張黎明,陳家斌,房 聰,周 露,胡金梅,郝尚斌,李文衛(wèi),王忠明,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 5009；.中國(guó)科學(xué)技術(shù)大學(xué)化學(xué)與材料科學(xué)學(xué)院,安徽 合肥 3006)

Cl-對(duì)碳納米管/過(guò)一硫酸鹽體系降解金橙G的影響

張黎明1,陳家斌1,房 聰1,周 露1,胡金梅1,郝尚斌1,李文衛(wèi)2,王忠明1,黃天寅1*(1.蘇州科技大學(xué)環(huán)境科學(xué)與工程學(xué)院,江蘇 蘇州 215009；2.中國(guó)科學(xué)技術(shù)大學(xué)化學(xué)與材料科學(xué)學(xué)院,安徽 合肥 230026)

采用碳納米管(CNT)活化過(guò)一硫酸鹽(PMS)的方法產(chǎn)生自由基,研究氯離子(Cl-)對(duì)CNT/PMS體系氧化降解金橙G(OG)的影響.發(fā)現(xiàn)Cl-對(duì)CNT/PMS體系氧化降解OG的過(guò)程具有雙重影響,低濃度Cl-會(huì)抑制OG的脫色,高濃度Cl-會(huì)促進(jìn)OG的脫色;無(wú)CNT存在時(shí)Cl-會(huì)直接與PMS作用使OG脫色.研究了CNT/PMS/Cl-體系降解OG的主要影響因素(PMS濃度、反應(yīng)溫度、OG初始濃度、Cl-濃度、初始pH)和反應(yīng)機(jī)制,結(jié)果表明PMS濃度為1.6mmol/L、反應(yīng)溫度為25℃時(shí)、OG初始濃度為0.8mmol/L、Cl-濃度為50mmol/L和pH=7的條件下, 25min內(nèi)OG脫色率可達(dá)到100%,反應(yīng)體系的活化能為88.45kJ/mol;隨著初始pH升高, OG脫色率先減后升,降解OG的活性物質(zhì)為和HOCl.對(duì)OG降解過(guò)程的礦化率分析表明,CNT存在條件下OG的礦化率要比無(wú)CNT存在時(shí)要好;然后通過(guò)紫外可見掃描光譜掃描和GC-MS分析,發(fā)現(xiàn)OG分子中偶氮鍵及萘環(huán)結(jié)構(gòu)被破壞后,生成了其他小分子物質(zhì).

碳納米管；Cl-；過(guò)一硫酸鹽；金橙G；脫色率

偶氮染料是分子結(jié)構(gòu)中含有一個(gè)或者多個(gè)偶氮基(—N=N—)的染料,是紡織、造紙、制革等工業(yè)常用染料,其生產(chǎn)廢水具有毒性、致突變、致癌、難降解等特點(diǎn)[1-3],不經(jīng)處理直接排放會(huì)對(duì)環(huán)境造成嚴(yán)重污染.偶氮染料廢水的常用的處理方法有吸附[4-5]、絮凝[6-7]、光催化[8-9]、臭氧化[10]

等.其中吸附和絮凝方法處理偶氮染料廢水可使偶氮染料分子轉(zhuǎn)移至吸附劑或絮凝劑去除,但是偶氮染料沒(méi)有得到降解和礦化;光催化和臭氧化對(duì)偶氮染料脫色的同時(shí)有降解和礦化的效果,但是他們也存在一些缺陷,比如光催化劑的效率低、穩(wěn)定性差、有毒性以及不易回收利用等,臭氧氧化對(duì)設(shè)備要求高、易產(chǎn)生有毒有害物質(zhì)等.

偶氮染料廢水普遍具有含鹽量高的特點(diǎn)[28],探索廢水基質(zhì)(如Cl-)在PMS活化過(guò)程中的作用對(duì)于將該技術(shù)用于染料廢水處理具有重要的意義.徐蕾等[29]報(bào)道了 Cl-對(duì)鈷/單過(guò)硫酸鹽體系降解 2,4,6-三氯苯酚(2,4,6-TCP)的影響,發(fā)現(xiàn)低濃度Cl-(0～10mmol/L)會(huì)與·反應(yīng)生成·,抑制2,4,6-TCP的降解,而高濃度Cl-(＞100mmol/L)會(huì)直接與單過(guò)硫酸鹽反應(yīng)產(chǎn)生 HOCl,促進(jìn)2,4,6-TCP的降解;本文在CNT活化PMS降解OG的基礎(chǔ)上,研究了Cl-對(duì)CNT/PMS體系降解OG過(guò)程的影響,并分析了其可能存在的機(jī)制以及主要影響因素.

1 材料與方法

1.1 材料與試劑

CNT(含量 95%,內(nèi)直徑 2～5nm,長(zhǎng)度 10～30μm)購(gòu)于南京先豐納米材料科技有限公司,過(guò)一硫酸鹽(KHSO5·0.5KHSO4·0.5K2SO4,PMS)購(gòu)于Sigma-Aldrich;金橙G(OG)購(gòu)于國(guó)藥集團(tuán)化學(xué)試劑有限公司,化學(xué)結(jié)構(gòu)式如圖 1所示,氯化鈉(NaCl)、亞硝酸鈉(NaNO2)、甲醇(CH3OH )、硫酸銨[(NH4)2·SO4]、氫氧化鈉(NaOH)、硫酸(H2SO4)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.

1.2 降解實(shí)驗(yàn)

在一定的溫度下,將一定量PMS和NaCl注入250mL的錐形瓶中,同時(shí)往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CNT和一定量的OG溶液,使得總?cè)芤哼_(dá)到250mL,采用磁力攪拌混合啟動(dòng)反應(yīng).每隔一段時(shí)間取樣,迅速加入過(guò)量淬滅劑NaNO2終止反應(yīng),猝滅后的樣品經(jīng) 0.45μm濾膜過(guò)濾后,收集濾液待后續(xù)測(cè)定.

圖1 金橙G的化學(xué)結(jié)構(gòu)式Fig.1 Molecule structure of Orange G

1.3 分析方法

使用Mapada UV-1600(PC)紫外可見分光光度計(jì),于OG最大吸收波長(zhǎng)479nm處測(cè)定濾液的吸光度,代入標(biāo)準(zhǔn)曲線求得濃度C.TOC采用總有機(jī)碳分析儀(TOC-LCPH,島津)測(cè)定.

降解產(chǎn)物采用 GC/MS測(cè)試分析,儀器型號(hào)為Agilent 7890A/5975C,色譜柱為HP-5毛細(xì)管柱(30m×320μm×0.25μm).質(zhì)譜檢測(cè)器(MSD)采用EI電離源(70eV),離子源溫度為 230℃.載氣(He)流量為 1.0mL/min,進(jìn)樣量 1μL,進(jìn)樣口溫度為250℃,采用不分流模式.升溫程序如下:40℃保持2min,然后以12℃/min的速率升溫到100℃,再以5℃/min的速率升溫到200℃,最后以20℃/min升溫到 270℃保持 5min.降解產(chǎn)物的鑒定采用Nist-11標(biāo)準(zhǔn)圖庫(kù),匹配度大于90%.

2 結(jié)果與討論

2.1 不同初始條件對(duì)OG的降解性能和機(jī)制

從圖2可看出,45min內(nèi)CNT單獨(dú)吸附體系OG的脫色率僅為9%,PMS單獨(dú)氧化體系OG的脫色率僅為5%,而PMS和CNT一起作用時(shí)OG的脫色率明顯增加,達(dá)到 85%;然后往 CNT/PMS體系加入Cl-,發(fā)現(xiàn)OG的脫色率會(huì)受到影響,當(dāng)Cl-濃度為10mmol/L時(shí),OG的脫色率受到抑制,減少到75%,而Cl-濃度增加到100mmol/L時(shí),OG的脫色效率顯著提高,僅15min就達(dá)到了100%,同時(shí)發(fā)現(xiàn)往單獨(dú)PMS體系里加入Cl-(100mmol/L),45min仍可使OG的脫色率達(dá)到100%,高于CNT/PMS體系的85%.

圖2 不同初始條件下Cl-濃度對(duì)OG脫色效率的影響Fig.2 Effect of chloride ion on the degradation of OGpH=7.0,T=298K,C(OG)=0.08mmol/L,C(CNT)=0.1g/L, C(PMS)=1.6mmol/L

由此得出,Cl-對(duì)CNT/PMS體系氧化降解OG具有雙重作用,即低濃度Cl-會(huì)抑制OG降解,高濃度Cl-會(huì)促進(jìn)OG的降解,且單獨(dú)PMS體系中加入 Cl-(100mmol/L)也能高效的氧化降解OG.Wang等[30]曾研究Cl-對(duì)Co2+/PMS體系降解AO7的影響,得出 Cl-濃度較低時(shí),Cl-會(huì)與·反應(yīng)生成氧化性較低的·,使AO7的降解受到抑制,而Cl-濃度提高時(shí),Cl-會(huì)直接與PMS反應(yīng)生成HOCl,在·和 HOCl的共同作用下,使得AO7的降解速率大大提高.同樣Cl-對(duì)CNT/PMS體系氧化降解OG具有雙重作用的原因,可能也是低濃度的 Cl-會(huì)與·反應(yīng)生成氧化性較小的物質(zhì),而高濃度的Cl-會(huì)直接與PMS反應(yīng)生成HOCl 氧化降解 OG.同時(shí)比較加入 100mmol/L Cl-的CNT/PMS體系和單獨(dú)PMS體系,后者仍可使OG快速脫色,說(shuō)明外加Cl-可以和PMS直接反應(yīng)并對(duì)OG進(jìn)行降解,同時(shí)該條件下OG的脫色率要小于有CNT存在時(shí)發(fā)生的自由基反應(yīng).

圖3 甲醇和對(duì)Cl-/CNT/PMS體系降解OG的影響Fig.3 Effect of methanol andon the degradation of OG in the Cl-/CNT/PMS systempH=7.0,T=298K,C(OG)=0.08mmol/L,C(CNT)=0.1g/L, C(PMS)=1.6mmol/L

為了驗(yàn)證CNT/PMS/Cl-體系降解OG的機(jī)理,往反應(yīng)體系中加入自由基(·、OH-·)淬滅劑甲醇[31]和HOCl淬滅劑加入的甲醇和濃度分別為0.16mol/L和100mmol/L.如圖3a所示,往 CNT/PMS/Cl-體系中添加 0.16mol/L甲醇淬滅反應(yīng),發(fā)現(xiàn)體系中無(wú)Cl-存在時(shí),OG的降解受到明顯抑制,脫色率從85%下降到29%,而隨著Cl-的加入CNT/PMS/Cl-體系降解OG的速率又開始提高,當(dāng) Cl-濃度分別為 50,75,100mmol/L時(shí),OG的脫色率均達(dá)到100%,且脫色速率分別為0.0725,0.2657,0.3516min-1.由此可知,在無(wú) Cl-的CNT/PMS/Cl-體系中,·幾乎被甲醇淬滅,導(dǎo)致OG 的脫色效果快速下降,而加入 Cl-的CNT/PMS/Cl-體系,由于 Cl-會(huì)直接與 PMS反應(yīng)產(chǎn)HOCl,盡管·被甲醇淬滅無(wú)法降解OG,但是HOCl不受甲醇影響,仍然可使OG脫色,且Cl-濃度越高產(chǎn)生的HOCl就越多,OG的脫色效果就越好.

為了進(jìn)一步證明CNT/PMS/Cl-體系降解OG的效果不受甲醇的影響,向反應(yīng)體系中同時(shí)加入甲醇和,如圖3b所示, OG的脫色率顯著下降,均小于32%,與圖3a僅加入甲醇時(shí)OG的脫色效率對(duì)比,發(fā)現(xiàn)加入甲醇和時(shí),Cl-濃度在0～100mmol/L范圍內(nèi),OG脫色反應(yīng)均被抑制;而僅加入甲醇時(shí),在Cl-濃度在0mmol/L時(shí),OG降解反應(yīng)被抑制,而Cl-濃度在50～100mmol/L,OG脫色反應(yīng)沒(méi)有受到抑制;說(shuō)明除了·外還存在別的氧化物(HOCl)可以使OG脫色,且這種氧化物(HOCl)可被淬滅,進(jìn)一步證明其就是HOCl.

2.2 PMS濃度和OG初始濃度對(duì)OG降解的影響

如圖 4a所示,PMS濃度從 0增加到1.6mmol/L,OG脫色率增大了83% ,PMS濃度為2.4mmol/L時(shí),僅15min OG脫色率就達(dá)到100%,通過(guò)動(dòng)力學(xué)擬合得出OG脫色的表觀速率常數(shù)k分別為 0.0011、0.0135、0.0544、0.1415、0.3609min-1.結(jié)果表明,PMS濃度越高OG脫色效率越快,即PMS濃度提高使得CNT活化PMS產(chǎn)生·或Cl-與PMS作用產(chǎn)生HOCl的效率增加,更有利于對(duì)偶氮染料OG的氧化降解.

由圖4b可看出OG初始濃度從0.04升高到0.8mmol/L,45min后偶氮染料OG脫色率從100%減少為21%,且OG脫色的表觀速率常數(shù)k也從0.2939減小為0.0027min-1.可知OG脫色效率隨著 OG初始濃度升高而降低;分析原因,可能是OG降解過(guò)程中的降解產(chǎn)物和礦化產(chǎn)物過(guò)多,與目標(biāo)污染物(OG)對(duì)·或HOCl形成競(jìng)爭(zhēng);也可能是反應(yīng)過(guò)程中活化產(chǎn)生·和HOCl的速率一定,當(dāng)OG的濃度較高時(shí),多余的OG分子無(wú)法被·或HOCl氧化降解.

圖4 PMS濃度和OG初始濃度對(duì)Cl-/CNT/PMS體系降解OG的影響Fig.4 Effect of PMS and OG initial concentration on the degradation of OG in the Cl-/CNT/PMS systempH=7.0,T=298K,C(Cl-)=50mmol/L,C(CNT)=0.1g/L

2.3 Cl-濃度對(duì)OG降解速率的影響

不同Cl-濃度對(duì)CNT/PMS/Cl-體系氧化降解OG的影響,如圖 5a所示,Cl-濃度分別為 0,5,10, 25,50,75,100mmol/L時(shí),45min后OG的脫色率分別為85%、83%、75%、99%、100%、100%、100%;圖5b顯示了, OG脫色的表觀速率常數(shù)K與Cl-濃度的關(guān)系.

結(jié)果表明,Cl-濃度在0～10mmol/L范圍內(nèi)時(shí), OG的脫色效率明顯受到抑制,Cl-濃度在 25～100mmol/L范圍內(nèi)時(shí),OG的脫色效率顯著增加,且隨著Cl-濃度增大而變快;結(jié)合2.1節(jié)的結(jié)論分析可知,Cl-濃度低時(shí) CNT/PMS/Cl-體系產(chǎn)生的·與 Cl-反應(yīng)變成氧化性較低的·,即部分的·被·取代,由于·對(duì)OG的脫色效率要小于·,使得OG的脫色率下降,而Cl-濃度高時(shí)Cl-可直接與PMS反應(yīng)產(chǎn)生HOCl使OG脫色,且Cl-濃度越高與PMS作用產(chǎn)生的HOCl越多,對(duì)OG的脫色效率就越高.

圖5 Cl-濃度對(duì)CNT/PMS體系降解OG動(dòng)力學(xué)及其表觀速率常數(shù)的影響Fig.5 Effect of chloride ion on kinetics and apparent rate constant for degradation of OG in the CNT/PMS systempH=7.0,T=298K,C(OG)=0.08mmol/L,C(CNT)=0.1g/L, C(PMS)=1.6mmol/L

2.4 無(wú)CNT存在 Cl-濃度對(duì)OG降解速率的影響

前文對(duì)圖2的分析已表明,在無(wú)CNT存在的條件下,Cl-能自發(fā)地與PMS反應(yīng)降解OG,為了研究Cl-濃度對(duì)PMS/Cl-體系降解OG過(guò)程的影響,控制pH值為7.0,溫度為298K,OG和PMS濃度分別為0.08mmol/L和1.6mmol/L,改變PMS/Cl-體系中Cl-濃度,觀察OG的脫色率變化情況.從圖6 可看出,Cl-濃度分別為 0,5,10,25,50,75, 100mmol/L時(shí),45min后OG的脫色率分別為5%、3%、43%、41%、82%、100%、100%.

圖6 Cl-濃度對(duì)單獨(dú)PMS體系降解OG的影響Fig.6 Effect of chloride ion on the degradation of OG in the PMS systempH=7.0,T=298K,C(OG)=0.08mmol/L,C(PMS)=1.6mmol/L

結(jié)果表明,基本上Cl-濃度越高PMS/Cl-體系氧化降解OG的速率越快,表明無(wú)CNT存在的條件下,Cl-能自發(fā)地與 PMS反應(yīng)產(chǎn)生活性氯物質(zhì)降解OG,Lou等[33]研究得出Cl-與PMS反應(yīng)產(chǎn)生活性氯物質(zhì)的反應(yīng),其反應(yīng)方程式如下:

體系中產(chǎn)生 HOCl是具有氧化活性的鹵化物,能夠直接迅速氧化降解OG.

2.5 初始pH值對(duì)OG降解的影響

如圖7所示,反應(yīng)初始pH分別為2、4、6、8、10時(shí),CNT/PMS/Cl-體系對(duì)OG的脫色率分別為97%、89%、91%、92%、100%,隨反應(yīng)體系初始pH值升高,染料OG降解效果是一個(gè)先減后升的過(guò)程.

已知 CNT/PMS/Cl-體系中產(chǎn)生的氧化物質(zhì)為·和HOCl,其中HOCl為弱酸性物質(zhì),隨著pH(2～8)升高會(huì)電離成ClO-和H+,而ClO-的氧化性要小于HOCl,使得氧化降解OG的速率下降;而pH=10時(shí),在強(qiáng)堿性條件下PMS可自發(fā)產(chǎn)生·[34],使得反應(yīng)體系中生成的·量增加,表現(xiàn)為 OG氧化降解速率提高;另外 pH為 4～8時(shí),OG氧化降解效果可能與CNT表面零電荷點(diǎn)(pHpzc)有關(guān),經(jīng)測(cè)得 CNT的 pHpzc為 7.2,當(dāng)溶液pH＜pHpzc時(shí),CNT表面為正電性,有利于陰離子染料OG的吸附;當(dāng)溶液pH＞pHpzc時(shí),CNT表面為負(fù)電性,不有利于陰離子染料 OG的吸附;在pH值為4、6時(shí),吸附到CNT表面的OG分子,會(huì)阻止CNT與PMS有效接觸,不利于·的產(chǎn)生,使得氧化降解 OG的速率下降;而 pH=8時(shí),CNT表面為負(fù)電性,不利于染料 OG吸附,使得CNT接觸活化PMS產(chǎn)生·的機(jī)率變大,進(jìn)而加快OG氧化降解速率.

圖7 初始pH對(duì)Cl-/CNT/PMS體系降解OG的影響Fig.7 Effect of initial pH on the degradation of OG in the Cl-/CNT/PMS systemT=298K,C(OG)=0.08mmol/L,C(CNT)=0.1g/L, C(Cl-)=0.1g/L, C(PMS)=1.6mmol/L

2.6 反應(yīng)溫度對(duì)OG降解的影響

為了研究溫度對(duì)CNT/PMS/Cl-降解OG的影響,反應(yīng)過(guò)程中控制 pH值為 7.0,OG、Cl-和PMS濃度分別為0.08,50,1.6mmol/L,CNT投加量為0.1g/L.如圖8a和圖8b所示,反應(yīng)溫度從25℃升高到55℃的過(guò)程中,20min后CNT/PMS/Cl-體系對(duì)OG的脫色率均達(dá)到100%,且隨著溫度升高降解OG的表觀速率常數(shù)k越來(lái)越大.說(shuō)明提高溫度有利于反應(yīng)的進(jìn)行,分析原因可能是提高溫度加大反應(yīng)體系中分子的運(yùn)動(dòng)速率,使得生成·和 HOCl速率變快,并且·和HOCl與OG分子的接觸頻率也更快.假設(shè)k與溫度間存在如下關(guān)系:

圖8 反應(yīng)溫度對(duì)Cl-/CNT/PMS體系降解OG的影響Fig.8 Effect of reaction temperature on the degradation of OG in the Cl-/CNT/PMS systempH=7.0,C(OG)=0.08mmol/L,C(CNT)=0.1g/L, C(PMS)=1.6mmol/L

對(duì)ln(K)和1/T進(jìn)行線性擬合,得到的直線的斜率為-10638.33,即-Ea/R的值,R的值已知,可以求出反應(yīng)過(guò)程中的活化能為88.45kJ/mol.

2.7 外加Cl-對(duì)CNT/PMS/Cl-體系TOC去除的影響

為研究 Cl-對(duì) CNT/PMS/Cl-體系氧化降解OG 礦化度的影響,實(shí)驗(yàn)對(duì)比了不同 Cl-濃度下,CNT存在和無(wú)CNT的CNT/PMS/Cl-體系氧化降解OG的礦化率.由圖9a可見,CNT存在的條件下,當(dāng)Cl-濃度分別為0,25,50,75,100mmol/L時(shí),OG的礦化率分別是28.1%、23.2%、19.5%、19.2%、19.6%.可知隨著Cl-濃度增加OG的礦化率在下降,分析原因可能是 CNT/PMS/Cl-體系同時(shí)發(fā)生CNT活化PMS產(chǎn)生·的自由基反應(yīng)和Cl-與PMS反應(yīng)產(chǎn)生HOCl的非自由基反應(yīng),兩種反應(yīng)產(chǎn)生的·和HOCl降解OG的礦化效果強(qiáng)弱不同所致,由于 Cl-濃度提高會(huì)導(dǎo)致CNT/PMS/Cl-體系中產(chǎn)生HOCl的數(shù)量增多,在氧化降解 OG的過(guò)程占的比重變大,而·占的比重變小,雖然最終結(jié)果是 OG的脫色率都達(dá)到100%(圖5a),但是Cl-濃度增加導(dǎo)致OG的礦化率變小,說(shuō)明HOCl對(duì)OG礦化效果比·要差.

圖9 不同Cl-濃度對(duì)CNT/PMS和單獨(dú)PMS體系降解OG礦化度的影響Fig.9 Effect of chloride ion on TOC changes for degradation of OG in the CNT/PMS and PMS systempH=7.0,T=298K,C(OG)=0.08mmol/L, C(Cl-)=50mmol/L, C(PMS)=1.6mmol/L

無(wú)CNT的條件下,當(dāng)Cl-濃度分別為0,25,50, 75,100mmol/L時(shí),PMS/Cl-體系對(duì)OG的礦化率分別是7.7%、9.8%、9.9%、11.1%(圖9b).盡管隨著Cl-濃度增加OG的礦化率在增加,但是在相同Cl-濃度的條件下,PMS/Cl-體系對(duì) OG的礦化效果要明顯弱于 CNT/PMS/Cl-體系,原因可能是CNT/PMS/Cl-體系同時(shí)發(fā)生CNT活化PMS產(chǎn)生·的自由基反應(yīng)和Cl-與PMS反應(yīng)產(chǎn)生HOCl的非自由基反應(yīng),其中前者更有利于OG的礦化,而PMS/Cl-體系只存在產(chǎn)生HOCl的非自由基反應(yīng),導(dǎo)致OG的礦化率不如CNT/PMS/Cl-體系,由此可知 CNT/PMS/Cl-體系中發(fā)生的自由基反應(yīng)更有利OG的降解.

2.8 OG降解過(guò)程分析

研究不同pH條件下,OG在CNT/PMS/Cl-體系降解過(guò)程中的紫外可見光譜.如圖10所示, OG有三處特征吸收波峰,分別在可見光區(qū)479nm處以及在紫外光區(qū)330nm和250nm處,根據(jù)文獻(xiàn)[35]可知,479nm 處對(duì)應(yīng)的是發(fā)色基團(tuán)偶氮鍵,330nm和 250nm處分別對(duì)應(yīng)的是萘環(huán)和苯環(huán)結(jié)構(gòu). 在各個(gè) pH條件下,隨著反應(yīng)時(shí)間的增加,OG 在479nm處和330nm處的兩處波峰強(qiáng)度都在減少,當(dāng)pH=2～4之間時(shí),OG 在479nm和330nm的兩處波峰強(qiáng)度下降速率表現(xiàn)為pH=2大于pH=4,然后隨著pH升高,OG 在479nm和330nm的兩處波峰強(qiáng)度下降速率變快,符合不同pH下OG降解的結(jié)果.由圖10d可看出,當(dāng)反應(yīng)體系pH為8.0時(shí)隨著反應(yīng)的進(jìn)行,位于479nm和330nm處分別代表偶氮鍵和萘環(huán)結(jié)構(gòu)的特征峰強(qiáng)度不斷下降,反應(yīng)至35min時(shí)兩處特征峰接近于消失,這表明OG結(jié)構(gòu)中的偶氮鍵和萘環(huán)結(jié)構(gòu)不斷被·和HOCl氧化.

表 1顯示了①(CNT/PMS)、②(PMS/Cl-)和③(CNT/PMS/Cl-)體系氧化降解 OG的中間產(chǎn)物,可以看出中間產(chǎn)物多以苯環(huán)為主要結(jié)構(gòu),即三個(gè)體系產(chǎn)生的氧化物質(zhì)都能破壞OG結(jié)構(gòu)中的偶氮鍵和萘環(huán),有學(xué)者得到了類似的結(jié)果,Lou等[33]發(fā)現(xiàn) Cl-和 PMS反應(yīng)生成 HOCl可氧化降解羅丹明 B,使其結(jié)構(gòu)中的偶氮鍵和萘環(huán)斷開降解為苯環(huán)類物質(zhì);Yang等[36]研究活性碳纖維催化PMS產(chǎn)生·氧化降解AO7,發(fā)現(xiàn) AO7降解的中間產(chǎn)物是以苯環(huán)為主要結(jié)構(gòu)的芳香族化合物.本實(shí)驗(yàn)中各體系均可氧化降解OG,其主要區(qū)別是體系①中產(chǎn)生的中間產(chǎn)物不含 Cl,而體系②和③產(chǎn)生的中間產(chǎn)物部分含有 Cl,由此可知 CNT/PMS/ Cl-體系產(chǎn)生的·和HOCl均可使OG結(jié)構(gòu)中的偶氮鍵和萘環(huán)斷開,且隨著Cl-濃度提高體系產(chǎn)生HOCl的數(shù)量增多,導(dǎo)致 OG降解過(guò)程中含氯的中間產(chǎn)物變多.

表1 GC/MS測(cè)得OG降解的降解產(chǎn)物Table 1 Degradation products of OG determined by GC/MS(注:①CNT/PMS②PMS/Cl-③CNT/PMS/Cl-)

3 結(jié)論

3.1 Cl-對(duì)CNT/PMS體系氧化降解OG的過(guò)程具有雙重影響,低濃度 Cl-(＜10mmol/L)會(huì)抑制OG的降解,高濃度Cl-(＞25mmol/L)能促進(jìn)OG的降解,且發(fā)現(xiàn)無(wú)CNT存在Cl-會(huì)直接與PMS作用使OG脫色.

3.2 體系中的PMS濃度、反應(yīng)溫度與OG的脫色率成正相關(guān);OG初始濃度與OG的脫色率成負(fù)相關(guān),初始pH越低有利于HOCl對(duì)OG脫色,初始pH越高有利于·對(duì)OG脫色.

3.3 CNT存在的條件下 OG的礦化率要比無(wú)CNT存在要好,OG在479nm和330nm處吸收峰強(qiáng)度明顯減少,表明OG分子中偶氮鍵及萘環(huán)結(jié)構(gòu)均一定程度被破壞.

3.4 對(duì)比PMS/Cl-、CNT/PMS和CNT/PMS/Cl-體系的GC-MS結(jié)果,得出·和HOCl均斷開OG結(jié)構(gòu)中的偶氮鍵和萘環(huán),且隨著Cl-濃度提高體系產(chǎn)生HOCl的數(shù)量增多,導(dǎo)致OG降解過(guò)程中含氯的中間產(chǎn)物變多.

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Effect of chloride ions on degradation of Orange G with peroxymonosulfate activated by carbon nanotubes.

ZHANG Li-ming1, CHEN Jia-bin1, FANG Cong1, ZHOU Lu1, HU Jin-mei1, HAO Shang-bin1, LI Wen-wei2, WANG Zhong-ming1, HUANG Tian-yin1*(1.School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, China；2.School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China). China Environmental Science, 2016,36(12)：3591～3600

The radical was formed by the carbon nanotube (CNT) activation of peroxymonosulfate (PMS). Effect of chloride ion (Cl-) on degradation of Orange G (OG) by CNT/PMS system were investigated. Cl-had a dual effect on OG decolorization in the CNT/PMS system. Low dosage of Cl-could inhibit OG decolorization, whereas high dosage could promote its decolorization. Meanwhile, Cl-could directly react with PMS alone to decolorize OG. In the CNT/PMS/Clsystem, effect of various factors were explored, including PMS dosage, reaction temperature, initial concentration of OG, Cl-concentration, and initial pH, and the degradation mechanism was further proposed. The results indicated that 100% decolorization of OG was observed after 25min when 1.6mmol/L of PMS, 0.08mmol/L of OG, 50mmol/L of Cl-were present at 25℃. The activation energy of reaction system was determined to be 88.45kJ/mol. With the increasing initial pH, OG decolorization was decreased first and then gradually increased. Both of SO4-· and HOCl were found to be responsible for OG degradation. The mineralization rate during the degradation of OG were analyzed, and higher mineralization rate was observed when CNT was present in the system. From the analysis of UV-vis spectra and GC-MS, the azo band and naphthaline ring of OG were destroyed to generate other small intermediates.

carbon nanotubes；chloride ion；peroxymonosulfate；Orange G；decolourization ratio

X703

A

1000-6923(2016)12-3591-10

張黎明(1991-),男,苗族,湖南懷化人,蘇州科技大學(xué)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.

2016-05-01

國(guó)家自然科學(xué)基金項(xiàng)目(51478283);蘇州科技學(xué)院學(xué)術(shù)學(xué)位研究生科研創(chuàng)新計(jì)劃項(xiàng)目(SKCX15_026)

* 責(zé)任作者, 教授, huangtianyin111@sohu.com