Fabrication Of Aerogels Research Articles

Property improvements of nano TiO<SUB align=right>2 in photodegradation of organic pollutions: a review

Nano TiO2 as a potential photocatalyst has been widely studied for application of environmental decontamination. In this paper, we examine and review the efforts in property improvements by modification, synthesis technique and operation parameter combined with some theory analysis. The effects of the modification by coupling with precious metal and narrow semiconductor, and doping with N, S, and/or C were reviewed. The improvement in synthesis technique includes the increase in amount of doping N, S, and/or C, processing dependence and fabrication of aerogels and nanotubes. The improvement in operation parameter involves approaches to obtain appropriate values of pH, light intensity, H2O2, temperature, catalyst concentration, and initial dyes concentration.

Fabrication of the Monolithic Silica Aerogels Using Sodium Silicate and its Network Strengthening

Silica wet gels were prepared from water glass (29 wt.% SiO2) by using Amberlite as a ion exchange resin. After washing in distilled water, the wet gels were further aged in a solution of TEOS/EtOH to strengthen the 3-dimensional network structure. With the increasing TEOS content in aging solution, BET surface area and porosity of the ambient dried silica aerogel were decreased, and the average pore diameter was decreased from 30nm to 10nm. Also, higher density and compressive strength were obtained in case of higher TEOS content. This is due to the precipitation of SiO2 nano particle by TEOS. Hence, TEOS addition plays an important role in both strengthening and increasing stiffness of silica wet gel network. By adding 30 vol.% TEOS, a crack-free monolithic silica aerogel tiles were obtained and its density, compressive strength, and thermal conductivity were shown 0.232 g/cm3, 7.3 MPa, and 0.029 W/mK, respectively.

Controllable fabrication of carbon aerogels

Nano-pore carbon aerogels were prepared by the sol-gel polymerization of resorcinol (1, 3-dihydroxybenzene)(C 6H 4(OH) 2) with formaldehyde (HCHO) in a slightly basic aqueous solution, followed by super-critical drying under liquid carbon dioxide as super-critical media and carbonization at 700 °C under N 2 gas atmosphere. The key of the work is to fabricate carbon aerogels with controllable nano-pore structure, which means extremely high surface area and sharp pore size distribution. Aiming to investigate the effects of preparation conditions on the gelation process, the bulk density, and the physical and chemical structure of the resultant carbon aerogels, the molar ratio of R/C (resorcinol to catalyst) and the amount of distilled water were varied, consequently two different sets of samples, with series of R/C ratio and RF/W (Resorcinol-Formaldehyde to water, or the content of reactant) ratio, were prepared. The result of N 2 adsorption/desorption experiment at 77 K shows that the pore sizes decreasing from 11.4 down to 2.2 nm with the increasing of the molar ratio of R/C from 100 to 400, and/or, the pore sizes decreasing from 3.8 down to 1.6 nm with the increasing of reactant content from 0.4 to 0.6.

The Fabrication and Characterization of Carbon Aerogels by Gelation and Supercritical Drying in Isopropanol

AbstractWe report a new method for the fabrication of carbon aerogels. Resorcinol and furfural were polymerized in isopropanol using HCl as a catalyst and the resulting alcogels were then dried directly using supercritical isopropanol, followed by carbonization under a nitrogen atmosphere. The carbon aerogels can be prepared over a range of densities (0.148–0.746 g/cm3), depending on the gelation temperature and the mass content of the reactants. The textural and transport properties of the aerogels materials were characterized by nitrogen adsorption/desorption analysis, high‐resolution transmission electron microscopy (HRTEM), magnetic susceptibility, and resistivity measurements. TEM observations show that the carbon aerogels are composed of interconnected nanoparticles with diameters ranging from 20 to 30 nm. All of the aerogel samples exhibit high Brunauer– Emmett–Teller (BET) surface areas in the range of 557–656 m2/g. The carbon aerogels produced by this new method have similar transport properties to those of carbon aerogels prepared by the traditional method.