[en] Highlights: • Microporous zirconium-cerium (hydr) oxides were synthetized. • Ce presence narrowed the band gap of the materials. • The samples showed a high efficiency for removal of CEES vapors. • 1,2-Bis (ethyl thio) ethane and ethyl vinyl sulfide were the main reaction products. • 5% (Ce/Zr mol) addition of cerium oxide results in the best performing material. - Abstract: Highly porous cerium oxide modified Zr(OH)_4 samples were synthesized using a simple one stage urea precipitation method. The amorphicity level of zirconium hydroxide did not change upon addition of cerium oxide particles. A unique aspect of the cerium oxide-modified materials is the presence of both the oxide (CeO_2) and hydroxide (Zr(OH)_4) phases resulting in a unique microporous structure of the final material. Extensive characterization using various chemical and physical methods revealed significant differences in the surface features. All synthesized materials were microporous and small additions of cerium oxide affected the surface chemistry. These samples were found as effective catalysts for a decontamination of mustard gas surrogate, 2-chloroethyl ethyl sulfide (CEES). Cerium oxide addition significantly decreased the band gap of zirconium hydroxide. Ethyl vinyl sulfide and 1,2-bis (Ethyl thio) ethane were identified as surface reaction products.

[en] Graphite oxide/aluminium-zirconium polycation composites were prepared using graphite oxide and commercial solution of Rezal. To improve the dispersion of graphene-like layers two different surfactant concentrations were used. The resulting materials were used as adsorbents of ammonia either in as received form or prehumidified for 2 h before the breakthrough test. The challenge gas was either dry or with 70% humidity. Although the highest amount adsorbed was measured on adsorbents after prehumidification, the strongest adsorption takes place at dry conditions. Water on the surface increases the amount adsorbed via acid-base reactions, whereas water in the challenge gas decreases the removal of ammonia owing to the competition with NH₃ for adsorption centers. The amount of surfactant used for dispersion affects the final performance. More surfactant likely leads to a higher degree of dispersion of graphene-like layers and thus relatively less undisturbed inlerlayer space where intercalation of ammonia can occur. Higher dispersion of graphene layers leads also to higher dispersion of polycations and thus greater adsorption on their Bronsted acidic centers.

[en] Highlights: • Heating rate and washing affected the porosity and chemistry of N/S-carbon. • FE for CO₂ reduction increased upon N and S-doping. • FE did not directly depend on the porosity and surface chemistry of N/S- carbons. • Relative dispersion of N/S groups on the surface strongly affected CO₂ reduction. The catalytic activity for CO₂ electrochemical conversion into CO on N-doped carbons has been previously suggested to be enhanced by introducing a sulfur co-dopant to the carbon matrix. In this study, nitrogen and sulfur-codoped porous carbons were synthesized by a high temperature treatment of commercial wood-based carbon impregnated with thiourea. By slightly changing synthesis conditions, three different carbons were obtained and used as electrocatalysts for reduction of CO₂. Detailed analyses of chemistry and texture showed differences in the amounts of N and S heteroatoms, in the speciation of surface groups, and in porosity. The best preforming sample had the highest dispersion/lowest density of nitrogen-containing groups and the low dispersion/high density of thiophenic groups. The dependence of the Faradaic efficiency for CO reduction on the ratio of the density of nitrogen groups to that of sulfur showed a linear decrease with an increase in the ratio, supporting the previously suggested enhancing effect of the high dispersion of N-containing catalytic centers and their activation by sulfur co-doping on CO₂ electroreduction. The results also indicated that the catalytic activity of pyridinic groups is more positively affected by sulfur co-doping than is that of quaternary nitrogen species.

[en] With an objective to increase an electrochemical performance, simple and effective modifications of activated carbon fiber textiles (ACT) were carried out prior to their testing as supercapacitors. The modifications included a high-temperature treatment of the textile impregnated with N- and S-containing species (i.e. dicyandiamide, urea and thiourea). This led to an improvement in an electrical conductivity and in an enhanced mechanical strength with a preserved porosity. Compared to the performance of the initial unmodified carbon textile, a urea-functionalized material showed an enhancement in the electrochemical capacitance. An increase from 177 to 209 F g⁻¹ at a scan rate 10 mV s⁻¹ in an alkaline electrolyte was recorded (3-cell CV measurements) and from 138 to 166 F g⁻¹ at 0.10 A g⁻¹ (2-cell galvanostatic charge-discharge). The results suggested that mechanically stable, flexible and conductive ACT have a potential to be used in textile-based flexible supercapacitors. Benefits coming from the applied modification routes can be also adapted for the fabrication of other types of carbon-based composite electrode materials.

[en] Highly porous wood-based activated carbon was impregnated with cerium, lanthanum and sodium chlorides using incipient impregnation method. On the samples prepared adsorption of NO₂ was carried out from moist (70% humidity) air either with or without the prehumidification. The materials were characterized using adsorption of nitrogen, thermal analysis, FTIR, and potentiometric titration. The results indicated that for all materials a significant amount of NO₂ was reduced to NO and released from the system. In the case of virgin carbons, the NO₂ interacting with the surface along with nitric and nitrous acids formed there in the presence of water significantly increased the acidity of the carbons by the formation of oxygen-containing groups and organic nitrates. On the other hand, when chlorides were present the capacity to interact with nitrogen dioxide increased since the inorganic phase, depending on the nature of metal, bound NO₂ in the forms of nitrates (Ce, La, Na), got oxidized/oxidized carbon surface (for Ce) or contributed to the formation of nitrosyl chloride (for Na).

[en] Highlights: ► Ce_1−yZr_yO_2−x mixed oxides were highly dispersed in mesoporous silica SBA-15. ► A strong increase in the NO₂ adsorption capacity was observed on composites. ► The insertion of Zr⁴⁺ in ceria fluorite structure promotes the reduction of Ce⁴⁺ into Ce³⁺. ► Ce³⁺ and –OH groups were found to be the main active centers for NO_x retention. ► The structure remains quite stable after exposure to NO₂ in ambient conditions. - Abstract: New silica-based composites were obtained using a slow precipitation of mixed oxide Ce_1−xZr_xO₂ on the surface of mesoporous silica, SBA-15. The samples were tested as NO₂ adsorbents in dynamic conditions at room temperature. The surface of the initial and exhausted materials was characterized using N₂ sorption, XRD, TEM, potentiometric titration, and thermal analysis before and after exposure to NO₂. In comparison with unsupported Ce_1−xZr_xO₂ mixed oxides, a significant increase in the NO₂ adsorption capacity was observed. This is due to the high dispersion of active oxide phase on the surface of SBA-15. A linear trend was found between the NO₂ adsorption capacity and the amount of Zr(OH)₄ added to the structure. Introduction of Zr⁴⁺ cations to ceria contributes to an increase in the amount of Ce³⁺, which is the active center for the NO₂ adsorption, and to an increase in the density of –OH groups. These groups are found to be involved in the retention of both NO₂ and NO on the surface. After exposure to NO₂, an acidification of the surface caused by the oxidation of the cerium as well as the formation of nitrite and nitrates took place. The structure of the composites appears not to be affected by reactive adsorption of NO₂.

[en] The capacitive performance of activated carbons of similar volume of ultramicropores but of marked differences in their pore size distributions was tested in aqueous electrolytes. Dramatic differences in the capacitive behavior were measured in H₂SO₄, KOH, or in Na₂SO₄. In the case of the carbon activated with CO₂, the sterical hindrances limited the access of Na⁺ ions to pores resulting in a small capacitance. The results indicated that even though the high volume of micropores is required for a good capacitive behavior, it is not a sufficient condition for granting a high capacitance. It was found that even subtle differences in the ultramicropore distribution can affect dramatically the capacitive behavior and, for a given carbon, the electrolyte type needs be adjusted, if the optimum performance is targeted. That adjustment should be made based on the size of the large ion and its compatibility/similarity with/to the predominant ultramicropore size. Carbon surface chemistry does not play a marked role for carbons with a high degree of microporosity when used as supercapacitor electrodes. Since the size of pores are critical for ion accessibility, it is suggested that enhanced adsorption potential in small pore might also contribute to the high capacitive performance in pores similar in size to ions.

[en] Highlights: • The ACs from cotton stalk feed was prepared with addition of TiO₂. • The perovskite was formed during the activation. • The formation of perovskite was related to the calcium content in the ACs. • The energy density achieved to 22.5 Wh kg⁻¹ at 5065 W kg⁻¹. • The sample possessed high stability of charging-discharging in two electrode system. Modifications of activated carbon materials (ACs) towards an increase in the electronic and ionic conductivities are expected to improve their capacitance in the absence of a conductive agent. Char derived from cotton straw feed were heat-treated at 800 °C in the presence of TiO₂. Simultaneously KOH and K₂CO₃ were used as activation agents. That process resulted in the formation of perovskite CaTiO₃ with an involvement of calcium present in carbon as an impurity. The composite were extensively characterized from the point of view of a texture, surface chemistry and electrochemical performance. The results indicated that perovskite with impurities affected the ionic conductivity and enhanced the capacitive performance of ACs. The capacitance measured on the electrode made of the best performing sample in both three- and two-electrode cell systems in the absence of a conductive agent - carbon black was 270 F g⁻¹ and 185 F g⁻¹ at current density of 0.5 A g⁻¹, respectively. The results suggest that the AC/perovskite composites are promising electrodes of the high-performance supercapacitors.

[en] The determination of an atomistic graphene oxide (GO) model has been challenging due to the structural dependence on different synthesis methods. In this work we combine temperature-programmed molecular dynamics simulation techniques and the ReaxFF reactive force field to generate realistic atomistic GO structures. By grafting a mixture of epoxy and hydroxyl groups to the basal graphene surface and fine-tuning their initial concentrations, we produce in a controllable manner the GO structures with different functional groups and defects. The models agree with structural experimental data and with other ab initio quantum calculations. Using the generated atomistic models, we perform reactive adsorption calculations for H₂S and H₂O/H₂S mixtures on GO materials and compare the results with experiment. We find that H₂S molecules dissociate on the carbonyl functional groups, and H₂O, CO₂, and CO molecules are released as reaction products from the GO surface. The calculation reveals that for the H₂O/H₂S mixtures, H₂O molecules are preferentially adsorbed to the carbonyl sites and block the potential active sites for H₂S decomposition. The calculation agrees well with the experiments. The methodology and the procedure applied in this work open a new door to the theoretical studies of GO and can be extended to the research on other amorphous materials

[en] The polyoxometalate hybrid (POM-h) nanorods were synthesized and tested as reactive adsorbents of the vapors of mustard gas surrogates, and in particular against 2-chloroethyl ethyl sulfide (CEES) and ethylethyl sulfide (EES). They were found to promote the photo-oxidation of the surrogates’ vapors to sulfoxide under ambient conditions and in the absence of an additional oxidation agent. The structural and morphological analysis by SEM, TEM, XRD, and BET showed that the non-porous bright-yellow powder consists of nanorods with diameter of 50–100 nm and length of around 1 μm, stacked together by forming star-like nanostructured aggregates. The FTIR, XRD, thermal analysis, and EDX mapping revealed that the obtained material consists of the Keggin-type cobalt containing heteropolytungstate polyoxometalate phase (K₅CoW₁₂O₄₀·20H₂O) and potassium persulfate. The estimated indirect band gap was in the blue region of the visible light. The decomposition/detoxification of CEES and EES vapors by POM-h occurred through various and complex photo-catalytic and photo-oxidative pathways. The degradation of the surrogates’ toxic vapors to non-toxic molecules was linked to the elevated surface photo-reactivity and the ability of the nanorods to form hydroxyl radicals. The latter ones were responsible for the cleavage of SC bonds and further photo-oxidation of the formed fragments to ethanol, formaldehyde and acetic acid. A fast and gradual color change of the nanomaterial upon exposure to surrogate vapors or droplets could be used in sensing/detecting the presence of toxic species.