Revisiting the chemistry of graphite oxides and its effect on ammonia adsorption

Graphite oxide (GO) was synthesized using two different methods: one with sulfuric acid as part of the oxidizing mixture (Hummers-Offeman method) and another one without the sulfur-containing compound involved in the oxidation process (Brodie method). They were both tested for ammonia adsorption in dynamic conditions, at ambient temperature, and characterized before and after exposure to ammonia by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, potentiometric titration, energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS) and elemental analysis. Analyses of the initial materials showed that besides epoxy, hydroxyl and carboxylic groups, a significant amount of sulfur is incorporated as sulfonic group for GO prepared by the Hummers-Offeman method. The process of ammonia adsorption seems to be strongly related to the type of GO. For GO prepared by the Brodie method, ammonia is mainly retained via intercalation in the interlayer space of GO and by reaction with the carboxylic groups present at the edges of the graphene layers. On the contrary, when GO prepared by the Hummers method is used, the ways of retention are different: not only is the intercalation of ammonia observed but its reaction with the epoxy, carboxylic and sulfonic groups present is also observed. In particular, during the ammonia adsorption process, sulfonic groups are converted to sulfates in the presence of superoxide anions O2-*. These sulfates can then react with ammonia to form ammonium sulfates. For both GOs, an incorporation of a significant part of the ammonia adsorbed as amines in their structure is observed as a result of reactive adsorption. © 2009 The Royal Society of Chemistry

Enhancement of Ti3C2 MXene Pseudocapacitance after Urea Intercalation Studied by Soft X ray Absorption Spectroscopy

MXenes have shown outstanding properties due to their highly active hydrophilic surfaces coupled with high metallic conductivity. Many applications rely on the intercalation between Ti3C2Tx Tx describes the OH, F and O surface terminations flakes by ions or molecules, which in turn might alter the Ti3C2Tx surface chemistry and electrochemical properties. In this work, we show that the capacitance, rate capability, and charge carrier kinetics in Ti3C2Tx MXene electrodes are remarkably enhanced after urea intercalation u Ti3C2Tx . In particular, the areal capacitance increased to 1100 mF cm2, which is 56 higher than that of pristine Ti3C2Tx electrodes. We attribute this dramatic improvement to changes in the Ti3C2Tx surface chemistry upon urea intercalation. The oxidation state and the oxygen bonding of individual Ti3C2Tx flakes before and after urea intercalation are probed by soft X ray absorption spectroscopy XAS at the Ti L and O K edges with 30 nm spatial resolution in vacuum. After urea intercalation, a higher Ti oxidation state is observed across the entire flake compared to pristine Ti3C2Tx. Additionally, in situ XAS of u Ti3C2Tx aqueous dispersions reveal a higher Ti oxidation similar to dry samples, while for pristine Ti3C2Tx the Ti atoms are significantly reduced in water compared to dry sample

Pd-Impregnated activated carbon and treatment acid to remove sulfur and nitrogen from diesel

ABSTRACT Removal of sulfur and nitrogen compounds from national commercial diesel through adsorption onto activated carbon was studied. Brazilian commercial activated carbon samples (AC) were modified by acid oxidation and, alternatively, were impregnated with palladium chloride. Modified carbon samples showed a significant increase in the quantity of acid sites, particularly those AC submitted to impregnation with palladium. Adsorption capacity of the carbon samples increased proportionally to the increase in the acid groups. Adsorption efficiency of the activated carbon impregnated with palladium chloride was over 85% for nitrogen compounds and over 60% for sulfur compounds. The treatment studied was found to be an efficient option for the removal of sulfur and nitrogen compounds present in commercial diesel, and thus it could be an alternative pretreatment in the conventional hydrotreatment process

Oxygen reduction on chemically heterogeneous iron-containing nanoporous carbon: The effects of specific surface functionalities

Abstract not availableMykola Seredych, Mark J. Biggs, Teresa J. Bandos

Electrical Characterization of Ammonia Carbon-Based Sensors

A sensor response parameters of the ammonia sensors which are prepared by using composite of graphene oxide and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt derived carbon are presented. Using the self-designed interdigitated electrode on the experimental setup, we were able to determine the capacity for gas sensing as a sensor response for low ammonia concentrations (20, 50, and 100 ppm)

Pyridinic-N groups and ultramicropore nanoreactors enhance CO\u3csub\u3e2\u3c/sub\u3e electrochemical reduction on porous carbon catalysts

Wood-based activated carbons, as received and modified by introduction of nitrogen and/or oxidation, were studied as CO2 electrochemical reduction reaction (CO2ERR) catalysts. The carbons have similar pore structures but they differ significantly in surface chemistry. An electrochemical reduction process applied to the surface before CO2 reduction increased their catalytic performance. On the carbons tested Faradaic efficiency for CO formation reached 40% and methane formation − 1.2% at −0.66 V vs. RHE. The high efficiency for the CO formation was linked mainly to positively charged carbon close to pyridinic nitrogen, which stabilizes CO2− intermediate in the pore system. On the other hand, the results indicate that quaternary nitrogen is less influential and it is less affected by the reduction process. N-oxides outside the ring (CN+O−) were also found as active sites for CO2ERR. Hydrogen evolution reaction and CO2ERR compete for these active sites. Owing to the specific texture of nanoporous carbon, Faradaic reactions might not be a unique mechanism of CH4 formation. It is also possible that CO, upon strong adsorption in ultramicropores of sizes less than 0.7 nm combines there with adsorbed H2 from water reduction resulting in the formation of methane. Thus, the ultramicropores can be considered as pseudo Fisher-Tropsch nanoreactors. The results also indicate that the acidic surface of the catalysts increases the overpotential of the maximum Faradaic efficiency of either CO or CH4 formation