劉艷雯,張倩倩*,張安超**,李成偉,代冰潔,梅艷陽,張 森,蘇 勝,向 軍

Ag-PANI/BiOI光催化劑濕法脫除氣態(tài)單質(zhì)汞

劉艷雯1,張倩倩1*,張安超1**,李成偉1,代冰潔1,梅艷陽1,張 森1,蘇 勝2,向 軍2

(1.河南理工大學(xué)機(jī)械與動力工程學(xué)院,河南 焦作 454000；2.華中科技大學(xué),煤燃燒國家重點(diǎn)實(shí)驗(yàn)室,湖北 武漢 430074)

采用原位光還原和簡易化學(xué)吸附法制備出新型的三元Ag負(fù)載聚苯胺/碘氧化鉍(PANI/BiOI)系列光催化劑,在模擬煙氣條件下考察了光催化劑的脫汞性能,研究了Ag負(fù)載量、反應(yīng)溫度和煙氣成分等對脫汞活性的影響,采用N2吸附-脫附、XRD、TEM、XPS、DRS等技術(shù)對光催化劑的物理化學(xué)屬性進(jìn)行表征.結(jié)果表明:添加PANI后,光催化劑的Hg0去除性能大幅提升.負(fù)載4wt%的Ag后,Ag(4%)PANI/BiOI具有約98%的脫汞性能.無機(jī)陰離子NO3?、Cl?和SO42?對光催化劑脫汞性能的抑制作用較小,但CO32?對光催化劑的活性抑制作用較大,脫汞效率明顯下降至82%.與PANI/BiOI相比,Ag(4%)PANI/BiOI的比表面積和總孔容增大,表明Ag納米顆粒高度分散在PANI/BiOI的表面.Ag-PANI/BiOI顯示出較強(qiáng)的光吸收能力.Ag納米顆粒的添加能顯著增強(qiáng)PANI/BiOI表面e?-h+對的有效分離.光催化劑高效脫汞的原因在于PANI、BiOI之間良好的帶隙匹配和Ag納米顆粒的表面等離子體共振(SPR)效應(yīng).

聚苯胺；碘氧化鉍；光催化劑；濕法；單質(zhì)汞脫除

汞作為一種主要的空氣污染物,具有強(qiáng)毒性、易揮發(fā)性、生物富集性和遷移性等屬性,已對人類生態(tài)構(gòu)成了嚴(yán)重威脅.燃煤電廠被認(rèn)為是汞排放的主要來源之一[1].中國作為世界上最大的煤炭生產(chǎn)國和消費(fèi)國,汞排放量居全球首位[2].燃煤煙氣中的汞主要以單質(zhì)汞(Hg0)、二價(jià)汞(Hg2+)以及顆粒態(tài)汞(Hgp)3種形式存在[3].Hg0由于其高揮發(fā)性、不溶性、化學(xué)穩(wěn)定性等特點(diǎn),不易被現(xiàn)有的煙氣污染治理設(shè)備脫除[4].因此,將Hg0轉(zhuǎn)化為Hg2+將極大地降低電廠煙氣汞排放量并且成為解決日益嚴(yán)重的汞問題的關(guān)鍵[5].

近年來,濕法脫汞技術(shù)的研究較多.其中,高級氧化工藝(AOPs)由于反應(yīng)條件溫和、氧化能力強(qiáng)、能產(chǎn)生強(qiáng)氧化能力的自由基等特點(diǎn)具有巨大的發(fā)展?jié)摿?作為AOPs的一種,基于可見光的光催化氧化技術(shù)受到重點(diǎn)關(guān)注.在各種光催化劑中,碘氧化鉍(BiOI)因其特殊的層狀結(jié)構(gòu)、適宜的禁帶寬度和較高的穩(wěn)定性,被廣泛用于光降解污染物[6-7].但在可見光照射下,BiOI的電子一空穴(e?-h+)對容易復(fù)合,使得其光催化活性大大降低[8].將2種半導(dǎo)體材料結(jié)合形成半導(dǎo)體/半導(dǎo)體異質(zhì)結(jié)可增強(qiáng)其光催化氧化性能[9].另外,通過摻雜貴金屬亦可以增強(qiáng)光催化劑的活性.而在Au、Ag、Pt等貴金屬中,價(jià)格便宜、穩(wěn)定性高、光催化能力強(qiáng)為特點(diǎn)的銀基光催化劑具有極大的應(yīng)用前景[10-11].通過水熱法制備的Ag/ZnO納米復(fù)合材料可大幅提高對污染物的降解性能[11].采用光還原沉積法將納米Ag顆粒成功負(fù)載至g-C3N4表面,在可見光下降解羅丹明的效率為單一g-C3N4的7倍[12].

聚苯胺(PANI)作為一種高分子化合物,其光學(xué)性質(zhì)比較特殊.大量的共軛p電子聚集在其分子主鏈上,在強(qiáng)光的作用下價(jià)帶中的電子會躍遷至導(dǎo)帶,產(chǎn)生e?-h+對.如今,PANI已被廣泛用來修飾其他半導(dǎo)體,在可見光照射下充當(dāng)有效的電子供體[13].例如,PANI/SnO2[14]、PANI/TiO2[15]、PANI/ Bi12O17Cl[16]等.此外,一些研究報(bào)道的BiVO4/ Ag3PO4/PANI[17]、PANI/BiOBr/ZnFe2O4[18]復(fù)合光催化劑均可用于降解污染物,并且較于相匹配的單一催化劑具有增強(qiáng)的光催化性能.因此,使用PANI對BiOI進(jìn)行改性是提高可見光利用率和光電荷分離效率的一種有前景的方法.

本文采用原位光還原和簡易化學(xué)吸附法制備出Ag負(fù)載PANI摻雜BiOI復(fù)合材料光催化劑,在濕法光催化裝置上研究光催化氧化濕法脫除氣態(tài)Hg0的性能,結(jié)合多種表征手段,探究催化劑在可見光下的高效脫汞反應(yīng)機(jī)理,以期為高效低廉的燃煤煙氣脫汞催化劑的開發(fā)及推廣提供參考.

1 材料與方法

1.1 催化劑的制備

PANI的制備:取5.705g過硫酸銨溶解在50mL去離子水中,逐滴加入2.328g苯胺單體溶液,在室溫下攪拌4h.然后靜置24h,得到黑綠色的沉淀,最后用乙醇和水混合物洗滌沉淀物數(shù)次,在真空中60℃烘干12h,即得到PANI材料.

PANI/BiOI催化劑的制備:取0.09g PANI分散在200mL四氫呋喃溶液中.將0.9g BiOI粉末置于上述溶液中(BiOI樣品的制備方法見文獻(xiàn)[8]),攪拌24h,用乙醇和水溶液洗滌數(shù)次,置于烘箱中80℃烘干,篩分至100目,即得到PANI/BiOI催化劑.

Ag-PANI/BiOI系列光催化劑的制備:首先,將2g PANI/BiOI和0.032g AgNO3分散在200mL含有10mL HCOOH的水溶液中,超聲處理30min,使其形成懸浮液;然后在機(jī)械攪拌的情況下,用60W高壓汞燈照射此懸浮液2h,將Ag+還原為Ag0納米顆粒并均勻負(fù)載于PANI/BiOI表面.最后,將沉淀物用乙醇和水的混合溶液洗滌數(shù)次,置于烘箱中60℃烘干,篩分至100目,即得到Ag(1%)PANI/BiOI,其中1%為Ag與PANI/BiOI的質(zhì)量分?jǐn)?shù).另外,改變AgNO3的質(zhì)量分別制備出Ag(=2%、4%、6%、8%、10%)PANI/BiOI光催化劑.

1.2 光催化劑性能評價(jià)

光催化劑的活性測試在自制小型實(shí)驗(yàn)臺上完成,主要包括模擬煙氣源、光催化反應(yīng)裝置、氣體檢測裝置以及尾氣吸收裝置等.設(shè)備的具體介紹和實(shí)驗(yàn)方法見文獻(xiàn)[19].N2、O2和CO2為基本煙氣成分,N2為平衡氣,后2種氣體含量分別為6%與12%.模擬煙氣的總流量、反應(yīng)溶液體積和光催化劑用量分別為1.5L/min、1.0L和0.2g,汞的初始含量(in)約為55μg/m3.實(shí)驗(yàn)所用光源為商用11W熒光燈,采用Fluorolog-3熒光光譜儀檢測熒光燈的波長主要為405,437,547nm的可見光區(qū)域,表明本實(shí)驗(yàn)所用熒光燈可近似為可見光光源.反應(yīng)前后Hg0蒸氣濃度由汞分析儀器實(shí)時(shí)監(jiān)測,光催化劑的脫汞效率(%)由下式計(jì)算得到:

式中:in和out分別表示濕法脫汞裝置進(jìn)出口Hg0的質(zhì)量濃度,μg/m3.

1.3 催化劑的表征

光催化劑的孔隙結(jié)構(gòu)特征測試在Autosorb?iQ型全自動物理吸附分析儀上完成;樣品的晶相檢測使用D8Advance型X?射線衍射(XRD)儀;光催化劑的透射電鏡圖像使用JEM-2010型透射電子顯微鏡(TEM)完成測試;光催化劑中元素的存在形態(tài)由Escalab 250Xi型X?射線光電子能譜(XPS)分析儀測定;光催化劑的紫外?可見光漫反射光譜(DRS)采用U-4100型紫外?可見分光光度計(jì)進(jìn)行測試;樣品的光致發(fā)光光譜(PL)在FLSP920熒光光譜儀上測試完成;可見光輻照下的活性自由基由ER200-SRC儀器測定,活性自由基的峰強(qiáng)度與其含量成正比.

2 結(jié)果與討論

2.1 脫汞性能分析

由圖1可以看出,PANI和BiOI樣品的脫汞性能均較差,分別為24%和30%.然而,PANI/BiOI的脫汞效率提升至83%,表明添加PANI后,光催化劑的Hg0去除活性大幅提升.負(fù)載Ag納米顆粒之后,所有Ag()PANI/BiOI系列光催化劑(=1%、2%、4%、6%、8%、10%)的脫汞活性均有較大提升,當(dāng)Ag含量達(dá)到4%時(shí),光催化劑的脫汞效率最高.上述現(xiàn)象可能歸因于PANI/BiOI之間合適的帶隙匹配和納米Ag0的SPR效應(yīng)[20].

由圖2(a)可知,無光催化劑時(shí),熒光燈的效率為7%;無熒光燈時(shí),Ag(4%)PANI/BiOI樣品的效率約為28%,意味著其單獨(dú)使用時(shí)脫汞性能均較差.然而,但當(dāng)熒光燈照射和Ag(4%)PANI/BiOI同時(shí)使用時(shí),脫汞效率顯著提高至98%,意味著熒光燈的存在對Ag(4%)PANI/BiOI樣品的高效脫汞極其重要.在熒光燈輻照條件下,脫汞效率維持在98%附近,關(guān)閉熒光燈120min內(nèi),脫汞效率僅有輕微的降低,繼續(xù)打開熒光燈,脫汞效率快速回升至最高值,可能是由于光照時(shí)反應(yīng)溶液中產(chǎn)生了較多的活性物種,在黑暗條件下仍然繼續(xù)參與反應(yīng),這可由自由基測試實(shí)驗(yàn)得到驗(yàn)證.

圖1 Ag負(fù)載量對脫汞效率的影響

圖2 不同試驗(yàn)條件對Ag(4%)PANI/BiOI脫汞效率的影響

由阿侖尼烏斯方程知,反應(yīng)溫度升高能夠降低活化能,進(jìn)而提高化學(xué)反應(yīng)的速率[21].由圖2(b)可以看出,當(dāng)溶液反應(yīng)溫度為20和40℃時(shí),光催化劑的脫汞效率均較高,分別為98.0%和98.5%.當(dāng)溶液溫度升高至60℃時(shí),光催化劑的脫汞效率下降至約70.0%.說明在可見光催化氧化體系中,存在最佳的反應(yīng)溶液溫度,較高的反應(yīng)溫度不利于汞的氧化脫除.由飽和溶解氧溫度對照表知,室溫～100℃范圍內(nèi),氧的溶解度隨溫度升高而降低.因此,其原因可能是高溫下反應(yīng)溶液對O2的溶解能力下降,導(dǎo)致反應(yīng)過程中活性超氧基團(tuán)(?O2?)含量降低,進(jìn)而影響汞的脫除效率.

研究表明[22],無機(jī)離子會與溶液中的活性基團(tuán)反應(yīng),減少參與催化氧化反應(yīng)的活性自由基,從而導(dǎo)致光催化劑性能的下降.考慮到實(shí)際燃煤煙氣中含有可溶性的無機(jī)化合物,因此有必要探索常見陰離子對光催化劑去除Hg0性能的影響.在實(shí)驗(yàn)中,分別將NaCl、NaNO3、Na2SO4和Na2CO3與Ag(4%) PANI/BiOI樣品同時(shí)加入反應(yīng)溶液,結(jié)果如圖2(c)所示.加入0.1mol/L的無機(jī)陰離子時(shí),NO3?、Cl?和SO42?對光催化劑的抑制作用較小,脫汞效率由96%分別下降至94%、93%和92%,而CO32?對光催化劑的抑制作用較大,脫汞效率明顯下降至82%.可能是由于CO32?離子消耗了活性物質(zhì)和水解產(chǎn)生了較多的OH?,致使脫汞性能下降,相關(guān)反應(yīng)式如下[23]:

不同O2、SO2和NO濃度下Ag(4%)PANI/BiOI樣品的脫汞性能如圖2(d)所示.當(dāng)O2濃度由0增加到6%時(shí),光催化劑的脫汞效率有稍微的增加.但是當(dāng)O2濃度增加到12%時(shí),相比于添加6%O2濃度時(shí)的脫汞效率有輕微下降.原因可能是,當(dāng)添加少量O2時(shí),O2與光生電子e?反應(yīng)生成具有強(qiáng)氧化性的?O2?,但是當(dāng)添加O2過量時(shí),O2則與光生電子e?反應(yīng)生成H2O2,H2O2進(jìn)而與e?反應(yīng)生成了?OH和OH?,?OH的脫汞活性比?O2?小.相關(guān)反應(yīng)式如下[24]:

當(dāng)添加125mg/m3的SO2時(shí),光催化劑的脫汞效率由98%急劇下降至68%,繼續(xù)增加SO2濃度至500mg/m3,脫汞效率降至45%,表明SO2抑制光催化劑的脫汞效率.SO2停止供給后,光催化劑的性能逐漸恢復(fù),脫汞效率短時(shí)間又提升至98%.其原因可能是SO2與溶液中的活性物質(zhì)發(fā)生反應(yīng),短時(shí)間內(nèi)未對光催化劑結(jié)構(gòu)造成破壞[25],具體反應(yīng)式如下:

以上現(xiàn)象表明,Ag(4%)PANI/BiOI光催化劑的抗硫性較差,鑒于目前濕法煙氣脫硫工藝已經(jīng)成熟,為了避免SO2對脫汞性能的影響,可以考慮在濕法煙氣脫硫裝置后增加光催化脫汞裝置.

當(dāng)添加350mg/m3的NO時(shí),光催化劑的脫汞效率由98%下降至91%,繼續(xù)增加NO濃度,脫汞效率的抑制作用增加明顯,切斷NO供應(yīng)后,光催化劑的脫汞效率恢復(fù)到初始值.其原因應(yīng)為NO的添加消耗了反應(yīng)溶液中的活性物質(zhì),引起了脫汞效率的下降[26],反應(yīng)式如下:

在光催化劑的實(shí)際商業(yè)應(yīng)用中,不僅要考慮光催化劑的催化活性,還需要其具有良好的穩(wěn)定性,以維持較長時(shí)間的應(yīng)用.結(jié)果如圖3所示,進(jìn)行4次循環(huán)脫汞實(shí)驗(yàn)的脫汞效率無顯著變化,脫汞效率均達(dá)95%以上,表明Ag(4%)PANI/BiOI光催化劑在熒光燈照射下具有良好的穩(wěn)定性.

圖3 Ag(4%)PANI/BiOI樣品的循環(huán)脫汞性能

2.2 光催化劑的表征

由表1所示,可以看出,BiOI、PANI/BiOI和Ag(4%)PANI/BiOI 3種樣品的比表面積和總孔容依次增大,表明Ag納米顆粒高度分散在PANI/BiOI表面,形成了新表面.然而相比于PANI/BiOI,Ag(4%) PANI-BiOI的平均孔徑有所降低,可能是由于負(fù)載Ag納米顆粒堵塞了BiOI樣品部分空隙所致.

表1 光催化劑的孔隙結(jié)構(gòu)參數(shù)

利用XRD對9種樣品進(jìn)行表征,其結(jié)果如圖4所示.BiOI、PANI/BiOI及Ag()PANI/BiOI系列樣品顯示的XRD特征衍射峰與BiOI標(biāo)準(zhǔn)譜(JCPDS 73-2062)吻合良好.對于PANI樣品,在2= 19°、25°處有2個特征衍射峰[27],然而在PANI/BiOI以及Ag()PANI/BiOI系列樣品中,并未觀察到明顯的PANI衍射峰,這可能是由于制備PANI/BiOI時(shí)加入的PANI含量過少或其分散性良好有關(guān).另外,還可以看出,Ag(= 1%、2%、4%、6%)PANI/BiOI系列樣品中未檢測到Ag0的衍射峰,原因是Ag0納米顆粒負(fù)載量過少所致.Ag(= 8%、10%)PANI/BiOI樣品在2= 38.11°出現(xiàn)了微弱的Ag0衍射峰[28],意味著Ag()PANI/BiOI表面負(fù)載有Ag0納米顆粒.

圖4 光催化劑的XRD圖譜

由圖5可見,PANI是棒狀結(jié)構(gòu),BiOI和PANI/ BiOI均是分層片狀結(jié)構(gòu).與BiOI相比,Ag(4%)PANI/ BiOI片層上分散有一些微納米顆粒,這些微納米顆粒應(yīng)為從AgNO3溶液中還原出來的Ag0納米顆粒.

圖6為PANI、BiOI和Ag(4%)PANI/BiOI的XPS圖譜.由圖6(a)可知,BiOI和Ag(4%)PANI/BiOI中位于164.4和159.1eV處的峰分別歸屬于Bi 4f5/2和Bi 4f7/2,來自于BiOI中Bi3+.BiOI中位于630.8和619.3eV處的峰對應(yīng)于I 3d3/2和I 3d5/2(圖6(b)),Ag(4%)PANI/BiOI中位于630.5和618.9eV的峰對應(yīng)I 3d3/2和I 3d5/2,均為BiOI中I?的特征峰.

圖5 光催化劑的TEM形貌

Ag 3d的XPS圖譜如圖6(c)所示,位于374.17和368.17eV的兩個峰對應(yīng)Ag 3d3/2和Ag 3d5/2,表明催化劑Ag(4%)PANI/BiOI中Ag的存在[29].圖6(d)為O 1s的XPS圖譜,相比于PANI,BiOI和Ag(4%) PANI/BiOI中的O 1s圖譜均有2個峰,其中低結(jié)合能處的峰代表晶格氧,高結(jié)合能處的峰代表著化學(xué)吸附態(tài)氧.高含量的化學(xué)吸附態(tài)氧有利于?O2?和?OH活性物質(zhì)的產(chǎn)生.很明顯,Ag(4%)PANI/BiOI中化學(xué)吸附態(tài)氧含量高于PANI和BiOI,這與脫汞活性實(shí)驗(yàn)結(jié)果相吻合.此外,對比BiOI,Ag(4%)PANI/BiOI樣品的I 3d和O 1s特征峰均向低結(jié)合能處偏移,這可能與Ag(4%)PANI/BiOI中各成分之間相互作用有關(guān).

DRS分析可以反映光催化劑對可見光的吸收能力[30].由圖7(a)可以看出,6種樣品都可以吸收波長小于650nm的可見光,其中PANI呈現(xiàn)出最低的吸收能力,PANI/BiOI的光吸收能力介于PANI和BiOI之間.相比PANI/BiOI,Ag(=1%,4%,10%)PANI/ BiOI系列光催化劑均呈現(xiàn)出較強(qiáng)的光吸收能力,其中,光催化劑Ag(=10%)PANI/BiOI呈現(xiàn)出最強(qiáng)的光吸收能力,這應(yīng)該與其表面Ag0微納米顆粒的SPR效應(yīng)有關(guān).DRS結(jié)果也間接證明了PANI/BiOI表面Ag的存在.

圖6 光催化劑的XPS圖譜

樣品的帶隙能可由公式g=hc/g=1240/g(其中,g和g分別代表材料的禁帶寬度和吸收邊緣波長值)進(jìn)行計(jì)算.由圖7(a)知,BiOI和Ag(4%) PANI/ BiOI的吸收邊緣波長約為681和658nm.經(jīng)計(jì)算, BiOI和Ag(4%) PANI/BiOI的帶隙能分別為1.82和1.88eV.樣品的導(dǎo)帶(CB)電位和價(jià)帶(VB)電位可由如下經(jīng)驗(yàn)公式獲得:

式中:CB和VB分別代表CB電位和VB電位;C是氫量計(jì)的氫電子能量(4.5eV);是半導(dǎo)體的絕對電負(fù)性,g是帶隙能量.結(jié)果可得BiOI的CB值為0.53eV,VB值為2.35eV.

通過PL光譜強(qiáng)度可以了解半導(dǎo)體光生電子-空穴(e?-h+)對的分離效率[31].研究發(fā)現(xiàn)[32],PL峰值越低,光生e?-h+對的復(fù)合率就越低,越容易產(chǎn)生強(qiáng)氧化性的活性成分.如圖7(b)在可見光區(qū)域,Ag(4%)PANI/ BiOI的PL光譜強(qiáng)度最弱,表明e?-h+對的分離效果最佳,這與Ag(4%)PANI/BiOI樣品的光催化脫汞活性一致.由此可見,樣品中e?-h+對的高效分離是增強(qiáng)光催化劑脫汞性能的因素之一.

由圖8可以看出,在黑暗狀態(tài)下捕捉不到?O2?和?OH的信號,然而對樣品進(jìn)行可見光照射4min后,可以清晰地觀察到?O2?和?OH的4個信號.繼續(xù)照射8和12min后,?O2?和?OH的信號逐漸增強(qiáng).表明在可見光照射下,Ag(4%)PANI/BiOI光催化劑能夠產(chǎn)生強(qiáng)氧化性的活性自由基?O2?和?OH.

2.3 機(jī)理分析

為確定PANI/BiOI和Ag(4%)PANI/BiOI樣品脫除Hg0時(shí)參與反應(yīng)的活性物質(zhì),進(jìn)行了活性物質(zhì)捕獲實(shí)驗(yàn).在捕集實(shí)驗(yàn)過程中,加入的乙二胺四乙酸二鈉(EDTA-2Na)、苯醌(BQ)和異丙醇(IPA)分別作為h+、?O2?和?OH的清除劑,其中EDTA-2Na、BQ和IPA的劑量分別為0.5g、0.5g和10mL.如圖9所示,加入BQ和EDTA-2Na后,光催化劑催化活性均大幅降低;加入IPA后,PANI/BiOI的脫汞性能幾乎無變化,而Ag(4%)PANI/BiOI的脫汞活性略微的降低,表明在兩種光催化劑反應(yīng)過程中,?O2?起主要作用,h+的作用次之,而?OH的作用較小.

基于實(shí)驗(yàn)與表征分析,可以繪制出PANI/BiOI和Ag(4%)PANI/BiOI光催化劑去除Hg0的反應(yīng)機(jī)理示意圖(圖10).如圖10所示,在可見光(能量2.95eV)照射下,帶隙能較窄的BiOI易被激發(fā)產(chǎn)生e?-h+對,且會發(fā)生e?的躍遷,CB邊緣上升至較低的電位邊緣(-0.6eV).根據(jù)文獻(xiàn)[33],PANI的LUMO(最低未占據(jù)能級分子軌道)和HOMO(最高占據(jù)能級分子軌道)電勢分別為-2.14和0.62eV.PANI能夠吸收可見光誘導(dǎo)π-π*躍遷,促使HOMO的激發(fā)態(tài)電子進(jìn)入LUMO.由于O2/?O2?的氧化電位(-0.33eVNHE)均高于BiOI的躍遷CB電勢和PANI的LUMO電勢,因此BiOI和PANI均有能力通過光誘導(dǎo)電子還原將O2轉(zhuǎn)為?O2?[34].以上分析可知,BiOI和PANI兩種材料具有合適的能級匹配,能夠產(chǎn)生協(xié)同效應(yīng)[34].將兩者復(fù)合后,PANI的LUMO上e?會轉(zhuǎn)移到BiOI的CB上,在e?轉(zhuǎn)移過程中與溶液中的溶解O2發(fā)生反應(yīng)產(chǎn)生具有強(qiáng)氧化性的?O2?;同時(shí)BiOI VB上的h+會轉(zhuǎn)移至PANI的HOMO,h+也是強(qiáng)氧化性能的活性物質(zhì).在可見光激發(fā)過程中,PANI/BiOI產(chǎn)生的?O2?、h+與氣態(tài)Hg0發(fā)生反應(yīng),將其氧化為Hg2+,從而達(dá)到脫除Hg0的目的.

圖9 添加不同消除劑后PANI/BiOI和Ag(4%)PANI/BiOI的脫汞效率

研究表明[35],Ag0具有較強(qiáng)的e?捕獲能力,且可見光輻照下Ag0納米顆粒的SPR效應(yīng)有利于其表面e?的激發(fā)和界面轉(zhuǎn)移.由于Ag0納米顆粒具有良好的e?流動性,PANI的LUMO上的e?轉(zhuǎn)移到BiOI的CB后,易被Ag0納米顆粒捕獲,更容易與溶液中溶解的O2發(fā)生反應(yīng)產(chǎn)生強(qiáng)氧化性的?O2?,使Ag(4%)PANI/ BiOI光催化劑具有更強(qiáng)的脫汞性能.然而,當(dāng)過多的Ag0納米顆粒負(fù)載在PANI/BiOI表面上時(shí),在可見光輻照下,Ag0納米顆粒會占據(jù)反應(yīng)活性位點(diǎn)攜帶大量的e?,這些帶負(fù)電的納米顆粒會捕獲溶液中的h+實(shí)現(xiàn)電荷重組,造成活性物質(zhì)的消耗,這與以前研究現(xiàn)象類似[36-37].因此,只有Ag0負(fù)載量合適時(shí),它對e?的界面轉(zhuǎn)移及其SPR效應(yīng)才能發(fā)揮到最佳,獲得最佳的光催化活性.

圖10 Ag(4%)PANI/BiOI光催化劑的高效脫汞機(jī)理

3 結(jié)論

3.1 PANI改性BiOI光催化劑呈現(xiàn)出良好的光催化活性.Ag0納米顆粒的添加顯著提升了復(fù)合光催化劑的汞去除能力,其中Ag(4%)PANI/BiOI光催化劑的脫汞效率高達(dá)98%.在Ag(4%)PANI/BiOI的高效脫汞過程中,?O2?和h+起重要作用.

3.2 添加Ag0納米顆粒能夠增強(qiáng)PANI/BiOI表面e?-h+對的有效分離,高效脫汞的原因是PANI、BiOI之間良好的帶隙匹配以及Ag0納米顆粒的SPR效應(yīng).

3.3 4次循環(huán)脫汞實(shí)驗(yàn)后,光催化劑的脫汞效率無顯著變化,表明Ag(4%)PANI/BiOI光催化劑在熒光燈照射下具有良好的穩(wěn)定性.

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Performance of Ag-PANI/BiOI photocatalyst for wet removal of gaseous elemental mercury.

LIU Yan-wen1, ZHANG Qian-qian1*, ZHANG An-chao1**, LI Cheng-wei1, DAI Bing-jie1, MEI Yan-yang1, ZHANG Sen1, SU Sheng2, XIANG Jun2

(1.School of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo 454000, China；2.State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China)., 2022,42(3)：1104～1112

Series of novel ternary Ag supported PANI/BiOI hybrids synthesized by an in-situ photoreduction and facile chemisorptions method were utilized to explore their activities for the removal of toxic elemental mercury (Hg0) under simulated flue gas condition. The effects of Ag content, reaction temperature and flue gas composition on Hg0removal activity were investigated. The physicochemical properties of the samples were characterized via N2adsorption desorption, XRD, TEM, XPS and DRS et al. The Hg0removal activity of photocatalyst was greatly increased because of the addition of PANI. After the load of 4wt% Ag,the mercury removal efficiency of Ag(4%)PANI/BiOI can reach as high as 98%. The inhibition of Hg0removal performance of photocatalyst was less by inorganic anions, such as NO3?, Cl?and SO42?, while CO32?possessed a greater inhibition on the activity of photocatalyst, with the Hg0removal efficiency decreasing to 82%. Compared with PANI/BiOI, the specific surface area and total pore volume of Ag(4%)PANI/BiOI increased, indicating that Ag nanoparticles were highly dispersed on the surface of PANI/BiOI. Ag-PANI/BiOI photocatalyst showed a strong light absorption capacity. Adding Ag nanoparticles resulted in an effective separation of e?-h+pair on PANI/BiOI surface. The reason for the higher efficiency Hg0removal of hybrid photocatalyst could be ascribed to the good band gap matching between PANI and BiOI and the surface plasmon resonance (SPR) effect of Ag nanoparticles.

polyaniline；bismuth oxyiodide；photocatalyst；wet progress；Hg0removal

X511

A

1000-6923(2022)03-1104-09

劉艷雯(1998-),女,河南信陽人,河南理工大學(xué)碩士研究生,主要從事燃煤煙氣多種污染物治理技術(shù)研究.發(fā)表論文2篇.

2021-08-01

國家自然科學(xué)基金資助項(xiàng)目(51676064);河南省高?？萍紕?chuàng)新人才資助項(xiàng)目(19HASTIT045);河南省科技攻關(guān)資助項(xiàng)目(182102310810)

*責(zé)任作者, 講師, zhangqianqian@hpu.edu.cn; ** 教授, anchaozhang@ 126.com