Revealing the competitive effect of N2 and H2O towards CO2 adsorption in N-rich ordered mesoporous carbons

The incorporation of heteroatoms improves CO2 adsorption on carbon-based materials, but it can also provide some hydrophilic character to the bare-carbon frameworks, making the hypothesis of competitive CO2/H2O adsorption not negligible. In this respect, the CO2 capture is here evaluated through a deep characterization of the sorption properties of N-rich ordered mesoporous carbons under dry and moisture conditions, and in CO2/N2 gas mixtures. The nanocasting strategy is used to obtain N-rich CMK-3-type carbons in one pot by impregnating D-glucosamine hydrochloride, a carbon/nitrogen source, into an SBA-15 silica template followed by pyrolysis treatment at 600, 750, and 900 °C. The fine-tuning of the pyrolysis treatment aims to find the right proportion of micropores and N content, which are important features for selective CO2 adsorption. The highest surface amount of N (11.3 at.%), in particular of the pyridinic type, enhances the CO2/N2 selectivity (1.03 mmol/g of adsorbed CO2 from a 20% CO2 in N2), but also the undesired increment in the H2O uptake. CO2 uptake under competitive CO2/H2O conditions is better preserved with 8.3 at.% of surface nitrogen (1.55, 1.52, 0.61, and 0.89 mmol/g of CO2 at a relative humidity of 0, 25, 50, and 75%, respectively). Interestingly, the N-CMK-3 materials retain their capture properties over repetitive adsorption-desorption cycles in pure CO2. In this respect, a TGA-FTIR study is performed to monitor the reusability of the sorbents after CO2 capture from moist flue gases to assess the effectiveness of the reactivation procedure towards the removal of the adsorbed species

Formation and Characterization of Crystalline Hydroxyapatite Coating with the (002) Texture

This study reports the effect of titanium (Ti) microstructure on the mechanical properties and surface wettability of thin (<800 nm) hydroxyapatite (HA) coating deposited via radio-frequency (RF) magnetron sputtering. It was revealed that the sand-blasting (SB) and acid etching (AE) of Ti prior deposition led to a wide range of surface roughness in nano/micro scale. After nanostructured HA coating deposition such physico-mechanical characteristics as nanohardness H, Young's modulus E, H/E ratio and H[3]/E[2] were significantly improved. Moreover, HA coatings exhibited improved wear resistance, lower friction coefficient and ability of the coating to wetting

INSIGHTS INTO THE CO2 ADSORPTION PROPERTIES OF NITROGEN-CONTAINING ORDERED MESOPOROUS CARBONS

The increase of global CO2 concentration is the main responsible for global warming. Nitrogen-containing ordered mesoporous carbons (NOMCs) are here proposed as CO2 adsorbents, thanks to their adsorption ability and selectivity in simulated flue gases mixtures. In this work, NOMCs are synthesized as replications of an ordered mesoporous silica hard template, using the well-known nanocasting route. This method is convenient for achieving a pore architecture composed of both micro- and mesopores able to promote at the same time improved capture performances and fast kinetics of gas diffusion, respectively. One of the drawbacks of the synthesis of NOMCs is the use of toxic carbon/nitrogen sources or the addition of post-synthesis treatments for the nitrogen doping process. A more sustainable approach is proposed in this work, using eco-friendly sources as nitrogen-rich carbon precursors. The effect of the pyrolysis temperature (varied from 600 to 900 °C) on the development of microporosity and N incorporation was related to pure CO2 adsorption and selectivity in CO2/N2 mixtures (20/80 v/v). A maximum CO2 adsorption capacity of 1.47 mmol g-1 was achieved by the sample pyrolized at the highest temperature (i.e., 900°C) at 30 °C / 0.9 bar / pure CO2, while a CO2 uptake of 0.82 mmol g-1 was obtained by the sample pyrolized at the lowest temperature (i.e., 600 °C) at 35 °C / 1 bar / 20 % CO2. The enhancement in pure CO2 adsorption is due to the increase of the micropore content. On the contrary, a lower pyrolysis temperature (600 °C) allowed for the retention of a higher amount of N, beneficial for the selective adsorption of CO2 in presence of N2

Nanocast Mixed Ni–Co–Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction

Nanocasting or hard-templating is a versatile method to produce ordered mesoporous mixed transition metal oxides (MTMOs) with promising potential for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a comprehensive investigation was conducted on various NixCoyMnzO4 replicated from large pore KIT-6 silica. The materials were calcined at different temperatures to study the influence of the oxide formation and the resulting pore structure ordering, as well as surface properties, on the electrochemical activity and stability of the catalysts. After a comprehensive characterization, electrocatalytic performances of the materials were investigated in detail for OER to find a structure–activity relationship. In OER, a correlation was established between calcination temperature, pore and surface properties, and the overall efficiency and stability. The best sample, NixCoyMnzO4 calcined at 300 °C, provided a reasonable current density (25 mA/cm2 at 1.7 V vs RHE) and an overpotential of 400 mV at 10 mA/cm2, and demonstrated increased current density (above 200 mA/cm2 at 1.7 V vs RHE) once loaded into a Ni foam compared to the bare foam. This sample also remained stable over 15 h. Our results indicate that the calcination temperature greatly affects the porosity, crystalline structure, phase composition, and the activity of the catalysts toward OER

Incorporation of Cu/Ni in Ordered Mesoporous Co-Based Spinels to Facilitate Oxygen Evolution and Reduction Reactions in Alkaline Media and Aprotic Li−O₂ Batteries

Ordered mesoporous CuNiCo oxides were prepared via nanocasting with varied Cu/Ni ratio to establish its impact on the electrochemical performance of the catalysts. Physicochemical properties were determined along with the electrocatalytic activities toward oxygen evolution/reduction reactions (OER/ORR). Combining Cu, Ni, and Co allowed creating active and stable bifunctional electrocatalysts. CuNiCo oxide (Cu/Ni≈1 : 4) exhibited the highest current density of 411 mA cm−2 at 1.7 V vs. reversible hydrogen electrode (RHE) and required the lowest overpotential of 312 mV to reach 10 mA cm−2 in 1 m KOH after 200 cyclic voltammograms. OER measurements were also conducted in the purified 1 m KOH, where CuNiCo oxide (Cu/Ni≈1 : 4) also outperformed NiCo oxide and showed excellent chemical and catalytic stability. For ORR, Cu/Ni incorporation provided higher current density, better kinetics, and facilitated the 4e− pathway of the oxygen reduction reaction. The tests in Li−O2 cells highlighted that CuNiCo oxide can effectively promote ORR and OER at a lower overpotential