氧化石墨烯復(fù)合材料吸附鈾的研究進(jìn)展

(1南華大學(xué) 核科學(xué)技術(shù)學(xué)院，湖南 衡陽421001；2南華大學(xué) 鈾礦冶生物技術(shù)國(guó)防重點(diǎn)學(xué)科實(shí)驗(yàn)室，湖南 衡陽421001；3南華大學(xué) 污染控制與資源化技術(shù)湖南省重點(diǎn)實(shí)驗(yàn)室，湖南 衡陽 421001)

鈾礦冶產(chǎn)生的大量低濃度含鈾放射性廢水對(duì)生態(tài)環(huán)境構(gòu)成嚴(yán)重威脅[1-2]。鈾作為一種重金屬，不僅具有放射性，且具有動(dòng)態(tài)的生物毒性和化學(xué)毒性[3-4]。我國(guó)的污水綜合排放標(biāo)準(zhǔn)規(guī)定鈾的最高允許排放濃度不超過0.05mg/L，而鈾礦冶等生產(chǎn)排放的廢水中鈾的質(zhì)量濃度一般在5mg/L左右[5]。因此，開展含鈾廢水處理技術(shù)的研究，使廢水達(dá)標(biāo)排放對(duì)于核工業(yè)可持續(xù)發(fā)展及環(huán)境保護(hù)具有重要的意義和應(yīng)用前景。廢水中鈾的傳統(tǒng)去除方法有化學(xué)沉淀法、離子交換法、吸附法、膜分離等[6-7]。吸附法以其操作簡(jiǎn)單、吸附速率快而被廣泛關(guān)注，在低濃度含鈾廢水處理領(lǐng)域得到了很快的發(fā)展，是目前該領(lǐng)域最有前景的處理技術(shù)之一[8-11]。吸附法的關(guān)鍵是選擇合適的吸附劑，目前研究者們致力于探索價(jià)廉高效的吸附劑，如黏土礦物[12-14]、二氧化硅[15-18]及沸石[19-22]等。石墨烯(graphene，GN)是一種由單原子層的碳原子通過sp2雜化，組成六角形呈蜂巢晶格狀的二維材料[23]，其理論比表面積高達(dá)2630m2/g，具有非常強(qiáng)的吸附能力，成為納米吸附劑研究中的熱點(diǎn)。氧化石墨烯(graphene oxide, GO)是石墨烯的氧化物，其表面有諸多含氧官能團(tuán)[24]，使其具有親水的特性，吸附性能更佳。Romanchuk等[25]將石墨烯氧化物原子薄片用于快速吸收受污染水中的放射性廢物，實(shí)驗(yàn)發(fā)現(xiàn)GO吸附U(VI) 的能力比傳統(tǒng)的吸附劑膨潤(rùn)土和活性炭要高很多。王云等[26]采用化學(xué)方法將多壁碳納米管打開得到富含氧基團(tuán)的氧化石墨烯納米帶，其對(duì)鈾的最大吸附量可達(dá)394mg/g。GO還可通過化學(xué)改性或與一些化學(xué)材料復(fù)合來接枝特定吸附功能基團(tuán)，來提高吸附效果和吸附選擇性[27-33]。學(xué)者們開展大量氧化石墨烯復(fù)合材料吸附鈾的研究，并取得一定的成果，但氧化石墨烯復(fù)合材料對(duì)鈾的吸附性能及作用機(jī)制的綜述仍然很少[31]。本文綜述了氧化石墨烯復(fù)合材料對(duì)鈾的吸附性能、吸附影響因素及吸附機(jī)理，并對(duì)它們?cè)阝檹U水處理中的應(yīng)用前景和發(fā)展趨勢(shì)做了展望，以期為后續(xù)相關(guān)研究及實(shí)際應(yīng)用提供參考依據(jù)。

1 氧化石墨烯復(fù)合材料對(duì)鈾的吸附性能

石墨烯的高比表面積使其成為理想的吸附材料[25,31]，然而，完整結(jié)構(gòu)的二維石墨烯晶體化學(xué)穩(wěn)定性高，呈惰性，另外其相鄰片層之間的π-π作用使石墨烯容易產(chǎn)生團(tuán)聚或者重新堆積成石墨，從而妨礙了石墨烯在吸附方面的研究及應(yīng)用，學(xué)者們通常利用石墨烯的衍生物——GO作為吸附材料[32-33]。石墨烯(圖1)[23]與GO的結(jié)構(gòu)(圖2)[24]大致相同，只是在二維基面上連有一些官能團(tuán)如羥基，環(huán)氧基，羧基，羰基等，這些含氧官能團(tuán)能賦予了GO一些新的特性如分散性、親水性及對(duì)聚合物的兼容性等，使GO成為一種優(yōu)良的支撐材料，可以結(jié)合化學(xué)功能基團(tuán)或復(fù)合其他材料，官能團(tuán)還可提供活性吸附位點(diǎn)吸附鈾等環(huán)境污染物，進(jìn)而有效分離廢水中的鈾等污染物[31-33]。目前學(xué)者們對(duì)氧化石墨烯復(fù)合材料吸附鈾的性能進(jìn)行了一些研究，表1匯總了氧化石墨烯材料對(duì)鈾吸附性能的主要參數(shù)[34-59]，這些研究發(fā)現(xiàn)該材料能有效吸附水中的鈾，等溫吸附模型能較好地符合Langmiur模型，吸附熱力學(xué)研究發(fā)現(xiàn)石墨烯基復(fù)合材料對(duì)鈾的吸附為自發(fā)放熱的過程。

圖1 石墨烯結(jié)構(gòu)示意圖[23]Fig.1 Basic structure of graphene[23]

圖2 氧化石墨烯的 Dékán 結(jié)構(gòu)模型[24]Fig.2 Dékán structural model of graphene oxide[24]

2 氧化石墨烯復(fù)合材料吸附鈾的影響因素分析

氧化石墨烯復(fù)合材料對(duì)鈾的吸附效果受到很多因素的影響，如溶液pH值、吸附溫度、離子強(qiáng)度、接觸時(shí)間和吸附劑用量等，因此，不同因素下氧化石墨烯復(fù)合材料對(duì)鈾離子的吸附性能往往存在一定的差異，且不同的氧化石墨烯材料的吸附能力受這些因素的影響各不相同。

2.1 溶液pH值對(duì)吸附的影響

2.2 溫度對(duì)吸附的影響

溫度是影響吸附的重要環(huán)境因子之一，對(duì)重金屬的吸附-解吸、沉淀-溶解、氧化-還原等一系列化學(xué)和物理過程都有不同程度的影響。因此，溫度的變化也可能導(dǎo)致吸附量的變化。Cheng等[37]研究發(fā)現(xiàn)溫度對(duì)氧化石墨烯/海泡石復(fù)合材料(GO@sepiolite)吸附鈾的影響較大，隨著溫度升高，GO@sepiolite對(duì)鈾的吸附效果提高，當(dāng)溫度從298K升高至338K時(shí)，GO@sepiolite對(duì)鈾的吸附量約增加到原來的2.2倍。Zhang等[45]研究了288.15～323.15K溫度范圍內(nèi)磺化氧化石墨烯(GOS)對(duì)鈾的吸附，結(jié)果表明，溫度越高越有利鈾的吸附。其他學(xué)者的相關(guān)研究也得到了一致的實(shí)驗(yàn)結(jié)論，發(fā)現(xiàn)氧化石墨烯復(fù)合材料對(duì)鈾的吸附是一個(gè)放熱自發(fā)的過程，溫度升高能促進(jìn)吸附反應(yīng)的進(jìn)行(見表1)[34-39,41-42,44-46,48-51]。這種現(xiàn)象可能是因?yàn)樗娜軇┗饔?，在水溶液中鈾離子以水合離子狀態(tài)存在，要吸附至石墨烯基材料表面上需要脫去鈾離子表面的水合鞘，這個(gè)脫水過程需要消耗能量，是吸熱過程，而離子吸附到吸附劑表面的過程是放熱過程[48,63]，當(dāng)鈾離子脫水的能量超過鈾離子吸附于氧化石墨烯材料放出的能量時(shí)，整個(gè)吸附過程表現(xiàn)為吸熱反應(yīng)，溫度越高鈾離子脫水越容易，因此越有利于氧化石墨烯材料對(duì)鈾離子的吸附[34]。

表1 石墨烯基復(fù)合材料對(duì)鈾的吸附容量及主要參數(shù)Table 1 Adsorption capacities and mainly parameters of graphene-based composite materials for uranium

Note:RT-room temperature; n.a.-not application.

2.3 離子強(qiáng)度對(duì)吸附的影響

溶液的離子強(qiáng)度會(huì)影響鈾離子存在形態(tài)，又能影響氧化石墨烯材料雙靜電層厚度而改變吸附劑的結(jié)合位點(diǎn)數(shù)，從而影響其對(duì)鈾離子的吸附[64]。不同氧化石墨烯材料吸附鈾的效果受離子強(qiáng)度影響的情況不盡相同，在一些實(shí)際的吸附研究中，它們吸附鈾的效果隨離子強(qiáng)度變化敏感[40,46]或不敏感的情況均有發(fā)生[36,45,47,49-52,54]。Zhang等[45]研究發(fā)現(xiàn)離子強(qiáng)度對(duì)氧化石墨烯和磺化氧化石墨烯吸附鈾的影響不顯著。Zhao等[36]研究發(fā)現(xiàn)在實(shí)驗(yàn)的pH值范圍內(nèi)偕胺肟磁性氧化石墨烯(AOMGO)對(duì)U(VI)的吸附效率幾乎不受離子強(qiáng)度的影響，這主要是由于U(VI)與AOMGO表面偕胺肟基及其他含氧官能團(tuán)形成了內(nèi)層表面絡(luò)合物，而不是形成外層表面絡(luò)合物或者發(fā)生離子交換[65]。Sun等[66]報(bào)道了pH值>4時(shí)離子強(qiáng)度對(duì)U(VI)吸附于氧化石墨烯和功能化氧化石墨烯上的影響甚微，同理，也是由于鈾吸附于材料是通過內(nèi)層表面絡(luò)合，且內(nèi)層表面絡(luò)合吸附機(jī)制通過常用于確定吸附劑與金屬離子之間的相互作用機(jī)制[67-68]的X射線吸收精細(xì)結(jié)構(gòu)譜(EXAFS)得以證實(shí)。而有些文獻(xiàn)則得出了不一樣的結(jié)論，Wang等[46]報(bào)道了氧化石墨烯納米帶 (GONRs)吸附鈾的能力對(duì)溶液離子強(qiáng)度的變化敏感。Song等[40]研究發(fā)現(xiàn)NaClO4濃度的增加會(huì)導(dǎo)致環(huán)糊精/氧化石墨烯(CD/GO)對(duì)鈾的吸附能力下降，因?yàn)榇嬖谟诟唠x子濃度溶液中的鈾離子，其活性會(huì)嚴(yán)重下降，從而抑制其轉(zhuǎn)移到CD/GO表面，此外，高離子強(qiáng)度能夠減少CD/GO材料之間的靜電斥力，從而導(dǎo)致CD/GO產(chǎn)生團(tuán)聚和吸附能力降低。

2.4 接觸時(shí)間對(duì)吸附的影響

達(dá)到吸附平衡所需要的反應(yīng)時(shí)間是影響吸附劑對(duì)鈾吸附能力的又一重要因素，吸附量隨吸附時(shí)間的變化情況也是吸附劑吸附動(dòng)力學(xué)的一個(gè)重要特征。在實(shí)際應(yīng)用中，吸附時(shí)間的長(zhǎng)短及處理周期會(huì)影響經(jīng)濟(jì)效益，氧化石墨烯及其復(fù)合材料非常大的比表面積及表面豐富的官能團(tuán)將有利于提高其吸附鈾離子的速率，從而能較快地達(dá)到吸附平衡狀態(tài)。Shao等[44]研究發(fā)現(xiàn)HO-CB[6]/GO對(duì)鈾的吸附非常迅速，僅在5min內(nèi)就能完成90%鈾的吸附，并能夠在20min內(nèi)達(dá)到吸附平衡，HO-CB[6]/GO對(duì)鈾的快速吸附有利于其實(shí)際應(yīng)用于去除大體積溶液中的鈾。Li等[35]利用Hummers方法制備得到的單層氧化石墨烯(GO)對(duì)鈾的吸附過程迅速，1h內(nèi)能達(dá)到吸附平衡狀態(tài)。Gu等[38]研究發(fā)現(xiàn)氧化石墨烯-碳納米管(GO-CNTs)在開始2h對(duì)U(VI)的吸附量增加較快，然后在9h內(nèi)逐漸達(dá)到平衡。Liu等[41]研究了接觸時(shí)間對(duì)GO和GO-NH2吸附U(VI)的影響，結(jié)果發(fā)現(xiàn)在接觸開始吸附速率迅速增加，這歸因在這一階段吸附劑上有大量的空置吸附位點(diǎn)可用。隨著時(shí)間的推移，空置的吸附位點(diǎn)逐漸被鈾酰離子填充，吸附變慢；對(duì)于GO-NH2，吸附量緩慢增加的時(shí)間段為80～240min之間，這是因?yàn)樵撾A段為內(nèi)擴(kuò)散階段，動(dòng)力學(xué)吸附時(shí)間更依賴于內(nèi)擴(kuò)散速度，可能需要較長(zhǎng)的時(shí)間來達(dá)到平衡。GO和GO-NH2對(duì)U(VI)的吸附平衡時(shí)間分別為60min和240min[41]。通常，吸附動(dòng)力學(xué)包括兩個(gè)階段：初始階段，該階段吸附迅速，對(duì)吸附平衡貢獻(xiàn)很重要，它為瞬時(shí)吸附或外表面吸附階段，此階段吸附劑上有大量可用的吸附位點(diǎn)數(shù)；第二階段，吸附過程較慢，為逐漸吸附階段，吸附速率受顆粒內(nèi)擴(kuò)散控制，一直到吸附達(dá)到平衡[41,69 ]。為了研究動(dòng)力學(xué)吸附機(jī)理，準(zhǔn)一級(jí)動(dòng)力學(xué)模型和準(zhǔn)二級(jí)動(dòng)力學(xué)模型常用于研究氧化石墨烯材料對(duì)鈾(VI)的吸附動(dòng)力學(xué)。大量文獻(xiàn)[34,36,38,41-43,45,48]報(bào)道的石墨烯基材料對(duì)鈾(VI)的吸附符合準(zhǔn)二級(jí)動(dòng)力學(xué)模型，說明這些材料對(duì)鈾(VI)的吸附過程主要受化學(xué)作用的控制。

2.5 吸附劑用量對(duì)吸附的影響

吸附劑用量也是影響吸附的重要參數(shù)，在實(shí)際應(yīng)用中是一個(gè)重要的考察指標(biāo)。吸附劑投加量直接影響氧化石墨烯材料與U(Ⅵ)的結(jié)合位點(diǎn)數(shù)目，進(jìn)而直接影響 U(Ⅵ)的吸附效率[70]。張偉強(qiáng)等[71]在鈾離子濃度為50mg/L，pH值為5.0的酸性條件下，考察了氨基三亞甲基膦酸改性石墨烯海綿材料(ATMP-GS)用量與鈾離子吸附的關(guān)系，結(jié)果表明當(dāng)吸附劑 ATMP-GS用量為7mg時(shí)，其對(duì)鈾離子的吸附量最大為96mg/g，隨后隨著ATMP-GS用量的增大吸附量出現(xiàn)下降，并在15mg以后不再變化。孫兆勇等[72]研究發(fā)現(xiàn)吸附劑用量在0.01～0.03g范圍內(nèi)，吸附率隨著吸附劑用量的增加而增加，當(dāng)吸附劑用量由0.01g增加到0.04g時(shí)，吸附率增加較明顯，達(dá)到35.14%，再增加吸附劑用量時(shí)，吸附率增加變得緩慢，僅為0.39%；而吸附量隨吸附劑用量的增加不斷降低。武里鵬等[73]通過實(shí)驗(yàn)研究了在吸附劑用量為0.01～0.03g范圍內(nèi)，磁性石墨烯對(duì)鈾的吸附容量及去除率隨吸附劑用量的變化，結(jié)果表明去除率隨吸附劑用量的增加而增大，在吸附劑用量為0.03g時(shí)去除率達(dá)到了90%以上；而吸附容量與吸附劑用量的關(guān)系與前者恰好相反。Song等[40]發(fā)現(xiàn)吸附劑用量的增加會(huì)提高CD/GO對(duì)U(VI)的吸附效率，因?yàn)殡S著吸附劑用量增加，參與U(VI)吸附的功能位點(diǎn)也隨之增加。本課題組[60]研究發(fā)現(xiàn)隨著GOS投加量的增加，U(Ⅵ)吸附率逐漸上升，吸附容量逐漸降低，這是由于隨著GOS用量的增加，GOS與U(Ⅵ)結(jié)合位點(diǎn)數(shù)目增多，從而使U(Ⅵ)的吸附率上升；但另一方面GOS投加量的增加導(dǎo)致GOS片層之間相互團(tuán)聚的概率增大，降低了有效結(jié)合位點(diǎn)數(shù)目，比表面積也隨之減少，導(dǎo)致單位質(zhì)量吸附劑吸附U(Ⅵ)的結(jié)合位點(diǎn)數(shù)目減少，所以吸附容量隨之降低。

氧化石墨烯材料吸附鈾的效果受吸附劑用量的影響，通常表現(xiàn)為高吸附劑用量使吸附效率提高，因?yàn)閁(Ⅵ)結(jié)合位點(diǎn)數(shù)目增多，而低吸附劑用量使吸附量更大，因其結(jié)合位點(diǎn)和表面積能夠得到有效利用[32,59]。因此，在實(shí)際應(yīng)用中，為保證吸附效果且使吸附劑能被充分利用，建議采用適當(dāng)?shù)奈絼┯昧俊?/p>

3 氧化石墨烯復(fù)合材料對(duì)鈾的吸附機(jī)理

目前已有大量關(guān)于鈾與GO基材料相互作用的研究，這些研究通過批量實(shí)驗(yàn)研究了不同因素對(duì)吸附作用的影響，進(jìn)行了吸附動(dòng)力學(xué)和吸附熱力學(xué)分析，并且采用表面絡(luò)合模型、光譜分析和理論計(jì)算等手段和方法，從實(shí)驗(yàn)數(shù)據(jù)和理論模擬、宏觀和微觀等角度闡述了GO基材料對(duì)鈾的吸附機(jī)制[28,50-58]。一些批量吸附實(shí)驗(yàn)的數(shù)據(jù)結(jié)果可以解釋鈾與GO基材料相互作用的機(jī)理,比如由吸附過程對(duì)離子強(qiáng)度敏感而對(duì)pH不敏感可以推導(dǎo)出吸附作用主要是通過外表面絡(luò)合或離子交換，而吸附過程對(duì)pH敏感而對(duì)離子強(qiáng)度不敏感主要是由于內(nèi)表面絡(luò)合作用[28,35,36]。表面絡(luò)合模型可以展示材料表面上鈾絡(luò)合物的構(gòu)成情況，從而可根據(jù)鈾絡(luò)合物的種類闡述吸附作用機(jī)理[54,66]。而通過擴(kuò)展X射線吸收精細(xì)結(jié)構(gòu)光譜(Extended X-ray Absorptionfine Structure Spectroscopy, EXAFS)，X射線光電子能譜(X-ray Photoelectric Spectroscopy, XPS)，X射線衍射(X-ray Diffraction, XRD)，拉曼光譜(Raman Spectroscopy, RS)，熒光時(shí)間衰減光譜(Time Resolved Laser Fluorescence Spectroscopy, TRLFS)，傅里葉變換紅外光譜法(Fourier Transformed Infrared Spectroscopy, FTIR)等光譜手段可以分析材料表面官能團(tuán)與鈾結(jié)合的微觀情況以及從分子水平揭示鈾的形態(tài)和微觀結(jié)構(gòu)[27-29]。理論計(jì)算如密度泛函理論是評(píng)價(jià)核素與固體材料之間物理化學(xué)作用的一種非常有用的手段[29,74-77]，例如，通過理論計(jì)算鈾與不同官能團(tuán)之間的結(jié)合能，可以確定物理吸附或化學(xué)吸附等的吸附性能，從而得到鈾與材料間的相互作用機(jī)理。不同實(shí)驗(yàn)條件下的研究結(jié)果表明石墨烯基材料對(duì)鈾有很強(qiáng)的吸附能力，主要是由于其表面或邊緣部位充斥著大量的含氧官能團(tuán)[47,57,77]。

3.1 表面絡(luò)合模型對(duì)吸附機(jī)理的研究

3.2 光譜技術(shù)分析

圖3 鈾在NZVI/rGO上的吸附與還原[79]Fig.3 Simultaneous adsorption and reduction of U(VI) onNZVI/rGO[79]

圖4 NZVI 、NZVI/GO、U(VI)作用后的NZVI 和NZVI/GO以及參考樣品的XANES光譜(a)和 EXAFS光譜(b)(T=(25±1)℃,I=0.01mol/L NaClO4,pH 5.0)[79]Fig.4 XANES spectra (a) and Fourier transform (FT) of EXAFSspectra (b) for reference samples and U(VI)-reacted NZVI andNZVI/GO(T=(25±1)℃, I=0.01mol/L NaClO4, pH 5.0)[79]

3.3 理論計(jì)算對(duì)吸附機(jī)理的研究

計(jì)算化學(xué)研究能從分子水平獲得GO與放射性核素之間所形成配合物的電子結(jié)構(gòu)、形態(tài)分布、配位性質(zhì)和熱力學(xué)性質(zhì)等數(shù)據(jù)，對(duì)闡明放射性核素與GO之間的固液界面作用機(jī)理起著重要作用[81-82]。利用理論計(jì)算研究得到的放射性核素與GO相互作用數(shù)據(jù)與實(shí)驗(yàn)結(jié)果進(jìn)行比較和相互驗(yàn)證，可以使實(shí)驗(yàn)研究更具說服力和可靠性。而對(duì)于一些比較難開展的實(shí)驗(yàn)，如所有的錒系元素，特別是具有放射性和毒性的超鈾元素，阻礙了實(shí)驗(yàn)研究開展，理論計(jì)算可以提供一條有效的途徑來補(bǔ)充有關(guān)錒系元素配合物的電子結(jié)構(gòu)及性質(zhì)等[76,81]。密度泛函理論(Density Functional Theory，DFT)是理論計(jì)算的重要工具之一，它能以有效的方式計(jì)算相關(guān)能量和形態(tài)等基礎(chǔ)數(shù)據(jù)而在計(jì)算化學(xué)研究領(lǐng)域得到非常好的應(yīng)用[83-84]。DFT常用于闡述局部相互作用表面分子的吸收，結(jié)合TRLFS，EXAFS，XPS等光譜分析結(jié)果能在分子水平上更好地闡明GO等材料與放射性核素的相互作用機(jī)制，為評(píng)價(jià)放射性核素在環(huán)境中的物理化學(xué)行為提供重要的參考價(jià)值。

近年來，一些研究者通過理論計(jì)算研究了鈾在石墨烯基材料表面的吸附行為。Wu等[76]利用DFT結(jié)合相對(duì)論小芯贗勢(shì)優(yōu)化了鈾酰離子和GO之間的22種配合物，研究的含氧官能團(tuán)有羥基、羧基、氨基和二甲基甲酰胺等，研究結(jié)果表明鈾原子和GO上氧原子之間的距離(U-OG)在陰離子GO配合物(鈾酰/GO-/2-)中要短于在中性GO配合物(鈾酰/GO)中，鈾酰/GO-/2-配合物中氫鍵的形成可以提高帶負(fù)電的GO對(duì)鈾酰離子的結(jié)合能力，此外，熱力學(xué)計(jì)算表明，鈾酰離子更容易與羥基和羧基功能化的陰離子GO配合物發(fā)生絡(luò)合反應(yīng)，同時(shí)幾何結(jié)構(gòu)和熱力學(xué)能量都表明，由羥基和羧基改性的GO對(duì)鈾酰離子的結(jié)合能力比氨基和二甲基甲酰胺基改性的GO要強(qiáng)得多。偕胺肟基和羧基經(jīng)常用于修飾石墨烯材料，Wang等[77]采用量子化學(xué)計(jì)算模擬了鈾與一系列通過烷基鏈嫁接偕胺肟基和羧基等基團(tuán)的吸附劑之間的相互作用，并研究了不同官能團(tuán)及其組合對(duì)配位結(jié)構(gòu)與萃取穩(wěn)定性等產(chǎn)生的影響。

圖5 rGOs-鈾酰配合物和GOs-鈾酰配合物的DFT優(yōu)化幾何結(jié)構(gòu)[66]Fig.5 DFT-optimized geometries of the rGOs-uranyl complexes and GOs-uranyl complexes[66]

4 結(jié)束語

氧化石墨烯復(fù)合材料由于其巨大的表面積及豐富的表面功能基團(tuán)對(duì)鈾能實(shí)現(xiàn)高效的吸附。從目前國(guó)內(nèi)外的研究現(xiàn)狀來看，石墨烯基復(fù)合材料對(duì)鈾的吸附機(jī)理的研究主要通過采用批量吸附實(shí)驗(yàn)研究不同因素對(duì)其吸附能力的影響，吸附動(dòng)力學(xué)以及吸附熱力學(xué)研究，以及利用表面絡(luò)合模型、光譜分析技術(shù)與理論計(jì)算等方法來實(shí)現(xiàn)。然而，由于氧化石墨烯含氧官能團(tuán)的多樣性(如羥基、羧基、羰基、環(huán)氧基等)，以及表面功能化修飾引入一些新的官能團(tuán)，而且鈾在環(huán)境中的化學(xué)形態(tài)變化復(fù)雜，因此盡管已有不少有關(guān)石墨烯基材料吸附鈾的研究工作，還需深入地開展石墨烯基材料對(duì)鈾的吸附行為及其開發(fā)應(yīng)用的研究，可在下述幾個(gè)方面進(jìn)行研究工作：

(1)將實(shí)驗(yàn)、模型模擬及理論計(jì)算，宏觀的批量實(shí)驗(yàn)與微觀的光譜技術(shù)結(jié)合起來運(yùn)用于研究石墨烯基材料對(duì)鈾的吸附行為，將實(shí)驗(yàn)與理論，宏觀與微觀的研究結(jié)論互相補(bǔ)充互相驗(yàn)證，以便更準(zhǔn)確深入地揭示石墨烯基材料與鈾的作用機(jī)理。

(2)目前研究發(fā)現(xiàn)GO基材料對(duì)鈾的高效吸附主要?dú)w因于其表面或邊緣的功能官能團(tuán)，但由于GO基材料表面或邊緣存在不同種類的官能團(tuán)，不同官能團(tuán)對(duì)吸附鈾的發(fā)揮作用大小卻缺乏深層次的理論和實(shí)驗(yàn)研究。

(3)關(guān)于氧化石墨烯材料脫附鈾的研究報(bào)道不多，應(yīng)研究溫度、脫附劑種類、離子強(qiáng)度和初始鈾濃度等對(duì)脫附效果的影響并探討相關(guān)脫附機(jī)理，為氧化石墨烯材料在鈾污染處理方面的重復(fù)利用提供理論基礎(chǔ)。

(4)隨著氧化石墨烯材料在多學(xué)科領(lǐng)域的大量應(yīng)用，部分GO基材料不可避免會(huì)被釋放到自然環(huán)境中而成為環(huán)境污染物。GO基材料在水中具有高分散性、高吸附性以及高化學(xué)活性，其有可能對(duì)水環(huán)境生態(tài)和水生生物造成不利影響[85-88]，因此，為保證GO基材料更安全和環(huán)保的應(yīng)用，未來的研究需要進(jìn)一步明確GO基材料的生態(tài)效應(yīng)及其環(huán)境行為，正確評(píng)估其環(huán)境風(fēng)險(xiǎn)。

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