本文選題：碳點 + 熒光　； 參考：《安徽大學(xué)》2016年碩士論文

【摘要】：碳量子點(carbon quantum dots,簡稱碳點)是一類尺寸小于10nm的“核-殼”型碳納米材料,其內(nèi)核由結(jié)晶或者非晶碳組成,表面殼層由大量含氧或含氮、硫等其他元素的有機官能團組成。自從2004年Walter A. Scrivens課題組發(fā)現(xiàn)并在2006年由Ya-Ping Sun課題組首次命名為碳點以來,經(jīng)過近十年的發(fā)展,碳點已經(jīng)成為碳納米材料家族中的一個新星。與傳統(tǒng)半導(dǎo)體量子點(如CdS和CdSe QDs)相比,碳點不僅具有高量子產(chǎn)率和優(yōu)越的上、下轉(zhuǎn)換熒光性能以及光致電子轉(zhuǎn)移性質(zhì),而且毒性更低,生物相容性和安全性更好,原料及制備手段也更價廉易得。碳點因其獨特的理化性質(zhì)以及具有的綜合優(yōu)勢,從而在生物顯影、金屬離子檢測、生化分析以及光催化等領(lǐng)域有著良好而廣泛的應(yīng)用。本文以綠茶為天然碳源,采用“一步”熱解法制備出一種表面富含羥基、平均粒徑為3.83 nm的水溶性碳點(命名為T-CNDs)。通過研究發(fā)現(xiàn),(1)該T-CNDs具有很高的熒光量子產(chǎn)率：以硫酸喹啉為參比,在330 nm激發(fā)光的激發(fā)下,T-CNDs在水中的熒光量子產(chǎn)率可達到64%；(2)T-CNDs在水中的熒光發(fā)射光譜具有激發(fā)光波長依賴性和pH值依賴性,在pH為10的水溶液中其熒光強度達到最大；(3)當激發(fā)光波長大于600 nm, T-CNDs呈現(xiàn)出上轉(zhuǎn)換熒光性能；(4)T-CNDs對Fe3+有很好的選擇性,即濃度為0.5 μM的Fe3+能夠使T-CNDs的熒光完全猝滅,這一特點與本實驗室之前報道的魔芋碳點相似；(5)T-CNDs具有明顯的光生電子轉(zhuǎn)移效應(yīng)：當T-CNDs水溶液在485 nm激發(fā)光照射下,無論向其中加入電子供體(N,N-二乙基苯胺)還是電子受體(2,4-二硝基甲苯),其熒光強度都會明顯減弱；當加入的兩種猝滅劑的濃度為0.03 M時,T-CNDs的熒光壽命分別從4.5 ns降低到2.2和2.0 ns,這個結(jié)果也表明該光照下碳點既是電子受體又是電子供體。雖然光催化是碳點的一個重要應(yīng)用領(lǐng)域,但是根據(jù)最近報道,碳點不僅具有優(yōu)異的光催化性質(zhì),而且因其表面具有羥基從而對一些有機縮合反應(yīng)具有較好的化學(xué)催化作用。在本文中,我們探索研究了碳點對自由基聚合反應(yīng)的催化作用。針對T-CNDs的水溶性,我們選擇了水溶性單體對苯乙烯磺酸鈉(NaSS)作為研究對象。相比于不加碳點的聚合反應(yīng),當把T-CNDs加入到NaSS的自由基聚合反應(yīng)體系中時,NaSS的單體轉(zhuǎn)化速率明顯加快,所得到的聚合產(chǎn)物—聚對苯乙烯磺酸鈉(PSSNa)的分子量也顯著增大,而且分子量分布指數(shù)(PDI=Mw/Mn)變窄。我們認為T-CNDs催化NaSS自由基聚合反應(yīng)的機理可能如下：由于碳點既是電子受體又是電子供體,在反應(yīng)初期即自由基引發(fā)階段,T-CND與引發(fā)劑過硫酸鉀(KPS)形成氧化-還原對(T-CND/KPS),使KPS分解產(chǎn)生S04-·自由基所需的活化能降低,即能夠加快KPS分解；同時T-CNDs能夠與NaSS上的不飽和雙鍵發(fā)生共軛,使得NaSS的雙鍵活化易于形成單體自由基,上述兩個因素共同作用,使得加快引發(fā)速度的同時也加快了NaSS的單體轉(zhuǎn)化速度。根據(jù)經(jīng)典的高分子化學(xué)理論,聚合物分子量與體系中自由基濃度成反比,然而與傳統(tǒng)的KPS熱引發(fā)(即一個KPS分子產(chǎn)生兩個S04-·自由基)不同,每對T-CND/KPS只產(chǎn)生一個S04·自由基,而且T-CNDs可以捕獲S04-·自由基在水中誘導(dǎo)產(chǎn)生的OH·自由基,即使把自由基引發(fā)效率提高的因素考慮進去,由T-CND/KPS氧化-還原對引發(fā)所產(chǎn)生的自由基濃度還是要大大低于傳統(tǒng)的KPS熱引發(fā),因此加入T-CNDs的NaSS自由基聚合反應(yīng)最終得到的PSSNa分子量反而會顯著增大,同時分子量分布變窄。進而,我們將T-CND s用于其他水溶性乙烯基單體如丙烯酰胺(AM)的自由基聚合反應(yīng),發(fā)現(xiàn)也有催化效果,但是T-CNDs對油溶性的乙烯基單體如甲基丙烯酸甲酯(MMA)的自由基聚合無明顯催化效果,這可能是因為MMA聚合使用的是有機溶劑甲苯和油溶性引發(fā)劑偶氮二異丁氰(AIBN),碳點在甲苯中溶解性差,而且也不能與AIBN形成氧化-還原引發(fā)對所導(dǎo)致的。上述結(jié)果表明T-CNDs對水溶性乙烯基單體的自由基聚合反應(yīng)有催化作用,而且這一結(jié)論具有一定的普適性。此外,我們還發(fā)現(xiàn)T-CNDs在苯甲醇引發(fā)的ε-己內(nèi)酯(CL)的開環(huán)聚合反應(yīng)中充當助催化劑,輔助有機酸如水楊酸、酒石酸和檸檬酸等一起來催化CL的開環(huán)聚合,即與不加T-CNDs的反應(yīng)體系相比,加入T-CNDs后不僅能夠加快CL的單體轉(zhuǎn)化速度,并且使獲得的聚ε-己內(nèi)酯(PCL)的分子量增大,同時其PDI變窄。雖然目前該碳點的助催化機理還不是很清楚,但是可能與T-CNDs的表面帶有大量羥基有關(guān)。
[Abstract]:A carbon quantum dot (carbon quantum dots) is a class of "nuclear shell" carbon nanomaterials with a size less than 10nm. The core consists of crystalline or amorphous carbon. The surface shell is composed of organic functional groups with a large amount of oxygen or other elements such as nitrogen, sulfur and other elements. Since the discovery of the Walter A. Scrivens project group in 2004 and in 2006, Ya-Ping Sun Since the project group was first named carbon point, after nearly ten years of development, carbon dots have become a new star in the family of carbon nanomaterials. Compared with traditional semiconductor quantum dots (such as CdS and CdSe QDs), carbon points not only have high quantum yield and superior, down conversion and photoinduced electron transfer properties, but also have lower toxicity and lower toxicity. As a result of its unique physical and chemical properties and comprehensive advantages, carbon dots have a good and extensive application in the fields of biological development, metal ion detection, biochemical analysis and photocatalysis because of their unique physical and chemical properties and comprehensive advantages. This paper uses green tea as a natural carbon source and adopts "one step" pyrolysis method. A water soluble carbon point with an average diameter of 3.83 nm (named T-CNDs) was prepared. It was found that (1) the T-CNDs has a high fluorescence quantum yield: with the reference of quinoline sulphate, the fluorescence yield of T-CNDs in water can reach 64% under the excitation of 330 nm stimulated luminescence; (2) the fluorescence emission of T-CNDs in water. The spectrum has the dependence on the long dependence of light wave and the dependence of pH value on the fluorescence intensity in the aqueous solution of pH 10. (3) when the excitation wavelength is greater than 600 nm, T-CNDs presents the upconversion fluorescence performance; (4) T-CNDs has a good selectivity to Fe3+, that is, the concentration of 0.5 u M can completely quenched the T-CNDs fluorescence, this characteristic and the original The Amorphophallus carbon point reported before the laboratory is similar; (5) T-CNDs has an obvious photoinduced electron transfer effect: when the T-CNDs aqueous solution is irradiated with 485 nm excitation light, whether the electron donor (N, N- two ethyl aniline) or the electron acceptor (2,4- two nitrotoluene) is added to it, the fluorescence intensity will be weakened obviously; when the two kinds of quencher are added When the concentration is 0.03 M, the fluorescence lifetime of T-CNDs decreases from 4.5 ns to 2.2 and 2 ns, and the results also show that the carbon dots are both electron acceptors and electron donors. Although photocatalysis is an important field of application of carbon dots, the carbon dots have not only excellent photocatalytic properties but also their surface mask, according to recent reports. In this paper, we explored the catalytic effect of carbon dots on free radical polymerization. In view of the water solubility of T-CNDs, we selected water-soluble monomers for sodium benzene sulfonate (NaSS) as a research object. When T-CNDs is added to the free radical polymerization reaction system of NaSS, the conversion rate of NaSS is obviously accelerated, and the molecular weight of poly (P) sodium sulfonate (PSSNa) is also increased significantly, and the molecular weight distribution index (PDI=Mw/Mn) is narrowed. The mechanism of T-CNDs catalyzing the reaction of NaSS radical polymerization may be as follows. Since the carbon point is both the electron acceptor and the electron donor, the activation energy required by the T-CND and the initiator potassium persulfate (KPS) is formed at the initial stage of the free radical initiation. The activation energy required for the decomposition of KPS to produce S04- free radicals is reduced, that is, the KPS decomposition can be accelerated, and T-CNDs can occur with the unsaturated double bond on NaSS. Conjugation, making the double bond activation of NaSS easy to form a monomer free radical, the two factors co acted together to accelerate the initiation of the velocity and speed up the conversion of NaSS. According to the classical polymer chemistry theory, the molecular weight of the polymer is inversely proportional to the free radical concentration in the system, but with the traditional KPS thermal initiation (that is, a KPS The molecule produces two S04- free radicals, which produces only one S04 free radical per pair of T-CND/KPS, and T-CNDs can capture OH free radicals induced by S04- free radicals in water. Even if the factor of increasing the efficiency of free radicals is taken into account, the free radical concentration produced by the oxidation of T-CND/KPS is still large. It is lower than the traditional KPS heat initiation. Therefore, the final PSSNa molecular weight obtained by the NaSS radical polymerization of T-CNDs can be significantly increased and the molecular weight distribution narrowed. Then, we use T-CND s for the free radical polymerization of other water-soluble vinyl monomers, such as acrylamide (AM), and also have a catalytic effect, but T-CNDs against oil. The free radical polymerization of soluble vinyl monomers, such as methyl methacrylate (MMA), has no obvious catalytic effect. This may be because MMA polymerization is due to the use of organic solvent toluene and oil soluble initiator azo two iso butyl cyanide (AIBN), the solubility of carbon points in toluene is poor, and it can not form oxidation reduction induced by AIBN. The results show that T-CNDs has a catalytic effect on the free radical polymerization of water-soluble vinyl monomers, and this conclusion has a certain universality. In addition, we also found that T-CNDs acts as a promoter in the open ring polymerization of epsilon - caprolactone (CL) induced by benzyl alcohol, assisted by organic acids such as salicylic acid, tartaric acid and citric acid. The open ring polymerization of CL, which is compared with the reaction system without T-CNDs, can not only accelerate the conversion of CL, but also increase the molecular weight of poly (PCL) and narrow the PDI. Although the catalytic mechanism of this carbon point is not very clear at present, it may have a large amount of hydroxyl on the surface of T-CNDs. It is related to the base.
【學(xué)位授予單位】：安徽大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：O631.5;O613.71

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相關(guān)博士學(xué)位論文 前1條

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本文編號：1975804