個速率常數來進行，模擬結果大致能良好擬合實驗所得的污染物去除率。

The widespread of micropollutants (MPs) in natural waters may cause adverse effects on ecosystem and even human health. Ozone (O3) is a strong oxidant. It can react with hydroxide ion in water to from hydroxyl radical (OH•). Ozonation has been used in water treatment since the 1970s. However, ozone can only oxidize selective moieties in a compound and results in ineffective abatement of ozone-recalcitrant compounds. Therefore, catalytic ozonation with GO and rGOs was investigated in this study to enhance the decomposition of ozone to form nonselective hydroxyl radical to remove ozone-recalcitrant compounds. GO was synthesized using the modified Hummers’ method and rGOs were prepared using GO as the precursor by thermal reduction method at different temperatures. Direct ozone reaction (kD), initiation (kI), promotion (kP) and inhibition (kS) rate constants of GO and rGOs in the ozone and OH• chain reaction were quantified. It was found that rGO-600 (synthesized at 600 oC) possessed the highest kI and kS, indicating that rGO-600 was not only the most effective initiator to yield OH• but also the strongest inhibitor to scavenge OH•. The removal of ozone-recalcitrant MPs including ketoprofen, ibuprofen and atrazine was enhanced when GO and rGOs were used as the catalysts in ozonation. The modelling of the MP removal by catalytic ozonation with GO/rGOs was conducted using the determined rate constants. The removal kinetics could be fitted fairly well with the experimental data by the model.