張 珂,許 芬,陳家斌,萬(wàn) 玲,黃天寅

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丙酮/氯離子協(xié)同活化過(guò)一硫酸鹽降解酸性橙

張 珂,許 芬,陳家斌*,萬(wàn) 玲,黃天寅

(蘇州科技大學(xué)環(huán)境科學(xué)與工程學(xué)院,江蘇 蘇州 215009)

采用丙酮/氯離子(Cl-)協(xié)同活化過(guò)一硫酸鹽(PMS)降解偶氮染料酸性橙7(AO7).研究發(fā)現(xiàn),與Cl-/PMS體系相比,丙酮/Cl-/PMS體系降解AO7的效果顯著增強(qiáng),相應(yīng)的AO7表觀速率常數(shù)從0.0767增加到0.1725min-1.考察了丙酮/Cl-/PMS體系降解AO7的主要影響因素(初始pH值、Cl-濃度、PMS濃度、丙酮濃度).結(jié)果表明,在堿性環(huán)境下,隨著Cl-、PMS和丙酮濃度的增加,AO7的降解效果有所增強(qiáng);研究丙酮/Cl-/PMS體系降解AO7的降解機(jī)制.自由基猝滅實(shí)驗(yàn)表明,丙酮/Cl-/PMS體系中沒(méi)有自由基(硫酸根自由基(SO4－?)和羥基自由基(HO?))的產(chǎn)生,而次氯酸根(ClO-)濃度在反應(yīng)過(guò)程中逐漸增加,得出丙酮作為催化劑促進(jìn)Cl-和PMS產(chǎn)生更多HClO的結(jié)論.通過(guò)紫外可見(jiàn)光譜分析,表明AO7分子中偶氮鍵及萘環(huán)結(jié)構(gòu)均被破壞.

氯離子；過(guò)一硫酸鹽；丙酮；酸性橙7；次氯酸

偶氮染料廣泛用于現(xiàn)代工業(yè)中,如紡織、造紙、制革等行業(yè).由于偶氮染料具有毒性強(qiáng)、含鹽量高、致癌、致突變等特點(diǎn)[1-3],若不經(jīng)處理直接排放會(huì)對(duì)環(huán)境和人類(lèi)健康造成嚴(yán)重危害.大多數(shù)偶氮染料可生化性不高,成分復(fù)雜,屬于生物難降解,傳統(tǒng)的廢水處理技術(shù)已無(wú)法滿足染料廢水的處理要求[4-6].近年來(lái),基于硫酸根自由基(SO－ 4?)的高級(jí)氧化技術(shù)已得到廣泛應(yīng)用[7-8].硫酸根自由基(SO－ 4?)有較高的氧化還原電位(0=2.5~3.1V)[9-11],可以通過(guò)加熱[12-14]、紫外光照射[15-17]、過(guò)渡金屬離子[18-21]活化過(guò)一硫酸鹽(PMS)產(chǎn)生.然而這幾種活化方法都具有一定的局限性.加熱和紫外光照射均需要提供大量的能量且成本較高.過(guò)渡金屬離子雖然有易獲取、成本低等優(yōu)點(diǎn)[22-23],但是其較低的回收率和可能造成的二次污染限制了此方法的廣泛運(yùn)用[24].因此,新型過(guò)硫酸鹽活化方法的研究成為目前過(guò)硫酸鹽高級(jí)氧化技術(shù)(AOPs)研究的熱點(diǎn).

氯離子(Cl-)是印染廢水中主要的無(wú)機(jī)成分.據(jù)報(bào)道,染料廢水中含有的無(wú)機(jī)鹽(NaCl)等可高達(dá)5~100mg/L[25-26].大量研究表明,氯離子(Cl-)對(duì)AOPs有很大影響[27-30].通過(guò)研究Cl-對(duì)鈷/單過(guò)硫酸鹽體系降解偶氮染料的影響,發(fā)現(xiàn)低濃度的Cl-(<5mmol/L)對(duì)染料脫色有明顯的抑制作用,高濃度Cl-(>50mmol/L)對(duì)染料降解的抑制作用會(huì)不斷減小,甚至?xí)铀偃玖系拿撋玔30].

通過(guò)研究Cl-濃度對(duì)單獨(dú)PMS體系降解金橙G(OG)的影響,得出Cl-與PMS反應(yīng)產(chǎn)生具有氧化活性的鹵化物HOCl,能夠直接降解OG[31].因此,探索PMS活化過(guò)程中廢水基質(zhì)(如Cl-)所起到的作用對(duì)于該技術(shù)用于染料廢水處理具有重要意義.

本文在研究新型過(guò)硫酸鹽活化方法的過(guò)程中,發(fā)現(xiàn)丙酮/Cl-可以協(xié)同活化PMS,加速染料降解.通過(guò)改變反應(yīng)條件,研究了丙酮/Cl-/PMS體系的主要影響因素,并通過(guò)自由基猝滅實(shí)驗(yàn)及采用熒光猝滅法分析了丙酮/Cl-/PMS體系降解AO7中可能存在的機(jī)制.

1 試劑與方法

1.1 實(shí)驗(yàn)試劑與設(shè)備

過(guò)一硫酸鹽(HKSO5· 0.5KHSO4· 0.5K2SO4, PMS)、硫酸耐爾藍(lán)A(C40H40N6O6S)、曲拉通X- 100((C2H4O)NC14H22O)購(gòu)于Sigma-Aldrich; 酸性橙7(AO7)購(gòu)于國(guó)藥集團(tuán)化學(xué)試劑有限公司,氯化鈉(NaCl) 、丙酮(C3H6O)、亞硝酸鈉(NaNO2)、甲醇(CH3OH)、叔丁醇(C4H9OH)、硫酸銨[(NH4)2·SO4]、醋酸(CH3COOH)、磷酸(H3PO4)、硼酸(H3BO3)、硫酸(H2SO4)、氫氧化鈉(NaOH)均為分析純購(gòu)于國(guó)藥集團(tuán)化學(xué)試劑有限公司.實(shí)驗(yàn)用水為超純水.實(shí)驗(yàn)用攪拌裝置購(gòu)于上海標(biāo)本模型廠(JB50-D型).

1.2 降解實(shí)驗(yàn)

在室溫下,將一定量PMS和NaCl注入150mL的錐形瓶中,同時(shí)在錐形瓶中加入一定量的超純水,并用稀H2SO4或NaOH調(diào)節(jié)pH值,然后迅速加入一定量的丙酮和一定量的AO7溶液,使得總?cè)芤哼_(dá)到100mL,反應(yīng)體系密封后置于磁力攪拌器混合并啟動(dòng)反應(yīng).每隔一段時(shí)間取樣,迅速加入過(guò)量猝滅劑NaNO2終止反應(yīng),猝滅后的樣品經(jīng)0.45μm濾膜過(guò)濾后,收集濾液24h內(nèi)測(cè)定,每組實(shí)驗(yàn)均重復(fù)3次以確保實(shí)驗(yàn)的重現(xiàn)性,最終結(jié)果取三次平均值.

1.3 分析方法

使用Mapada UV-1600(PC)紫外可見(jiàn)分光光度計(jì),于AO7最大吸收波長(zhǎng)484nm處測(cè)定濾液的吸光度,代入標(biāo)準(zhǔn)曲線求得濃度.次氯酸根濃度采用PerkinElmer LS55熒光分光光度計(jì)測(cè)定,熒光吸收波長(zhǎng)為686nm,激發(fā)波長(zhǎng)為634nm.應(yīng)用Excel2016、Origin9.0進(jìn)行數(shù)據(jù)分析和作圖

2 結(jié)果與討論

2.1 不同體系下AO7的降解效果

圖1顯示了不同體系下AO7的降解效果.結(jié)果表明,PMS單獨(dú)存在時(shí),AO7在20min內(nèi)降解了21%,丙酮單獨(dú)存在時(shí),AO7在20min內(nèi)幾乎不降解.在PMS體系中加入Cl-,AO7在20min內(nèi)降解了38%;而在Cl-/PMS體系中加入丙酮,AO7在20min內(nèi)降解了97%.分析原因可能是,Cl-和PMS反應(yīng)產(chǎn)生HOCl和Cl2,而丙酮催化Cl-/PMS體系產(chǎn)生更多HOCl[見(jiàn)式(1)~(4)][4,32]. HOCl具有強(qiáng)氧化性,可以有效氧化AO7.

圖1 不同體系下AO7的降解效果

[AO7]=50μM, [PMS]=1mM, [Cl-]=10mM, [丙酮]=10mM,pH=9.0,= 20℃

HSO

5

-

+ Cl

-

→ SO

4

2

-

+ HOCl (1)

HSO

5

-

+ 2Cl

-

+H

+

→ SO

4

2

-

+ Cl

2

+ H

2

O (2)

HOCl → ClO

-

+ H

+

(3)

HSO

5

-

+ Cl

-

OCl

-

+ H

+

+ SO

4

2

-

(4)

2.2 丙酮/Cl-/PMS體系對(duì)AO7的降解機(jī)制

為了確定丙酮/Cl-/PMS體系降解AO7的反應(yīng)機(jī)理,向反應(yīng)體系中加入自由基(SO－ 4?、HO?)猝滅劑甲醇(Me)和叔丁醇(TBA)[33]以及HOCl猝滅劑NH4+[34-35],加入Me、TBA濃度均為100mmol/L,NH4+濃度從10增加到100mmol/L.如圖2所示,在丙酮/Cl-/PMS體系中加入Me和TBA后,對(duì)AO7的降解幾乎沒(méi)有影響,而加入NH4+后,AO7的降解受到明顯抑制.當(dāng)NH4+濃度增加到100mmol/L時(shí), AO7在20min內(nèi)的降解率從97%下降到19%.說(shuō)明在丙酮/Cl-/PMS體系中AO7的降解并不是自由基的作用,而是產(chǎn)生的HOCl氧化降解的結(jié)果.因此,丙酮對(duì)Cl-/PMS體系的促進(jìn)機(jī)理可能是催化作用.

為了進(jìn)一步證明丙酮對(duì)Cl-/PMS體系的催化作用,實(shí)驗(yàn)建立了以硫酸耐爾藍(lán)A為探針的熒光光譜法,體系最大激發(fā)和最大發(fā)射波長(zhǎng)分別位于634, 686nm處.實(shí)驗(yàn)基于在pH=2.0的緩沖溶液中,ClO-和熒光物質(zhì)分子硫酸耐爾藍(lán)A借助分子間作用力,在基態(tài)時(shí)生成不發(fā)光的配合物,從而導(dǎo)致熒光強(qiáng)度減弱,ClO-濃度與熒光猝滅程度成正比,通過(guò)測(cè)量熒光強(qiáng)度的猝滅程度判斷ClO-濃度[36-38].實(shí)驗(yàn)結(jié)果如圖3所示,在PMS、Cl-/PMS、丙酮/Cl-/PMS體系中檢測(cè)到的熒光猝滅強(qiáng)度依次增強(qiáng),說(shuō)明與PMS、Cl-/PMS體系相比,丙酮的加入使得反應(yīng)體系中HOCl的量增加,即丙酮在Cl-/PMS體系中催化Cl-和PMS產(chǎn)生更多HOCl,這與Gallopo等[32]報(bào)道的文獻(xiàn)結(jié)果一致.

圖2 叔丁醇、甲醇、NH4+對(duì)丙酮/Cl-/PMS體系降解AO7的影響

[AO7]=50μmol/L, [PMS]=1mmol/L, [Cl-]=10mmol/L,[丙酮]=10mmol/L, pH=9.0,= 20℃

圖3 體系的熒光光譜

[AO7]=50μmol/L, [PMS]=1mmol/L, [Cl-]=10mmol/L, [丙酮]=10mmol/L, pH=2.0,= 20℃

2.3 PMS濃度對(duì)AO7降解的影響

不同PMS濃度對(duì)降解AO7的影響如圖4(a)所示,PMS濃度從0增加到0.5mmol/L時(shí),AO7在20min內(nèi)的降解率增大了88%,當(dāng)PMS濃度增加到3mmol/L時(shí),AO7的降解率僅10min就達(dá)到了97%,如圖4(b)所示,通過(guò)動(dòng)力學(xué)擬合得出PMS降解AO7符合一級(jí)降解動(dòng)力學(xué),相應(yīng)的表觀速率常數(shù)分別為0、0.01304、0.10681、0.22994、0.39969min-1.結(jié)果表明,在一定范圍內(nèi),PMS濃度越高,AO7的降解效率就越快.但當(dāng)PMS濃度過(guò)高時(shí)(本實(shí)驗(yàn)取PMS濃度為10mmol/L),反應(yīng)速率沒(méi)有進(jìn)一步增大,且與PMS濃度為0.5mmol/L的反應(yīng)速率相當(dāng),相應(yīng)的AO7的表觀速率常數(shù)為0.14028min-1.原因可能是在PMS濃度過(guò)量的情況下,催化劑和Cl-的含量制約著反應(yīng)速率,部分PMS不能夠被及時(shí)活化而發(fā)生無(wú)效分解.

[AO7]=50μmol/L, [Cl-]=10mmol/L,[丙酮]=10mmol/L,pH=9.0,= 20℃

2.4 丙酮投加量對(duì)AO7降解的影響

丙酮投加量對(duì)AO7降解效率的影響如圖5(a)所示.當(dāng)投加量分別為0,5,10,20mmol/L時(shí),20min時(shí)AO7的降解率分別為41%、73%、96%、100%;繼續(xù)增大丙酮投加量至100mmol/L,AO7全部脫色僅需要10min.圖5(b)顯示了,AO7降解的表現(xiàn)速率常數(shù)與丙酮投加量的關(guān)系.可以看出,隨著丙酮投加量的增加,AO7的表現(xiàn)速率常數(shù)也在隨之增大.這說(shuō)明丙酮投加量增大,催化Cl-與PMS產(chǎn)生更多的活性氯物質(zhì),從而使AO7的降解效率及降解速率均有所升高.

[AO7]=50μmol/L, [PMS]=1mmol/L, [Cl-]=10mmol/L, pH=9.0,= 20℃

2.5 Cl-濃度對(duì)AO7降解的影響

保持其他試劑濃度以及反應(yīng)條件不變,考察不同Cl-濃度對(duì)AO7降解效果的影響.如圖6(a)所示,從圖6可以看出, Cl-濃度對(duì)AO7降解效果的趨勢(shì)與丙酮投加量相似.當(dāng)Cl-濃度從0增加到100mmol/L時(shí),AO7的降解率從35%增加到100%.圖6(b)顯示了, Cl-濃度對(duì)AO7降解符合一級(jí)降解動(dòng)力學(xué),AO7的表觀速率常數(shù)分別為0.02095、0.11471、0.18260、0.23335、0.26109、0.75005min-1.由此可知, Cl-濃度越高, Cl-與PMS產(chǎn)生的活性氯物種HOCl越多,丙酮/Cl-/PMS體系氧化降解AO7的速率越快.值得注意的是,當(dāng)Cl-濃度為0mmol/L時(shí),20min時(shí)AO7的降解率為35%,原因可能是丙酮催化PMS分解產(chǎn)生單線態(tài)氧分子(1O2)[39-40],對(duì)AO7起到一定的氧化降解作用.

[AO7]=50μmol/L, [PMS]=1mmol/L, [丙酮]=10mmol/L, pH=9.0,= 20℃

2.6 初始pH值的影響

pH值是影響PMS活化的重要因素,于是考查了不同初始pH值對(duì)丙酮/Cl-/PMS體系氧化降解AO7的影響.通過(guò)0.1mol/L的NaOH和稀硫酸調(diào)節(jié)反應(yīng)初始pH值,結(jié)果如圖7所示.從圖7可以看出,在初始pH值為5.0、6.0時(shí),AO7幾乎不發(fā)生降解;當(dāng)初始pH值為7.0、8.0、9.0時(shí),AO7的降解率分別為42%、46%、100%.由此得出,在pH值為5.0、6.0時(shí)的酸性環(huán)境下,AO7幾乎不脫色,隨反應(yīng)體系初始pH值的升高,染料AO7降解效果逐漸增加. Montgomery[40]曾研究丙酮催化PMS反應(yīng)的影響,得出在弱堿性環(huán)境下,丙酮可以更有效的催化PMS進(jìn)行一系列的反應(yīng).

圖7 初始pH值對(duì)丙酮/Cl-/PMS體系降解AO7的影響

[AO7]=50μmol/L, [PMS]=1mmol/L, [丙酮]=10mmol/L, pH=9.0,= 20℃

2.7 腐殖酸濃度的影響

圖8 HA濃度對(duì)丙酮/Cl-/PMS體系降解AO7的影響

[AO7]=50μmol/L, [PMS]=1mmol/L, [丙酮]=10mmol/L, [Cl-]=10mmol/L, pH=9.0,= 20℃

水體中含有大量的有機(jī)物,有研究表明自然水體中所含有的溶解性有機(jī)物質(zhì)(DOM)會(huì)對(duì)水體中污染物的降解有顯著影響[41].本實(shí)驗(yàn)選取腐殖酸作為研究對(duì)象,研究其在丙酮催化Cl-/PMS體系降解AO7中的作用.圖8給出了在保持其他試劑濃度及反應(yīng)條件不變的情況下,不同濃度的腐殖酸(HA)對(duì)丙酮/Cl-/PMS體系中AO7降解的影響情況.從圖中可以看出,當(dāng)HA的濃度分別為0,5,10,20mg/L時(shí), 20min時(shí)AO7的降解效率分別為100%、96%、95%、94%, AO7并未受到明顯的抑制作用,分析原因可能是: (1)AO7與腐殖酸之間作用力很弱,因此不會(huì)影響AO7;(2)由于PMS的存在,阻礙了腐殖酸與電子的結(jié)合.

2.8 AO7降解過(guò)程分析

圖9所示為丙酮/Cl-/PMS體系降解AO7過(guò)程中紫外可見(jiàn)光譜.從圖9可以看出,AO7主要有兩處特征吸收峰,分別位于可見(jiàn)光區(qū)484nm和紫外光區(qū)310nm處,有研究表明[42-44]484nm處對(duì)應(yīng)的是發(fā)色基團(tuán)偶氮鍵,310nm 處對(duì)應(yīng)的是萘環(huán)結(jié)構(gòu).隨著體系反應(yīng)的進(jìn)行,AO7在484nm 和310nm處的特征峰強(qiáng)度不斷下降,表明AO7的偶氮鍵和萘環(huán)結(jié)構(gòu)不斷被氧化斷裂,如前文所述,該氧化物質(zhì)即為HOCl,15min后,偶氮鍵和萘環(huán)的特征峰接近消失.

圖9 AO7降解的紫外可見(jiàn)光譜

[AO7]=50μmol/L, [PMS]=1mmol/L, [丙酮]=10mmol/L, [Cl-]=10mmol/L, pH=9.0,= 20℃

3 結(jié)論

3.1 在PMS體系中,丙酮或Cl-單獨(dú)存在,AO7在20min內(nèi)分別降解了0和38%,而當(dāng)丙酮和Cl-同時(shí)存在,AO7在20min內(nèi)降解了97%.由此可知,丙酮/Cl-協(xié)同活化PMS降解AO7的效果顯著,通過(guò)熒光光譜法可以證實(shí)丙酮催化Cl-/PMS產(chǎn)生更多的HOCl,使AO7脫色.

3.2 體系中的PMS濃度、丙酮濃度、Cl-濃度與AO7的降解率成正相關(guān);初始pH值對(duì)AO7的降解有較大的影響,弱堿性如pH=9條件下有利于反應(yīng)進(jìn)行;腐殖酸濃度分別為0,5,10,20mg/L時(shí),20min時(shí)AO7的降解效率分別為100%、96%、95%、94%.因此,腐殖酸的加入對(duì)AO7的降解幾乎不產(chǎn)生影響.

3.3 隨著體系反應(yīng)的進(jìn)行, AO7在484nm和310nm處的特征峰強(qiáng)度不斷下降,表明體系中產(chǎn)生的HOCl不斷氧化破壞AO7的偶氮鍵和萘環(huán)結(jié)構(gòu),從而達(dá)到降解的目的.

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Acetone and chloride ion Synergistically activate peroxymonosulfate to decolorize acid orange.

ZHANG Ke, XU Fen, CHEN Jia-bin*, WAN Ling, HUANG Tian-yin

(School of Enviromental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, China)., 2018,38(11)：4159~4165

Acetone and chloride ion (Cl-) were used to synergistically activate peroxymonosulfate (PMS) to decolorize the azo dye, acid orange 7 (AO7). It was found that the first-order rate constant increased from 0.0767 to 0.1725min-1when acetone was added in Cl-/PMS systemIn the acetone/Cl-/PMS system, effect of various factors were explored, including initial pH, Cl-concentration, PMS and acetone dosage. The results indicated that the degradation of AO7 increased with the increase of Cl-、PMS、acetone concentration under alkaline conditions. The degradation mechanism of AO7 in acetone /Cl-/PMS system showed that neither sulfate radical(SO－ 4?) nor hydroxyl(HO?) was produced therein. Instead, the HOCl concentration was proved to be increased during the reaction. Hence, acetone could promote the reaction between PMS and Cl-to generate more HOCl. From the analysis of UV-vis spectra, the azo bond and naphthalene ring in AO7 was found being destructed.

chloride ion；peroxymonosulfate；acetone；acid orange 7；hypochlorous acid

X703.1

A

1000-6923(2018)11-4159-07

張 珂(1993-),女,安徽太和人,碩士研究生,主要研究方向?yàn)槲鬯幚砼c回用技術(shù).發(fā)表論文1篇.

2018-04-18

國(guó)家自然科學(xué)基金資助項(xiàng)目(51478283);江蘇省研究生實(shí)踐創(chuàng)新計(jì)劃項(xiàng)目(SJCX17_0677)

* 責(zé)任作者, 講師, chenjiabincn@163.com