Bacterial Nanocellulose from Komagataeibacter Medellinensis in Fique Juice for Activated Carbons Production and Its Application for Supercapacitor Electrodes.

This paper presents the results obtained from the chemical activation of bacterial nanocellulose (BCN) using fique juice as a culture medium. BNC activation (BNCA) was carried out with H3PO4 and KOH at activation temperatures between 500 °C to 800 °C. The materials obtained were characterized morphologically, physicochemically, superficially, and electrochemically, using scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), the physisorption of gases N2 and CO2 at 77 K and 273 K, respectively, cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy (EIS). The samples activated with H3PO4 presented specific surface areas (SBET) around 780 m2 g-1, while those activated with KOH values presented specific surface areas between 680 and 893 m2 g-1. The XPS analysis showed that the PXPS percentage on the surface after H3PO4 activation was 11 wt%. The energy storage capacitance values ranged between 97.5 F g-1 and 220 F g-1 by EIS in 1 M H2SO4. The samples with the best electrochemical performance were activated with KOH at 700 °C and 800 °C, mainly due to the high SBET available and the accessibility of the microporosity. The capacitance of BNCAs was mainly improved by electrostatic effects due to the SBET rather than that of pseudocapacitive ones due to the presence of phosphorus heteroatoms.

A new approach to obtain kinetic parameters of corn cob pyrolysis catalyzed with CaO and CaCO3.

A new approach is proposed to obtain the kinetic parameters of biomass pyrolysis mixed with calcium catalyst. This approach involves the optimization of least squares (LS) with the Coats-Redfern integral method to avoid mathematical biases that may appear when applying the linear regression approach. The method was applied to the TGA data of pyrolysis of corn cob and corn cob mixed with 20 or 40 % by weight of CaO or CaCO3 under N2 atmosphere at temperatures between 25 and 700 °C. For raw cob, r2 reaches 0.997. For corn cob mixed with 20 % by weight of CaO or CaCO3, r2 reached 0.996-0.998, and for 40 % by weight, r2 reached 0.836-0.957. Applying this method, the activation energy (EA) value of the raw cob pyrolysis is 58.35 kJ mol-1, while the addition of CaO or CaCO3 increases the EA to 69.33 and 66.07 kJ mol-1, respectively. The method is simple to use and allows reliable values of kinetic parameters.

Carbon xerogel microspheres and monoliths from resorcinol-formaldehyde mixtures with varying dilution ratios: preparation, surface characteristics, and electrochemical double-layer capacitances.

Carbon xerogels in the form of microspheres and monoliths were obtained from the sol-gel polymerization of resorcinol and formaldehyde in the presence of potassium carbonate as catalyst, using water as solvent and two different molar dilution ratios. The objectives of this study were as follows: to investigate the effect of the dilution ratio, polymerization reaction time, and temperature on the rheological properties of the sols used to prepare the carbon xerogel microspheres and monoliths; and to determine the influence of their preparation methods and shapes on their surface characteristics and electrochemical double-layer (EDL) capacitance. An increase in the molar dilution ratio produced a decrease in the apparent activation energy of the sol-gel transition. Carbon xerogel microspheres were steam-activated at different burnoff percentages. The morphology, surface area, porosity, and surface chemistry of samples were determined. The main difference between the carbon xerogel microspheres and monoliths was that the latter are largely mesoporous. Better electrochemical behavior was shown by carbon xerogels in monolith than in microsphere form, but higher gravimetric and volumetric capacitances were found in activated carbon xerogel microspheres than in carbon xerogel monoliths.

Activated carbons from KOH-activation of argan (Argania spinosa) seed shells as supercapacitor electrodes.

Activated carbons were prepared by KOH-activation of argan seed shells (ASS). The activated carbon with the largest surface area and most developed porosity was superficially treated to introduce oxygen and nitrogen functionalities. Activated carbons with a surface area of around 2100 m(2)/g were obtained. Electrochemical measurements were carried out with a three-electrode cell using 1M H(2)SO(4) as electrolyte and Ag/AgCl as reference electrode. The O-rich activated carbon showed the lowest capacitance (259 F/g at 125 mA/g) and the lowest capacity retention (52% at 1A/g), due to surface carboxyl groups hindering electrolyte diffusion into the pores. Conversely, the N-rich activated carbon showed the highest capacitance (355 F/g at 125 mA/g) with the highest retention (93% at 1A/g), due to its well-developed micro-mesoporosity and the pseudocapacitance effects of N functionalities. This capacitance performance was among the highest reported for other activated carbons from a large variety of biomass precursors.