高鐵酸鉀氧化降解氧氟沙星的機(jī)理

李亞男,馮 卓,王嘉琪,郭 凱,張國(guó)凱

高鐵酸鉀氧化降解氧氟沙星的機(jī)理

李亞男1*,馮 卓1,王嘉琪1,郭 凱1,張國(guó)凱2

(1.太原理工大學(xué)環(huán)境科學(xué)與工程學(xué)院,山西 晉中 030600；2.中海國(guó)亞環(huán)保工程有限公司,山西 太原 030012)

以喹諾酮類抗生素氧氟沙星(OFL)為目標(biāo)物質(zhì),研究高鐵酸鉀(Fe(VI))對(duì)OFL的去除及氧化機(jī)理.采用高效液相色譜儀(HPLC)、液相色譜-質(zhì)譜聯(lián)用儀(UPLC-QTOF-MS)等方法,考察Fe(VI)投加量、pH值、溫度和共存物質(zhì)等因素對(duì)OFL降解效果的影響,分析反應(yīng)動(dòng)力學(xué),計(jì)算過程中Fe(VI)的貢獻(xiàn)率,識(shí)別Fe(VI)氧化OFL的產(chǎn)物并推測(cè)主要反應(yīng)路徑.結(jié)果表明:當(dāng)Fe(VI)與OFL的物質(zhì)的量比為40:1、pH值為8、溫度為25°C時(shí),反應(yīng)30min后OFL的降解率達(dá)到92.38%,前5min快速反應(yīng)階段,OFL的降解符合偽二級(jí)反應(yīng)動(dòng)力學(xué).反應(yīng)過程的活化能為28.17kJ/mol.反應(yīng)中Fe(VI) 及中間高價(jià)態(tài)鐵的貢獻(xiàn)率為70.34%,且腐殖酸會(huì)顯著抑制該反應(yīng).通過對(duì)氧化產(chǎn)物進(jìn)行分析提出了Fe(VI)氧化OFL的3條主要路徑.OFL經(jīng)脫羧、去甲基、脫羰、羥基化等反應(yīng),實(shí)現(xiàn)其分子上喹諾酮取代基、哌嗪基環(huán)及惡嗪基環(huán)的開環(huán).

高鐵酸鉀；氧氟沙星；影響因素；共存物質(zhì)；中間產(chǎn)物；降解路徑

氧氟沙星(OFL)是一種第二代氟喹諾酮類抗生素(FQs),具有抗菌譜廣、易于吸收的特點(diǎn),是人類和動(dòng)物傳染病治療中應(yīng)用最廣泛的抗生素之一[1],也是自然水體和廢水中最常見的抗生素[2].OFL在地表水和廢水中檢測(cè)到的濃度在ng/L至mg/L之間[3-4],在地下水和飲用水中也能檢測(cè)到一定濃度[1,5].自然水體中殘留的OFL不僅會(huì)污染環(huán)境,也會(huì)導(dǎo)致水環(huán)境中細(xì)菌的耐藥性不斷增加,對(duì)人類健康和生態(tài)系統(tǒng)產(chǎn)生不利影響[6].因此,需尋求高效去除水中OFL的方法,為OFL在水體中的污染控制提供理論與技術(shù)支持.

研究表明,高級(jí)氧化或化學(xué)氧化法對(duì)含藥物廢水的處理效果較好.如Fenton試劑、高錳酸鹽、過硫酸鹽和臭氧等氧化劑因其高反應(yīng)性而具有獨(dú)特的氧化去除藥物污染物的能力[7-10].高鐵酸鹽(Fe(VI))作為一種綠色氧化劑,在酸性條件下的氧化還原電位為2.20V,高于大部分常見的氧化劑,在堿性條件下的氧化還原電位為0.72V,在較大的pH值范圍內(nèi)都具有較強(qiáng)的氧化性能[11],因此Fe(VI)可以在處理藥物污染物時(shí)起到良好的效果[12-13],并且Fe(VI)在使用后的還原產(chǎn)物為具有絮凝作用的Fe(III),也可對(duì)目標(biāo)物的去除起到一定作用[14].

Fe(VI)可氧化降解水中部分FQs,如Fe(VI)能去除水體中微量濃度的環(huán)丙沙星、恩諾沙星和諾氟沙星,去除率達(dá)到85%以上[15-17]. Fe(VI)與FQs的反應(yīng)主要是Fe(VI)通過親電反應(yīng)對(duì)喹諾酮環(huán)及含氮環(huán)進(jìn)行攻擊,隨后發(fā)生脫羧、去甲基、脫羰、羥基化反應(yīng)最終實(shí)現(xiàn)對(duì)FQs的氧化降解[15,18]. OFL由于含有惡嗪取代基,且哌嗪取代基的結(jié)構(gòu)不同,分子結(jié)構(gòu)更為復(fù)雜.但是,有關(guān)Fe(VI)氧化OFL的影響因素及反應(yīng)機(jī)理的研究尚未報(bào)道.

基于此,開展高鐵酸鉀去除水中OFL的效能及機(jī)理研究,考察Fe(VI)投加量、pH值、溫度和共存物質(zhì)等因素對(duì)OFL去除效果的影響,分析反應(yīng)過程中的產(chǎn)物,推測(cè)降解路徑,明晰Fe(VI)氧化OFL的反應(yīng)機(jī)制,完善Fe(VI)氧化氟喹諾酮類有機(jī)物理論,以期為含痕量抗生素廢水的處理提供參考.

1 材料和方法

1.1 試劑與儀器

OFL(分析純,純度>98%)、高鐵酸鉀(分析純,純度395%)、叔丁醇(分析純,純度399.0%),均購(gòu)自上海麥克林生化科技有限公司;乙腈(HPLC級(jí)),購(gòu)自賽默飛世爾科技有限公司;腐殖酸(黃腐殖酸FA390%),購(gòu)自阿拉丁試劑有限公司;甲酸、鹽酸羥胺、磷酸氫二鈉、磷酸二氫鈉、硼酸、硼砂、氯化鈉、碳酸氫鈉、硝酸鈉、硫酸鈉、硫酸銅、硫酸鎂、硫酸鈣及無(wú)水硫酸鈉均為分析純,購(gòu)自太原津昌華科貿(mào)有限公司.實(shí)驗(yàn)中所有溶液均由超純水配置.

恒溫磁力加熱攪拌器; G711A型高效液相色譜儀HPLC ,美國(guó)安捷倫科技有限公司;pHS-3C型pH計(jì),上海雷磁儀器廠; 1290型超高效液相色譜儀UPLC,美國(guó)安捷倫科技有限公司;6550型高分辨質(zhì)譜儀QTOF,美國(guó)安捷倫科技有限公司.

1.2 實(shí)驗(yàn)方法

OFL儲(chǔ)備液:稱取100mg OFL置于250mL燒杯中,加入超純水后置于超聲波清洗機(jī)中在100kHz超聲頻率下超聲15min至完全溶解,移至1L容量瓶中定容,配置得到100mg/L的標(biāo)準(zhǔn)儲(chǔ)備液,低溫避光保存,使用時(shí)稀釋至所需濃度.

Fe(VI)儲(chǔ)備液:取0.1096g K2FeO4溶于硼砂-硼酸緩沖溶液(pH=8)中,繼續(xù)用緩沖溶液定容至20mL,得到K2FeO4儲(chǔ)備液,現(xiàn)配現(xiàn)用.

Fe(VI)氧化OFL實(shí)驗(yàn):取5mL儲(chǔ)備液,用緩沖溶液定容至100mL,得到5mg/L反應(yīng)液,移至200mL燒杯,將一定量的Fe(VI)儲(chǔ)備液加入反應(yīng)液中,在一定溫度下攪拌并開始計(jì)時(shí),反應(yīng)過程中在不同時(shí)間點(diǎn)取樣3mL上清液移至預(yù)先加入過量鹽酸羥胺終止劑的試管中,用0.22μm有機(jī)相濾膜過濾后,測(cè)定OFL濃度.

羥基自由基HO·的掩蔽實(shí)驗(yàn):在進(jìn)行Fe(VI)氧化OFL實(shí)驗(yàn)前在反應(yīng)液中加入過量的叔丁醇進(jìn)行HO·掩蔽,過程中測(cè)定OFL濃度.

共存物質(zhì)影響實(shí)驗(yàn):在Fe(VI)氧化OFL實(shí)驗(yàn)中加入一定濃度的常見陰、陽(yáng)離子(Cl-、NO3-、SO42-、HCO3-、Mg2+、Ca2+和Cu2+)、腐殖酸進(jìn)行實(shí)驗(yàn),檢測(cè)其對(duì)Fe(VI)氧化降解OFL的影響情況.

UPLC-QTOF-MS樣品預(yù)處理:實(shí)驗(yàn)過程中取樣并終止反應(yīng)后,加入氯化鈉至飽和,再加入15mL甲醇,震蕩20min后將混合液移至分液漏斗中靜置分層,收集有機(jī)層.進(jìn)行2次萃取操作后向所得有機(jī)相中加入過量無(wú)水硫酸鈉吸干水分,使用旋轉(zhuǎn)蒸發(fā)器將所得樣品濃縮至2mL,進(jìn)行產(chǎn)物檢測(cè).

1.3 分析方法

1.3.1 動(dòng)力學(xué)分析 OFL的降解速率采用偽二級(jí)反應(yīng)動(dòng)力學(xué)描述,如式(1)所示:

式中:為任意時(shí)刻OFL剩余濃度,mg/L;0為OFL初始濃度,mg/L;obs為OFL的降解反應(yīng)速率常數(shù),L/(mg·min);為反應(yīng)時(shí)間,min.

1.3.2 活化能計(jì)算 Fe(VI)氧化OFL的活化能根據(jù)阿倫尼烏斯公式進(jìn)行計(jì)算,如式(2)所示:

式中:為溫度,K;a為表觀活化能,J/mol;為表觀指前因子,單位與obs一致,為摩爾氣體常數(shù),8.314J/(mol·K).

1.3.3 測(cè)試方法 OFL濃度測(cè)定:利用HPLC進(jìn)行測(cè)定,色譜柱為InfinityLab Poroshell 120,流動(dòng)相為乙腈:甲酸水(體積分?jǐn)?shù)0.1%)=20:80(),流量0.8mL/min,進(jìn)樣量為50μL,檢測(cè)波長(zhǎng)為288nm.

LC-QTOF-MS檢測(cè):OFL氧化產(chǎn)物測(cè)定通過超高效液相色譜-串聯(lián)高分辨質(zhì)譜儀(UPLC-QTOF- MS)進(jìn)行.色譜柱為waters BEH C18(2.1mm× 50mm×1.7μm),流動(dòng)相由A(0.1%甲酸水)和B(乙腈)組成.梯度洗脫程序見表1.流速0.3mL/min,進(jìn)樣量5μL,在ESI+模式下進(jìn)行質(zhì)譜掃描,掃描范圍為20～ 500/,脫溶劑氣體流速12L/min,脫溶劑溫度350°C.

表1 梯度洗脫程序

所有實(shí)驗(yàn)數(shù)據(jù)均經(jīng)過3次平行實(shí)驗(yàn)測(cè)定得到,數(shù)據(jù)分析及曲線圖、柱狀圖繪制均采用OriginPro 8.0軟件,降解路徑推測(cè)圖使用Kingdraw繪制.

2 結(jié)果與討論

2.1 Fe(VI)降解OFL的影響因素

2.1.1 Fe(VI)投加量對(duì)OFL去除效果的影響 由圖1a可知,Fe(VI)氧化OFL的反應(yīng)主要發(fā)生在前5min且OFL的降解效果明顯,隨著反應(yīng)的進(jìn)行,OFL的去除率趨于平緩.當(dāng)(K2FeO4):(OFL)為10:1,20:1,30:1,40:1,50:1時(shí),30min內(nèi)OFL的去除率分別為30.76%,53.10%,74.18%,92.38%,94.98%.可見,OFL的去除率隨著Fe(VI)投加量的增大而顯著提高.隨著Fe(VI)投加量的增大,Fe(VI)與OFL分子發(fā)生反應(yīng)的概率相應(yīng)增加,因此OFL的去除率逐漸增大.當(dāng)Fe(VI)的投加量從40:1增加至50:1時(shí),OFL的去除率只增加了2.60%,這可能是因?yàn)檫^量的Fe(VI)在水中的自分解反應(yīng)加劇[19],導(dǎo)致其在反應(yīng)液中的有效濃度低于理論濃度.結(jié)合最終去除效果及經(jīng)濟(jì)成本因素,本實(shí)驗(yàn)選用的投加量為(K2FeO4):(OFL)=40:1.該投加量與Fe(VI)氧化氯霉素的最佳投加量相同[20].

不同F(xiàn)e(VI)投加量下的反應(yīng)動(dòng)力學(xué)參數(shù)見表2,結(jié)合圖1b可以看出,在前5min快速反應(yīng)階段,1/- 1/0與存在顯著的線性關(guān)系,說(shuō)明OFL的降解速率符合偽二級(jí)動(dòng)力學(xué)模型,而Fe(VI)氧化許多有機(jī)物時(shí)的反應(yīng)均符合二級(jí)動(dòng)力學(xué)模型[21].

0=5mg/L、pH=8、溫度25°C

表2 不同F(xiàn)e(VI)投加量下的動(dòng)力學(xué)參數(shù)

2.1.2 pH值對(duì)OFL去除效果的影響 由圖2a可見,反應(yīng)30min內(nèi),pH值從5上升至7時(shí),OFL的最大去除率從45.36%降低至39.02%,在pH=8時(shí)去除率達(dá)到最大值,為92.38%,pH值上升至9時(shí),去除率卻降低至68.98%,可見pH=8時(shí)Fe(VI)對(duì)OFL的氧化效果最佳.

不同pH值下的反應(yīng)動(dòng)力學(xué)參數(shù)見表3,結(jié)合圖2b可知,pH值為5時(shí)反應(yīng)速率常數(shù)略大于pH值為6和7時(shí),這是因?yàn)镕e(VI)在酸性環(huán)境下具有較高的質(zhì)子化程度,大部分以HFeO4-和H2FeO4的形式存在,氧化還原電位較高,因此Fe(VI)能更快地與目標(biāo)物發(fā)生反應(yīng)[22].但酸性環(huán)境在促進(jìn)反應(yīng)快速發(fā)生的同時(shí)也會(huì)削弱Fe(VI)自身的穩(wěn)定性,促使Fe(VI)自分解反應(yīng)的進(jìn)行[23],導(dǎo)致部分Fe(VI)在與OFL發(fā)生反應(yīng)前就被氧化為Fe(III)和O2,而O2在溶液中的氧化能力不足以降解OFL,因此OFL的去除率變低.

0=5mg/L、(K2FeO4):(OFL)=40:1、溫度25°C

而在堿性條件下,Fe(VI)的自分解反應(yīng)變慢,實(shí)際參與氧化OFL的有效濃度大.且在該環(huán)境下,溶液pH值大于OFL的酸解離常數(shù)(pa2=7.90～8.22),OFL分子上的羧基官能團(tuán)會(huì)發(fā)生去質(zhì)子化反應(yīng),使OFL分子大部分帶負(fù)電[24-25].而Fe(VI)氧化反應(yīng)具有選擇性[26],與含富電子基團(tuán)的物質(zhì)有較高的反應(yīng)速率[27].因此,在堿性條件下,Fe(VI)更易與OFL分子發(fā)生化學(xué)反應(yīng),且可彌補(bǔ)該條件下Fe(VI)氧化能力弱的缺點(diǎn),最終提高整體去除率.相反,在酸性條件下,溶液pH值小于OFL的酸解離常數(shù)(pa1=5.70～6.05),OFL分子上哌嗪基環(huán)上的氨基官能團(tuán)帶一個(gè)正電荷,使OFL分子大部分帶正電,不利于其與Fe(VI)發(fā)生反應(yīng)[24-25].

表3 不同pH值下的反應(yīng)動(dòng)力學(xué)參數(shù)

0=5mg/L、(K2FeO4):(OFL)=40:1、pH=8

可見,pH值對(duì)OFL去除的影響要綜合考慮Fe(VI)的氧化能力、穩(wěn)定性及OFL的存在形態(tài)等,酸性環(huán)境可以提高Fe(VI)的氧化能力,但OFL分子大部分帶正電,而堿性環(huán)境可以維持Fe(VI)的有效濃度,且OFL分子大部分帶負(fù)電. Zhou等[15]在研究Fe(VI)氧化環(huán)丙沙星時(shí)也發(fā)現(xiàn)在pH值為8,9時(shí)目標(biāo)物質(zhì)的去除率均能達(dá)到90%以上.鑒于Fe(VI)自身的穩(wěn)定性及其發(fā)生氧化反應(yīng)的選擇性,反應(yīng)的最佳pH值為8.

2.1.3 溫度對(duì)OFL去除效果的影響 由圖3a可知,當(dāng)反應(yīng)溫度從15°C,升高至45°C,時(shí),OFL的去除率逐漸增加,但增加的幅度都不大,降解率分別為90.36%,92.38%,93.16%和94.08%.

不同溫度下的反應(yīng)動(dòng)力學(xué)參數(shù)見表4,結(jié)合圖3b可知,溫度的升高加快了整體反應(yīng)速率,反應(yīng)速率常數(shù)obs從0.205L/(mg·min)升至0.571L/(mg·min).這可能是因?yàn)樯郎貢r(shí)分子運(yùn)動(dòng)速率增大,Fe(VI)與OFL分子的有效碰撞頻率增加.但升溫的同時(shí)也會(huì)降低Fe(VI)自身的穩(wěn)定性,使得參與氧化OFL的Fe(VI)的有效濃度降低,因此溫度升高沒有顯著提升OFL的去除率.

對(duì)不同溫度下的obs與溫度進(jìn)行擬合,發(fā)現(xiàn)obs與的關(guān)系符合阿倫尼烏斯公式,ln(obs)與1/具有良好的線性關(guān)系(2=0.95409),反應(yīng)活化能a=28.17kJ/ mol,說(shuō)明反應(yīng)極易發(fā)生,且反應(yīng)速率較快.

其設(shè)計(jì)思路為分別將多種模式的中頻結(jié)構(gòu)都提前設(shè)計(jì)好,采用模式選擇的方式來(lái)完成各種通信模式的切換,實(shí)現(xiàn)兼容多種通信模式信號(hào)功能。并行多模數(shù)字中頻結(jié)構(gòu)的實(shí)現(xiàn)比較容易,只需要將各種單模的中頻模塊類比復(fù)制設(shè)計(jì)即可,通過模式選擇模塊實(shí)現(xiàn)各種模式的選擇切換。但是該方案會(huì)犧牲很多硬件資源,對(duì)于資源有限的FPGA而言并不是一種性價(jià)比高的設(shè)計(jì)。

表4 不同溫度下的反應(yīng)動(dòng)力學(xué)參數(shù)

2.2 HO·掩蔽實(shí)驗(yàn)

Fe(VI)氧化降解有機(jī)物主要有2種途徑:Fe(VI)直接氧化和反應(yīng)過程中生成的新自由基HO·間接氧化[28](式3和式4).

因此,基于上述最佳反應(yīng)條件,在反應(yīng)體系中加入過量HO·掩蔽劑叔丁醇,考察Fe(VI)直接氧化和HO·間接氧化在Fe(VI)氧化OFL中的貢獻(xiàn)率.

由圖4可知,反應(yīng)液中加入叔丁醇后OFL的去除率由92.38%降低至70.34%,這是因?yàn)槿芤褐械氖宥〈紩?huì)中斷Fe(VI)的自由基鏈反應(yīng),并消耗Fe(VI)生成的HO·[29],但Fe(VI) 及中間高價(jià)態(tài)鐵仍然發(fā)揮著重要的氧化作用.通過對(duì)比兩組實(shí)驗(yàn)中OFL的最終去除率可知,Fe(VI)及中間高價(jià)態(tài)鐵對(duì)OFL去除的貢獻(xiàn)率為70.34%,HO·及其它活性物質(zhì)的貢獻(xiàn)率為22.04%.Fe(VI)及中間高價(jià)態(tài)鐵對(duì)OFL去除的貢獻(xiàn)率較高,進(jìn)一步證明了穩(wěn)定性較高的Fe(VI)易與帶負(fù)電的OFL發(fā)生氧化反應(yīng).

圖4 叔丁醇對(duì)Fe(VI)氧化降解OFL的影響

2.3 共存物質(zhì)對(duì)OFL降解的影響

2.3.1 共存離子對(duì)OFL去除效果的影響 在OFL初始濃度為5mg/L,pH=8,溫度為25°C,高鐵酸鉀投加量為(K2FeO4):(OFL)=40:1的條件下,考察自然水體及廢水中較為常見的陰離子(Cl-、NO3-、SO42-和HCO3-)、陽(yáng)離子(Mg2+、Ca2+和Cu2+)對(duì)OFL降解效果的影響.所有離子濃度均為5mmol/L,反應(yīng)時(shí)間為30min.實(shí)驗(yàn)結(jié)果如圖5所示.

圖5 共存離子對(duì)OFL降解率的影響

可見,4種陰離子對(duì)OFL的去除效果影響較小.當(dāng)反應(yīng)液中不含共存離子時(shí),OFL去除率為92.38%,在Cl-、NO3-、SO42-和HCO3-存在的情況下OFL的去除率分別降低了1.21%,2.30%,3.02%和4.50%,其中HCO3-對(duì)OFL去除效果的影響較為明顯.一方面,HCO3-可能會(huì)與Fe(OH)3發(fā)生絡(luò)合,削弱Fe(OH)3的吸附能力[30]從而導(dǎo)致OFL的去除率降低.另一方面,HCO3-會(huì)與HO·發(fā)生反應(yīng),消耗溶液中的自由基[31],導(dǎo)致OFL的去除率降低.但HCO3–對(duì)溶液pH值的影響仍在硼酸-硼砂緩沖溶液的緩沖范圍內(nèi),對(duì)Fe(VI)氧化效果的影響仍然較小,這也與已報(bào)道的研究結(jié)果一致[18,32-33].

相對(duì)地,3種陽(yáng)離子對(duì)OFL的去除效果影響較大.當(dāng)二價(jià)堿金屬離子Mg2+和Ca2+存在時(shí),OFL的去除效果受到了明顯的抑制,去除率分別降低13.22%和15.53%,Ca2+的抑制效果略大于Mg2+,這是因?yàn)槿芤褐械腗g2+和Ca2+加劇了Fe(VI)的自分解反應(yīng)[34],導(dǎo)致OFL的去除率降低.而反應(yīng)液中存在過渡金屬離子Cu2+時(shí),OFL的去除率降低11.36%,這可能是因?yàn)檫^渡金屬離子傾向于與有機(jī)分子形成絡(luò)合物,而Fe(VI)與金屬絡(luò)合物的反應(yīng)較為緩慢,對(duì)Fe(VI)與目標(biāo)物之間的反應(yīng)產(chǎn)生負(fù)面影響[18].

2.3.2 腐殖酸對(duì)OFL去除效果的影響 在OFL初始濃度為5mg/L,pH=8,溫度為25°C,高鐵酸鉀投加量為(K2FeO4):(OFL)=40:1的條件下,當(dāng)反應(yīng)液中HA濃度分別為0,1,5,10mg/L時(shí),OFL的去除率逐漸降低,分別為92.38%、89.08%、79.76%、72.12%.Feng等[18]研究顯示,隨著HA濃度增加,Fe(VI)對(duì)氟甲喹的氧化效果呈非線性下降趨勢(shì),當(dāng)HA濃度為15mg/L時(shí),氟甲喹去除率下降了40%.Yang等[35]在使用Fe(VI)氧化四溴雙酚A和雙酚A時(shí),添加20mg/L的HA后,四溴雙酚A和雙酚A降解率分別從70%下降到33.2%和28.4%.這可能是因?yàn)楦乘岬囊恍┎伙柡突鶊F(tuán)如羥基、酚羥基會(huì)與OFL形成競(jìng)爭(zhēng)[36],干擾Fe(VI)氧化降解OFL,從而降低OFL的去除率.

2.4 Fe(VI)降解OFL的產(chǎn)物分析和路徑推測(cè)

將實(shí)驗(yàn)樣品進(jìn)行預(yù)處理后,進(jìn)行UPLC-QTOF- MS產(chǎn)物測(cè)定.通過分析質(zhì)譜圖,得到總計(jì)15種OFL降解的中間產(chǎn)物(表5),并推測(cè)Fe(VI)氧化OFL的反應(yīng)路徑(圖6).

表5 OFL的降解中間產(chǎn)物

在路徑I中,由于喹諾酮取代基環(huán)上烯烴雙鍵為富電子基團(tuán),所以Fe(VI)會(huì)優(yōu)先與喹諾酮取代基上的烯烴雙鍵發(fā)生1,3-偶極環(huán)加成反應(yīng),使得喹諾酮取代基上吡啶環(huán)開環(huán)生成P1[18],隨后發(fā)生脫羰反應(yīng)生成P2,繼而生成P3,P3羥基化后(P4)進(jìn)一步生成P5,最終母苯環(huán)上與哌嗪取代基環(huán)連接的C-N鍵被Fe(VI)攻擊斷裂后生成P6[37].

在路徑II與路徑III中,Fe(VI)會(huì)以不同的方式破壞哌嗪基環(huán).路徑II中OFL的哌嗪基環(huán)失去2個(gè)碳原子后形成P7,隨后形成P8,在Fe(VI)氧化環(huán)丙沙星的過程中也有類似反應(yīng)發(fā)生[15]. 哌嗪基環(huán)與喹諾酮取代基相連的C-N鍵被攻擊斷裂后生成P9.而路徑III中,OFL經(jīng)去甲基反應(yīng)生成P10后,因哌嗪基環(huán)側(cè)鏈氧化減少至1個(gè)氨基后形成P11[38].P11可發(fā)生去甲基反應(yīng)生成P12.另一方面,P11上的惡嗪基環(huán)可能被破壞形成P13[39],通過脫氨、脫羧基和吡啶基上C-N鍵的斷裂形成P14,最終通過吡啶環(huán)開環(huán)、脫氟反應(yīng)后得到P15[40].

綜上所述,Fe(VI)在氧化OFL時(shí)主要通過脫羧、去甲基、脫羰、羥基化等反應(yīng)實(shí)現(xiàn)喹諾酮取代基、哌嗪基環(huán)及惡嗪基環(huán)的開環(huán),從而達(dá)到氧化降解OFL的目的.

圖6 Fe(VI)氧化OFL的途徑

3 結(jié)論

3.1 Fe(VI)氧化OFL的最佳條件為:溫度為25℃、(K2FeO4):(OFL)=40:1、pH值為8時(shí),反應(yīng)30min后,OFL的去除率可達(dá)92.38%.反應(yīng)前5min為快速反應(yīng)階段,OFL的降解符合偽二級(jí)反應(yīng)動(dòng)力學(xué)模型,反應(yīng)速率常數(shù)obs=0.361L/(mg·min).

3.2 Fe(VI)氧化OFL時(shí),Fe(VI) 及中間高價(jià)態(tài)鐵起到主要作用,對(duì)OFL去除的貢獻(xiàn)率為70.34%,反應(yīng)過程中生成的HO·及其他活性物質(zhì)的貢獻(xiàn)率為22.04%.

3.3 Cl-、NO3-、SO42-和HCO3-對(duì)降解效果的影響較小,Mg2+、Ca2+和Cu2+對(duì)降解效果有小幅抑制作用,腐殖酸對(duì)OFL的降解起到顯著的抑制作用.

3.4 OFL被Fe(VI)氧化時(shí)可能存在3種降解路徑,主要通過脫羧、去甲基、脫羰、羥基化等反應(yīng)實(shí)現(xiàn)OFL分子上喹諾酮取代基、哌嗪基環(huán)及惡嗪基環(huán)的開環(huán).

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Oxidation and degradation mechanisms of ofloxacin by potassium ferrate.

LI Ya-nan1*,FENG Zhuo1,WANG Jia-qi1,GUO Kai1,ZHANG Guo-kai2

(1.Department of Environmental Science and Engineering,Taiyuan University of Technology,Jinzhong 030600,China；2.Chinasea Group Co. Ltd.,Taiyuan 030012,China).,2022,42(8)：3696～3703

The oxidation and degradation mechanisms of quinolone antibiotic ofloxacin (OFL) by potassium ferrate (Fe (VI)) were studied.High performance liquid chromatography(HPLC),liquid chromatograph mass spectrometer(UPLC-QTOF-MS) and other methods were used to investigate the effects of Fe (VI) dosage,pH,temperature and coexisting substances on OFL removal,analyze the reaction kinetics,calculate the contribution rate of Fe(VI) in the process of OFL oxidation,identify the products of Fe(VI) and predict the main reaction pathways.The results show that the degradation efficiency of OFL reached 92.38% after 30 minutes of oxidation,with the molar ratio of Fe (VI) to OFL of 40:1,pH of 8 and temperature of 25°C. In the first 5 minutes’ rapid reaction stage,OFL degradation conformed to pseudo second-order reaction kinetics,and the activation energy was 28.17kJ/mol. The contribution of Fe (VI) and the high-valent intermediate iron species to OFL removal was 70.34%,and humic acid significantly inhibited the reaction. Three main oxidation pathways for OFL degradation by Fe (VI) were proposed based on the analysis of reaction products,and the ring cleavages of quinolone,piperazine and oxazine rings were mainly achieved through decarboxylation,demethylation,decarbonylation and hydroxylation.

potassium ferrate；ofloxacin；influencing factors；coexisting substances；intermediate products；degradation pathway

X703

A

1000-6923(2022)08-3696-08

2022-01-01

山西省應(yīng)用基礎(chǔ)研究計(jì)劃項(xiàng)目(20210302123121);自然資源部生態(tài)地球化學(xué)重點(diǎn)實(shí)驗(yàn)室開放基金(ZSDHJJ201804)

* 責(zé)任作者,副教授,liyanan@tyut.edu.cn

李亞男(1983-),女,山西呂梁人,副教授,主要從事污廢水處理技術(shù)研究.發(fā)表論文30余篇.