We present experimental data that directly shows the effect of pore size on hydrogen uptake in high surface area porous carbons. A direct study of the influence of pore size has been made possible by comparing the uptake capacity of porous carbons with identical surface areas but with different pore sizes and pore size distributions. A variety of synthesis methods have been used to prepare carbon materials with similar surface areas with pore sizes ranging from the micropore range (12 Å) to supermicropore/lower mesopore (23 Å) and lower mesopore (31 Å) range. This allowed a simple and straightforward analysis of the influence of pore size without any changes in total surface area. The pore size essentially defines the hydrogen uptake with no apparent regard to the similar surface areas. The excess and total hydrogen uptake (at −196 °C and 20 bar) of carbons with identical surface areas of 3340 m 2 /g, increased from 3.7 and 5.4 wt % (31 Å sample), to 4.8 and 6.3 wt % (23 Å sample) and to 6.3 and 7.3 wt % for a 12 Å sample. The excess hydrogen storage density (μmol H 2 •m −2 ) decreases linearly with pore size from 9.5 at 12 Å to 7.3 at 23 Å and 5.5 at 31 Å. Thus at a surface area of 3340 m 2 /g, a change of pore size from 31 to 12 Å improves the excess hydrogen storage by a staggering 70%. The pore size effect has general applicability; for carbons with similar surface areas of 2770 m 2 /g, the excess and total hydrogen storage was 1.7 and 3.0 wt % for a 28 Å sample and increased to 5.6 and 6.4 wt % for and 15 Å sample. In this case, a change of pore size from 28 to ca. 15 Å results in a more than 3-fold increase in excess hydrogen storage. Therefore, to improve hydrogen storage capacity of carbons, we need to increase the surface area, but with pores of the right size. A high surface area and pore volume associated with large pores cannot compensate for "unfavorably" sized pores.
The wide-scale application of silver nanoparticles (AgNPs) in areas such as chemical sensing, nanomedicine, and electronics has led to their increased demand. Current methods of AgNPs synthesis involve the use of hazardous reagents and toxic solvents. There is a need for the development of new methods of synthesizing AgNPs that use environmentally safe reagents and solvents. This work reports a green method where silver nanoparticles (AgNPs) were synthesized using silver nitrate and the aqueous extract of Citrullus lanatus fruit rind as the reductant and the capping agent. The optimized conditions for the AgNPs synthesis were a temperature of 80°C, pH 10, 0.001 M AgNO3, 250 g/L watermelon rind extract (WMRE), and a reactant ratio of 4 : 5 (AgNO3 to WMRE). The AgNPs were characterized by Ultraviolet-Visible (UV-Vis) spectroscopy exhibiting a λmax at 404 nm which was consistent with the spectra of spherical AgNPs within the wavelength range of 380–450 nm, and Cyclic Voltammetry (CV) results showed a distinct oxidation peak at +291 mV while the standard reference AgNPs (20 nm diameter) oxidation peak occurred at +290 mV, and Transmission Electron Microscopy (TEM) revealed spherical shaped AgNPs. The AgNPs were found to have an average diameter of 17.96 ± 0.16 nm.
We describe a very simple method for the formation of high surface area carbon aerogels from melamine-formaldehyde resins, via metal salt (CaCl 2 ) templating, wherein subcritical drying is used and no activation is required. The metal salt acts as a porogen to generate carbon aerogels with surface area of up to 1100 m 2 g 21 , which exhibit significant CO 2 uptake of up to 2.2 mmol g 21 at 298 K and 1 bar.
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