Sun Hongjuan

Synthesis and Structural Characterization of Graphene-Based Membranes

A stable hydrosol of graphene was synthesized by oxidation reduction and then a flow assembly of this graphene was used to form a graphene-based membrane by vacuum extraction filtering method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, particle size analysis, and scanning probe microscopy (SPM) were used to characterize the crystal structure, granularity, and characteristic change of the molecular spectrum of the samples in the reaction. FTIR tests show that the structural layer of graphite during the oxidation process bonds to a large number of functional groups and parts of these stable functional groups remain on the reduced structural layer of graphene. X-ray diffraction results show that the peaks of the graphite oxide shift to lower angles, become broader and the original graphite peak disappears. Suspensions of graphene oxide form condensed matter and graphene flocculating constituent during film deposition. Particle size analysis and SPM tests show that the particle sizes of the graphene oxide sheets that are dispersed in water show a tailing peak and a broad distribution while the graphene sheets show a singlet, narrower distribution, and smaller dimensions. Raman results show that during oxidation and reduction, the D peak and G peak of the samples gradually extend, ID/IG increases gradually and the degree of sample disorder increases. On the basis of the above analyses, the structural characteristics of the samples in the reaction are summarized.

Influence of Thermal Reduction Temperature on the Humidity Sensitivity of Graphene Oxide

In order to explore the influence of thermal reduction temperature on the humidity sensitivity of graphene oxide (GO), we treat the prepared graphene oxide (GOS) thin film under different temperature conditions and obtained the GOS thin film humidity elements of different reduction degrees. Thermostability, function groups, and structural defects of the GOS samples are characterized by TG-DTA, FTIR, and Raman. After thermal reduction at 60 and 100°C, the function groups of GOS are not decomposed and the GOS has better humidity sensitivity and shows the characteristics of n-type semiconductor. After thermal reduction at 150–200°C, the function groups are decomposed and the humidity sensitivity is decreased due to thermal reduction on GOS. Particularly, the GOS shows the characteristics of p-type semiconductor in the relative humidity lower than 75.3%, and shows the characteristics of n-type semiconductor in the relative humidity higher than 75.3%. After thermal reduction at 250°C, the GOS thin film has no humidity sensitivity. After thermal reduction at 300–450°C, the carbon skeleton of GOS is combusted to form new structure defects and the humidity sensitivity is getting better, and the GOS shows the characteristics of p-type semiconductor.

Factor Group Analysis of Molecular Vibrational Modes of Graphene and Density Functional Calculations

The molecular vibrational modes of graphene were analyzed theoretically by factor group analysis.The molecular vibrational modes of graphene and the spectral characteristics of each vibrational mode were calculated successfully.The molecular vibrational frequency and mode of graphene were also calculated by first-principles density functional theory based on establishment of the graphene Bravais crystal unit cell.The number of vibrational modes and corresponding vibrational frequency spectral properties calculated were consistent with the results obtained using factor group analysis.The above calculations and systematic comparison between the infrared and Raman spectra of graphene and graphite were used to determine why the infrared active vibrational modes A 2u and E 1u with D 6h point group did not appear on the experimental infrared spectrum of graphene.

Effect of the Hydrothermal Reaction Temperature on Three-Dimensional Reduced Graphene Oxide's Appearance, Structure and Super Capacitor Performance

Three-dimensional reduction of graphene oxide with a series of different degrees of reduction was performed by the hydrothermal method in the temperature range from 120 to 220 °C, with graphene oxide sols as the precursor and prepared by graphite oxide gels. The effect of the temperature of the hydrothermal reaction on the materials¹ appearance, structure, and super capacitor performance was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The results show that the prepared three dimensional reduction of graphene oxide was porous and reticulated, and its volume and inner mesh aperture gradually decreased with increasing temperature, while its degree of reduction and order increased at the same time, and its structure gradually transformed to the graphite oxide structure. However, thematerialsspecific capacitance

Study of oxidation process occurring in natural graphite deposits

This paper aimed to investigate the chemical bond characteristics and oxidation properties of graphite deposits found in Nanjiang County, Sichuan Province, China. The mineral content, crystal structures and chemical compositions of bulk samples from typical surface weathering and alteration zones were analyzed using XRD, FT-Raman, XPS, and optical microscope studies, and other spectral characterization methods. The results showed that natural graphite can be oxidized and bond with oxygen-containing functional groups, such as carbonyl (–COOH), hydroxyl (C–OH) and epoxy (C–O–C), during the process of geologic action or non-artificial oxidation. The graphitic products were found to have similar structural and spectral characteristics to artificial graphite oxide. The data suggested that the natural graphitic products had different crystal characteristics with varying degrees of weathering alteration. Overall, these findings confirmed the existence of natural graphite oxide, which may be of important future scientific and practical significance.

Synthesis of Zeolite A from Natural Ca-Bentonite Using a Direct Alkali Hydrothermal Approach

Ca-bentonite can be converted into zeolite A via hydrothermal alkaline treatment by varying the synthetic parameters. This paper focuses on the effects of SiO2/Al2O3 molar ratio, Na2O/SiO2 molar ratio, reaction temperature, reaction time on the synthesis of zeolite A. Phase-pure zeolite A was synthesised under optimum conditions of 3Na2O:0.25Al2O3:1SiO2:150H2O by heated at 90°C for 12 h, whose shape and average crystal sizes are the cube of 1∼3 μm by the SEM micrograph. Compared with chemical synthesis method, one-step alkali fusion method has the advantages of low cost, simple operation, short time etc, which are worthy of further consideration in industrialization.

pH值对聚合钛离子/蒙脱石复合结构及其TiO 2 纳米粒子的影响研究

采用水解－插层复合法, 以TiOSO 4 ·2H 2 O为TiO 2 的前驱体, 蒙脱石为复合基体, 通过控制蒙脱石悬浊液pH值, 制备了不同的蒙脱石复合结构样品. 采用XRD研究了样品的结构、物相、晶粒大小等属性的变化. 结果表明, 蒙脱石悬浊液的pH值对TiOSO 4 ·2H 2 O水解属性有较大的影响, 从而影响水合氧化钛/蒙脱石的复合结构特性, 当蒙脱石悬浊液pH为0.5时, 电价较低且聚合度较小的聚合钛离子易于进入蒙脱石层间域, 对蒙脱石结构层的分散剥离作用最好; 经700℃热处理的TiO 2 /蒙脱石复合结构样品中, 锐钛矿晶粒尺寸最小达到13.4 nm; 经1100℃热处理后, 复合结构中锐钛矿相对含量达到35%; 与纯纳米TiO 2 样品相比, TiO 2 /蒙脱石复合结构中的TiO 2 具有更高的锐钛矿相向金红石相转变的温度及更小的晶粒尺寸. 蒙脱石结构层对TiO 2 的相转变和晶粒长大都具有明显的阻滞作用.采用水解－插层复合法, 以TiOSO 4 ·2H 2 O为TiO 2 的前驱体, 蒙脱石为复合基体, 通过控制蒙脱石悬浊液pH值, 制备了不同的蒙脱石复合结构样品. 采用XRD研究了样品的结构、物相、晶粒大小等属性的变化. 结果表明, 蒙脱石悬浊液的pH值对TiOSO 4 ·2H 2 O水解属性有较大的影响, 从而影响水合氧化钛/蒙脱石的复合结构特性, 当蒙脱石悬浊液pH为0.5时, 电价较低且聚合度较小的聚合钛离子易于进入蒙脱石层间域, 对蒙脱石结构层的分散剥离作用最好; 经700℃热处理的TiO 2 /蒙脱石复合结构样品中, 锐钛矿晶粒尺寸最小达到13.4 nm; 经1100℃热处理后, 复合结构中锐钛矿相对含量达到35%; 与纯纳米TiO 2 样品相比, TiO 2 /蒙脱石复合结构中的TiO 2 具有更高的锐钛矿相向金红石相转变的温度及更小的晶粒尺寸. 蒙脱石结构层对TiO 2 的相转变和晶粒长大都具有明显的阻滞作用.