Tailoring the mesoporous texture of graphitic carbon nitride.

Recently, graphitic carbon nitride (g-C3N4) materials have received a great attention from many researchers due to their various roles as a visible light harvesting photocatalyst, metal-free catalyst, reactive template, nitrogen source of nitridation reaction, etc. g-C3N4 could be prepared by temperature-induced polymerization of cyanamide or melamine. In this study, we report a preparation of mesoporous graphitic carbon nitrides with tailored porous texture including pore size, and specific surface area from cyanamide and colloidal silica nanoparticles (Ludox). At first, cyanamide-silica nanocomposites were prepared by mixing colloidal silica with different size in the range of 7-22 nm and cyanamide, followed by evaporating the solvent in the resulting mixture. Mesoporous g-C3N4 samples were prepared by calcining cyanamide-silica nanocomposite at 550 degrees C for 4 hrs and removing the silica nanoparticles by using ammonium hydrogen fluoride. The formation of g-C3N4 was confirmed by the sharp (002) peak (d = 3.25 A) of graphitic interlayer stacking, and the broad (100) peak (d = 6.86 A) of in-plane repeating unit in the X-ray diffraction patterns. According to N2 adsorption-desorption analysis, the pore size of mesoporous carbon nitrides was similar to the size of colloidal silica used as hard template (7-22 nm). The specific surface area of mesoporous g-C3N4 could be tailored in the range of 189 m2/g-288 m2/g.

Does Charge Balancing Ensure the Safety of the Electrical Stimulation and Is It Power Efficientƒ.

Safety issues are the most important concern in electrical stimulation. Equating the charge in the anodic and cathodic phases, namely charge balancing or charge equalizing, is a well-known method to avoid tissue damage and/or electrode corrosion. The electrode-tissue interface is not ideal in practice and with a charge-balanced waveform, the electrode voltage becomes more positive compared to the pre-pulse value and corrosion happens. In this paper, we show that a charge balancer ensures the safety of stimulation if the rate of the irreversible Faradaic reactions is negligible, or when the pulse width of the stimulation phases is not comparable to the time constant of the electrode-tissue interface. Furthermore, charge balancing is studied with mathematical modeling for different types of tissue models, and the results are used to show the conditions that charge balancing does not ensure the safety of the electrical stimulation, and employing charge balancing not only increases the power consumption of the electrical-stimulation systems but also increases the rate of the electrode corrosion in these conditions. The main goal of this paper is to show that a charge controller is a general solution for ensuring the safety of the electrical stimulation, with an efficient, not excessive, amount of charge for the reversal phase and should be employed instead of charge balancers in generic stimulators.