氧化石墨（烯）材料的制备、吸附性能及机理研究

发布时间：2018-05-23 08:04

本文选题：氧化石墨(烯) + 氧化程度　；参考：《西南科技大学》2017年硕士论文

【摘要】：石墨碳原子层之间相互平行叠置且以短程范德华力相联系,其间形成相对疏松的层间域,结构层上的π键具有金属键的性质。因此具有良好的可插层,可氧化及剥分性。然而石墨氧化的难易程度、反应速率、反应条件及化学试剂的选择直接或间接的影响氧化石墨(GO)产物结构中官能团的类型和含量,进而影响结构和阳离子交换性能。可控制备特定官能团类型的GO,既可直接作为优良的吸附材料,而且能为基于GO功能化材料在吸附领域的应用提供更佳的前躯体。本论文采用浓H_2SO_4和KMnO_4为反应体系的Hummers法可控制备不同氧化程度的GO,研究了GO制备过程中的阶段性特征;采用甲醛缩合法对不同氧化程度GO的阳离子交换容量(CEC)进行测定,并对GO的干、湿状态及阳离子交换过程产物对比研究,查明阳离子交换机制及交换过程对GO结构的影响;在GO制备、结构和理化性质(CEC性能)研究基础上,进一步研究剥离后的GO即单层氧化石墨烯(GOs)对亚甲基蓝(MB)的吸附性能及机理。研究表明氧化剂(KMnO_4)足量时,反应时间和温度对产物结构特征有显著影响。可控制备的低温(0~4°C)反应时间为180 min,中温(37°C)反应时间为120 min,以及在原始氧化石墨(PGO)中因加水而引起的升温温度控制在65~75°C最佳,改变KMnO_4剂量时,石墨(002)面网的最大底面间距随KMnO_4剂量发生规律性变化;可控制备获得低氧化程度的GO结构层上碳羟基(C-OH)相对含量较高,高氧化程度时环氧基(C-O-C)和羰基(C=O)含量较高;通过高倍光学显微镜对石墨的氧化过程在线分析发现KMnO_4是石墨发生氧化插层的充分条件,而浓H_2SO_4与石墨不发生插层反应,氧化过程由边缘或缺陷处率先发生,并逐渐向面内延伸。不同氧化程度的GO官能团类型和含量上都表现出较大的差异,采用甲醛缩合法测定CEC结果表明并非随着氧化程度的增加CEC一直增大,而是与结构中含氧基团C-OH和-COOH含量(即可解离出H+的量)相关,可控氧化过程使GO-4样品的CEC达到最大值541.81 mmol?(100g)-1,继续增大氧化程度,反而使CEC减小;水介质中GO层间域内的H+与其它阳离子可发生交换,并在层间域内形成水化阳离子层,阳离子交换过程可逆;[NH4(H_2O)6]+和[Ca(H_2O)6]2+以水合阳离子形式在层间域内与GO结构层上的C-O-以氢键结合,阳离子交换前后GO结构及官能团未发生明显变化。GO结构层上的负电性及开放的层间域环境使其CEC值为蒙脱石的5~6倍,剥离后的GO(GOs-n)吸附亚甲基蓝(MB)的最大饱和吸附量依次为728.44、965.63和807.29 mg·g-1,吸附过程符合准二级动力学模型,吸附量与GOs结构中C-OH和-COOH含量成正相关;GOs结构上去质子化的C-O-和-COO-为主要活性位点与MB+发生化学控速的单分子层吸附;在氧化程度低时,GOs结构中C-OH和-COOH官能团之间以离子交换吸附为主导取代H;氧化程度高时,GOs结构中的C-O-C和C=O含量增加与MB以氢键吸附作用增强,对吸附量的影响凸显。
[Abstract]:The graphite carbon layers are parallel to each other and connected by short range van der Waals force, forming a relatively loose interlaminar domain. The 蟺 bonds on the structural layers have the properties of metal bonds. Therefore, it has good intercalation, oxidation and stripping properties. However, the degree of ease of graphite oxidation, reaction rate, reaction conditions and the selection of chemical reagents directly or indirectly affect the type and content of functional groups in the structure of graphite oxide (GOO) products, thus affecting the structure and cation exchange properties. The controllable preparation of specific functional group type goo can be used as an excellent adsorption material directly, and it can provide a better precursor for the application of go functionalized materials in adsorption field. In this paper, the phase characteristics of go preparation process were studied by using Hummers method with concentrated H_2SO_4 and KMnO_4 as reaction system, and the cation exchange capacity of go with different degree of oxidation was determined by formaldehyde condensation method. The dry, wet and cation exchange products of go were compared, and the effects of cation exchange mechanism and exchange process on go structure were investigated, and the preparation, structure and physical and chemical properties of go were studied. The adsorption properties and mechanism of GOs3 on MBM were studied. The results show that the reaction time and temperature have a significant effect on the structure of the product when the quantity of oxidizer KMnO4 is sufficient. The reaction time of controlled preparation is 180 min at low temperature (4 掳C) and 120 min at moderate temperature (37 掳C). The optimum temperature of water added in the raw graphite oxide is 6575 掳C, when the dosage of KMnO_4 is changed, The maximum bottom surface spacing of the graphite mesh varies regularly with the dose of KMnO_4, and the content of C-OH) on the go structure layer with low oxidation degree is relatively high, and the content of C-O-C) and carbonyl cationic acid on the go structure layer with high oxidation degree is higher. The on-line analysis of the oxidation process of graphite by high power optical microscope shows that KMnO_4 is the sufficient condition for the oxidation intercalation of graphite, while the strong H_2SO_4 does not intercalate with graphite, and the oxidation process occurs first from the edge or defect. And gradually extended into the plane. The types and contents of go functional groups with different degree of oxidation showed great differences. The results of CEC determination by formaldehyde condensation showed that CEC did not increase with the increase of oxidation degree. It is related to the content of oxygen group C-OH and -COOH in the structure (the amount of H can be dissociated). The controlled oxidation process can make the CEC of GO-4 sample reach the maximum value of 541.81 mmol / L ~ (100) g / m ~ (-1), and increase the degree of oxidation and decrease the content of CEC. In water medium, H in go interlayer can be exchanged with other cations, and a hydrated cationic layer is formed in the interlayer domain, and the cation exchange process is reversible. [NH4(H_2O)6] and [Ca(H_2O)6] 2 bond with C-O- on go structure layer in the form of hydrated cations in the interlayer domain. There was no obvious change in go structure and functional group before and after cation exchange. The negative electrical properties of go structure layer and the open interlayer environment made the CEC value of go layer 5 times than that of montmorillonite. The maximum saturated adsorption capacity was 728.44965.63 and 807.29 mg g ~ (-1), respectively. The adsorption process was in accordance with the quasi-second-order kinetic model. The adsorption capacity was positively correlated with the content of C-OH and -COOH in the GOs structure. The deprotonated C-O- and -COO- on the GOs structure were the main active sites for monolayer adsorption of MB at chemically controlled rate. When the oxidation degree is low, the adsorption of C-OH and -COOH in GOs structure is dominated by ion exchange adsorption, and the increase of C-O-C and Con O content in GOs structure with high degree of oxidation increases with the hydrogen bond adsorption of MB, and the effect on adsorption capacity is obvious.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O613.71

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