丙酮/氯離子協同活化過一硫酸鹽降解酸性橙

2018-11-28 03:47陳家斌黃天寅

中國環境科學 2018年11期

張珂,許芬,陳家斌,萬玲,黃天寅

張珂,許芬,陳家斌*,萬玲,黃天寅

(蘇州科技大學環境科學與工程學院,江蘇蘇州 215009)

采用丙酮/氯離子(Cl-)協同活化過一硫酸鹽(PMS)降解偶氮染料酸性橙7(AO7).研究發現,與Cl-/PMS體系相比,丙酮/Cl-/PMS體系降解AO7的效果顯著增強,相應的AO7表觀速率常數從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).結果表明,在堿性環境下,隨著Cl-、PMS和丙酮濃度的增加,AO7的降解效果有所增強;研究丙酮/Cl-/PMS體系降解AO7的降解機制.自由基猝滅實驗表明,丙酮/Cl-/PMS體系中沒有自由基(硫酸根自由基(SO4－?)和羥基自由基(HO?))的產生,而次氯酸根(ClO-)濃度在反應過程中逐漸增加,得出丙酮作為催化劑促進Cl-和PMS產生更多HClO的結論.通過紫外可見光譜分析,表明AO7分子中偶氮鍵及萘環結構均被破壞.

氯離子；過一硫酸鹽；丙酮；酸性橙7；次氯酸

偶氮染料廣泛用于現代工業中,如紡織、造紙、制革等行業.由于偶氮染料具有毒性強、含鹽量高、致癌、致突變等特點[1-3],若不經處理直接排放會對環境和人類健康造成嚴重危害.大多數偶氮染料可生化性不高,成分復雜,屬于生物難降解,傳統的廢水處理技術已無法滿足染料廢水的處理要求[4-6].近年來,基于硫酸根自由基(SO－ 4?)的高級氧化技術已得到廣泛應用[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],可以通過加熱[12-14]、紫外光照射[15-17]、過渡金屬離子[18-21]活化過一硫酸鹽(PMS)產生.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.過渡金屬離子雖然有易獲取、成本低等優點[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用[24].因此,新型過硫酸鹽活化方法的研究成為目前過硫酸鹽高級氧化技術(AOPs)研究的熱點.

氯離子(Cl-)是印染廢水中主要的無機成分.據報道,染料廢水中含有的無機鹽(NaCl)等可高達5~100mg/L[25-26].大量研究表明,氯離子(Cl-)對AOPs有很大影響[27-30].通過研究Cl-對鈷/單過硫酸鹽體系降解偶氮染料的影響,發現低濃度的Cl-(<5mmol/L)對染料脫色有明顯的抑制作用,高濃度Cl-(>50mmol/L)對染料降解的抑制作用會不斷減小,甚至會加速染料的脫色[30].

通過研究Cl-濃度對單獨PMS體系降解金橙G(OG)的影響,得出Cl-與PMS反應產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活化過程中廢水基質(如Cl-)所起到的作用對于該技術用于染料廢水處理具有重要意義.

本文在研究新型過硫酸鹽活化方法的過程中,發現丙酮/Cl-可以協同活化PMS,加速染料降解.通過改變反應條件,研究了丙酮/Cl-/PMS體系的主要影響因素,并通過自由基猝滅實驗及采用熒光猝滅法分析了丙酮/Cl-/PMS體系降解AO7中可能存在的機制.

1 試劑與方法

1.1 實驗試劑與設備

過一硫酸鹽(HKSO5· 0.5KHSO4· 0.5K2SO4, PMS)、硫酸耐爾藍A(C40H40N6O6S)、曲拉通X- 100((C2H4O)NC14H22O)購于Sigma-Aldrich; 酸性橙7(AO7)購于國藥集團化學試劑有限公司,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)均為分析純購于國藥集團化學試劑有限公司.實驗用水為超純水.實驗用攪拌裝置購于上海標本模型廠(JB50-D型).

1.2 降解實驗

在室溫下,將一定量PMS和NaCl注入150mL的錐形瓶中,同時在錐形瓶中加入一定量的超純水,并用稀H2SO4或NaOH調節pH值,然后迅速加入一定量的丙酮和一定量的AO7溶液,使得總溶液達到100mL,反應體系密封后置于磁力攪拌器混合并啟動反應.每隔一段時間取樣,迅速加入過量猝滅劑NaNO2終止反應,猝滅后的樣品經0.45μm濾膜過濾后,收集濾液24h內測定,每組實驗均重復3次以確保實驗的重現性,最終結果取三次平均值.

1.3 分析方法

使用Mapada UV-1600(PC)紫外可見分光光度計,于AO7最大吸收波長484nm處測定濾液的吸光度,代入標準曲線求得濃度.次氯酸根濃度采用PerkinElmer LS55熒光分光光度計測定,熒光吸收波長為686nm,激發波長為634nm.應用Excel2016、Origin9.0進行數據分析和作圖

2 結果與討論

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.結果表明,PMS單獨存在時,AO7在20min內降解了21%,丙酮單獨存在時,AO7在20min內幾乎不降解.在PMS體系中加入Cl-,AO7在20min內降解了38%;而在Cl-/PMS體系中加入丙酮,AO7在20min內降解了97%.分析原因可能是,Cl-和PMS反應產生HOCl和Cl2,而丙酮催化Cl-/PMS體系產生更多HOCl[見式(1)~(4)][4,32]. HOCl具有強氧化性,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

+ Cl

→ SO

+ HOCl (1)

HSO

+ 2Cl

→ SO

+ Cl

+ H

O (2)

HOCl → ClO

+ H

(3)

HSO

+ Cl

OCl

+ H

+ SO

(4)

2.2 丙酮/Cl-/PMS體系對AO7的降解機制

為了確定丙酮/Cl-/PMS體系降解AO7的反應機理,向反應體系中加入自由基(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AO7的降解幾乎沒有影響,而加入NH4+后,AO7的降解受到明顯抑制.當NH4+濃度增加到100mmol/L時, AO7在20min內的降解率從97%下降到19%.說明在丙酮/Cl-/PMS體系中AO7的降解并不是自由基的作用,而是產生的HOCl氧化降解的結果.因此,丙酮對Cl-/PMS體系的促進機理可能是催化作用.

為了進一步證明丙酮對Cl-/PMS體系的催化作用,實驗建立了以硫酸耐爾藍A為探針的熒光光譜法,體系最大激發和最大發射波長分別位于634, 686nm處.實驗基于在pH=2.0的緩沖溶液中,ClO-和熒光物質分子硫酸耐爾藍A借助分子間作用力,在基態時生成不發光的配合物,從而導致熒光強度減弱,ClO-濃度與熒光猝滅程度成正比,通過測量熒光強度的猝滅程度判斷ClO-濃度[36-38].實驗結果如圖3所示,在PMS、Cl-/PMS、丙酮/Cl-/PMS體系中檢測到的熒光猝滅強度依次增強,說明與PMS、Cl-/PMS體系相比,丙酮的加入使得反應體系中HOCl的量增加,即丙酮在Cl-/PMS體系中催化Cl-和PMS產生更多HOCl,這與Gallopo等[32]報道的文獻結果一致.

圖2 叔丁醇、甲醇、NH4+對丙酮/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AO7降解的影響

不同PMS濃度對降解AO7的影響如圖4(a)所示,PMS濃度從0增加到0.5mmol/L時,AO7在20min內的降解率增大了88%,當PMS濃度增加到3mmol/L時,AO7的降解率僅10min就達到了97%,如圖4(b)所示,通過動力學擬合得出PMS降解AO7符合一級降解動力學,相應的表觀速率常數分別為0、0.01304、0.10681、0.22994、0.39969min-1.結果表明,在一定范圍內,PMS濃度越高,AO7的降解效率就越快.但當PMS濃度過高時(本實驗取PMS濃度為10mmol/L),反應速率沒有進一步增大,且與PMS濃度為0.5mmol/L的反應速率相當,相應的AO7的表觀速率常數為0.14028min-1.原因可能是在PMS濃度過量的情況下,催化劑和Cl-的含量制約著反應速率,部分PMS不能夠被及時活化而發生無效分解.

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

2.4 丙酮投加量對AO7降解的影響

丙酮投加量對AO7降解效率的影響如圖5(a)所示.當投加量分別為0,5,10,20mmol/L時,20min時AO7的降解率分別為41%、73%、96%、100%;繼續增大丙酮投加量至100mmol/L,AO7全部脫色僅需要10min.圖5(b)顯示了,AO7降解的表現速率常數與丙酮投加量的關系.可以看出,隨著丙酮投加量的增加,AO7的表現速率常數也在隨之增大.這說明丙酮投加量增大,催化Cl-與PMS產生更多的活性氯物質,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AO7降解的影響

保持其他試劑濃度以及反應條件不變,考察不同Cl-濃度對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AO7降解效果的趨勢與丙酮投加量相似.當Cl-濃度從0增加到100mmol/L時,AO7的降解率從35%增加到100%.圖6(b)顯示了, Cl-濃度對AO7降解符合一級降解動力學,AO7的表觀速率常數分別為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Cl-濃度為0mmol/L時,20min時AO7的降解率為35%,原因可能是丙酮催化PMS分解產生單線態氧分子(1O2)[39-40],對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值對丙酮/Cl-/PMS體系氧化降解AO7的影響.通過0.1mol/L的NaOH和稀硫酸調節反應初始pH值,結果如圖7所示.從圖7可以看出,在初始pH值為5.0、6.0時,AO7幾乎不發生降解;當初始pH值為7.0、8.0、9.0時,AO7的降解率分別為42%、46%、100%.由此得出,在pH值為5.0、6.0時的酸性環境下,AO7幾乎不脫色,隨反應體系初始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反應的影響,得出在弱堿性環境下,丙酮可以更有效的催化PMS進行一系列的反應.

圖7 初始pH值對丙酮/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物,有研究表明自然水體中所含有的溶解性有機物質(DOM)會對水體中污染物的降解有顯著影響[41].本實驗選取腐殖酸作為研究對象,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條件不變的情況下,不同濃度的腐殖酸(HA)對丙酮/Cl-/PMS體系中AO7降解的影響情況.從圖中可以看出,當HA的濃度分別為0,5,10,20mg/L時, 20min時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,因此不會影響AO7;(2)由于PMS的存在,阻礙了腐殖酸與電子的結合.

2.8 AO7降解過程分析

圖9所示為丙酮/Cl-/PMS體系降解AO7過程中紫外可見光譜.從圖9可以看出,AO7主要有兩處特征吸收峰,分別位于可見光區484nm和紫外光區310nm處,有研究表明[42-44]484nm處對應的是發色基團偶氮鍵,310nm 處對應的是萘環結構.隨著體系反應的進行,AO7在484nm 和310nm處的特征峰強度不斷下降,表明AO7的偶氮鍵和萘環結構不斷被氧化斷裂,如前文所述,該氧化物質即為HOCl,15min后,偶氮鍵和萘環的特征峰接近消失.

圖9 AO7降解的紫外可見光譜

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

3 結論

3.1 在PMS體系中,丙酮或Cl-單獨存在,AO7在20min內分別降解了0和38%,而當丙酮和Cl-同時存在,AO7在20min內降解了97%.由此可知,丙酮/Cl-協同活化PMS降解AO7的效果顯著,通過熒光光譜法可以證實丙酮催化Cl-/PMS產生更多的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;初始pH值對AO7的降解有較大的影響,弱堿性如pH=9條件下有利于反應進行;腐殖酸濃度分別為0,5,10,20mg/L時,20min時AO7的降解效率分別為100%、96%、95%、94%.因此,腐殖酸的加入對AO7的降解幾乎不產生影響.

3.3 隨著體系反應的進行, AO7在484nm和310nm處的特征峰強度不斷下降,表明體系中產生的HOCl不斷氧化破壞AO7的偶氮鍵和萘環結構,從而達到降解的目的.

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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

1000-6923(2018)11-4159-07

張珂(1993-),女,安徽太和人,碩士研究生,主要研究方向為污水處理與回用技術.發表論文1篇.

2018-04-18

國家自然科學基金資助項目(51478283);江蘇省研究生實踐創新計劃項目(SJCX17_0677)

* 責任作者, 講師, chenjiabincn@163.com