水溶性荧光碳量子点的合成及其催化自由基聚合反应的研究

发布时间：2018-06-04 04:02

本文选题：碳点 + 荧光　；参考：《安徽大学》2016年硕士论文

【摘要】：碳量子点(carbon quantum dots,简称碳点)是一类尺寸小于10nm的“核-壳”型碳纳米材料,其内核由结晶或者非晶碳组成,表面壳层由大量含氧或含氮、硫等其他元素的有机官能团组成。自从2004年Walter A. Scrivens课题组发现并在2006年由Ya-Ping Sun课题组首次命名为碳点以来,经过近十年的发展,碳点已经成为碳纳米材料家族中的一个新星。与传统半导体量子点(如CdS和CdSe QDs)相比,碳点不仅具有高量子产率和优越的上、下转换荧光性能以及光致电子转移性质,而且毒性更低,生物相容性和安全性更好,原料及制备手段也更价廉易得。碳点因其独特的理化性质以及具有的综合优势,从而在生物显影、金属离子检测、生化分析以及光催化等领域有着良好而广泛的应用。本文以绿茶为天然碳源,采用“一步”热解法制备出一种表面富含羟基、平均粒径为3.83 nm的水溶性碳点(命名为T-CNDs)。通过研究发现,(1)该T-CNDs具有很高的荧光量子产率：以硫酸喹啉为参比,在330 nm激发光的激发下,T-CNDs在水中的荧光量子产率可达到64%；(2)T-CNDs在水中的荧光发射光谱具有激发光波长依赖性和pH值依赖性,在pH为10的水溶液中其荧光强度达到最大；(3)当激发光波长大于600 nm, T-CNDs呈现出上转换荧光性能；(4)T-CNDs对Fe3+有很好的选择性,即浓度为0.5 μM的Fe3+能够使T-CNDs的荧光完全猝灭,这一特点与本实验室之前报道的魔芋碳点相似；(5)T-CNDs具有明显的光生电子转移效应：当T-CNDs水溶液在485 nm激发光照射下,无论向其中加入电子供体(N,N-二乙基苯胺)还是电子受体(2,4-二硝基甲苯),其荧光强度都会明显减弱；当加入的两种猝灭剂的浓度为0.03 M时,T-CNDs的荧光寿命分别从4.5 ns降低到2.2和2.0 ns,这个结果也表明该光照下碳点既是电子受体又是电子供体。虽然光催化是碳点的一个重要应用领域,但是根据最近报道,碳点不仅具有优异的光催化性质,而且因其表面具有羟基从而对一些有机缩合反应具有较好的化学催化作用。在本文中,我们探索研究了碳点对自由基聚合反应的催化作用。针对T-CNDs的水溶性,我们选择了水溶性单体对苯乙烯磺酸钠(NaSS)作为研究对象。相比于不加碳点的聚合反应,当把T-CNDs加入到NaSS的自由基聚合反应体系中时,NaSS的单体转化速率明显加快,所得到的聚合产物—聚对苯乙烯磺酸钠(PSSNa)的分子量也显著增大,而且分子量分布指数(PDI=Mw/Mn)变窄。我们认为T-CNDs催化NaSS自由基聚合反应的机理可能如下：由于碳点既是电子受体又是电子供体,在反应初期即自由基引发阶段,T-CND与引发剂过硫酸钾(KPS)形成氧化-还原对(T-CND/KPS),使KPS分解产生S04-·自由基所需的活化能降低,即能够加快KPS分解；同时T-CNDs能够与NaSS上的不饱和双键发生共轭,使得NaSS的双键活化易于形成单体自由基,上述两个因素共同作用,使得加快引发速度的同时也加快了NaSS的单体转化速度。根据经典的高分子化学理论,聚合物分子量与体系中自由基浓度成反比,然而与传统的KPS热引发(即一个KPS分子产生两个S04-·自由基)不同,每对T-CND/KPS只产生一个S04·自由基,而且T-CNDs可以捕获S04-·自由基在水中诱导产生的OH·自由基,即使把自由基引发效率提高的因素考虑进去,由T-CND/KPS氧化-还原对引发所产生的自由基浓度还是要大大低于传统的KPS热引发,因此加入T-CNDs的NaSS自由基聚合反应最终得到的PSSNa分子量反而会显著增大,同时分子量分布变窄。进而,我们将T-CND s用于其他水溶性乙烯基单体如丙烯酰胺(AM)的自由基聚合反应,发现也有催化效果,但是T-CNDs对油溶性的乙烯基单体如甲基丙烯酸甲酯(MMA)的自由基聚合无明显催化效果,这可能是因为MMA聚合使用的是有机溶剂甲苯和油溶性引发剂偶氮二异丁氰(AIBN),碳点在甲苯中溶解性差,而且也不能与AIBN形成氧化-还原引发对所导致的。上述结果表明T-CNDs对水溶性乙烯基单体的自由基聚合反应有催化作用,而且这一结论具有一定的普适性。此外,我们还发现T-CNDs在苯甲醇引发的ε-己内酯(CL)的开环聚合反应中充当助催化剂,辅助有机酸如水杨酸、酒石酸和柠檬酸等一起来催化CL的开环聚合,即与不加T-CNDs的反应体系相比,加入T-CNDs后不仅能够加快CL的单体转化速度,并且使获得的聚ε-己内酯(PCL)的分子量增大,同时其PDI变窄。虽然目前该碳点的助催化机理还不是很清楚,但是可能与T-CNDs的表面带有大量羟基有关。
[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.
【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O631.5;O613.71

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