片狀Bi2O3的制備及其光催化性能

張問問,陳東輝

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片狀Bi2O3的制備及其光催化性能

張問問,陳東輝*

(東華大學環(huán)境科學與工程,上海 201620)

利用化學沉淀法,分別以Bi(NO3)3×5H2O為鉍源、稀HNO3為溶劑和HTMA為沉淀劑,制備出片狀Bi2O3光催化劑.利用SEM、XRD和BET分別對制備的Bi2O3形貌、厚度、晶型和比表面積進行表征,并借助紫外可見漫反射和光化學反應(yīng)儀對材料的光催化性能進行測試.結(jié)果表明:制備的片狀Bi2O3光催化劑形貌較好,厚度均一,a-Bi2O3晶型,對可見光的吸收較強,表現(xiàn)出較好的光催化性能.在模擬可見光300W下,3.0h后Bi2O3光催化劑對四環(huán)素溶液的降解率可以達到82.6 %,遠遠高于市售納米Bi2O3顆粒.

片狀；Bi2O3；沉淀法；四環(huán)素

制藥行業(yè)產(chǎn)生的廢水因其成分復雜、有機物含量高、毒性大、色度深和含鹽量高,特別是生化性差、間歇排放、廢水的pH值和水質(zhì)水量波動大等特點成為難處理的工業(yè)廢水.近年來,隨著我國醫(yī)藥工業(yè)的發(fā)展,制藥廢水已逐漸成為重要的水污染源之一,如何處理該類廢水是當今環(huán)境保護需要解決的一個難題[1-3].根據(jù)近些年對廢水處理技術(shù)的深入研究,高級氧化技術(shù)特別是光催化技術(shù)因綠色、高效、穩(wěn)定性好、無二次污染等優(yōu)點,在廢水處理領(lǐng)域引起了極大的關(guān)注[4-7].但是該技術(shù)目前也存在一些問題,比如光催化劑的制備成本高、對自然光的利用率低和重復利用性差等問題.針對這些問題,進一步研發(fā)高催化活性的光催化材料是目前該領(lǐng)域最重要的研究課題之一.

無機納米材料由于其獨特的物理化學性,被廣泛應(yīng)用在藥學、電學、光學、生物包埋和機械制造等領(lǐng)域[8-11],對人類生活水平的提高以及社會的發(fā)展做出重要貢獻.在光催化領(lǐng)域,納米材料,特別是納米片狀結(jié)構(gòu)的材料因其粒徑小,比表面積大,材料表面可提供的活性位點多,更有利于提高光催化性能[12-14],而受到越來越多研究者的青睞.Bi2O3材料具有較多的氧空位,較強的光生電子和空穴分離能力,較高的對自然光的利用率等特點而被認為是最具有發(fā)展前途的光催化劑之一[15-16].自1988年Harriman等[17]首次提出Bi2O3可以作為光催化劑開始,國內(nèi)外關(guān)于Bi2O3作為光催化劑處理有機廢水方面的研究就越來越多.雖然,國內(nèi)外采用氧化、沉積沉降和溶劑熱等方法已經(jīng)成功制備了Bi2O3或者其復合物[18-21],基本建立了Bi2O3纖維狀、顆粒狀、球狀、花狀、網(wǎng)狀等形貌[22-26]的制備方法.但是目前對片狀Bi2O3的制備報道最多是模板法[27-28],對于液相沉淀法制備片狀Bi2O3未見報道,更別提對其光催化性能研究的報道.

因此,本文擬通過一種簡便、低成本的方法制備片狀Bi2O3(SBO)光催化劑,研究SBO光催化劑的形貌、片狀厚度、晶型和比表面積并在模擬可見光下對比市售納米Bi2O3(CBO),以制藥廢水-四環(huán)素(Tetracycline,縮寫:TT)為處理對象,探究其光催化性能.

1 材料與方法

1.1 材料

五水合硝酸鉍(Bi(NO3)3?5H2O,AR)、硝酸(HNO3,AR,65-68%)、六亞甲基四胺(C6H12N4,RG, HTMA)、無水乙醇(C2H5OH、AR)、市售納米氧化鉍顆粒(CBO)、四環(huán)素(Tetracycline,TT),實驗中所用的試劑均是購買后不作任何處理,直接使用,所用的去離子水(DT)是由本學校自供.

1.2 實驗方法

SBO光催化材料的具體制備步驟如下:分別量取15.0mL DT和5.0mL HNO3溶液到稱量瓶內(nèi),再稱取0.002mol Bi(NO3)3·5H2O,溶解后加入裝有50.0mL DT且搭建冷凝管的三口燒瓶中,攪拌加熱至70℃, 30min后加入溶解有5.0g HTMA的20mL DT,繼續(xù)加熱攪拌1.0h后停止加熱,再攪拌1.0h后離心洗滌三口燒瓶內(nèi)的渾濁液(兩次DT,一次C2H5OH)后在70℃烘箱中烘干,最后在550℃管式爐中煅燒2.0h后得到目標產(chǎn)物.

1.3 樣品的光催化性能實驗

稱取60mg的SBO加入100mL 20mg/L的TT溶液,暗處理60min后開氙燈(功率調(diào)至300W,光源和反應(yīng)器的距離保持在8.0cm)來模擬可見光,按照設(shè)定好的取樣時間點進行取樣,每次均取樣4.5mL,在轉(zhuǎn)速為6000r/min下離心3.0min后取上清液在TT溶液的最大吸收波長358nm處測量其吸光度,根據(jù)吸光度的變化來判定材料對TT溶液的降解率.CBO和空白對照組的實驗步驟同上.

2 結(jié)果與討論

2.1 TG分析

材料的煅燒溫度對材料形貌和性能的影響不容忽視,因此利用熱重分析儀研究材料在不同溫度下的失重率,將有利于得到適宜的煅燒溫度,圖1是制備的SBO前驅(qū)體材料的熱重曲線.從圖中可以明顯看出在50~500℃之間,SBO前軀體一直在慢慢失重,重量損失約7.0%,在500~545℃之間,失重速率較快,達到7.4%,此后,隨著溫度的升高,重量不再發(fā)生變化.分析失重的原因可能是沉淀法制備的SBO不是一開始就形成的,而是形成了前驅(qū)體.剛開始前驅(qū)體內(nèi)的結(jié)晶水在慢慢減少,隨著溫度的升高,前驅(qū)體最終被氧化成Bi2O3.由此可知該方法制備的SBO的煅燒溫度至少要達到545℃,方可將前驅(qū)體徹底氧化成SBO.本著綠色環(huán)保的理念,本文選擇的煅燒溫度是550℃.

圖1 SBO前驅(qū)體的熱重曲線

2.2 SEM-EDS分析

光催化劑的催化性能和材料形貌的相關(guān)性很大,因此研究光催化材料的形貌具有一定的意義.圖2是CBO和SBO的SEM和EDS圖,觀察圖2(A)可知:CBO呈無規(guī)則納米顆粒狀,且由大小不太均一的小顆粒堆積而成,分散性較差,顆粒的直徑約在50~100nm之間;觀察圖2(B)可知:SBO呈片狀,類似六邊形,分散性較好,片狀的厚度大約為100nm(圖2(C)).該方法制備的SBO的形成機理可能是加入沉淀劑后,形成的納米顆粒沉淀自發(fā)的聚集在一起來降低暴露面進而減少表面能,并進一步自組裝成類六邊形片狀形貌,達到穩(wěn)定[29].為了確定制備材料的元素組成,利用和SEM連用的EDS對材料進行掃描分析.如圖2(D)和(E)所示,分別為CBO和SBO的元素譜圖.由于制樣中為了增加材料的導電性而用鋁箔作為底層進行制樣,所以會有Al元素出現(xiàn),忽略其影響,主要元素就是Bi和O,因此CBO和SBO材料的組成就是Bi2O3.

2.3 XRD分析

圖3 CBO和SBO的XRD圖譜

氧化鉍有著不同的晶體結(jié)構(gòu)和化學性質(zhì),究其原因是由其具有4種不同的晶型(-Bi2O3、- Bi2O3、-Bi2O3和-Bi2O3)決定的,因此本文借助XRD來表征材料的晶型.如圖3是CBO和SBO的XRD圖譜,顯示了CBO和SBO在2為10°~90°范圍內(nèi)的所有的峰.通過對比JCPDS 數(shù)據(jù)庫(NO. 41–1449,NO.71-2274和NO.27-0050)可知:CBO的出峰較多,基本上涵蓋了β-Bi2O3的特征峰(201,002, 220,222,400,203,421,402)[22];而SBO對應(yīng)單斜結(jié)構(gòu)-Bi2O3的特征衍射峰,結(jié)果和NO.71-2477相吻合[30],因此制備的SBO的晶型是-Bi2O3.此外,圖中SBO的峰值都較強,意味著其結(jié)晶程度高,在光催化性能上可能會有所優(yōu)勢.

2.4 BET分析

為累積孔容;為孔徑

在光催化領(lǐng)域,較大的比表面積有利于更多反應(yīng)物在催化劑表面進行吸附,而更高的孔體積有利于各種反應(yīng)物和產(chǎn)物在光催化反應(yīng)過程中迅速擴散,從而提高光催化活性,使有機物更快的被降解[31],因此表征光催化劑的比表面積和孔分布有利于研究材料的光催化性能.圖4是CBO和SBO的N2吸附-脫附等溫線和孔大小分布曲線.圖4(A)表明CBO和SBO屬于介孔材料, CBO的比表面積是27.56m2/g,而制備的SBO可以達到33.21m2/g.從圖4(B)中可以很明顯地看出:CBO和SBO的孔徑分布都主要集中在5~10nm,但是SBO材料含孔的比例較高于CBO.理論上來說,在光催化領(lǐng)域,SBO比CBO有優(yōu)勢,因為其比表面積稍大,孔較多.

2.5 DRUVS分析

圖5 CBO和SBO的固體紫外漫反射圖譜

2.6 材料光催化性能

利用TT溶液在可見光下的降解率來評價材料的光催化性能.圖6是可見光下加入SBO和CBO以及空白對照組的TT溶液的降解率.光照之前,先暗處理1.0h使得光催化材料對TT吸附達到飽和.如圖6所示:CBO和SBO對TT的吸附在40min內(nèi)就基本上就達到了吸附平衡且SBO對TT的吸附能力較好,大約是CBO的3倍.在暗處理過程中,TT溶液沒有發(fā)生自降解;但是當可見光照射時,TT溶液發(fā)生了自降解現(xiàn)象,3.0h后的自降解率達到27.0%,這歸因于可見光下,TT可以吸收光子產(chǎn)生O2-·直接光解并同時進行自敏化光解[34-35].加入光催化材料后,加快了TT溶液的降解率;3.0h后加入CBO的TT溶液降解率是42.7%,相對空白組僅僅提高了15.7 %;而加入SBO的TT溶液的降解率達到了82.6%,降解率提高了55.6%,這可能歸因于片狀結(jié)構(gòu)有助于提高材料對光的吸收強度和電子-空穴的分離,進而有利于材料進行光催化作用.根據(jù)方程分析ln(0/C)與光照時間()之間的關(guān)系,如圖6(b)所示, ln(0/C)和的關(guān)系明顯是線性的,表明光催化降解遵循偽一級的反應(yīng)動力學.通過分析數(shù)據(jù)可知: SBO的光催化效率= 8.6′10-2是CBO的5.2倍(= 1.65′10-2),進一步表明所制備的SBO具有更強的光催化性能,在廢水處理和保護領(lǐng)域具有廣泛的應(yīng)用前景.

2.7 材料穩(wěn)定性

光催化劑的穩(wěn)定性和再利用性對其實際應(yīng)用具有重要的重用.圖7顯示了SBO在相同實驗條件下的回收利用測試.SBO的回收是通過分別利用DT和C2H5OH離心洗滌3次,然后在80℃烘箱中烘干備用.從圖7可以看出SBO在經(jīng)過3次循環(huán)利用后,對TT溶液的降解率依然達到80%以上,表明SBO具有較好的穩(wěn)定性和重復利用性,在廢水處理領(lǐng)域具有應(yīng)用的潛能.

圖7 SBO的回用測試

3 結(jié)論

3.1 通過化學沉淀法,制備出的SBO材料不僅純度比CBO高,而且對可見光表現(xiàn)出較強的吸收.

3.2 在模擬功率為300W的可見光下照射3.0h后,對TT的降解率達到82.6%,遠遠優(yōu)先于CBO的42.7%.而且經(jīng)過3次重復利用,對TT的降解率依然保持在80%以上.

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Preparation of Bi2O3with plate-like and its photocatalytic property.

ZHANG Wen-wen, CHEN Dong-hui*

(College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China)., 2019,39(5)：1961~1966

Bi2O3photocatalyst with plate-like morphology was successfully prepared by the method of chemical precipitation which using Bi(NO3)3×5H2O as the source of bismuth, HNO3as solvent and HTMA as precipitants, respectively. The morphology, thickness, crystal form and specific surface area of the as-prepared Bi2O3were characterized by SEM, XRD and BETrespectively. Furthermore, the photocatalytic performance of the materials was tested by UV-Vis diffuse reflection and photochemical reaction apparatus. The results showed that the obtained Bi2O3photocatalyst with plate-like morphology has good morphology, uniform thickness, a-Bi2O3, stronger absorbent for visible-light and exhibits good photocatalytic property. Under the simulated visible light of 300W, the degradation rate of tetracycline wastewater can be reached to 82.6 % after 3.0h, which is much higher than that of commercially nanoparticles Bi2O3.

plate-like；Bi2O3；precipitation method；tetracycline

X703.5,O643

A

1000-6923(2019)05-1961-06

張問問(1989-),男,安徽亳州人,東華大學博士研究生,主要研究方向為環(huán)境污染控制.發(fā)表論文3篇.

2018-09-06

上海地方高校資助項目(50578020)

*責任作者, 教授, chendhisit@163.com