Fabrication of super-elastic graphene aerogels by ambient pressure drying and application to adsorption of oils

Three-dimensional graphene-based aerogels have promising applications in oil adsorption and environmental restoration.However,current research of graphene-based aerogels is often hindered by high preparation cost,poor mechanical properties and low recycling efficiency.Here,superelastic graphene aerogel(SGA)was prepared through one-step freezing and twice hydrothermal reduction followed by drying under ambient pressure.The simple atmospheric drying provides a possibility for large-scale preparation of high performance graphene-based aerogels.The prepared SGA not only has the ability of highly repeatable compression rebound,but also exhibits excellent oil adsorption performance.And the overall performance of SGA is better than most of graphenebased aerogels prepared by freeze drying.After the SGA was cyclically compressed with 70%strain for 300 times,it can return to the original shape and height substantially.SGA retained about 90%of the initial adsorption capacity after 50 cycles of adsorption and compression regeneration for cyclohexane.

Optimized Synthesis of Carbon Aerogels via Ambient Pressure Drying Process as Electrode for Supercapacitors

Carbon aerogels were synthesized via ambient pressure drying process using resorcinolformaldehyde as precursor and P123 to strengthen their skeletons. CO2 activation technology was implemented to improve surface areas and adjust pore size distribution. The synthesis process was optimized, and the morphology, structure, adsorption properties and electrochemical behavior of different samples were characterized. The CO2-activated samples achieved a high specific capacitance of 129.2 F/g in 6 M KOH electrolytes at the current density of 1 m A/cm^2 within the voltage range of 0-0.8 V. The optimized activation temperature and duration were determined to be 950 ℃ and 4 h, respectively.

Synthesis of monolithic carbon aerogels with high mechanical strength via ambient pressure drying without solvent exchange

A simple,fast and cost-effective method for monolithic carbon aerogels(CAs) preparation was proposed through sol-gel polycondensation of resorcinol with fo rmaldehyde in a basic aqueous solution followed by ambient pressure drying without solvent exchange,and carbonization.The microstructure and network strength of CAs were tailored by adju sting the catalyst concentration([resorcinol]/[sodium carbonate] in the range of 300-2000),water content([deionized water]/[resorcinol] equals to 17 and 24,respectively),and gelation temperature(Tgel in the range of 30-90℃).Resultantly,the CAs with a wide range of density(0.30-1.13 g/cm3),high specific surface area(465-616 m2/g),high compressive strength(6.5-147.4 MPa)and low thermal conductivity(0.065-0.120 W·m-1 K-1) were obtained in this work.Moreover,the largesized CAs(100×100×20 mm3) can also be prepared by this method since the formed robust skeleton network can resist shrinkage/collapse of pore structure and prevent cracking during drying.The improved mechanical strength and monolithic forming abilities could be mainly attributed to the uniform arrangement of carbon particles and pores,fine particle size,abundant network structure and enhanced particle neck.

Preparation and Characterization of Silica Aerogels Derived from Ambient Pressure

Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives （polyethoxydisiloxanes, E40）, followed by silylation and drying under ambient pressure. The specific surface area, pore size distribution and thermal conductivity of the silica aerogels were investigated and the results showed that the diameter of the silica particles is about 6 nm and the average pore size of the silica aerogels is 14.7 nm. The specific surface area of which is about 1000 m^2.g^-1 and the thermal conductivity is about 0.014 wm^-l.K^-1 at room temperature and pressure of 1.01×10^5 Pa. The Si-CH3 groups were also detected on the internal surface of the silica aerogels, which show hydrophobic. Silica aerogels derived by this technique is low cost and have wide applications.

Effect of sodium bicarbonate solution on methyltrimethoxysilane-derived silica aerogels dried at ambient pressure

Here we present an economical ambient pressure drying method of preparing monolithic silica aerogels from methyltrimethoxysilane precursor while using sodium bicarbonate solution as the exchanging solvent.We prepared silica aerogels with a density and a specific surface area of 0.053 g·cm^(-3) and 423 m^(2)·g^(-1) respectively.The average pore diameter of silica aerogels is 23 nm as the pore specific volume is 1.11 cm^(3)·g^(-1),Further,the contact angle between water droplet and the surface of silica aerogels in specific condition can be as high as 166°,which indicates a super-hydrophobic surface of aerogels.

Preparation and Properties of PMMA Modified Silica Aerogels from Diatomite

Diatomite was used as raw material to prepare sodium silicate with a modulus of 3.1 by alkali dissolution method and the resulted sodium silicate solution was employed as a precursor. Methyl methaerylate monomers were introduced in wet gels through solution-immersion, and upon heating at 70 ℃, the mesoporous surfaces throughout the skeletal framework were coated with the polymer layer. PMMA modified silica aerogels were successfully synthesized via ambient pressure drying. The properties were investigated by FT- IR, NMR, TGA, nitrogen adsorption-desorption, FESEM and nano-indentation, etc. Results indicate that with the increasing of PMMA incorporated into silica aerogels, the bulk density and the BET surface area increase, the porosity decreases. Through the observation of FESEM, it is found that the interconnecting pores and the big pores add, the pore size distribution expands from 5-17 to 28-150 urn. By comparison, the PMMA modified silica aerogels achieve a 52-fold increase in hardness and a 10-fold increase in modulus.

Synthesis and Characterization of Multi-walled Carbon Nanotube Doped Silica Aerogels

Multi-walled carbon nanotube doped silica aerogels（MWCNT-SAs） were synthesized from a wet gel of well-dispersed MWCNT by one-step solvent exchange/surface modification and ambient pressure drying（APD）. Waterglass was employed as a precursor to prepare wet gel. The content of MWCNT varied from 0 to 15% volume by wet gel. The surface group, thermal stability and microstructure of pure silica aerogel and MWCNT-SAs were investigated by FTIR, DTA, and TEM. Experimental results show that MWCNT-SAs are hydrophobic when the temperature is below 400 ℃, MWCNT-SAs exhibit a mesoporous network structure, and they achieve the largest scale with least shrinkage and lowest density when doped with 5 vol% MWCNT.

Carbon Dot-Modified TiO_(2)@SiO_(2) Aerogel as an Anode for Lithium-Ion Batteries

Titanium oxides have been considered promising anode materials for lithium-ion batteries(LIBs).However,the poor conductivity and low specific capacity of bulk titanium oxides limit their application.In this study,a carbon dot-modified TiO_(2)@SiO_(2)aerogel was successfully fabricated through a facile ambient pressure drying strategy and used as an anode material of LIBs.Benefiting from the crosslinking of carbon dots and the surface modification of SiO_(2),the as-prepared hierarchical aerogel exhibited a high initial discharge capacity of 974 mAh g^(−1)and maintained a capacity of 299 mAh g^(−1)after 100 cycles at 0.1 A g^(−1).It also retained a discharge capacity of 111 mAh g^(−1)with a CE of 99.9%at 3 A g^(−1).The carbon dot-modified cross-linking skeleton contributes to the structural integrity of the TiO_(2)@SiO_(2)aerogel during repeated insertion/extraction of lithium ions,guaranteeing outstanding cycling and high-rate performance.This ambient pressure drying strategy provides a facile and feasible way to produce high-performance aerogel anode materials for lithium-ion storage.