RGO/ZnO納米棒復(fù)合材料的合成及光催化性能

蘆 佳，王輝虎,2，董一帆，常 鷹，馬新國，董仕節(jié),2

(1 湖北工業(yè)大學(xué) 機(jī)械工程學(xué)院，武漢 430068；2 湖北工業(yè)大學(xué)綠色輕工材料湖北省重點(diǎn)實(shí)驗(yàn)室，武漢 430068;3 湖北工業(yè)大學(xué)材料學(xué)院，武漢 430068;4 湖北工業(yè)大學(xué) 理學(xué)院，武漢 430068)

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RGO/ZnO納米棒復(fù)合材料的合成及光催化性能

蘆 佳1，王輝虎1,2，董一帆1，常 鷹3，馬新國4，董仕節(jié)1,2

(1 湖北工業(yè)大學(xué) 機(jī)械工程學(xué)院，武漢 430068；2 湖北工業(yè)大學(xué)綠色輕工材料湖北省重點(diǎn)實(shí)驗(yàn)室，武漢 430068;3 湖北工業(yè)大學(xué)材料學(xué)院，武漢 430068;4 湖北工業(yè)大學(xué) 理學(xué)院，武漢 430068)

采用水熱合成法制備ZnO納米棒及RGO/ZnO納米棒復(fù)合材料。研究不同含量的RGO對(duì)RGO/ZnO納米棒復(fù)合材料光催化活性的影響。采用X射線衍射儀(XRD)、場發(fā)射電子顯微鏡(FESEM)、光電子能譜儀(XPS)及漫反射紫外-可見吸收光譜(UV-Vis)檢測手段對(duì)RGO/ZnO進(jìn)行表征。結(jié)果顯示：RGO與ZnO納米棒成功復(fù)合。加入GO的含量不同，獲得的RGO/ZnO樣品在可見光區(qū)域的吸光度值不同。以甲基橙作為模擬污染物的光催化結(jié)果表明，RGO/ZnO復(fù)合材料具有高的紫外-可見光光降解效率，加入GO與ZnO的質(zhì)量比為3%時(shí)，樣品紫外-可見光光催化性能最佳，120min內(nèi)甲基橙基本可以完全降解；且在波長大于400nm可見光照射下，RGO/ZnO具有一定的可見光活性，180min內(nèi)其降解甲基橙效率最大可達(dá)26.2%。同時(shí)，RGO/ZnO具有較好的光穩(wěn)定性。

還原石墨烯；ZnO；光催化；甲基橙

近年來，利用納米半導(dǎo)體對(duì)有機(jī)污染物進(jìn)行凈化已引起廣泛關(guān)注。ZnO具有價(jià)格低廉、無毒、生產(chǎn)工藝簡單及性能穩(wěn)定等優(yōu)點(diǎn)[1,2]，但是，ZnO作為光催化劑在實(shí)際應(yīng)用中還存在一些問題。一方面，光生載流子的快速復(fù)合導(dǎo)致ZnO具有較低的量子效率和較差的光催化效率[3,4]；另一方面，ZnO在室溫下禁帶寬度為3.37eV[5,6]，較大的禁帶寬度限制其只能在紫外光作用下被激發(fā)。因此，人們采用了不同的方法來提高ZnO光催化活性及其吸收光波長，如貴金屬修飾[7,8]、金屬化合物沉積[9,10]等。但這些改性方法工藝復(fù)雜、制備條件苛刻、成本高。此后碳納米管、石墨烯等碳系材料相繼出現(xiàn)，由于它們的特殊性能被逐漸引入到光催化體系中并受到了廣泛重視。石墨烯是由sp2-鍵片層碳原子組成的二維晶格材料，具有較高導(dǎo)電性、高載流子遷移率(2×105cm2·V-1·s-1)、大比表面積(2600m2·g-1)[11,12]。目前，石墨烯表面沉積金屬或與金屬氧化物復(fù)合所獲得的復(fù)合材料被證明具有優(yōu)異的光催化性能[13,14]。但是石墨烯的不溶性與難加工性使得其實(shí)際使用受到極大限制。

還原石墨烯(Reduced Graphene Oxide，RGO)是先氧化石墨烯得到氧化石墨烯(Graphene Oxide，GO)，之后還原去除GO表面含氧官能團(tuán)獲得的產(chǎn)物，其層間距遠(yuǎn)大于石墨烯。通常采用的還原方法有化學(xué)法[15]、電化學(xué)法[16]和熱還原法[17]等。RGO與石墨烯特性相似，將其引入到光催化體系中形成的還原石墨烯基復(fù)合材料同樣具有優(yōu)異的光催化特性。Liu等[6]在非水介質(zhì)中采用微波輔助將分散的納米ZnO顆粒沉積在RGO片上，發(fā)現(xiàn)RGO的復(fù)合不但能增加ZnO的比表面積，而且能促進(jìn)光生電子的傳輸轉(zhuǎn)移。Liu等[18]采用紫外線輔助催化法合成RGO/ZnO粉末。研究發(fā)現(xiàn)，RGO/ZnO紫外光降解Cr(VI)效率比純ZnO高30%。Zhang等[19]通過機(jī)械混合RGO粉末與ZnO納米顆粒，發(fā)現(xiàn)混合物在紫外光照射下降解亞甲基藍(lán)的效果顯著。Pant等[4]采用花狀ZnO和Ag納米顆粒復(fù)合RGO片，同樣發(fā)現(xiàn)獲得的復(fù)合材料表現(xiàn)出優(yōu)良的紫外光光催化性能。Dong等[20]將氧化鋅納米團(tuán)簇嵌入RGO納米片，發(fā)現(xiàn)復(fù)合后的RGO/ZnO具有可見光活性，且降解甲硝噠唑效率比純ZnO高32.4%。

與傳統(tǒng)的ZnO粉末相比，ZnO納米棒具有較高的光捕獲率、較大的比表面積及較快的光生電子轉(zhuǎn)移速率[21]。但很少有人采用ZnO納米棒復(fù)合RGO片來制備RGO/ZnO納米棒復(fù)合材料，并研究其光催化性能[5]。本工作在水熱法制備ZnO納米棒的基礎(chǔ)上，通過同時(shí)加入GO粉末，利用水熱過程中GO粉末的還原，一步合成RGO/ZnO納米棒復(fù)合材料。利用X射線衍射儀、場發(fā)射電子顯微鏡、光電子能譜儀及漫反射紫外-可見吸收光譜等研究了RGO/ZnO納米棒復(fù)合材料的微觀特性，并將甲基橙(Methyl Orange，MO)作為模擬污染物，研究了RGO含量對(duì)RGO/ZnO納米棒復(fù)合材料的光催化性能及光穩(wěn)定性的影響規(guī)律，分析了其光催化機(jī)制。

1 實(shí)驗(yàn)材料與方法

實(shí)驗(yàn)中所用原料均為分析純。GO采用Hummer法[22]制得。在反應(yīng)器中倒入一定量的濃硫酸，加入2g石墨粉、1g硝酸鈉和6g高錳酸鉀攪拌，控制反應(yīng)溫度低于20℃。反應(yīng)一段時(shí)間后升溫至35℃，繼續(xù)攪拌2h。然后緩慢加入少量的去離子水，98℃攪拌15min后，加入適量雙氧水還原殘留的氧化劑使溶液變?yōu)榱咙S色，趁熱過濾，采用5～8mL的鹽酸溶液及去離子水洗滌，直到濾液中無硫酸根被檢測到為止。最后將樣品置于真空干燥箱中充分干燥得到GO粉末。

RGO/ZnO采用一步水熱法制備。將0.58g乙酸鋅和0.53g氫氧化鈉與一定量的GO混合，加入80mL無水乙醇，25℃下攪拌30min。將獲得的混合溶液轉(zhuǎn)移至反應(yīng)釜內(nèi)，密封加熱到160℃，保溫24h后自然冷卻至室溫，取出進(jìn)行抽濾、洗滌。重復(fù)上述步驟3～5次后于60℃干燥12h，研磨得到RGO/ZnO樣品。根據(jù)加入的GO量不同，將GO與ZnO質(zhì)量比為1%，3%，5%，7%的樣品分別記為1%RGO/ZnO，3%RGO/ZnO，5%RGO/ZnO，7%RGO/ZnO。

配置20mg/L的甲基橙(MO)溶液，加入50mg的RGO/ZnO粉末，振蕩、攪拌獲得均勻混合溶液。以300W氙燈為光源，對(duì)其光照120min?？梢姽夤獯呋钚詼y試時(shí)，采用400nm濾光片濾去紫外光。反應(yīng)過程中每15min取一次試樣，離心取上層MO清液，采用紫外分光光度計(jì)測試，在464nm處取得吸光度值，計(jì)算其濃度。

光穩(wěn)定性研究選用3%RGO/ZnO樣品進(jìn)行測試，采用上述方法，經(jīng)過紫外-可見光照射120min，之后將反應(yīng)產(chǎn)物洗滌抽濾，然后放入干燥箱內(nèi)干燥。循環(huán)5次后，根據(jù)MO降解效率的變化分析RGO/ZnO光穩(wěn)定特性。

采用X射線粉末衍射儀(X’pert Pro MPD)分析樣品晶相組成，掃描范圍為10°～80°，掃描速率為2(°)/min；通過掃描電子顯微鏡(Quanta 450)觀察分析樣品表面形貌，加速電壓為10kV；采用X射線光電子能譜儀(VG Multilab 2000)分析樣品表面組成，XPS譜線峰位均以吸附的碳?xì)浠衔锏腃ls(Eb= 284.6eV)譜為參照；通過紫外可見分光光度計(jì)(U-3900)對(duì)樣品進(jìn)行紫外漫反射光譜分析，以BaSO4作參照，掃描范圍為200～700nm。

2 結(jié)果與分析

2.1 XRD分析

圖1為RGO，ZnO和RGO/ZnO樣品的XRD譜圖。由圖1可知，RGO樣品XRD譜的衍射峰位于23.6°和42.6°，表明水熱反應(yīng)過程中GO在高溫高壓下成功還原成RGO，這與其他文獻(xiàn)結(jié)果一致[23,24]。在ZnO及RGO/ZnO樣品的XRD譜中，位于31.8°, 34.4°, 36.3°, 47.5°, 56.6°, 66.4°, 68.0°和69.9°的衍射峰對(duì)應(yīng)于纖鋅礦結(jié)構(gòu)ZnO[25,26]。RGO/ZnO樣品的衍射峰與純ZnO一致，未出現(xiàn)明顯的RGO衍射峰，這可能是因?yàn)镽GO/ZnO粉末中的RGO含量極少，不易被檢測出的緣故。

圖1 RGO，ZnO和RGO/ZnO樣品的XRD譜圖Fig.1 XRD patterns of RGO,ZnO and RGO/ZnO samples

2.2 FESEM分析

圖2為1%RGO/ZnO, 3%RGO/ZnO, 5%RGO/ZnO, 7%RGO/ZnO的FESEM照片?？梢钥闯? 產(chǎn)物中RGO以分散的片狀形式存在。經(jīng)過水熱反應(yīng)后, 在片狀RGO表面均可形成ZnO納米棒且分布均勻，這可能是由于RGO片層表面具有多種極性含氧官能團(tuán)，極性含氧基團(tuán)使得Zn2+離子以氫鍵和靜電吸附的方式結(jié)合在這些活性點(diǎn)上進(jìn)一步水解，同時(shí)生成的ZnO能夠有效阻止RGO片層間的相互作用[27]。GO加入量的增加，一方面，使RGO片層數(shù)量增加，片層表面生成的ZnO納米棒也更加分散；另一方面，使負(fù)載ZnO的活性位點(diǎn)增多，RGO片層表面吸附的ZnO納米棒也隨之增多，促使RGO/ZnO復(fù)合材料片層尺寸有所增大。

圖2 RGO/ZnO樣品的FESEM圖 (a)1%RGO/ZnO;(b)3%RGO/ZnO;(c)5%RGO/ZnO;(d)7%RGO/ZnOFig.2 FESEM images of RGO/ZnO samples (a)1%RGO/ZnO;(b)3%RGO/ZnO;(c)5%RGO/ZnO;(d)7%RGO/ZnO

2.3 XPS分析

通過XPS檢測可以進(jìn)一步分析RGO/ZnO樣品的表面元素組成。圖3為3%RGO/ZnO的C1s，O1s和Zn2p的XPS譜圖。由圖3(a)可以看出，C1s譜具有3個(gè)峰，分別位于284.6，286.3eV與288.5eV，對(duì)應(yīng)C-C，C-O，C=O鍵[28,29]。圖3(b)中O1s譜的兩個(gè)峰分別位于531.2，532.9eV，前者為ZnO中的晶格氧，后者為RGO/ZnO中C-OH/C-O-C鍵的氧[26]。圖3(c)中Zn2p的峰位于1021.8eV，表明Zn以Zn+的形式存在[28,30]。

圖3 3%RGO/ZnO樣品的C1s(a),O1s(b)和Zn2p(c) XPS譜圖Fig.3 C1s(a),O1s(b) and Zn2p(c) XPS spectra of 3%RGO/ZnO sample

2.4 UV-Vis檢測

圖4為RGO，ZnO和RGO/ZnO樣品的漫反射紫外-可見吸收光譜圖，吸光曲線邊緣在紫外光區(qū)域。由圖4顯示，純RGO樣品吸收光譜在260nm處有最大吸收峰。純ZnO樣品呈白色，加入RGO后顏色發(fā)生改變。隨著RGO含量的不斷增加，RGO/ZnO顏色從白色逐漸變成黑色，由于物質(zhì)的顏色越深，吸光度值越大，因此RGO/ZnO樣品在可見光區(qū)域內(nèi)的吸光度值隨GO含量的增加而增加，此結(jié)果與其他文獻(xiàn)一致[1,31]。

圖4 RGO，ZnO和RGO/ZnO樣品的UV-Vis譜圖Fig.4 UV-Vis spectra of RGO,ZnO and RGO/ZnO samples

2.5 光催化性能

圖5為ZnO和RGO/ZnO樣品在紫外-可見光照射下降解MO效率曲線。由圖5可知， RGO/ZnO都具有優(yōu)異的光催化活性。相比與純ZnO，RGO/ZnO降解MO效率明顯提高。同時(shí)，GO的加入量對(duì)RGO/ZnO納米棒復(fù)合材料的光催化活性具有很大影響。3%RGO/ZnO樣品的MO降解效率最高，在120min內(nèi)達(dá)到97.5%。但隨著GO加入量的繼續(xù)增加，MO降解率開始下降。這可能是因?yàn)镽GO自身能吸收紫外光，隨著加入的GO量不斷增多并超過3%時(shí)，ZnO與RGO之間存在著光捕獲競爭關(guān)系，減少了ZnO納米棒的光吸收。除此之外，過量的RGO可能會(huì)充當(dāng)光生電荷的復(fù)合載體，抑制光生電子與空穴的分離，最終降低RGO/ZnO的光催化活性[18,32]。

圖5 ZnO和RGO/ZnO樣品紫外-可見光降解MO曲線Fig.5 Degradation curves of MO for ZnO and RGO/ZnO samples under UV-Vis

圖6為ZnO和RGO/ZnO樣品在可見光照射下降解MO曲線?？梢钥闯?，純ZnO沒有可見光催化活性，但復(fù)合了RGO后，可見光下對(duì)MO具有降解效果。根據(jù)加入的GO量不同，RGO/ZnO光催化降解MO效率為：3%RGO/ZnO >5%RGO/ZnO > 1%RGO/ZnO > 7%RGO/ZnO。3%RGO/ZnO樣品的可見光光催化性能最佳，180min內(nèi)甲基橙降解效率達(dá)26.2%。

圖6 ZnO和RGO/ZnO樣品可見光降解MO曲線Fig.6 Degradation curves of MO for ZnO and RGO/ZnO samples under visible irradiation

圖7為3%RGO/ZnO紫外-可見光照射下循環(huán)降解MO的柱狀圖?？芍?jīng)過5次循環(huán)使用后，3%RGO/ZnO降解MO效率基本保持不變。實(shí)驗(yàn)結(jié)果表明RGO/ZnO復(fù)合材料光穩(wěn)定性較好。

圖7 3%RGO/ZnO樣品5次循環(huán)降解MO圖Fig.7 Degradation of MO for 3%RGO/ZnO sample for five cycles

3 結(jié)論

(1)采用一步水熱法，以ZnO納米棒為載體成功制備了RGO/ZnO納米復(fù)合材料。隨著復(fù)合材料中RGO含量的增加，RGO/ZnO納米復(fù)合材料中層片狀物質(zhì)尺寸增大，同時(shí)其在可見光區(qū)域的吸光度值增加。

(2)光催化降解甲基橙的實(shí)驗(yàn)結(jié)果表明，3%RGO/ZnO樣品在紫外-可見光照射下光催化活性最佳，其在120min內(nèi)降解甲基橙的效率是純ZnO的2.5倍；在波長大于400nm的可見光照射下，該樣品在180min內(nèi)降解甲基橙的效率達(dá)到26.2%，表明RGO/ZnO納米復(fù)合材料具有一定的可見光活性。

(3)5次循環(huán)光降解甲基橙實(shí)驗(yàn)結(jié)果表明，3%RGO/ZnO復(fù)合材料具有較好的光穩(wěn)定性。

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Synthesis and Photocatalytic Performance of RGO/ZnO Nanorod Composites

LU Jia1,WANG Hui-hu1,2,DONG Yi-fan1,CHANG Ying3,MA Xin-guo4，DONG Shi-jie1,2

(1 School of Mechanical Engineering,Hubei University of Technology,Wuhan 430068,China;2 Hubei Provincial Key Laboratory of Green Materials for Light Industry,Hubei University of Technology,Wuhan 430068,China;3 School of Materials Science and Technology,Hubei University of Technology,Wuhan 430068,China;4 School of Science,Hubei University of Technology,Wuhan 430068,China)

ZnO nanorods and RGO/ZnO nanorods composites were prepared by hydrothermal method. The influence of RGO content on the photocatalytic activity of RGO/ZnO nanorods composites was studied. ZnO nanorods and RGO/ZnO nanocomposites were characterized by X-ray diffraction (XRD), field emission electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance UV-visible absorption spectroscopy techniques. The results show that RGO/ZnO samples are synthesized successfully. With different additions of GO, the RGO/ZnO samples obtained exhibit different absorption characteristics in visible light region. The photocatalytic results of using methyl orange (MO) as the simulated pollutant show that RGO/ZnO nanorods composites exhibit high degradation efficiency under UV-Vis light illumination. The highest photocatalytic performance is obtained for RGO/ZnO composites when the mass ratio of RGO to ZnO is 3%. MO is almost completely degraded in 120min. RGO/ZnO also shows the visible-light-driven photocatalytic activity under visible light illumination (λ>400nm), and the maximum MO degradation efficiency in 180min can reach 26.2%, meanwhile, RGO/ZnO samples exhibit good photostability.

reduced graphene oxide;ZnO;photocatalysis;methyl orange

10.11868/j.issn.1001-4381.2016.12.008

O643

A

1001-4381(2016)12-0048-06

國家自然科學(xué)基金資助項(xiàng)目(51202064,51472081)；湖北省自然科學(xué)基金資助項(xiàng)目(2013CFA085)；武漢市青年晨光科技計(jì)劃資助項(xiàng)目(2013070104010016)

2015-01-09;

2016-04-27

王輝虎(1978-)，男，副教授，博士，研究方向?yàn)榧{米材料制備與性能，聯(lián)系地址：湖北省武漢市洪山區(qū)南湖李紙路一村1號(hào)湖北工業(yè)大學(xué)機(jī)械工程學(xué)院(430068)，E-mail:wanghuihu@126.com