蘇曉軒,徐國(guó)鵬,李獻(xiàn)眾,劉力章,陳建新*

PSF多相UV-Fenton體系原兒茶酸與龍膽酸的增效對(duì)比

蘇曉軒1,2,徐國(guó)鵬1,2,李獻(xiàn)眾1,2,劉力章3,陳建新1,2*

(1.南昌大學(xué)資源環(huán)境與化工學(xué)院,江西 南昌 330031；2.鄱陽(yáng)湖環(huán)境與資源利用教育部重點(diǎn)實(shí)驗(yàn)室,江西 南昌 330031；3.江西省環(huán)境科學(xué)研究院,江西 南昌 330077)

對(duì)比研究了原兒茶酸和龍膽酸對(duì)聚合硅酸鐵(PSF)多相 UV-Fenton體系降解橙Ⅱ的增效能力,分析了兩種增效體系中鐵離子轉(zhuǎn)化、H2O2分解以及·OH生成之間的關(guān)系,探討了兩種增效試劑對(duì)PSF多相UV-Fenton體系的增效機(jī)制.結(jié)果表明:原兒茶酸和龍膽酸均能夠有效促進(jìn)催化劑Fe2+生成與釋放,進(jìn)而提高體系·OH的濃度、促進(jìn)橙Ⅱ的降解.相對(duì)原兒茶酸,龍膽酸對(duì)PSF的還原能力更強(qiáng),其相應(yīng)增效體系中·OH的濃度更高、橙Ⅱ的降解速度更快.0.2mmol/L的增效濃度下,橙Ⅱ在原兒茶酸和龍膽酸增效體系中第一段脫色速率常數(shù)能分別從基礎(chǔ)體系的0.11min-1提高至1.68和2.48min-1,分別增加14.27倍和21.55倍.原兒茶酸和龍膽酸能夠循環(huán)增效PSF多相UV-Fenton體系降解橙Ⅱ,反應(yīng)結(jié)束后PSF對(duì)Fe3+的再吸附使得溶液總鐵離子濃度低于5mg/L,從而避免催化劑鐵元素的損失以及鐵離子的二次污染,表明原兒茶酸和龍膽酸均是PSF多相UV-Fenton 體系的高效增效試劑.

多相UV-Fenton體系；聚合硅酸鐵；原兒茶酸；龍膽酸；橙Ⅱ

隨著我國(guó)工業(yè)的發(fā)展,高效處理工業(yè)廢水技術(shù)的開(kāi)發(fā)日益迫切.染料廢水因其色度高、難降解、毒性大、水量大、化學(xué)需氧量高等特點(diǎn),成為我國(guó)最難處理的工業(yè)廢水之一[1].傳統(tǒng)的物化法、生化法、化學(xué)法等處理技術(shù)對(duì)染料廢水的處理效果難以保證[2-4].高級(jí)氧化技術(shù)(AOPs)因其高效性被廣泛應(yīng)用于染料廢水處理.其中,多相UV-Fenton技術(shù)具有對(duì)染料脫色速度快、礦化徹底、無(wú)二次污染等優(yōu)點(diǎn),是最受關(guān)注的染料廢水有效處理技術(shù)之一[5].

對(duì)于多相UV-Fenton體系,催化劑的開(kāi)發(fā)和催化過(guò)程的調(diào)控是技術(shù)核心[6].目前國(guó)內(nèi)外對(duì)鐵氧化合物[7-9]、鐵硫化合物[10-12]以及有機(jī)鐵(二茂鐵)[13-14]等多相UV-Fenton催化劑開(kāi)展過(guò)廣泛的研究.聚合硅酸鐵(PSF)作為一種新型混凝劑,其在高級(jí)氧化技術(shù)中的應(yīng)用近年來(lái)引起廣泛關(guān)注[15-18].研究發(fā)現(xiàn),將低硅-鐵比的PSF作為多相催化劑應(yīng)用于UV- Fenton降解染料廢水,發(fā)現(xiàn)其催化能力遠(yuǎn)高于鐵氧化合物,是一種高效的多相UV-Fenton催化劑.相同條件下,體系中染料脫色一級(jí)動(dòng)力學(xué)常數(shù)高達(dá)0.26min-1,分別是Fe2O3、Fe3O4、α-FeOOH、Fe2O3@γ Fe3O4的3.15倍、2.39倍、1.51倍和1.99倍[19].

多相UV-Fenton體系中,低效的亞鐵離子轉(zhuǎn)化率是其處理廢水能力的限制性因素,提高亞鐵離子轉(zhuǎn)化率是該體系處理能力提升的關(guān)鍵[20].研究發(fā)現(xiàn)原兒茶酸對(duì)Fe3+具有較好的化學(xué)還原能力,能夠有效增加類(lèi)芬頓體系(Fe3+-H2O2)中Fe2+的生成,并使該體系降解甲草胺的速率提高10000倍[21].龍膽酸是原兒茶酸的一種同分異構(gòu)體,是水楊酸經(jīng)人體腎臟代謝之后的一種次要產(chǎn)物[22].據(jù)報(bào)道,龍膽酸也具有較強(qiáng)的還原能力[22-23].在PSF多相UV-Fenton體系中,將原兒茶酸與龍膽酸作為還原試劑引入,能夠進(jìn)一步增效該體系中亞鐵離子的生成,有望開(kāi)發(fā)染料等有機(jī)工業(yè)廢水的高效處理技術(shù).目前,國(guó)內(nèi)外對(duì)PSF多相UV-Fenton體系有機(jī)酸同分異構(gòu)體之間增效能力的差異缺乏深入研究,通過(guò)研究其化學(xué)還原催化劑釋放亞鐵離子的能力和有機(jī)物降解的增效能力的規(guī)律,能夠?yàn)樾滦驮鲂г噭┑倪x擇提供新思路.

本文選用二羥基苯甲酸的兩種同分異構(gòu)體原兒茶酸和龍膽酸作為增效試劑,對(duì)比研究了兩者對(duì)PSF多相 UV-Fenton體系降解染料橙Ⅱ的增效能力,分析了兩種增效體系中鐵離子的轉(zhuǎn)化、H2O2分解和·OH 生成之間的關(guān)系,探討其對(duì)PSF多相UV-Fenton體系的增效機(jī)制,為高效多相 UV- Fenton水處理技術(shù)的開(kāi)發(fā)提供理論依據(jù).

1 材料與方法

1.1 實(shí)驗(yàn)儀器

PH400 基礎(chǔ)酸度計(jì)(上海安萊立思儀器科技有限公司);V-1600可見(jiàn)分光光度計(jì)(上海翱藝儀器有限公司);UV2300紫外/可見(jiàn)分光光度計(jì)(上海天美科技有限公司);Optima 2100DV ICP發(fā)射光譜儀(美國(guó) Perkin Elmer公司),Multi N/C2100型總有機(jī)碳分析儀(德國(guó)耶拿分析儀器股份有限公司),Nicolet is50 傅立葉變換紅外光譜儀(美國(guó)熱電尼高力公司); ESCALAB25OXi 型X射線光電子能譜儀(賽默飛世爾有限公司).

1.2 實(shí)驗(yàn)試劑

以下試劑如無(wú)特殊說(shuō)明均為分析純:硅酸鈉、硝酸鐵、鹽酸、硝酸、鄰菲羅啉、乙酸、乙酸銨、硫酸(優(yōu)級(jí)純)、硫酸鈦(化學(xué)純)、磷酸氫二鈉、磷酸二氫鈉、亞硫酸鈉、氫氧化鈉、30%過(guò)氧化氫、購(gòu)于西隴科學(xué)有限公司;香豆素(99%)和橙Ⅱ(生物染色劑)購(gòu)于Aladdin(上海);3、4-二羥基苯甲酸(原兒茶酸)、2、5-二羥基苯甲酸(龍膽酸)購(gòu)于上海麥克林生化科技有限公司;溶液均用去離子水配置.

1.3 催化劑的制備

本實(shí)驗(yàn)所用聚合硅酸鐵以硝酸鐵和硅酸鈉為原料通過(guò)溶膠凝膠法制得[24-25].具體步驟為:將硅酸鈉溶液逐滴加入到硝酸鐵溶液中并不斷攪拌,同時(shí)檢測(cè)體系中pH值.當(dāng)體系中pH值穩(wěn)定到(8±0.2)時(shí),停止滴加.靜置1h后,放于60℃恒溫水浴箱中老化6h.緩慢傾倒上清液,保留底部沉淀,反復(fù)用去離子水清洗[19,26],直至上清液為中性.將沉淀于60℃烘干、研磨過(guò)200目篩,制得催化劑(PSF)成品避光干燥保存.

1.4 實(shí)驗(yàn)方法

反應(yīng)在自制的光化學(xué)反應(yīng)器中進(jìn)行[7],反應(yīng)器由外層恒溫水浴層、中間光催化反應(yīng)層和內(nèi)置紫外燈(6W 254nm)的石英套管光源層3部分組成.底部放置磁力攪拌器使體系保持均勻混合.反應(yīng)器放置于自制避光空間中,以避免其他光源的干擾.

具體的橙Ⅱ降解實(shí)驗(yàn)為:將1.0g/L的催化劑、增效試劑和750mL 0.2mmol/L pH值為3.0的橙Ⅱ溶液加入到反應(yīng)器的反應(yīng)層,然后保持30℃恒溫水浴并磁力攪拌.暗光攪拌30min吸附平衡后,加入10mmol/L H2O2的同時(shí)打開(kāi)紫外燈并開(kāi)始計(jì)時(shí),以此作為反應(yīng)零時(shí)刻,最后在預(yù)設(shè)的反應(yīng)時(shí)刻取樣.

羥基自由基的定量分析用香豆素?zé)晒夤舛确╗8-9]:在預(yù)設(shè)的時(shí)間取反應(yīng)溶液5mL加入50mL 2mol/L香豆素溶液(pH=3.0)中,立刻將混合液放入另一個(gè)避光空間相同紫外燈下持續(xù)攪拌5min.過(guò)濾后立即取2.2mL濾液與0.5mL終止劑[27](pH=7.2 的NaH2PO4和Na2HPO4混合溶液)均勻混合,測(cè)量其熒光強(qiáng)度.溶液中總鐵和亞鐵離子的測(cè)定用0.22μm水相濾頭過(guò)濾,其它樣品均用0.45μm水相濾頭過(guò)濾.

催化劑使用前后用傅里葉紅外光譜儀(FTIR)和X射線光電子能譜儀進(jìn)行分析.反應(yīng)后的溶液靜置、沉淀、干燥回收催化劑進(jìn)行一次表征.第一次反應(yīng)完成后向體系中加入0.2mmol/L濃度的目標(biāo)污染物橙Ⅱ和增效試劑,暗光攪拌30min后加入H2O2反應(yīng)后同樣的方法回收催化劑進(jìn)行2次循環(huán)的表征.第三次循環(huán)的實(shí)驗(yàn)方法同上.

1.5 分析方法

橙Ⅱ濃度的測(cè)定采用分光光度計(jì)法,測(cè)量不同時(shí)刻其最大吸收波長(zhǎng)(484nm)處的吸光度,通過(guò)標(biāo)準(zhǔn)曲線進(jìn)行換算.橙Ⅱ的脫色速率常數(shù)用一級(jí)動(dòng)力學(xué)方程擬合計(jì)算:

-ln(c/0)=(1)

式中:0為初始橙Ⅱ濃度,mg/L;t為設(shè)定時(shí)刻的橙Ⅱ濃度,mg/L;為橙Ⅱ的脫色速率常數(shù),min-1;為反應(yīng)時(shí)間,min.

羥基自由基與香豆素生成7-羥基香豆素,測(cè)量其在460nm處的熒光強(qiáng)度,通過(guò)標(biāo)準(zhǔn)曲線進(jìn)行換算,用上述試驗(yàn)方法,實(shí)測(cè)數(shù)值是稀釋了13.5倍后的濃度值.總鐵用ICP發(fā)射光譜儀測(cè)定;亞鐵通過(guò)鄰菲羅啉分光光度計(jì)法測(cè)定;過(guò)氧化氫通過(guò)硫酸鈦分光光度計(jì)法測(cè)定.除表征實(shí)驗(yàn)外,所有實(shí)驗(yàn)重復(fù)3次,數(shù)據(jù)取3次結(jié)果平均值.

2 結(jié)果與討論

2.1 原兒茶酸和龍膽酸增效PSF多相UV-Fenton體系降解橙Ⅱ的對(duì)比

由圖1可見(jiàn),2種增效試劑均能明顯加速橙Ⅱ的脫色,表明2種酸均是PSF多相UV-Fenton體系的高效增效試劑.

近年研究表明,在高效高級(jí)氧化體系中,染料的脫色可以明顯分為2個(gè)階段,用分段擬合法計(jì)算體系中染料的脫色速率常數(shù)更為合理[8,28].根據(jù)圖1數(shù)據(jù),用一級(jí)動(dòng)力學(xué)方程分別對(duì)基礎(chǔ)體系和增效體系中橙Ⅱ脫色的2個(gè)階段進(jìn)行回歸擬合,結(jié)果見(jiàn)圖2;回歸計(jì)算得到的“第一段”和“第二段”2個(gè)階段的橙Ⅱ脫色速率常數(shù)列于表1.

如圖2所示,在PSF多相UV-Fenton體系中,原兒茶酸和龍膽酸的加入能夠?qū)⒊娶虻摹暗谝欢巍泵撋窝永m(xù)的時(shí)間從3min縮短到1min;相應(yīng)地,橙Ⅱ“第一段”脫色的速率常數(shù)均能得到極大地提高;隨原兒茶酸與龍膽酸濃度的增加,兩種增效體系中橙Ⅱ的“第一段”脫色速率常數(shù)呈現(xiàn)先快速上升后緩慢降低的趨勢(shì).

由表1可見(jiàn),龍膽酸對(duì)PSF多相UV- Fenton體系降解橙Ⅱ的增效能力明顯強(qiáng)于原兒茶酸.以增效試劑0.2mmol/L為例,原兒茶酸能使橙Ⅱ“第一段”脫色速率常數(shù)從0.11min-1增加至1.68min-1,其速率常數(shù)可以增加14.27倍;而龍膽酸能使橙Ⅱ“第一段”脫色速率常數(shù)從0.11min-1增加至2.48min-1,其速率常數(shù)增加至21.55倍.此外,隨增效試劑濃度的增加,橙Ⅱ“第一段”脫色速率常數(shù)急劇增加;當(dāng)兩種增效試劑濃度大于0.2mmol/L時(shí),橙Ⅱ“第一段”脫色速率常數(shù)的增效倍數(shù)均增加趨緩;當(dāng)兩種增效試劑濃度高達(dá)0.4mmol/L時(shí),橙Ⅱ“第一段”脫色速率常數(shù)和增效倍數(shù)均出現(xiàn)下降的現(xiàn)象.在原兒茶酸和龍膽酸增效的PSF多相UV-Fenton體系中,消耗羥基自由基的主要物種是有機(jī)染料橙Ⅱ和有機(jī)增效試劑自身.

C16H11N2NaO4S+42H2O2→16CO2+2HNO3+NaHSO4(2)

C7H6O4+13H2O2→7CO2+16H2O(3)

由于增效體系中活性因子·OH氧化有機(jī)物并無(wú)選擇性,其在氧化降解橙Ⅱ的同時(shí)也會(huì)氧化降解增效試劑,因此增效試劑的用量尤為關(guān)鍵.合適的增效試劑用量既要滿足對(duì)橙Ⅱ降解的有效增效,同時(shí)也要保證有足夠濃度的·OH降解礦化橙Ⅱ.從理論分析可知,過(guò)量的增效試劑必然會(huì)干擾橙Ⅱ的降解和礦化.

為了探究原兒茶酸與龍膽酸對(duì)橙Ⅱ降解的影響,分別對(duì)基礎(chǔ)體系及其增效體系(0.2mmol/L的增效試劑)不同時(shí)刻的反應(yīng)溶液進(jìn)行了全波長(zhǎng)掃描,結(jié)果如圖3所示.可見(jiàn),與基礎(chǔ)體系相對(duì)應(yīng),增效體系橙Ⅱ的降解過(guò)程并無(wú)新的吸收峰出現(xiàn),該結(jié)果與本文前期研究結(jié)果一致[19,26];此外,相較于基礎(chǔ)體系,增效體系反應(yīng)溶液分別歸屬于偶氮鍵和萘環(huán)(484和310nm)處的吸收峰[29]降低的速率更為迅速,說(shuō)明增效試劑的引入不僅能加速橙Ⅱ脫色,而且能加速其礦化.

為考察增效體系中橙Ⅱ的礦化情況,測(cè)定了不同時(shí)刻反應(yīng)溶液的TOC值,結(jié)果見(jiàn)圖4.與增效脫色結(jié)果相一致,相對(duì)于原兒茶酸,龍膽酸對(duì)橙Ⅱ的增效礦化效果更佳.反應(yīng)20min時(shí),原兒茶酸增效體系的TOC去除率為73.57%,而龍膽酸增效體系的TOC去除率高達(dá)79.63%;反應(yīng)60min時(shí),原兒茶酸與龍膽酸增效體系的TOC去除率分別高達(dá)92.09%和92.98%.此外,對(duì)比增效體系橙Ⅱ的脫色和礦化結(jié)果,同時(shí)結(jié)合反應(yīng)溶液不同時(shí)刻全波長(zhǎng)掃描結(jié)果,可以推斷橙Ⅱ的降解過(guò)程中有無(wú)色的降解中間產(chǎn)物形成,該結(jié)果與Maezono等[27]的研究結(jié)論一致.

表1 2種增效試劑濃度對(duì)PSF多相UV-Fenton體系橙Ⅱ脫色一級(jí)動(dòng)力學(xué)分段擬合的影響

圖4 橙Ⅱ在PSF多相UV-Fenton 體系中的礦化曲線

綜上所述,原兒茶酸和龍膽酸均是PSF多相UV-Fenton體系的高效增效試劑.結(jié)合橙Ⅱ的脫色和礦化速率以及增效效果分析,認(rèn)為在實(shí)驗(yàn)條件下,其濃度為0.2mmol/L時(shí)為較佳的增效濃度.

2.2 原兒茶酸與龍膽酸增效PSF多相 UV-Fenton 體系中·OH的生成

研究表明,在鐵離子與過(guò)氧化氫構(gòu)建的芬頓或類(lèi)芬頓體系中,由于Fe2+的催化能力遠(yuǎn)高于Fe3+(式(4)和(5))[30],因此體系中亞鐵離子的濃度對(duì)于羥基自由基的生成極為關(guān)鍵.

H2O2+Fe2+→ Fe3++ ·OH + OH-

=76L/(mol·s)(4)

H2O2+Fe3+→ Fe2++ ·OOH + H+

=0.02L/(mol·s)(5)

多相UV-Fenton體系降解有機(jī)污染物的過(guò)程,本質(zhì)上是利用多相催化劑在UV光照下發(fā)生光還原生成并釋放Fe2+,從而催化過(guò)氧化氫生成羥基自由基并將有機(jī)污染物降解的過(guò)程[31].而外加還原性的增效試劑,是在光還原基礎(chǔ)上增加化學(xué)還原的途徑進(jìn)一步提高催化劑生成和釋放Fe2+的能力,從而能夠增效多相UV-Fenton體系對(duì)有機(jī)污染物的降解.因此,增效試劑對(duì)多相催化劑的化學(xué)還原能力至關(guān)重要.為了比較原兒茶酸與龍膽酸對(duì)PSF的化學(xué)還原能力,監(jiān)測(cè)了橙Ⅱ降解過(guò)程增效體系溶液中Fe2+向Fe3+的轉(zhuǎn)化,結(jié)果見(jiàn)圖5.

由圖5可見(jiàn),對(duì)于原兒茶酸增效體系,反應(yīng)0min時(shí)(無(wú)光攪拌30min)溶液中Fe2+的濃度可以達(dá)到2.62mg/L,說(shuō)明原兒茶酸能夠有效地化學(xué)還原PSF并使之釋放亞鐵離子,該結(jié)果與秦雅鑫等對(duì)原兒茶酸增效Fe@Fe2O3降解羅丹明B的研究結(jié)果相類(lèi)似[32].當(dāng)在0min加入過(guò)氧化氫、打開(kāi)紫外燈啟動(dòng)UV-Fenton反應(yīng)時(shí),催化劑PSF在化學(xué)還原的同時(shí)增加了光還原,使得溶液中Fe2+的濃度進(jìn)一步增加并于1min時(shí)達(dá)到峰值3.93mg/L,而后由于體系中芬頓反應(yīng)(式(4))速度遠(yuǎn)大于類(lèi)芬頓反應(yīng)速度(式(5)),Fe2+快速向Fe3+轉(zhuǎn)化導(dǎo)致前者濃度快速下降.同時(shí),體系中有機(jī)污染物降解中間產(chǎn)物對(duì)催化劑PSF上鐵離子的增溶作用[33],使得溶液中總鐵離子的濃度在15min時(shí)達(dá)到峰值9.00mg/L;隨中間產(chǎn)物的降解,總鐵離子濃度能夠通過(guò)PSF對(duì)Fe3+的吸附[34]而降低至60min時(shí)的0.96mg/L.對(duì)于龍膽酸增效體系,反應(yīng)0min時(shí)溶液中Fe2+的濃度已高達(dá)6.72mg/L,說(shuō)明龍膽酸對(duì)催化劑PSF的化學(xué)還原能力遠(yuǎn)高于原兒茶酸.由于其化學(xué)還原能力較高,以至于掩蓋了光還原對(duì)Fe2+生成的影響,只能觀察到溶液中Fe2+濃度單方向的降低趨勢(shì).隨UV-Fenton反應(yīng)的進(jìn)行溶液中Fe2+持續(xù)向Fe3+轉(zhuǎn)化,反應(yīng)60min時(shí)Fe2+濃度降至0.42mg/L.同時(shí),由于龍膽酸增效體系礦化能力更強(qiáng),導(dǎo)致溶液中總鐵離子的濃度峰值9.13(mg/L)縮短至10min出現(xiàn),而后降至60min時(shí)的0.83mg/L.

Fe2+向Fe3+的轉(zhuǎn)化過(guò)程與H2O2的分解和·OH的生成緊密相關(guān).在橙Ⅱ降解過(guò)程中,增效體系中H2O2和·OH濃度隨時(shí)間變化情況見(jiàn)圖6.

由圖6可見(jiàn),基礎(chǔ)體系中過(guò)氧化氫的分解比較緩慢,相應(yīng)的溶液中羥基自由基的濃度增加也比較緩慢,在15min時(shí)達(dá)到9.52μmol/L的濃度峰值;而后,由于體系中有機(jī)物降解的消耗導(dǎo)致羥基自由基濃度平緩下降.對(duì)于原兒茶酸增效體系,化學(xué)還原產(chǎn)生的亞鐵離子濃度使芬頓反應(yīng)(式(4))能夠有效進(jìn)行,因此體系中過(guò)氧化氫能夠快速分解產(chǎn)生羥基自由基.溶液中羥基自由基的濃度在5min時(shí)高達(dá)20.14μmol/L,是基礎(chǔ)體系最高值的2.13倍.

相對(duì)于基礎(chǔ)體系和原兒茶酸增效體系,龍膽酸增效體系中的亞鐵離子濃度在0min時(shí)最高,因此其芬頓反應(yīng)(式(4))最為劇烈,溶液中羥基自由基的濃度在5min時(shí)高達(dá)23.70μmol/L.一方面,體系中羥基自由基在短時(shí)間內(nèi)大量生成,會(huì)引發(fā)自由基的二聚反應(yīng)(式6)[35],反應(yīng)能夠重新生成過(guò)氧化氫使得其濃度在1min內(nèi)急劇降低后呈現(xiàn)平緩下降的趨勢(shì);另一方面,體系中羥基自由基在短時(shí)間內(nèi)大量生成還會(huì)引發(fā)羥基自由基與過(guò)氧化氫的副反應(yīng)(式(7))[35].因此,龍膽酸增效體系中羥基自由基的濃度雖大于原兒茶酸增效體系,但未呈現(xiàn)隨亞鐵離子濃度按比例增加的規(guī)律,類(lèi)似的現(xiàn)象在本文前期對(duì)草酸根增效體系的研究中也有發(fā)現(xiàn)[9].

·OH + ·OH →H2O2(6)

H2O2+ ·OH → ·OOH + H2O(7)

總體而言,龍膽酸相對(duì)于原兒茶酸能夠使PSF多相 UV-Fenton 體系產(chǎn)生更多的·OH,這正是其增效體系中橙Ⅱ脫色和礦化更為迅速的原因.

2.3 原兒茶酸與龍膽酸對(duì)PSF多相 UV-Fenton 體系的循環(huán)增效

利用原兒茶酸與龍膽酸對(duì)PSF多相UV-Fenton體系的循環(huán)增效實(shí)驗(yàn),進(jìn)一步驗(yàn)證了相關(guān)增效方法的穩(wěn)定性,循環(huán)增效過(guò)程中橙Ⅱ的脫色情況和溶液中總鐵離子的變化見(jiàn)圖7.

兩種增效體系中,隨增效循環(huán)次數(shù)增加溶液中總鐵離子峰值會(huì)逐漸增大、橙Ⅱ的脫色速率能進(jìn)一步提高.每次增效循環(huán)結(jié)束時(shí),溶液中總鐵離子濃度均低于5mg/L,說(shuō)明增效體系反應(yīng)結(jié)束后能夠避免鐵離子的二次污染[36].需要指出的是,為切合工程實(shí)際,本文增效循環(huán)實(shí)驗(yàn)過(guò)程并未對(duì)催化劑進(jìn)行固-液分離和洗滌操作.根據(jù)增效體系中橙Ⅱ的礦化分析(圖4),可以推斷,在循環(huán)增效實(shí)驗(yàn)中,存在少量殘留無(wú)色中間產(chǎn)物進(jìn)入到下一個(gè)增效循環(huán)的現(xiàn)象.由此,無(wú)色中間產(chǎn)物與鐵離子的絡(luò)合作用,可能導(dǎo)致PSF對(duì)鐵離子的釋放程度增加[9].根據(jù)本文前期研究,若能適當(dāng)延長(zhǎng)反應(yīng)時(shí)間、進(jìn)一步提高TOC的去除率,反應(yīng)結(jié)束后鐵離子的溶出有望進(jìn)一步降低[33].聚合硅酸鐵的XRF分析顯示,PSF主要由Si,O和Fe 3種元素組成,這3種元素分別占PSF成分的24.13%、42.31%和30.10%.由此,原兒茶酸與龍膽酸對(duì)PSF多相UV-Fenton體系的循環(huán)增效過(guò)程中,催化劑PSF上鐵元素的總損失分別為3.07%和2.95%,相對(duì)損失較小.

為進(jìn)一步驗(yàn)證催化劑PSF在循環(huán)增效過(guò)程中的穩(wěn)定性,對(duì)PSF循環(huán)使用3次前后的紅外光譜、XPS全光譜以及Fe2p的高分辨光譜進(jìn)行了分析,結(jié)果如圖8和9所示.

聚合硅酸鐵的XRF分析表明,PSF為高硅-鐵比聚合物,其Si與Fe量之比為1.6:1,其結(jié)構(gòu)中的Si- Fe-O鍵以“Si-O-Fe-O-Si”形式為主.PSF的紅外光譜中,其在1010cm-1處的峰由Si-O-Fe鍵的振動(dòng)吸收引發(fā)[37],471cm-1處的峰則與Fe-O鍵的振動(dòng)有關(guān)[38].此外,可能是高度縮合的原因,PSF的紅外光譜未呈現(xiàn)FeⅢ連接的-OH基團(tuán)的拉伸振動(dòng)峰(1383cm-1處)[39].總體上,循環(huán)增效過(guò)程中PSF表面的官能團(tuán)并未發(fā)生較大改變,證實(shí)PSF具有較高的穩(wěn)定性.此外,循環(huán)增效結(jié)束后催化劑PSF紅外譜圖并無(wú)與橙Ⅱ有關(guān)的吸收峰出現(xiàn)(例如1621cm-1處苯環(huán)骨架中C=C鍵的伸縮振動(dòng)和1508cm-1處萘環(huán)的骨架伸縮振動(dòng)等[40]),表明溶液中TOC降低的主要原因是橙Ⅱ等有機(jī)物的礦化而非PSF的吸附所致,這與溶液中橙Ⅱ的脫色和礦化結(jié)果相一致.

PSF使用前后的光電子能譜圖中出現(xiàn)了Fe2p、Si2p和O1s峰(圖9),這也證明了PSF主要成分是Fe、Si、O.通過(guò)對(duì)能譜圖中Fe2p的高分辨譜圖分析,711.7和713.6eV處的峰表明PSF表面存在大量FeⅢ[41].鐵-氧的結(jié)合能在反應(yīng)前后未明顯變化,證明了聚合硅酸鐵結(jié)構(gòu)具有較高的穩(wěn)定性.

2.4 原兒茶酸與龍膽酸對(duì)PSF多相 UV-Fenton 體系增效降解橙Ⅱ的機(jī)制

如圖10所示,首先,原兒茶酸與龍膽酸可以將聚合硅酸鐵上的≡FeⅢ-PSF直接化學(xué)還原成≡FeⅡ- PSF(式(8)),后者在引發(fā)催化劑表面多相Fenton反應(yīng)的同時(shí)(式(9)),可以被體系中氫離子通過(guò)離子交換的方式釋放到反應(yīng)溶液中(式(10)),并引發(fā)均相Fenton反應(yīng)(式(11)).

≡FeⅡ-PSF + H2O2→ ≡FeⅢ-PSF + ·OH + OH-(9)

≡FeⅡ-PSF + H+→ Fe2++ ≡H+-PSF(10)

H2O2+Fe2+→ Fe3++ ·OH + OH-(11)

體系紫外燈開(kāi)啟后,催化劑表面和溶液中三價(jià)鐵離子光解還原成≡FeⅡ-PSF和Fe2+[26],因此體系的Fenton反應(yīng)能夠持續(xù)進(jìn)行,反應(yīng)產(chǎn)生的·OH能夠高效降解和礦化體系中的有機(jī)物.

反應(yīng)后期,當(dāng)有機(jī)物礦化殆盡,溶液中的亞鐵離子通過(guò)Fenton反應(yīng)轉(zhuǎn)化生成的Fe3+,后者能夠通過(guò)離子交換重新被聚合硅酸鐵所吸附,從而降低體系中的鐵離子濃度避免其二次污染發(fā)生(式(12)).

Fe3++ ≡H+-PSF→≡FeⅢ-PSF+ H+(12)

相較于原兒茶酸,龍膽酸對(duì)聚合硅酸鐵的還原能力更強(qiáng),能產(chǎn)生更多的二價(jià)鐵離子并釋放到均相體系中,因此體系中Fenton反應(yīng)更為劇烈、羥基自由濃度更高,從而使得染料更加快速的脫色及礦化.由于Fenton反應(yīng)存在最佳的鐵離子與過(guò)氧化氫濃度比例[42],因此龍膽酸濃度是增效聚合硅酸鐵多相UV- Fenton體系的重要參數(shù).在合適的龍膽酸濃度下,增效體系中金橙Ⅱ的脫色和礦化速度更快、更徹底.

圖10 2種增效試劑對(duì)PSF多相UV-Fenton體系增效降解橙Ⅱ的機(jī)制

3 結(jié)論

3.1 原兒茶酸和龍膽酸均是PSF多相UV-Fenton 體系的高效增效試劑,且龍膽酸的增效能力強(qiáng)于原兒茶酸.增效體系中,原兒茶酸和龍膽酸濃度是影響橙Ⅱ脫色和礦化的重要因素,0.2mmol/L是較佳的增效濃度.在該增效濃度下,原兒茶酸和龍膽酸能使橙Ⅱ“第一段”脫色速率常數(shù)分別增加14.27倍和21.55倍.

3.2 原兒茶酸和龍膽酸增效的原因在于促進(jìn)催化劑Fe2+生成與釋放,進(jìn)而提高體系羥基自由基的濃度.相對(duì)原兒茶酸,龍膽酸對(duì)PSF的還原能力更強(qiáng),其相應(yīng)增效體系中羥基自由基的濃度更高、橙Ⅱ的降解速度更快.

3.3 原兒茶酸和龍膽酸能夠循環(huán)增效PSF多相UV-Fenton 體系降解橙Ⅱ,PSF還原釋放的Fe2+會(huì)通過(guò)Fenton反應(yīng)快速轉(zhuǎn)化成Fe3+.反應(yīng)結(jié)束時(shí),PSF對(duì)Fe3+的再吸附使得溶液總鐵離子濃度低于5mg/L,從而避免催化劑鐵元素的損失以及鐵離子的二次污染.

[1] Li W, Mu B G, Yang Y Q. Feasibility of industrial-scale treatment of dye wastewater via bio-adsorption technology [J]. Bioresource Technology, 2019,277:157-170.

[2] Yuan D, Zhang C, Tang S, et al. Enhancing CaO2fenton-like process by Fe(II)-oxalic acid complexation for organic wastewater treatment [J]. Water Research, 2019,163:1-11.

[3] 郝思宇,張 艾,劉亞男.臭氧與過(guò)氧化鈣協(xié)同降解甲基紅廢水[J]. 中國(guó)環(huán)境科學(xué), 2019,39(2):591-597. Hao S Y, Zhang A, Liu Y N. Removal of methyl red in aqueous by O3/CaO2treatment: influencing factors and synergetic effects [J]. China Environmental Science, 2019,39(2):591-597.

[4] 曾 萍,劉詩(shī)月,張俊珂,等.芬頓法深度處理生物處理排水中的四環(huán)素抗性基因[J]. 中國(guó)環(huán)境科學(xué), 2017,37(9):3315-3323. Zeng P, Liu S Y, Zhang J K, et al. Advanced Fenton oxidation treatment of tetracycline resistance genes in effluent discharged from biological wastewater treatment [J]. China Environmental Science, 2017,37(9):3315-3323.

[5] Law J C, Leung K S. Redox mediators and irradiation improve fenton degradation of acesulfame [J]. Chemosphere, 2019,217:374-382.

[6] Liang X L, Zhong Y H, Zhu S Y, et al. The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetit [J]. Journal of Hazardous Materials, 2012,199-200:247-254.

[7] 徐淑英,陳建新,王 琳,等.不同晶型鐵氧化物Fenton和UV-Fenton降解橙Ⅱ的催化性能[J]. 安全與環(huán)境學(xué)報(bào), 2017,17(4):1448-1453. Xu S Y, Chen J X, Wang L, et al. Catalytic features of iron oxides with different crystal forms during Orange Ⅱdegradation in Fenton and UV-Fenton systems [J]. Journal of Safety and Environment, 2017,17(4):1448-1453.

[8] 戴慧旺,陳建新,苗笑增,等.醇類(lèi)對(duì)UV-Fenton體系羥基自由基淬滅效率的影響[J]. 中國(guó)環(huán)境科學(xué), 2018,38(1):202-209. Dai H W, Chen J X, MiaoX Z, et al. Effect of alcohols on scavenging efficiencies to hydroxyl radical in UV-Fenton system [J]. China Environmental Science, 2018,38(1):202-209.

[9] 苗笑增,戴慧旺,陳建新,等.草酸根對(duì)α-FeOOH多相UV-Fenton催化能力的增效實(shí)驗(yàn)[J]. 環(huán)境科學(xué), 2018,39(3):1202-1211. MiaoX Z, Dai H W, Chen J X, et al. Experiment to enhance catalytic activity of α-FeOOH in heterogeneous UV-Fenton system by addition of oxalate [J]. Environmental Science, 2018,39(3):1202-1211.

[10] Gao J, Liu Y, Xia X, et al. Mechanisms for photo assisted Fenton of synthesized pyrrhotite at neutral pH [J]. Applied Surface Science, 2019,463:863-871.

[11] Zeng L, Gong J, Dan J, et al. Novel visible light enhanced Pyrite- Fenton system toward ultrarapid oxidation of p-nitrophenol: Catalytic activity, characterization and mechanism [J]. Chemosphere, 2019, 228:232-240.

[12] 馮 勇,吳德禮,馬魯銘.黃鐵礦催化類(lèi)Fenton反應(yīng)處理陽(yáng)離子紅X-GRL廢水[J]. 中國(guó)環(huán)境科學(xué), 2012,32(6):1011-1017. Feng Y, Wu D L, Ma L M. Treatment of Cationic Red X-GRL wastewater by pyrite catalyzed Fenton-like reaction [J]. China Environmental Science, 2012,32(6):1011-1017.

[13] Li Y J, Ning P, Tian S L. Ferrocene-catalyzed heterogeneous Fenton- like degradation mechanisms and pathways of antibiotics under simulated sunlight: A case study of sulfamethoxazole [J]. Journal of Hazardous Materials, 2018,353:26–34.

[14] 張彪軍,田森林,李英杰,等.光助-二茂鐵/H2O2非均相體系降解磺胺二甲基嘧啶[J]. 環(huán)境科學(xué), 2018,39(11):5043-5050. Zang B J, Tian S L, Li Y J, et al. Photo-assisted degradation of sulfamethazine by ferrocene-catalyzed heterogeneous Fenton-like system [J]. Environmental Science, 2018,39(11):5043-5050.

[15] 李志麗,張瀟逸,楊 萍,等.基于小角度激光光散射的聚硅酸鐵絮體特性研究[J]. 中國(guó)給水排水, 2017,33(11):91-96. Li Z L, Zhang X Y, Yang P, et al. Flocs Characteristics of poly- silicic-ferric coagulant based on small-angle laser light scattering [J]. China Water and Wastewater, 2017,33(11):91-96.

[16] Liu Y, Shen J, Chen Z, et al. Degradation of p-chloronitrobenzene in drinking water by manganese silicate catalyzed ozonation [J]. Desalination, 2011,279:219-224.

[17] 劉 玥,陳忠林,楊 磊,等.聚合硅酸鐵催化臭氧氧化硝基氯苯的效能[J]. 哈爾濱工業(yè)大學(xué)學(xué)報(bào), 2010,42:914-918. Lu Y, Chen Z L, Yang L, et al. Iron silicate polymer catalyzed ozonation for removing chloronitrobenzenes in drinking water [J]. Journal of Harbin Institute of Technology, 2010,42:914-918.

[18] 侯炳江,沈吉敏,李太平,等.硅酸鐵催化臭氧去除水中的阿特拉津和硝基苯[J]. 黑龍江大學(xué)自然科學(xué)學(xué)報(bào), 2015,32(2):223-228. Hou B J, Shen J M, Li T P, et al. Removal of atrazine and nitrobenzene in water by iron silicate catalyzed ozonation [J]. Journal Of Natural Science of Hellongjiang University, 2015,32(2):223-228.

[19] Liu Z Q, Chen J X,Zhu J X, et al. The catalytic process of poly- silicate-ferric (PSF) and generation mechanism of hydroxyl radical based on photo-Fenton system [J]. Water Science and Technology, 2020,81:709-719.

[20] Zhou W, Gao J H, Zhao H Q, et al. The role of quinone cycle in Fe2+-H2O2system in the regeneration of Fe2+[J]. Environmental technology, 2017,38(15):1887-1896.

[21] Qin Y X, Song F H, Zhang L Z, et al. Protocatechuic acid promoted alachlor degradation in Fe(III)/H2O2Fenton system [J]. Environmental Science And Technology, 2015,49:7948-7956.

[22] Hosokawa S, Shukuya K, Sogabe K, et al. Novel absorbance peak of gentisic acid following the oxidation reaction [J]. PloS one, 2020, 15:232-263.

[23] Abedi F, Razavi B M, Hosseinzadeh H. A review on gentisic acid as a plant derived phenolic acid and metabolite of aspirin: Comprehensive pharmacology, toxicology, and some pharmaceutical aspects [J]. Phytotherapy Research, 2020,34:729-741.

[24] Fu Y, Yu S L, Yy Y Z, et al. Reaction mode between Si and Fe and evaluation of optimal species in poly-silicic-ferric coagulant [J]. Journal of Environmental Sciences , 2007,19:678-688.

[25] Sun T, Sun C H, Zhu G L, et al. Preparation and coagulation performance of poly-ferric-aluminum-silicate-sulfate from fly ash [J]. Desalination, 2011,268(1):270-275.

[26] 姜自立,李獻(xiàn)眾,劉治慶,等.苯醌對(duì)聚合硅酸鐵多相UV-Fenton體系的增效機(jī)制[J]. 中國(guó)環(huán)境科學(xué), 2020,40(7):2943-2951. Jiang Z L, Li X Z, Liu Z Q, et al. The enhanced mechanism of benzoquinone (BQ) on poly-silicate-ferric (PSF) in heterogeneous UV-Fenton system [J]. China Environmental Science, 2020,40(7): 2943-2951.

[27] Maezono T, Tokumura M, Sekine M, et al. Hydroxyl radical concentration profile in photo-Fenton oxidation process: generation and consumption of hydroxyl radicals during the discoloration of azo-dye Orange Ⅱ [J]. Chemosphere, 2011,82(10):1422-1430.

[28] Wei X P, Wu H H, He G P, et al. Efficient degradation of phenol using iron-montmorillonite as a Fenton catalyst: Importance of visible light irradiation and intermediates [J]. Journal of Hazardous Materials, 2017, 321:408-416.

[29] Zhong X, Royer S, Zhang H, et al. Mesoporous silica iron-doped as stable and efficient heterogeneous catalyst for the degradation of C.I. Acid Orange 7using sono-photo-Fenton process [J]. Separation and Purification Technology, 2011,80:163-171.

[30] Han X, Chen T, Li J W, et al. Synthesis of (Ni, Mg, Cu) Fe2O4from nickel sulfide ore: A novel heterogeneous photo-Fenton-like catalyst with enhanced activity in the presence of oxalic acid [J]. Journal of Photochemistry and Photobiology, A: Chemistry, 2020,390:11230- 11238.

[31] Wang Y, Lin X G, Shao Z Z, et al. Comparison of Fenton, UV-Fenton and nano-Fe3O4catalyzed UV-Fenton in degradation of phloroglucinol under neutral and alkaline conditions: Role of complexation of Fe3+with hydroxyl group in phloroglucinol [J]. Chemical Engineering Journal, 2017,313:938-945.

[32] Qin Y X, Li G Y, Zhang L Z, et al. Protocatechuic acid promoted catalytic degradation of rhodamine Bwith Fe@Fe2O3core-shell nanowires by molecular oxygen activation mechanism [J]. Catalysis Today, 2019,335:144-150.

[33] 劉治慶.聚合硅酸鐵多相UV-Fenton體系中羥基自由基的生成機(jī)理和橙Ⅱ的脫色動(dòng)力學(xué)模型[D]. 南昌:南昌大學(xué), 2020. Liu Z Q. The formation mechanism of hydroxyl radicals and decolorization kinetic model of orange Ⅱin poly-silicate-ferric heterogeneous UV-Fenton system [D]. Nanchang: Nanchang University, 2020.

[34] 姜自立.煅燒溫度對(duì)聚合硅酸鐵多相UV-Fenton催化性能的影響機(jī)制[D]. 南昌:南昌大學(xué), 2020. Jiang Z L. The influence mechanism of calcination temperature on the catalytic activity of poly-silicate-ferric in heterogeneous UV-Fenton system [D]. Nanchang: Nanchang University, 2020.

[35] 鄧景衡,文湘華,李佳喜.碳納米管負(fù)載納米四氧化三鐵多相類(lèi)芬頓降解亞甲基藍(lán) [J]. 環(huán)境科學(xué)學(xué)報(bào), 2014,34:1436-1442. Deng J H, Wen X H, Li J X. Degradation of methylene blue by heterogeneous Fenton-like reaction using Fe3O4/carbon nanotube composites [J]. Cacta Scientae Curstantiae, 2014,34:1436-1442.

[36] Lenoble V, Laclautre C, Deluchat V, et al. Arsenic removal by adsorption on iron(III) phosphate [J]. Journal of Hazardous Materials, 2005,B123:262-268.

[37] Sun T, Liu L L, Wan L L, et al. Effect of silicon dose on preparation and coagulation performance of poly-ferric-aluminum-silicate- sulfate from oil shale ash [J]. Chemical Engineering Journal, 2010, 163:48-54.

[38] Li J F, Li J G, Liu X Y, et al. Effect of silicon content on preparation and coagulation performance of poly-silicic-metal coagulants derived from coal gangue for coking wastewater treatment [J]. Separation and Purification Technology, 2018,202:149-156.

[39] Fu Y, Yu S L, Han C W. Morphology and coagulation performance during preparation of poly-silicic-ferric (PSF) coagulant [J]. Chemical Engineering Journal, 2009,149:1-10.

[40] Lenz S, B?hm K, Ottner R, et al. Determination of leachate compounds relevant for landfill aftercare using FT-IR spectroscopy [J]. Waste Management, 2016,55:321-329.

[41] Huai Y, Plackowski C, Peng Y. The effect of gold coupling on the surface properties of pyrite in the presence of ferric ions [J]. Applied Surface Science, 2019,488:277-283.

[42] Ferrentino R, Merzari F, Andreottola G. Optimisation of Fe2+/H2O2ratio in Fenton process to increase dewaterability and solubilisation of sludge [J]. Environmental Technology, 2019:1-9.

Comparison of the enhanced effect of protocatechuic acid and gentisic acid on the heterogeneous UV-Fenton system with Poly-Silicate-Ferric(PSF) as catalyst.

SU Xiao-xuan1,2, XU Guo-peng1,2, LI Xian-zhong1,2, LIU Li-zhang3, CHEN Jian-xin1,2*

(1.School of Resources, Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, China；2.Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, Nanchang 330031, China；3.Jiangxi Academy of Environmental Sciences, Nanchang 330077, China)., 2021,41(4)：1624~1633

The capability of protocatechuic acid and gentisic acid in enhancing the degradation of orange II in the heterogeneous UV-Fenton system with PSF as catalystwas compared, and the relationship among iron ion conversion, H2O2decomposition and ·OH generation in the two systems was analyzed. The enhancement mechanisms of the two reagents in heterogeneous UV-Fenton system with PSF as catalystwas further discussed. The experimental results showed that both protocatechuic acid and gentisic acid couldeffectively promote the formation and release of Fe2+, thereby increasing ·OH concentration and promoting orange II degradation. Compared with protocatechuic acid, gentisic acid showed better capacity for reducing PSF. As a result, higher·OH concentration and fasterorange IIdegradation rate were achieved in the gentisic acid system. With the addition of 0.2mmol/L reagent, the "first" kinetic rate constant fororange II decolorization increased from 0.11 to 1.68min-1for the protocatechuic acid system, and to 2.48min-1for thegentisic acid system, which increased by 14.27 and 21.55 times, respectively. During consecutive runs, both the two acids could enhanceorange II degradation. After treatment, the readsorption of Fe3+by PSF made the total iron ion concentration in solution lower than 5mg/L, avoiding the loss of iron ions and the secondary pollution. Our results indicated that protocatechuic acid and gentisic acid were both highly effective enhancement reagents to heterogeneous UV-Fenton systemwith PSF as catalyst.

heterogeneous UV-Fenton system；PSF；protocatechuic acid；gentisic acid；orange Ⅱ

X703

A

1000-6923(2021)04-1624-10

蘇曉軒(1996-),男,新疆石河子人,南昌大學(xué)碩士研究生,主要從事水污染控制研究.

2020-08-24

國(guó)家自然科學(xué)基金資助項(xiàng)目(21966021,21367021);廣東省科技計(jì)劃資助項(xiàng)目 (2017B030314175)

* 責(zé)任作者, 副教授, jxchen@ncu.edu.cn