鄧 芠,劉國光,呂文英,陳 平,王楓亮,潘夏玲,張利朋,馬京帥,林曉璇

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水中無機(jī)氮形態(tài)變化對(duì)酮洛芬光降解的影響

鄧 芠,劉國光*,呂文英,陳 平,王楓亮,潘夏玲,張利朋,馬京帥,林曉璇

(廣東工業(yè)大學(xué)環(huán)境科學(xué)與工程學(xué)院,廣東 廣州 510006)

研究了模擬太陽光照射下水環(huán)境中不同形態(tài)氮(NO3－、NO2－和NH4+)對(duì)酮洛芬(KET)光解的影響.結(jié)果表明,KET在平均波長(200~450nm)下量子產(chǎn)率o為0.14. NO3－濃度從0.01mmol/L-增至1.0mmol/L時(shí), KET光解速率常數(shù)從0.0109降至0.0085; NO2－濃度從0.01mmol/L增至1.0mmol/L時(shí), KET光解速率常數(shù)從0.0095降至0.0069, NH4+對(duì)KET的光解基本無影響. NO3－的光掩蔽現(xiàn)象對(duì)KET光解的影響起主要作用; NO2－則通過光掩蔽現(xiàn)象和羥基自由基猝滅來抑制KET的光解.同時(shí)研究了當(dāng)水環(huán)境中pE值發(fā)生變化而引起水中無機(jī)氮形態(tài)轉(zhuǎn)化時(shí),不同形態(tài)氮共存對(duì)KET光解的復(fù)合影響,隨著pE值的增大,KET的光解速率先減小后增大;當(dāng)NO2－和NH4+共存時(shí),兩者對(duì)KET光解的影響存在拮抗作用,這一拮抗作用也存在于NO2－和NO3－之間.

酮洛芬；光降解；不同形態(tài)氮；量子產(chǎn)率；pE值；光屏蔽因子；羥基自由基

藥物及個(gè)人護(hù)理品(PPCPs)通常在污水處理廠僅略被轉(zhuǎn)化或甚至不受任何降解即進(jìn)入水生環(huán)境[1-6],在環(huán)境中結(jié)構(gòu)穩(wěn)定或假穩(wěn)定[7-11],在生物體中生物累積具有潛在危險(xiǎn)[12-14].所以,PPCPs在環(huán)境中的存在,影響和風(fēng)險(xiǎn)的研究一直成為焦點(diǎn)[15].

酮洛芬(KET)為1-(3-苯氧基)苯丙酸,是一種重要的非甾體消炎藥,目前我國每年生產(chǎn)和使用KET約92t[16].KET在水環(huán)境中經(jīng)常被檢測出來[17-19],在我國,CAO等[20]在漳衛(wèi)南運(yùn)河流域中測得KET的濃度為31.4ng/L.存在于水體中的KET對(duì)生物體具有潛在的風(fēng)險(xiǎn)[21].前人研究了KET在模擬水環(huán)境中受紫外光照的光解行為及降解產(chǎn)物[22,31],然而對(duì)于在模擬太陽光下水中共存物質(zhì)對(duì)KET光解的影響研究仍較欠缺.

當(dāng)PPCPs類污染物在天然水體中發(fā)生光解時(shí)[23],水中存在的光敏性物質(zhì)會(huì)對(duì)其光解行為產(chǎn)生影響[24-25].天然水體中存在著大量的無機(jī)氮,其存在形態(tài)通常為NO3－,NO2－及NH4+,其中NO3－, NO2－具有光化學(xué)活性可受光產(chǎn)生·OH等中間活性體(ROS)[26],本文采用350W氙燈模擬太陽光,對(duì)含有不同形態(tài)氮的KET水溶液進(jìn)行光照,研究水中不同形態(tài)氮對(duì)KET光降解的影響.

1 材料與方法

1.1 試劑

酮洛芬,純度>98.0%,TCI試劑公司;乙腈,色譜純,美國ACS恩科化學(xué);草酸鐵鉀,純度>98.0%,中國Alfa Aesar化學(xué);氫氧化鈉,硫酸,硝酸鈉,亞硝酸鈉,冰乙酸均為分析純,成都科試.

1.2 實(shí)驗(yàn)方法

光化學(xué)實(shí)驗(yàn) 實(shí)驗(yàn)使用乙腈配制1g/L的KET母液.配制濃度為4mg/L的KET溶液時(shí),準(zhǔn)確移取0.8mL母液于200mL容量瓶中,使用高純氮吹干乙腈,并用超純水(Smart2Pure超純水/純水一體化系統(tǒng),德國TKA)定容.當(dāng)配制含有NO3－的4mg/LKET溶液時(shí),準(zhǔn)確移取0.8mL母液于200mL容量瓶中,使用高純氮吹干乙腈后,分別加入不同量的硝酸鈉溶液,使用超純水定容,使得NO3－濃度分別為0, 0.01, 0.1, 1.0mmol/L,并用0.1%NaOH和H2SO4調(diào)溶液pH值至中性.模擬太陽光光照下的降解實(shí)驗(yàn)采用SGY-ⅡB.Y1型旋轉(zhuǎn)光化學(xué)反應(yīng)儀,其裝置如圖1所示.移取20mL的反應(yīng)溶液于25mL的石英試管中,并置于旋轉(zhuǎn)反應(yīng)儀中進(jìn)行反應(yīng),控制反應(yīng)器溫度為(25±1)℃,用350W氙燈照射(350W Xe arc lamp, 南京斯東柯電氣設(shè)備有限公司),每隔30s取樣一次,每個(gè)時(shí)間點(diǎn)的樣品至少設(shè)3個(gè)重復(fù),取平均值.含有NO2－和NH4+的KET溶液的配制和光解方法同上.

1.2.2 模擬水體pE值變化 pE值是用于衡量體系接收或遷移電子的能力(pE=-lge,e為電子活度)的參數(shù)[26,29-30].水中N主要是以NO3－和NH4+的形式存在,但在某些條件下,也有中間氧化態(tài)NO2－的存在,不同形態(tài)N之間會(huì)隨著環(huán)境氧化還原電位的不同而發(fā)生轉(zhuǎn)換,如半反應(yīng)式(1)和(3)所示.通過控制不同形態(tài)N的添加濃度來模擬不同pE值引起的氮的形態(tài)變化,以考察當(dāng)水體pE值發(fā)生變化,不同形態(tài)N共存對(duì)KET光解的影響.設(shè)定水體中的總氮濃度為1.00×10-3mol/L.

含有NO2－和NH4+的半反應(yīng)為:

根據(jù)含有NO2－和NH4+的半反應(yīng)可求得:

含有NO3－和NO2－的半反應(yīng)為:

根據(jù)含有NO3－和NO2－的半反應(yīng)可求得:

1.3 分析測定方法

高效液相色譜儀(LC-20AT,SHIMADZU),色譜條件:流動(dòng)相是乙腈-0.5%冰乙酸(45:55,體積比);色譜柱(InertSustain C18,GL Sciences);檢測器為光電二極管陣列檢測器(SPD-M20A),檢測波長為260nm,流速為1mL/min,進(jìn)樣量10μL,柱溫40℃.紫外分光光度計(jì)(UV-2100,北京瑞利).

1.4 光量子產(chǎn)率及光屏蔽因子的測定方法

1.4.1 光量子產(chǎn)率測定方法光量子產(chǎn)率0是指光照過程中產(chǎn)生的激發(fā)態(tài)分子物質(zhì)的量與所吸收光子物質(zhì)的量的比率.使用草酸鐵(K3Fe(C2O4)3)作為露光計(jì)來計(jì)算底物的量子產(chǎn)率[26-27].

式中:為KET;a為草酸鐵鉀;為反應(yīng)速率常數(shù);為摩爾吸光系數(shù);L為入射光強(qiáng),a=1.2.

1.4.2 光屏蔽因子測定方法 含不同濃度的NO3－對(duì)直接光解的影響可由光屏蔽因子(λ)來評(píng)估[27].含不同NO3－濃度的溶液由紫外分光光度計(jì)掃描,掃描波長范圍為200~450nm.收集到的吸光度被用于計(jì)算某一波段點(diǎn)光屏蔽因子及總屏蔽因子:

式中:S為NO3－在波長下對(duì)KET的光屏蔽因子;∑S為NO3－(或NO2－)在紫外吸收波長范圍內(nèi)對(duì)KET的總屏蔽因子;為NO3－(或NO2－)在波長下的吸光度;為KET在波長下的摩爾吸光系數(shù);1為光程;L為氙燈的光強(qiáng)百分比.

2 結(jié)果與討論

2.1 不同形態(tài)氮對(duì)KET溶液光解的影響

2.1.1 NO3－對(duì)KET光降解的影響 在350W氙燈模擬太陽光照射下,KET在純水中光解的一級(jí)動(dòng)力學(xué)反應(yīng)速率常數(shù)o為0.0114(表1),而草酸鐵鉀(0.01mol/L)的光解反應(yīng)速率常數(shù)a為0.0541 (圖2).根據(jù)式(5)計(jì)算其平均波長(200~450nm)量子產(chǎn)率o為0.14,與Martinez等[31]對(duì)KET光解的量子產(chǎn)率計(jì)算結(jié)果相似.

從表2可以看出, 在模擬太陽光照射下,在添加不同濃度 NO3－的情況下, KET的光解動(dòng)力學(xué)均較好地符合偽一級(jí)反應(yīng)動(dòng)力學(xué)方程.與不添加NO3－的KET溶液相比,添加NO3－的KET溶液光解速率減小,且當(dāng)NO3－濃度從0.01mmol/L增至1.0mmol/L時(shí),KET光解速率從0.0109降至0.0085,表明NO－會(huì)抑制KET的光解,并且,抑制率隨共存 NO3－濃度的增大而增大,這與這與NO3－對(duì)啶蟲脒在水溶液中光解的影響[32]的實(shí)驗(yàn)現(xiàn)象一致.

表1 NO3－對(duì)KET光降解影響的動(dòng)力學(xué)方程及相關(guān)常數(shù)Table 1 Photodegradation rate constants of KET with NO3－

如反應(yīng)式(8)、(9)、(10)所示[29],NO3－中可以產(chǎn)生O2·－,而O2·－迅速和水反應(yīng),生成它本身的共軛酸·OH,一種強(qiáng)烈的氧化劑,所以從理論上講,NO3－的加入可促進(jìn)KET的光氧化降解.

(10)

從圖3可見,NO3－的吸收光譜范圍為200~ 330nm,而KET的吸收光譜范圍為200~320nm,所以在模擬太陽光的照射下,NO3－與KET的吸收光譜范圍有重合,即會(huì)發(fā)生NO3－與KET競爭吸收光子,從而抑制KET的降解.

由表2可知,隨著NO3－濃度的增大,掩蔽效果增強(qiáng).將∑S與KET在純水中光解時(shí)所得反應(yīng)速率常數(shù)o相乘可得KET在各NO3－濃度下因光掩蔽影響時(shí)光解的理論光解反應(yīng)速率常數(shù)值o∑S.理論o∑S值與實(shí)際s值相差不大.由此可知,在添加了NO3－的KET光解反應(yīng)中,NO3－的光掩蔽現(xiàn)象對(duì)KET光解的影響起主導(dǎo)作用,而體系中沒明顯出現(xiàn)生成ROS來促進(jìn)KET光降解的現(xiàn)象.

表2 不同濃度NO3－、NO2－下KET光解動(dòng)力學(xué)常數(shù)及光屏蔽因子Table 2 Apparent rate constants with NO3－or NO2－in different concentrations and screening factor

2.1.2 NO2－對(duì)KET光降解的影響 從表3可以看出,在添加不同濃度NO2－的情況下,KET的光解動(dòng)力學(xué)較好地符合偽一級(jí)反應(yīng)動(dòng)力學(xué)方程. 與不添加NO2－的KET溶液相比,添加NO2－的KET溶液光解速率減小,且當(dāng)NO2－濃度從0.01mmol/L增至1.0mmol/L時(shí),KET光解速率從0.0095降至0.0069,表明NO2－會(huì)抑制KET的光解,抑制率隨共存NO2－濃度的增大而增大.本課題組研究NO2－對(duì)萘普生[28]和雙氯酚酸光解的影響[25]表明,NO2－同樣存在光抑制作用.

表3 NO2－對(duì)KET光降解影響的動(dòng)力學(xué)方程及相關(guān)常數(shù)Table 3 Photodegradation rate constants of KET with NO2－

從圖3可見,NO2－的吸收光譜范圍為200~ 400nm,而KET的吸收光譜范圍為200~320nm, NO2－與KET的吸收光譜有重合,從而NO2－與KET產(chǎn)生競爭吸收,抑制KET的直接光解.

本研究同樣引入光掩蔽系數(shù)來研究NO2－對(duì)KET的抑制作用.由表2可知,隨著NO2－濃度的增大,總掩蔽系數(shù)也隨之增大,但增大效果不明顯.根據(jù)式(6)、(7)計(jì)算出理論o∑S值,通過與實(shí)際s值做比較,發(fā)現(xiàn)KET在不同NO2－濃度下光降解的理論o∑S值均大于相應(yīng)的實(shí)際s值,且隨著NO2－濃度的增大,兩者之間的差值越大.

NO2－會(huì)清除·OH,如反應(yīng)式(12)所示[27].

由此推測此差值是由于NO2－猝滅羥基自由基引起的,NO2－濃度越大,NO2－猝滅羥基自由基的作用越大,導(dǎo)致KET的光解速率下降越明顯.通過對(duì)比加入和不加入異丙醇(猝滅羥基自由基)體系KET的光解反應(yīng)速率,結(jié)果如表4所示.

表4的結(jié)果證實(shí),KET在純水中單獨(dú)光解會(huì)生成羥基自由基(自敏化光解),并由式(14)估算出·OH對(duì)KET光解的貢獻(xiàn)率[29]為13.2%.本研究對(duì)50,100mmol/L的異丙醇進(jìn)行猝滅實(shí)驗(yàn),結(jié)果一致.

式中:·OH為·OH對(duì)KET光降解的貢獻(xiàn)率;o、isopropanol分別為KET分別在純水和添加了·OH的光解過程的速率常數(shù).

猝滅實(shí)驗(yàn)表明,KET光解過程中生成羥基自由基參與反應(yīng).由此證明,NO2－對(duì)KET光解的影響除光屏蔽現(xiàn)象外,還有對(duì)自由基的猝滅作用,且對(duì)羥基自由基的猝滅在體系中起到主要的抑制作用.

表4 ·OH猝滅實(shí)驗(yàn)及KET光解動(dòng)力學(xué)參數(shù)及貢獻(xiàn)率Table 4 Photodegradation kinetic parameters of KET with ·OH quenching experiment and the rate of contribution

注:異丙醇濃度為100mmol/L.

2.1.3 NH4+對(duì)KET光降解的影響 從表5可見,NH4+對(duì)KET光解影響不大,NH4+濃度從0.01mmol/L增加到1mmol/L,KET的光解半衰期無明顯變化,這與NH4+對(duì)水楊酸在水溶液中光解的影響[30]的實(shí)驗(yàn)結(jié)果一致.這是由于NH4+在紫外可見光范圍內(nèi)沒有光吸收,既不會(huì)通過競爭光子來抑制KET的光解(圖3),也不會(huì)產(chǎn)生ROS來促進(jìn)其光解.

表5 NH4+對(duì)KET光降解影響的動(dòng)力學(xué)方程及相關(guān)常數(shù)Table 5 Photodegradation rate constants of KET with NH4+

2.2 水體pE值對(duì)無機(jī)氮降解KET的影響

表6表明,pE值從4.82增至6.85時(shí),無機(jī)N對(duì)KET的光解抑制率逐漸增大;pE值從6.85增至8.15時(shí),無機(jī)N對(duì)KET的光解抑制率逐漸下降,且其對(duì)KET的抑制作用不是簡單的疊加關(guān)系. NO2－和NO3－對(duì)KET的降解都起抑制作用,且NO2－的抑制率大于NO3－,NH4+對(duì)KET的降解基本無影響.所以,當(dāng)pE值從4.82上升到6.85時(shí),反應(yīng)液中NO2－的濃度增大,即反應(yīng)液中無機(jī)N對(duì)KET光解的總抑制率隨著NO2－濃度的增大而增大,故降解速率降低;當(dāng)pE值從6.85上升至8.15時(shí),反應(yīng)液中NO2－的濃度減少,即反應(yīng)液中無機(jī)N對(duì)KET光解的總抑制率隨著NO2－濃度的減小而減小,故降解速率變快.同時(shí),對(duì)比在不同pE值下,無機(jī)N對(duì)KET光解的實(shí)際抑制率和理論抑制率,可以發(fā)現(xiàn),當(dāng)NH4+和NO2－共存時(shí),實(shí)際抑制率小于理論抑制率,說明NO2－和NH4+對(duì)KET光解的影響是起拮抗作用的.這可以解釋為NO2－和NH4+共存時(shí)發(fā)生氨氧化反應(yīng)[33-34],如式(13),使NO2－濃度降低,減弱了對(duì)KET光解的抑制;而NO3－和NO2－共存時(shí),發(fā)現(xiàn)實(shí)際抑制率也小于理論抑制率,所以這種拮抗作用也同樣存在于NO3－和NO2－之間,由圖4可知(以0.2mmol/L NO3－和0.8mmol/L NO2－共存為例), NO3－與NO2－共存時(shí),其吸光度小于兩者單獨(dú)存在時(shí)之和,減弱了與KET的光的競爭,從而減弱了對(duì)KET光解的抑制.這與我們之前分別研究pE值對(duì)磺胺二甲基嘧啶[35]和雙氯芬酸在水溶液中光解的影響[26]的實(shí)驗(yàn)現(xiàn)象一致.

注:理論抑制率*是由不同形態(tài)N單獨(dú)存在時(shí)的光解抑制率相加之和.

3 結(jié)論

3.1 模擬太陽光照射下,KET的光解符合一級(jí)動(dòng)力學(xué)規(guī)律.

3.2 NO3－與NO2－均抑制KET的降解,而且隨著NO3－和NO2－濃度的增加,其抑制作用逐漸增強(qiáng).這主要由于NO3－和NO2－的吸收光譜波長范圍(200~400nm)與KET的吸收光譜波長范圍(200~ 320nm)重疊,產(chǎn)生與KET競爭吸收光子的現(xiàn)象.

3.3 NO3－對(duì)KET光解的光掩蔽現(xiàn)象是其對(duì)KET光解影響的主要原因,在光解過程中沒有明顯產(chǎn)生ROS來促進(jìn)其光解. NO2－對(duì)KET光解的影響除光屏蔽現(xiàn)象外,還有對(duì)羥基自由基的猝滅作用.

3.4 NH4+對(duì)KET的光解基本無影響,是由于NH4+在紫外可見光范圍內(nèi)沒有光吸收,既不會(huì)通過競爭吸光來抑制KET光解,也不會(huì)產(chǎn)生ROS來促進(jìn)其光解.

3.5 模擬水體pE值發(fā)生變化時(shí),無機(jī)氮對(duì)KET光解的影響表明,當(dāng)NO2－和NH4+共存時(shí),兩者對(duì)KET的光解存在拮抗作用,且這一拮抗作用也存在于NO2－和NO3－之間.

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致謝：感謝劉國光教授對(duì)本論文的指導(dǎo)以及陳平等對(duì)本實(shí)驗(yàn)的協(xié)助.

* 責(zé)任作者, 教授, liugg615@163.com

Photodegradation of ketoprofen in aquatic environment: Effect of different forms of nitrogen

DENG Wen, LIU Guo-guang*, LV Wen-ying, CHEN Ping, WANG Feng-liang, PAN Xia-ling, ZHANG Li-peng, MA Jing-shuai, LIN Xiao-xuan

(School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China)., 2016,36(5)：1456~1462

The impacts of different nitrogen forms (NO3－, NO2－and NH4+) on the photodegradation of KET were investigated under Xe lamp irradiation. The direct photolysis solar quantum yield of KET was observed to be 0.14. Increasing the concentration of NO3－from 0.01mmol/L to 1.0mmol/L, the apparent rate constants of KET were decreased from 0.0109 to 0.0085. The apparent rate constants of KET decreased from 0.0095 to 0.0069when the concentration of NO2－increased from 0.01mmol/L to 1.0mmol/L. NH4+had no influence on KET photolysis. The screening effect of NO3－was the major factor on KET photolysis while NO2－inhibited photolysis via both attenuating light and quenching×OH. Photodegradation of KET was also investigated under different pE values. The photodegradation rate of KET decreased at first, then it increased with the increasing pE values. The antagonistic effect existed on the photodegradation of KET when NO2－coexisted with NH4+. And it also existed when NO2－coexisted with NO3－on the photodegradation of KET.

ketoprofen；photodegradation；different forms of nitrogen；quantum yield；pE values；screening factor；×OH

X703

A

1000-6923(2016)05-1456-07

鄧 芠(1991-),廣東廣州人,廣東工業(yè)大學(xué)碩士研究生,主要研究方向?yàn)榄h(huán)境化學(xué)及水中污染物治理與環(huán)境行為.

2015-11-09

國家自然科學(xué)基金資助項(xiàng)目(21377031);廣東省科技項(xiàng)目(2013B020800009)