Controlling N-Doping Nature at Carbon Aerogels from Biomass for Enhanced Oxygen Reduction in Seawater Batteries.

Pyridinic N-type doped at carbon has been known to have better electrocatalytic activity toward the oxygen reduction reaction (ORR) than the others. Herein, we proposed to prepare pyridinic N doped at carbon aerogels (CaA) derived from biomass, i.e., coir fiber (CF) and palm empty fruit bunches (PEFBs), by adjusting the pyrolysis temperature during carbonization of the biomass-based-cellulose aerogels. The cellulose aerogels were prepared by the ammonia-urea system as the cellulose solvent, in which ammonia also acted as a N source for doping and urea as the cellulose cross-linker. The as-prepared cellulose aerogels were directly pyrolyzed to produce N-doped CaA. It was found that the type of N doping is dominated by pyrrolic N at pyrolysis temperature of 600 °C, pyridinic N at 700 °C, and graphitic N at 800 °C. The pyridinic N exhibited better performance as an electrocatalyst for the ORR than pyrrolic N and graphitic N. The ORR using pyridinic N follows the four-electron pathway, which quantitatively implies a more electrochemically stable process. When used as a cathode for the Mg-air battery using a 3.5% NaCl electrolyte, the pyridinic N CaA exhibited excellent performance by giving a cell voltage of approximately 1.1 V and delivered a high discharge capacity of 411.64 mA h g-1 for CF and 492.64 mA h g-1 for PEFB corresponding to an energy density of 464.23 and 529.49 mW h g-1, respectively.

Amine-functionalized porous silica production via ex- and in-situ method using silicate precursors as a selective adsorbent for CO2 capture applications.

A comparison of the amine-modified silica particle's characteristics via ex- and in-situ routes and their application as a CO2 gas adsorbent is reported. Modifying silica particles via ex-situ involves two separate steps: forming porous silica particles with sodium lauryl sulfate (SLS) as a template and impregnation using ultrasound assistance. In contrast to ex-situ modification, in-situ modification of silica particles is carried out in one step by mixing directly between the silica source and the modifying agent. Controlling the characteristics of modified silica particles via in-situ is carried out by adding an SLS template removed simultaneously with particle formation to increase the surface area and porosity. Increasing the SLS template concentration shows a linear relationship between increasing particle surface area and amine loading. However, two different modification routes exert a direct influence on aminopropyl distribution. Silanization via in-situ which involves a simultaneous condensation reaction produces a higher amine loading reaching 1.2845 mmol/g of silica than via ex-situ which is only 0.9610 mmol/g of silica. The amount of aminopropyl that can be grafted on the silica surface shows a linear relationship to the quantity of CO2 gas adsorption capacity. Amine-modified silica particles obtained the highest adsorption capability via the in-situ route with an SLS 3 CMC template of 2.32 mmol/g silica at an operating pressure of 6 bar.

Bubble formation phenomenon on the absorber column for CO2 absorption and to produce precipitated silica sodium carbonate.

CO2 absorption using sodium silicate aqueous solution in a bubble column has been studied. Sodium silicate aqueous solutions are classified as non-Newtonian fluids that can affect the bubble distribution. The goal of this research is to investigate the effect of a superficial gas velocity (0.85 cm s-1, 2.55 cm s-1, and 4.25 cm s-1) and sodium silicate concentration (0.2% v, 0.6% v, and 1.0% v) on the phenomenon formation of spherical-bubbles, ellipsoidal-bubble, and rod-shape bubbles in bubble column. The experiment was carried out in one minute interval during the five minutes operation. The CO2 absorption and the gel formation is influenced by the pH of the solution where the gas holdup plays an important role in changing the pH. The characterization of the precipitated particles showed that the trona phase (C2H5Na3O8) reached 88% in the preparation of 1% aqueous sodium silicate at a superficial gas velocity of 4.25 cm s-1. The superficial velocity of the gas and the concentration of the sodium silicate solution influence the formation of bubbles. Spherical bubbles and ellipsoidal bubbles were observed in CO2 absorption experiments using a plate sparger, while rod-shaped bubbles were observed in experiments using a ball sparger.

Hydrophobic Modification of Sulfonated Carbon Aerogels from Coir Fibers To Enhance Their Catalytic Performance for Esterification.

The hydrophilicity of sulfonic acid-functionalized solid catalysts tends to accelerate the deactivation of the catalyst for chemical reactions where water is produced during the process. In this work, we proposed a hydrophobic carbon aerogel acid catalyst derived from coir fibers by a sulfonation-hydrophobization route via the diazo reduction method. Sulfonation using the diazo reduction method offers some advantages such as the process takes only a few minutes and the modified surface can be easily modified further to be hydrophobic. The carbon aerogel was produced by direct pyrolysis of cellulose aerogels derived from coir fibers using an NH4OH-urea method and then sulfonated and hydrophobized using sulfanilic acid and 4-tert-butylaniline (TBA), respectively. The carbon aerogel exhibited a very high surface area (2624.93-3911.05 m2 g-1), which provides a lot of number of sites for sulfonate groups (2.30-2.70 mmol g-1). The water contact angle of the sulfonated catalyst after hydrophobization ranged from 70 to 115°, depending on the mass ratio of the TBA-to-solid catalyst. The hydrophobic catalyst exhibited better catalytic performance toward esterification of acetic acid with ethanol. A conversion of 65-74% could be achieved in a brief time using the hydrophobic catalyst. The conversions were much higher than that obtained by the unmodified hydrophilic catalyst. Our study offers a strategy to tune the surface hydrophobicity of the sulfonated solid acid catalyst to match for specific chemical reactions.

Preparation of rGO/MnO2 Composites through Simultaneous Graphene Oxide Reduction by Electrophoretic Deposition.

We report the preparation of manganese dioxide (MnO2) nanoparticles and graphene oxide (GO) composites reduced by an electrophoretic deposition (EPD) process. The MnO2 nanoparticles were prepared by the electrolysis of an acidic KMnO4 solution using an alternating monopolar arrangement of a multiple-electrode system. The particles produced were γ-MnO2 with a rod-like morphology and a surface area of approximately 647.2 m2/g. The GO particles were produced by the oxidation of activated coconut shell charcoal using a modified Hummers method. The surface area of the GO produced was very high, with a value of approximately 2525.9 m2/g. Fourier transform infrared spectra indicate that a significant portion of the oxygen-containing functional groups was removed from the GO by electrochemical reduction during the EPD process after sufficient time following deposition of the GO. The composite obtained by the EPD process was composed of reduced graphene oxide (rGO) and γ-MnO2 and exhibited excellent electrocatalytic activity toward the oxygen reduction reaction following a two-electron transfer mechanism. This approach opens the possibility for assembling rGO composites in an efficient and effective manner for electrocatalysis.