Yutie Bi

Facile synthesis of structure-controllable, N-doped graphene aerogels and their application in supercapacitors

N-doped graphene aerogels (NGAs) were first synthesized by using graphene oxide (GO) and melamine via a self-assembly process by one-pot hydrothermal method. The morphology and structure of the as-prepared materials were characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, XPS spectroscopy and nitrogen adsorption/desorption measurement. The electrochemical performances of NGAs were studied by cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. Importantly, the microstructure, surface area and capacitance of NGAs could be facilely controlled by changing the melamine/GO mass ratio. Compared with the pure graphene aerogel (80 F g−1 at 0.5 A g−1), NGA-3 with the mass ratio of 1/15 displayed enhanced specific capacitance (116 F g−1) and retained 94% of its initial capacitance after 1000 cycles. It provided a possible way to obtain graphene based materials with high surface area and capacitance.

One-pot synthesis and characterization of acid-catalyzed melamine formaldehyde/SiO2 aerogel via sol–gel technology

This paper reports a rapid synthesis of a novel melamine–formaldehyde (MF)/SiO2 aerogel with good transparency carried out by acid-catalyzed chemical dehydration and polycondensation of poly (melamine-co-formaldehyde) methylated and hydrolyzed tetraethoxysilane respectively in one pot via sol–gel process and subsequently supercritical drying with CO2. The one-pot method improves the efficiency and reduces the cost of MF/SiO2 aerogels. The gelation time can be as short as 13xa0h under the appropriate conditions, much less than that of MF aerogel obtained by traditional process. The structural properties of the aerogels were characterized by the field emission scanning electron microscopy, the Fourier transformed infrared spectroscopy and the Brunauer–Emmett–Teller methods. The results indicate the hybrid aerogel has a micro-mesoporous structure with a high surface area about 747xa0m2/g and the two components combine with each other by physical interaction.

Facile fabrication of flexible graphene/porous carbon microsphere hybrid films and their application in supercapacitors

Graphene/porous carbon microsphere hybrid films were fabricated by vacuum filtration of graphene oxide nanosheets and porous carbon microspheres, followed by reduction, leavening and compressing. The as-prepared hybrid films were characterized by means of scanning electron microscopy, X-ray diffraction, Raman spectroscopy and four-point probe measurements. After reduction and leavening, the leavened foam film displayed a moderate capacitive performance (183 F g−1 at 0.2 A g−1) in KOH aqueous solution. Additionally, over 112.1% of the initial capacitance was retained after repeating the cyclic voltammetry test for 1000 cycles. After compressing, the flexible thin film had a moderate capacitive performance of 144 F g−1 at 0.2 A g−1 for a single electrode and over 99.7% of the initial capacitance. Moreover, the thin film had good capacitive behaviour retainability after multiple cycles of excessive bending experiments.

Influence of supercritical drying fluids on structures and properties of low-density Cu-doped SiO2 composite aerogels

The Cu-doped SiO2 composite aerogels were successfully prepared by sol–gel process and subsequently supercritical drying with ethanol and CO2. The Cu-doped SiO2 composite aerogels had porous texture, low density (<100xa0mgxa0cm−3) and high specific surface area (>800xa0m2xa0g−1), which were investigated by FESEM and nitrogen adsorption desorption porosimetry. The FTIR spectra of the aerogels showed that the ethanol-dried aerogels had been modified by ethyl while the corresponding CO2-dried aerogels had more Si–OH groups. The phase structure and thermal stability were investigated by XRD and TGA, respectively. Due to the reducibility of ethanol, the copper was crystalline in ethanol-dried sample. The Cu-doped SiO2 composite aerogels dried with supercritical ethanol had larger pore diameter and better thermal stability under 400xa0°C in comparison with CO2-dried composite aerogels. The structures and properties of Cu-doped SiO2 composite aerogels are obviously affected by supercritical drying conditions. The effect research could instruct the synthesis of different state of Cu in composite aerogels.

Facile fabrication of mechanical monolithic polyamide aerogels via a modified sol–gel method

The good-formability polyamide (PA) aerogel via a modified sol–gel technology was facilely fabricated by using melamine and isophthaloyl chloride with the acid-binging agent followed by CO2 supercritical drying. The synthesis procedure was straightforward and simple, relying on no nitrogen-based protective atmosphere. The influences of various parameters, such as the amount of acid-binging agent, reaction temperature and precursor concentration, on the aerogel structure were discussed. The structural properties of PA aerogels were characterized by the scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller methods and Fourier transform infrared spectroscopy. The results indicated that the PA aerogel had a typical three-dimensional porous structure. Due to the moderate mechanical property of the PA aerogel, the aerogel had potential for the use in construction and building materials.Graphical AbstractWe reported that the good-formability polyamide (PA) aerogel via a modified sol–gel technology was facilely fabricated by using melamine and isophthaloyl chloride with the acid-binging agent followed by CO2 supercritical drying. The synthesis procedure was straightforward and simple, relying on no nitrogen-based protective atmosphere. The dimethylacetamide (DMAC) as the acid-binging agent could indeed remove the hydrochloric acid to accelerate the cross-linking degree of the PA prepolymer and improve the formation of a fine porous structure of the PA aerogel. Thus, the specific surface area of the PA aerogel after the addition of acid-binging agent could be enhanced as high as 391u2009m2/g, higher than that (282u2009m2/g) of the one without the DMAC. Furthermore, it also showed the influences of various parameters, such as reaction temperature and precursor concentration, on the aerogel structure. According to the structure analysis, the results indicated that the PA aerogel had a typical three-dimensional structure with various porous size. Due to the moderate mechanical property, the PA aerogel had potential for use in construction and building materials.

Rapid fabrication of low density melamine–formaldehyde aerogels

Low density melamine–formaldehyde (MF) aerogels were fabricated rapidly by adding the alkali to low concentration MF sol precursor before the formation of cross-linking. The gelation of the MF sol with the precursor concentration as low as 4% could be accomplished by the modified method. The gelation time for MF wet gels could be also reduced to even 5xa0h. After solvent exchanging and CO2 supercritical drying, the MF areogel with the lowest density of about 55xa0mg/cm3 could be prepared. The samples were also characterized by scanning electron microscopy, transmittance electron microscope, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption isotherms. The results indicated that the addition of the alkali to the MF sol precursor not only sped up the gelation process without changing the reaction mechanism, but also accomplished the low density MF aerogel.

A novel starch-enhanced melamine-formaldehyde aerogel with low volume shrinkage and high toughness

A new hybrid aerogel with low volume shrinkage and high toughness was prepared by aqueous condensation of melamine, starch and formaldehyde and extracting the solvent from the wet gel with carbon dioxide under the supercritical condition. The sizes of the wet gel and aerogel were measured by vernier calipers and the volume shrinkage of the aerogel was as low as 1.8%. The results from BET and SEM indicated that the hybrid aerogel belonged to the mesoporous material, which showed a typical three-dimensional porous structure with a specific surface area about 366.2xa0m2/g and pore diameter about 12.9xa0nm. To study the mechanical properties of the hybrid aerogel, we measured the compressive stress as a function of strain and the hybrid aerogel demonstrated excellent elasticity and mechanical durability.

Photoluminescence of monolithic zinc oxide aerogel synthesised by dispersed inorganic sol–gel method

Abstract Zinc oxide aerogels possess significantly potential applications in gas sensors, photocatalysis, and photodetector. In this regard, monolithic zinc oxide aerogel was prepared successfully by using the dispersed inorganic sol–gel method (DIS method) combined with a furnace calcining in mixed atmosphere of 500°C. With subsequent thermal treatment in selected atmospheres and designed heating program, the aerogel is featured with high porosity, large specific area (177 m2 g−1) and narrow particle sizes distribution. The photoluminescence spectrum (PL) with no temperature dependent shifts of the maximum of the spectral PL intensity concerning the zinc oxide aerogel being investigated suggests that it is relative to the structural and optical properties. In summary, the attractive properties of the zinc oxide aerogel expound the potentially optical and optoelectronic applications of ZnO nanostructures.

Characterization of the microstructures of copper-based aerogels on the sol–gel process

In this thesis, we will elaborate on the sol–gel process during the preparation of monolithic copper-based aerogel. The microstructure of the copper-based aerogel appears to be various due to the different amounts of raw materials, such as polyacrylic acid, propene oxide, deionized water (H2O) and copper(II) chloride (CuCl2) in the sol–gel process. The proper molar ratios between these reactants play a crucial factor in mediating the morphology of the aerogel. The aerogels are characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and Brunauer–Emmett–Teller methods. The combined results indicate that the copper-based aerogel shows a typical three-dimensional porous structure with a large surface areas about 568xa0m2/g, and the skeleton structure of the aerogel is composed of a large number of primary particles with the size about a few nanometers.

Assembly of methylated hollow silica nanospheres toward humidity-resistant antireflective porous films with ultralow refractive indices

Humidity-resistant antireflective (AR) porous films with ultralow refractive indices were prepared via an one-step sol–gel process by assembly of methylated hollow silica nanospheres (HSNs). The hydrophobicity and refractive indices of silica-based AR porous films could be varied between 66.0° and 115.0°, and between 1.08 and 1.14, respectively, by tuning the MTES/TEOS molar ratios. A possible assembly mechanism was proposed according to the microstructure of methylated HSNs and porous films. The various properties of silica-based AR porous films were investigated and the AR porous film could demonstrate a good AR capability of 97.6% and excellent humidity resistance.