郭天宇,范祥瑞,白德豪,祁 彧,王紅濤*
異質(zhì)結(jié)CeO2/BiOBr的構(gòu)筑及其光催化降解羅丹明B
郭天宇1,2,范祥瑞1,白德豪3,祁 彧1,王紅濤1*
(1.太原理工大學(xué)環(huán)境科學(xué)與工程學(xué)院,山西 晉中 030600;2.氣體能源高效利用山西省重點(diǎn)實驗室,山西 太原 030024;3.中石油煤層氣有限責(zé)任公司忻州分公司,山西 忻州 036600)
通過水熱法合成了CeO2、BiOBr和不同物質(zhì)的量比的CeO2/BiOBr復(fù)合光催化劑,采用不同的測試手段對光催化劑的形貌、結(jié)構(gòu)和光電化學(xué)性能進(jìn)行了表征,并通過可見光照射下羅丹明B (RhB)的降解來評價其光催化性能.結(jié)果表明,引入適量CeO2(10%)的CeO2/BiOBr (CB-10)異質(zhì)結(jié)顯著地增強(qiáng)了光催化活性,在30min內(nèi)可降解99%的RhB,且表現(xiàn)出優(yōu)異的可回收性和循環(huán)穩(wěn)定性.另當(dāng)pH值為3,復(fù)合催化劑與RhB濃度分別為0.5g/L、20mg/L時,降解效率在20min內(nèi)可達(dá)最高(96.1%).根據(jù)自由基捕獲試驗和催化劑的能帶結(jié)構(gòu),提出了CeO2/BiOBr異質(zhì)結(jié)光催化過程可能的反應(yīng)機(jī)理.研究結(jié)果可為制備Bi 基復(fù)合催化劑提供一種新的思路與方法.
光催化降解;CeO2/BiOBr;異質(zhì)結(jié);羅丹明B
高濃度的有機(jī)染料廣泛存在于紡織工業(yè)廢水中,造成了環(huán)境污染與水資源短缺,工業(yè)廢水中的污染物具有很強(qiáng)的穩(wěn)定性和持久性,對人類具有累積毒性與致癌性[1-2].其中,羅丹明B (RhB)作為一種具有熒光效應(yīng)的合成染料,具有色澤深、結(jié)構(gòu)復(fù)雜、化學(xué)穩(wěn)定性強(qiáng)等特點(diǎn)[3-4].因此,亟需開發(fā)一種高效、綠色且廉價的去除廢水中有機(jī)污染物的處理技術(shù).
目前,已有去除RhB等有機(jī)污染物的方法可分為化學(xué)、物理和生物三種方法,即絮凝、膜分離、吸附、高級氧化、電化學(xué)、光催化、生物降解等工藝[5].然而,物理與化學(xué)方法主要是通過降低染料濃度,將染料從液相轉(zhuǎn)移到固相,容易造成二次污染[6-7].光催化技術(shù)作為一種新的光化學(xué)技術(shù),具有高效、綠色環(huán)保、成本低、反應(yīng)條件溫和及壽命長等優(yōu)點(diǎn)[3,8-9],且光催化材料具有無毒、經(jīng)濟(jì)等特點(diǎn),因此去除有機(jī)染料的效率相對較高.
在已有報道的光催化劑中,作為一種典型的p型半導(dǎo)體,BiOBr由于其具有合適的帶隙(E=2.64~ 2.9eV)[10]以及良好的化學(xué)穩(wěn)定性,且具有四方馬氏體和特殊的層狀結(jié)構(gòu),提升了光電化學(xué)性能并促進(jìn)了載流子的分離,有效提高了光催化活性,因而在光催化領(lǐng)域受到了廣泛的關(guān)注,但其應(yīng)用受限于可見光吸收能力差和高載流子復(fù)合速率[10-12].有研究報道,構(gòu)筑BiOBr異質(zhì)結(jié)結(jié)構(gòu)可以有效地促進(jìn)光生電子空穴對的分離和提高可見光的利用率[13-14].近年來,氧化鈰(CeO2)因其廉價、環(huán)境友好及良好的儲放氧能力等突出特點(diǎn)而在光催化領(lǐng)域備受關(guān)注[15-16].在構(gòu)建異質(zhì)結(jié)時,CeO2的引入可以抑制光生電子空穴對的復(fù)合,增加化學(xué)吸附氧的濃度,從而有利于光催化性能的提高.例如,Wang等[17]構(gòu)筑了CeO2/TiO2異質(zhì)結(jié)結(jié)構(gòu),抑制了光致載流子的重組,擴(kuò)大了光響應(yīng)范圍,從而提高了苯酚的降解率.Liu等[18]合成了具有Z型異質(zhì)結(jié)和氧空位的CeO2/Bi7O9I3花狀納米球,促進(jìn)了電子的傳遞,提高了對重金屬污染物Hg0的去除率.基于上述分析,本文通過水熱法制備了CeO2/BiOBr光催化材料,并應(yīng)用于可見光下降解RhB,以探究材料的光催化降解性能,采用多種表征技術(shù)對CeO2/BiOBr光催化劑微觀結(jié)構(gòu)及光電性能進(jìn)行分析,且根據(jù)自由基捕獲實驗和能帶結(jié)構(gòu),探討了該光催化材料的作用機(jī)制.
本實驗所有化學(xué)藥品均為分析純.五水合硝酸鉍(Bi(NO3)3·5H2O)、溴化鉀(KBr)、六水合硝酸鈰(Ce (NO3)3·6H2O)、異丙醇(IPA)、對苯醌(BQ)、乙二胺四乙酸二鈉(EDTA-2Na)、無水甲醇(CH3OH)均購自國藥集團(tuán)化學(xué)試劑有限公司,乙二醇((CH2OH)2)購自天津科密歐化學(xué)試劑有限公司,氫氧化鈉(NaOH)購自天津致遠(yuǎn)化學(xué)試劑有限公司.
1.2.1 CeO2的制備 將2.60g的Ce(NO3)3·6H2O溶解于10mL的去離子水中,磁力攪拌至完全溶解后,得到溶液A;另15mL的去離子水中加入8g的NaOH,同樣待完全溶解后記為溶液B.將溶液B緩慢倒入溶液A中,磁力攪拌30min后,將混合溶液轉(zhuǎn)移至100mL的聚四氟乙烯內(nèi)襯的反應(yīng)釜中,在180oC條件下反應(yīng)12h.為了去除雜質(zhì),將反應(yīng)后的樣品先后用去離子水和無水乙醇各洗滌三次,最后在80oC干燥12h.
1.2.2 CeO2/BiOBr的制備 取3mmol的Bi(NO3)3·5H2O在磁力攪拌下加入到24mL乙二醇與12mL無水甲醇的混合溶液中,攪拌至完全溶解,得到溶液A;取3mmol的溴化鉀和物質(zhì)的量比分別為5%、10%以及15%的CeO2分別分散在10mL的去離子水中并超聲10min,得到懸浮液B.將懸浮液B緩慢倒入到溶液A中,并在室溫下攪拌30min后,將上述混合溶液轉(zhuǎn)移到100mL的反應(yīng)釜內(nèi),在180oC加熱12h;待反應(yīng)釜冷卻后,取出樣品,經(jīng)去離子水和無水乙醇分別洗滌3次,然后離心,得到的樣品在80oC干燥12h后,即得到CeO2/BiOBr復(fù)合光催化劑.根據(jù)所加CeO2量分別記為CB-5, CB-10, CB-15.為了進(jìn)行對比實驗,在不加CeO2時,用相同的方法合成了純相BiOBr.
采用X射線粉末衍射儀(XRD, Rigaku MiniFlex X),以Cu Kα為輻射源測定樣品的晶型和物相組成, 掃描范圍為2=10°~80°.通過掃描電子顯微鏡(SEM, SU8180)觀察樣品的形貌和結(jié)構(gòu).利用X射線光電子能譜(XPS, Thermo ESCALAB 250XI)表征樣品的元素組成和價態(tài).采用物理吸附儀(Micromeritics, Tristar Ⅱ 3020)分析N2吸附-脫附曲線和孔徑分布.通過紫外可見漫反射光譜(UV- Vis DRS, UV-1800)測定樣品的光學(xué)吸收性能.使用光致發(fā)光光譜(PL, Hitachi F-4700)對樣品的電子-空穴分離效率進(jìn)行分析.采用電化學(xué)工作站(VersaSTAT-3, Ametek Princeton, USA)測試樣品的電化學(xué)阻抗和瞬態(tài)光電流.在三電極體系中,使用Pt網(wǎng)和Ag/AgCl電極分別作為對電極和參比電極,涂覆光催化材料的ITO電極作為工作電極. 0.5mol/L Na2SO4作為電解液溶液.
利用光反應(yīng)設(shè)備(PLS-SEX300, perfect, China)在可見光照射下降解RhB染料,來測定合成材料的光催化活性.采用300W裝有420nm濾光片的氙燈作為可見光光源.首先,將光催化劑加入到100mL的RhB溶液中,并轉(zhuǎn)移到光反應(yīng)器中,在黑暗環(huán)境下將混合溶液進(jìn)行磁力攪拌30min,以達(dá)到吸附-脫附平衡.然后,開啟光源,在可見光照射下進(jìn)行光催化降解,實驗期間每隔5min取出3mL反應(yīng)液,進(jìn)行離心分離后,使用0.22μm聚醚砜濾膜進(jìn)行過濾,所得濾液用紫外可見分光光度計(=554nm)測量RhB的濃度.此外,研究了催化劑用量(0.1, 0.3, 0.5, 0.7和0.9g/L), RhB濃度(10, 20, 30和40mg/L),以及溶液pH值(3, 5, 7, 9, 11)對RhB去除效率的影響.
為了探究光催化材料的活性成分,對RhB降解反應(yīng)進(jìn)行自由基捕獲實驗.使用1mmol的乙二胺四乙酸二鈉(EDTA-2Na)、對苯醌(BQ)和異丙醇(IPA)分別用來捕獲空穴(h+)、超氧自由基(·O2-)和羥基自由基(·OH).
利用Excel 2016軟件對RhB降解過程中的濃度進(jìn)行分類整理,并用降解公式進(jìn)行RhB的降解效率計算:E= (1-C/0) × 100%,其中,E為RhB的降解率,0和C分別為反應(yīng)前和反應(yīng)時刻的RhB濃度;通過Origin 2018軟件繪制RhB濃度隨降解時間的變化曲線并對RhB降解的動力學(xué)進(jìn)行擬合.
2.1.1 XRD分析 采用X射線衍射儀對所制備樣品的晶相結(jié)構(gòu)進(jìn)行分析,如圖1所示.由曲線可以看出,在2為10.93°, 21.97°, 25.20°, 31.70°, 32.22°, 39.30°, 46.22°, 50.67°, 57.15°和76.67°處的特征峰與四方晶相BiOBr(JCPDs No. 09-0393)的(001), (002), (101), (102), (110), (112), (200), (104), (212)和(310)晶面衍射峰相吻合[19-20].CeO2樣品在2為28.55°, 33.08°, 47.48°, 56.33°處出現(xiàn)的衍射峰分別對應(yīng)于立方螢石相CeO2的(111), (200), (220), (311)晶面(JCPDS No. 34-0394)[21-22].此外,在復(fù)合材料中,CeO2在2為28.55°處可觀察到一個衍射峰,但這個衍射峰較弱,說明其結(jié)晶度較低[23]或CeO2的含量較低[24],同時說明了CeO2成功地負(fù)載到了BiOBr材料中.隨著CeO2含量的增加,BiOBr材料的特征峰并沒有發(fā)生明顯的變化,說明CeO2的加入并沒有改變BiOBr樣品的結(jié)晶度和晶體類型.
2.1.2 形貌和結(jié)構(gòu)分析 通過SEM來觀察BiOBr和CeO2/BiOBr樣品的微觀形貌和結(jié)構(gòu),結(jié)果見圖2.圖2(a), (b)表明所制備的BiOBr由緊密堆積的納米片和尺寸較小的納米片所組成.適量的CeO2引入(CB-5和CB-10樣品),使納米片的尺寸變小,且呈現(xiàn)由納米片自組裝成的類花狀結(jié)構(gòu)(圖2(c)-(f)),此結(jié)構(gòu)有利于增加光反射并增強(qiáng)有效光反應(yīng)表面,從而提高光催化性能[25].進(jìn)一步,過量的CeO2(CB-15樣品)破壞了BiOBr類花狀結(jié)構(gòu),呈現(xiàn)出尺寸較小的類正方形納米片形貌(圖2(g), (h)).可以看出, CeO2的引入及其含量的變化會影響B(tài)iOBr納米片的形貌、結(jié)構(gòu)和尺寸大小.然而,并未觀察到明顯的CeO2形貌,這可能是由于SEM只能檢測到樣品的表面形貌,且XRD已經(jīng)證實了CeO2的存在,可推測出在復(fù)合催化劑中CeO2的含量較少,被BiOBr覆蓋在了材料的內(nèi)部.EDS譜圖進(jìn)一步證實了CB-10樣品由Bi, O, Br和Ce 4種元素所組成(圖2(i)-(l)),同時表明了CeO2/BiOBr復(fù)合材料的成功合成.
圖1 BiOBr、CeO2和CeO2/BiOBr樣品的XRD譜圖
圖2 不同樣品的SEM圖和CB-10樣品的EDS圖(i~l)
a,b. BiOBr;c,d. CB-5; e,f. CB-10; g,h. CB-15
2.1.3 XPS分析 CB-10樣品的化學(xué)組成與元素價態(tài)用XPS進(jìn)行分析.從XPS全譜可知(圖3(a)), CB-10復(fù)合材料存在Bi、O、Br、Ce和C元素,說明CeO2成功地復(fù)合到BiOBr中,C 1s峰的出現(xiàn)來源于設(shè)備中的校準(zhǔn)峰.圖3(b)為Bi 4f的高分辨XPS能譜,在158.98eV以及164.30eV處的特征峰與BiOBr中的Bi3+4f7/2和4f5/2相對應(yīng)[26].O 1s的XPS能譜圖中(圖3(c))位于結(jié)合能529.91和531.31eV處的兩個峰分別歸功于吸附氧和CB-10中的晶格氧(Bi-O鍵和Ce-O鍵)[27-28].從Br 3d的XPS能譜圖中可知(圖3(d)),結(jié)合能位于67.99與69.03eV處的兩個特征峰分別對應(yīng)于Br 3d5/2和Br 3d3/2[29].在Ce 3d精細(xì)能譜中(圖3(e)),可以擬合為8個特征峰,其中,916.71, 906.52, 900.72, 898.05, 889.21和882.20eV對應(yīng)Ce4+, 902.11和884.12eV對應(yīng)Ce3+, 表明Ce3+和Ce4+在CeO2中共存[21,30].
2.1.4 比表面積和孔結(jié)構(gòu)分析 圖4(a)為BiOBr和CB-10樣品的N2吸附-脫附等溫線圖,這兩種材料均表現(xiàn)出IV型等溫線和H3滯后環(huán),表明樣品中存在介孔結(jié)構(gòu),且屬于片狀粒子堆積形成的狹縫孔[31-32]. BiOBr和CB-10樣品的比表面積分別為11.79和13.01m2/g.圖4(b)顯示了樣品的孔徑分布,通過BJH法計算樣品的孔徑大小,得出BiOBr和CB-10的平均孔徑分別為14.80和12.77nm.
圖3 CB-10樣品的XPS光譜圖
圖4 BiOBr和CB-10樣品的氮?dú)馕?脫吸等溫線和孔徑分布曲線
利用紫外-可見漫反射光譜儀(UV-Vis DRS)來研究材料的能帶結(jié)構(gòu)和對可見光的吸收能力.如圖5(a)所示,BiOBr的吸收帶邊在440nm附近,由于CeO2的引入,導(dǎo)致CeO2/BiOBr復(fù)合光催化劑的吸收邊相較于純BiOBr均發(fā)生了一定程度的紅移.此結(jié)果表明,BiOBr與CeO2復(fù)合后,拓寬了可見光的利用范圍.半導(dǎo)體的帶隙可以根據(jù)Tauc方法獲得[33],其公式為=(-E)/2,其中,,,E和分別是吸收系數(shù)、普朗克常數(shù)、光頻率、帶隙能量以及常數(shù),BiOBr與CeO2均為間接半導(dǎo)體且值為4[34],得出BiOBr, CeO2和CB-10樣品的帶隙值分別為2.54, 2.68和2.48eV (圖5(b)),即CB-10的帶隙值較小,這有利于電子的激發(fā)和轉(zhuǎn)移,從而提高了光催化活性[35].
為了分析光生-電子空穴對的分離效率,對BiOBr和CB-10樣品進(jìn)行了光致發(fā)光光譜(PL)表征,結(jié)果如圖 5(c)所示.可以看出,相比于純BiOBr和CeO2, CB-10材料的PL峰強(qiáng)度更低,較低的峰強(qiáng)度表明光致載流子的復(fù)合速率較低[36],說明CeO2的引入有效抑制了光生電子-空穴對的重組,產(chǎn)生了更多活躍的光生電子-空穴對,這有利于光催化活性的提高.
為進(jìn)一步探究電荷分離和轉(zhuǎn)移效率,分別對光電流響應(yīng)和電化學(xué)阻抗進(jìn)行了測試.如圖6(a)所示,顯然CB-10具有更強(qiáng)的光電流響應(yīng),其電流密度約為2.0μA/cm2,比純BiOBr高出1.42倍,說明BiOBr與CeO2構(gòu)建的異質(zhì)結(jié)結(jié)構(gòu)提升了光生載流子的遷移效率,有效地阻礙了電子-空穴對的復(fù)合[37].從圖6(b)可以看出,CB-10的弧半徑明顯小于BiOBr的弧半徑,通常情況下,弧半徑越小說明電荷界面?zhèn)鬏旊娮柙叫38],表明復(fù)合光催化材料有效地降低了電荷的傳輸電阻,從而有利于光催化活性的提升.這一結(jié)果與其瞬態(tài)光電流結(jié)果相一致.
圖6 BiOBr和CB-10的瞬態(tài)光電流響應(yīng)曲線和電化學(xué)阻抗譜
為研究所制備樣品的光催化性能,本文設(shè)計在可見光照射下,選擇100mL濃度為20mg/L的RhB為光催化降解的目標(biāo)污染物(催化劑用量為50mg),如圖7(a)所示.在黑暗條件下,將光催化劑與染料持續(xù)攪拌30min后,所有樣品在暗反應(yīng)中均表現(xiàn)出一定的吸附性能.在光照與未添加催化劑的條件下, RhB濃度幾乎未發(fā)生變化,表明其具有較強(qiáng)的穩(wěn)定結(jié)構(gòu),可以忽略光解對反應(yīng)的影響.而在加入催化劑后,CeO2對RhB染料幾乎沒有降解作用, BiOBr, CB-5, CB-10和CB-15在20min光照下, RhB的降解率分別達(dá)到了83.3%, 85.8%, 94.7%和83.9%,即CeO2的引入后,使得復(fù)合材料的光催化性能獲得了提升,當(dāng)CeO2的負(fù)載量為10%時,光催化性能最高.這是因為CeO2與BiOBr之間形成了異質(zhì)結(jié),提高了可見光的利用率和光生電子-空穴對的轉(zhuǎn)移及分離.當(dāng)CeO2負(fù)載量進(jìn)一步增多時,光催化活性反而降低,這可能是因為過量的CeO2抑制了光生載流子的轉(zhuǎn)移所致[39].通過偽一級反應(yīng)動力學(xué)對數(shù)據(jù)進(jìn)行擬合,如圖7(b)所示, CB-10的降解速率常數(shù)為0.200min–1,且分別為BiOBr (0.108min–1)、CB-5 (0.116min–1)及CB-15 (0.112min–1)的1.85、1.72和1.79倍,進(jìn)一步證明了CB-10材料顯示了優(yōu)異的光降解性能.
圖7 可見光下RhB在BiOBr及其復(fù)合材料上的光降解曲線及其偽一階動力學(xué)
通過改變催化劑投加量(0.1~0.9g/L)、RhB初始濃度(10~40mg/L)和初始溶液pH值(3~11),評估了不同條件下復(fù)合材料的RhB降解效率.如圖8(a)所示,當(dāng)投加量從0.1g/L增加到0.5g/L時,降解效率得到了顯著提升,這是由于隨著催化劑用量的增加,為反應(yīng)提供了更多的活性位點(diǎn)以及吸附了更多的RhB分子,從而提高了光降解效率[40-41].當(dāng)催化劑用量提升至0.7g/L時,光催化活性僅獲得小幅提升,且在25min后仍能達(dá)到99%左右.在用量繼續(xù)提升至0.9g/L時,光解效率反而出現(xiàn)下降趨勢,這主要是因為光催化劑含量增大后導(dǎo)致溶液濁度變大,從而引起光散射增強(qiáng)導(dǎo)致可見光的穿透率降低[1].因此,以光解效率最佳情況下即催化劑用量為50mg (0.5g/L)作進(jìn)一步研究(圖8(b)).可以看出,當(dāng)RhB溶液濃度為10, 20, 30和40mg/L時,反應(yīng)30min后,其降解效率分別為100%, 99.8%, 86.7%和76.4%,也就是說,隨著RhB染料濃度的提高,光降解效率出現(xiàn)下降的現(xiàn)象,這是因為較高的RhB染料濃度會使光子傳輸路徑和透光率降低,并進(jìn)一步減少了可利用的自由基活性基團(tuán)[42].因此,選取擁有相似降解效率的較高初始污染物濃度(20mg/L)作為后續(xù)的研究.
反應(yīng)pH值是影響實際廢水中光催化降解的一個重要因素,pH值對改變催化劑和有機(jī)染料的表面電荷起著重要的作用,從而影響光催化降解速率[43].本文在催化劑用量為0.5g/L與RhB溶液濃度為20mg/L的條件下,通過改變pH值,來分析其對降解效率的影響.由圖8(c)可以看出,在酸性和中性條件下(pH=3, 5, 7), RhB的去除效率獲得有效的提升,當(dāng)pH值為3時,降解效率最大,反應(yīng)20min后,可達(dá)到96.1%.然而,在堿性溶液中(pH=9和11),去除效率呈現(xiàn)明顯的下降.即在酸性條件下很容易將RhB染料進(jìn)行降解,這主要?dú)w功于酸性條件有利于RhB分子的吸附,可以產(chǎn)生更多的質(zhì)子和光生氧化劑[44].
催化劑的可循環(huán)性和光化學(xué)穩(wěn)定性是作為工業(yè)實際應(yīng)用重要的評價指標(biāo).為了評價BC-10的穩(wěn)定性,進(jìn)行了3次RhB光降解循環(huán)實驗.操作步驟為: CB-10樣品在經(jīng)過光催化降解實驗后,通過真空抽濾分離反應(yīng)后的光催化劑,用去離子水和無水乙醇洗滌并離心,在80 ℃烘箱中干燥12h后用于下一次循環(huán)實驗.圖8(d)顯示,催化劑1st~3rd的降解效率分別為99%、92%和85%.此結(jié)果表明,雖然降解效率在三次循環(huán)實驗中呈現(xiàn)下降趨勢,但降解效率仍能達(dá)到85%以上,表明CB-10具有良好的穩(wěn)定性和可循環(huán)性.通過XRD圖可知(圖9(a)),反應(yīng)前后CB-10樣品的衍射峰沒有明顯的變化,證實了催化劑具有較好的結(jié)構(gòu)穩(wěn)定性.此外,催化劑的SEM圖像與反應(yīng)前催化劑具有相似的納米片結(jié)構(gòu)(圖9(b)),同樣表明了催化劑的結(jié)構(gòu)穩(wěn)定性.
圖9 CB-10光催化循環(huán)前后的XRD圖譜和循環(huán)后的SEM圖
為了探究光催化過程中的主要活性基團(tuán),進(jìn)行了自由基捕獲試驗.試驗過程與光催化降解RhB染料過程大致相同,僅在降解之前加入EDTA-2Na、BQ和IPA分別作為空穴(h+)、超氧自由基(?O2–)和羥基自由基(?OH)的捕集劑[45].結(jié)果如圖10所示,在加入IPA后,光催化活性幾乎沒有受到影響,僅降低了2.8%,而EDTA-2Na和BQ的引入則顯著降低了光催化性能,即在光照射30min后,RhB降解率分別從99.8%降至53.8%和58.14%,表明光催化過程受到了強(qiáng)烈抑制,證實了h+和?O2–是主要的活性物種,而?OH在光催化降解過程中幾乎不起作用.
圖10 不同捕獲劑30min光照下的RhB降解曲線
通過CB-10樣品的能帶結(jié)構(gòu)進(jìn)一步探索了其光催化機(jī)理.如圖11(a), (b)所示, BiOBr和CeO2的XPS-VB光譜顯示其價帶值(VB)分別為1.50和1.86eV,通過方程VB=g+CB[46]計算BiOBr和CeO2的導(dǎo)帶(CB)位置分別為-1.04和-0.82eV.基于以上分析, CB-10復(fù)合材料降解RhB的機(jī)理如圖11(c)所示.在可見光照射下, BiOBr和CeO2吸收光能后,在價帶上的電子躍遷至導(dǎo)帶,從而產(chǎn)生光生電子和空穴. BiOBr導(dǎo)帶電子的電勢(-1.04eV)比CeO2半導(dǎo)體導(dǎo)帶電子的電勢(-0.82eV)更負(fù), CeO2價帶空穴的電勢(1.86eV)比BiOBr價帶空穴的電勢(1.50eV)要正.這時BiOBr導(dǎo)帶上的電子會轉(zhuǎn)移到CeO2的導(dǎo)帶上,同時激發(fā)空穴從CeO2價帶上移動到BiOBr的價帶上,這歸因于傳統(tǒng)的Ⅱ型交錯帶排列和電位差[30].因此,電子和空穴分別聚集在CeO2的導(dǎo)帶和BiOBr的價帶上.通過兩者間緊密接觸界面上的內(nèi)電場,這種電子-空穴對的遷移方式顯著加快了電荷載體的分離效率.此外,由于CeO2的導(dǎo)帶電位比O2/?O2–的氧化還原電位(-0.33eV)更負(fù),BiOBr價帶的氧化還原電位小于OH–/?OH的氧化電位(2.38eV),因此電子將吸附在催化劑表面的氧氣還原成超氧自由基(?O2–),而不會產(chǎn)生?OH自由基,可推出h+和?O2–在降解過程中起主要作用,這與捕獲實驗的結(jié)果相符.
3.1 采用溶劑熱法成功地制備了具有異質(zhì)結(jié)結(jié)構(gòu)的CeO2/BiOBr光催化材料,表征結(jié)構(gòu)表明,BiOBr呈現(xiàn)緊密堆積的納米片形貌,且CeO2成功地引入到了BiOBr的結(jié)構(gòu)中,顯著提高了RhB降解的光催化性能.
3.2 CeO2引入后,改善了CeO2/BiOBr的可見光吸收能力、禁帶寬度和電子-空穴對復(fù)合速率等性能,提高了BiOBr光催化劑對RhB的去除效率.當(dāng)CeO2摻雜量為10%時,CeO2/BiOBr復(fù)合光催化劑降解效率最高,在30min內(nèi),可降解99%的RhB染料.
3.3 經(jīng)過3次循環(huán)實驗后,CB-10光催化材料具有良好的循環(huán)穩(wěn)定性,降解效率在30min內(nèi)仍能達(dá)到85%以上.
3.4 自由基捕獲實驗證明,h+和?O2–是主要的活性物種.
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Construction of CeO2/BiOBr heterojuction for photocatalytic degradation of Rhodamine B.
GUO Tian-yu1,2, FAN Xiang-rui1, BAI De-hao3, QI Yu1, WANG Hong-Tao1*
(1.College of Environment Science and Engineering, Taiyuan University of Technology, Jinzhong 030600, China;2.Shanxi Key Laboratory of Gas Energy Efficient and Clean Utilization, Taiyuan 030024, China;3.Xinzhou Branch of Petrochina Coalbed Methane Co. LTD, Xinzhou 036600, China)., 2023,43(11):5845~5854
In this study, CeO2, BiOBr and CeO2/BiOBr photocatalysts were synthesized by a hydrothermal method, and the morphology, structure and photoelectrochemical properties of the photocatalysts were characterized by different techniques. The photocatalytic performance was evaluated by degrading Rhodamine B (RhB) under visible light irradiation. The experimental results showed that the CeO2/BiOBr (CB-10) catalyst with the appropriate amount of CeO2(10%) exhibited enhanced photocatalytic activity, recyclability and cycling stability and the degradation rate of RhB reached 99% within 30min. Furthermore, the catalyst attained the highest degradation efficiency (96.1%) within 20min when the catalyst dosage was 0.5g/L, the RhB concentration was 20mg/L and pH value was 3. The possible reaction mechanism of CeO2/BiOBr heterojunctional material in photocatalytic process was proposed based on the radical capture test and the energy band structure of material. This study can provide a new idea and method for the preparation of Bi-based composite catalysts.
photocatalytic degradation;CeO2/BiOBr;heterojunction;Rhodamine B
X703.5
A
1000-6923(2023)11-5845-10
郭天宇(1989-),女,山西太原人,講師,博士,主要從事環(huán)境催化領(lǐng)域的研究.發(fā)表論文10余篇.tyguo1117x@163.com.
郭天宇1,2,范祥瑞1,白德豪,等.異質(zhì)結(jié)CeO2/BiOBr的構(gòu)筑及其光催化降解羅丹明B [J]. 中國環(huán)境科學(xué), 2023,43(11):5845-5854.
Guo T Y, Fan X R, Bai D H, et al. Construction of CeO2/BiOBr heterojuction for photocatalytic degradation of Rhodamine B [J]. China Environmental Science, 2023,43(11):5845-5854.
2023-04-23
國家自然科學(xué)基金資助項目(51572185);山西省應(yīng)用基礎(chǔ)研究計劃項目(202203021211158,20210302123176)
* 責(zé)任作者, 副教授, wanghongtao@tyut.edu.cn