Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen‐ and oxygen‐containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H2SO4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X‐ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea‐ and melamine‐treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 Å. On the other hand, pores between 5 Å and 6 Å are most effective in a double‐layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic‐N‐oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen.

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Characterization of the adsorbed protein film that forms upon implantation of a biomedical device is a long-standing interest in biomaterials research. Time-of-flight secondary ion mass spectrometry (ToF−SIMS) is a powerful method for the characterization of adsorbed proteins on biomaterial surfaces due to its chemical specificity and surface sensitivity. However, the SIMS fragmentation patterns for proteins are quite complex due to the heterogeneity of the protein sequence. Therefore, the multivariate analysis technique principal components analysis (PCA) was used to obtain a more detailed interpretation of the protein SIMS spectra. This study utilizes single component adsorbed protein films on three model substrates and multivariate analysis of the ToF−SIMS data to determine the identity of protein films. Furthermore, ToF−SIMS and PCA were used to give insight into the composition of a 1% bovine plasma protein film. The single component spectra from 13 different proteins were readily distinguishable using PCA. The major component of the 1% bovine plasma film was found to shift from fibrinogen to γ-globulins over the course of 2 h, in agreement with the current literature. This study shows how combination of ToF−SIMS and PCA provides new insights into the composition of adsorbed protein films on biomaterial surfaces.

Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) have attracted significant attention due to their electronic, electrochemical, chemical, and optical properties. However, understanding of their thermal stability is still lacking. To date, MXenes are synthesized via top-down wet chemical etching, which intrinsically results in surface terminations. Here, we provide detailed insight into the surface terminations of three carbide MXenes (Ti 3 C 2 T x , Mo 2 CT x , and Nb 2 CT x ) by performing thermal gravimetric analysis with mass spectrometry analysis (TA−MS) up to 1500 °C under a He atmosphere. This specific technique enables probing surface terminations including hydroxyl (−OH), oxy (O), and fluoride (−F) and intercalated species, such as salts and structural water. The MXene hydrophilicity depends on the type of etching (hydrofluoric acid concentration and/or mixed acid composition) and subsequent delamination conditions. We show that the amount of structural water in Ti 3 C 2 T x increases with decreasing O-containing surface terminations. The thermal stability of Ti 3 C 2 T x is improved by employing a low HF concentration or using a mixture of etchant acids, such as H 2 SO 4 /HF or HCl/HF instead of only HF, due to the reduced defect density. When tetramethylammonium hydroxide (TMAOH) is used for delamination, new N-containing species appear on the MXene surface. Moreover, free-standing films produced from Ti 3 C 2 T x etched with different HF concentrations and delaminated using TMAOH have similar TA−MS profiles, indicating that the post-treatment of Ti 3 C 2 T x controls its surface chemistry. The thermal stability of MXenes strongly depends on their chemical composition and structure; Ti 3 C 2 T x is more thermally stable than the fewer-atomic-layered Mo 2 CT x or Nb 2 CT x , and Mo 2 CT x is more/less thermally stable than Nb 2 CT x .

Graphical content entryThe mechanism of ammonia adsorption on graphite oxide (GO) is strongly related to the GO preparation and chemical features, especially to the sulfur-containing groups present on its surface. SummaryGraphite 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 sulfurcontaining compound involved in the oxidation process (Brodie method). They were both tested for ammonia adsorption in dynamic conditions, at ambient temperature, and characterized before 2 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, ways of retention are different: not only does the intercalation of ammonia is observed but also its reaction with the epoxy, carboxylic and sulfonic groups present. In particular, during the ammonia adsorption process, sulfonic groups are converted to sulfates in presence of superoxide anions O 2 -* . 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.