The Impact of N/O-Functional Groups on the Sorption Capabilities of Activated Carbons Derived from Furfuryl Alcohol.

This work describes the effect of nitrogen and oxygen functional groups on the sorption properties of activated carbons produced from furfuryl alcohol. The poly(furfuryl) alcohol underwent carbonization in nitrogen, ammonia, and ammonia and air (in a 3:2 proportion) atmospheres at 600 °C for 4 h. The resulting materials were subsequently activated in a carbon dioxide atmosphere for 1 h at temperatures of 700 °C, 800 °C, 900 °C, and 1000 °C. The X-ray photoelectron spectroscopy (XPS) findings suggest that ammoxidation is superior to amination in terms of nitrogen doping. The maximum nitrogen concentration achieved after ammoxidation was 25 at.%, which decreased to 4 at.% after activation. Additionally, it was observed that oxygen functional groups have a greater impact on porous structure development compared to nitrogen functional groups. The materials activated through carbonization under an ammonia/air atmosphere attained the highest oxygen concentration of roughly 19 at.% as confirmed by XPS. The materials were evaluated for their sorption capacities for carbon dioxide and ethylene, which were 2.2 mmol/g and 2.9 mmol/g, respectively, at 30 °C.

The Influence of NH4NO3 and NH4ClO4 on Porous Structure Development of Activated Carbons Produced from Furfuryl Alcohol.

The influence of NH4NO3 and NH4ClO4 on the porous texture and structure development of activated carbons produced from a non-porous polymeric precursor synthesized from furfuryl alcohol has been studied. The non-doped counterparts were prepared and studied for comparison purposes. NH4NO3 and NH4ClO4-doped polymers were carbonized under N2 atmosphere at 600 °C, followed by CO2 activation at 1000 °C and the obtained carbon materials and activated carbons were thoroughly characterized. The porosity characterization data have shown that NH4NO3-derived ACs present the highest specific surface area (up to 1523 m2/g in the experimental conditions studied), and the resulting porosity distributions are strongly dependent on the activation conditions. Thus, 1 h activation is optimum for the microporosity development, whereas larger activation times lead to micropores enlargement and conversion into mesopores. The type of doping salts used also has a substantial impact on the surface chemical composition, i.e., C=O groups. Moreover, NH4NO3 and NH4ClO4 constitute good sources of nitrogen. The type and contribution of nitrogen species are dependent on the preparation conditions. Quaternary nitrogen only appears in doped samples prepared by carbonization and pyrrolic, pyrydinic, and nitrogen oxide groups appear in the NH4NO3 -series. NH4NO3 incorporation has led to optimized materials towards CO2 and C2H4 sorption with just 1 h activation time.

Sorption and Textural Properties of Activated Carbon Derived from Charred Beech Wood.

The aim of this study was to prepare activated carbon materials with different porous structures. For this purpose, the biomass precursor, beech wood, was carbonized in an inert atmosphere, and the obtained charcoal was physically activated using carbon dioxide at 1273 K. Different porous structures were obtained by controlling the time of the activation process. Prepared materials were characterized in terms of textural (N2 sorption at 77 K), structural (XRD), and sorption properties (CO2, C2H4, C4H10). The shortest activation time resulted in a mostly microporous structure, which provided a high sorption of CO2. Increasing the activation time led to an increasing of the pores' diameters. Therefore, the highest ethene uptake was obtained for the material with an intermediate activation time, while the highest butane uptake was obtained for the material with the highest activation time.

Changes in Porous Parameters of the Ion Exchanged X Zeolite and Their Effect on CO2 Adsorption.

Zeolite 13X (NaX) was modified through ion-exchange with alkali and alkaline earth metal cations. The degree of ion exchange was thoroughly characterized with ICP, EDS and XRF methods. The new method of EDS data evaluation for zeolites was presented. It delivers the same reliable results as more complicated, expensive, time consuming and hazardous ICP approach. The highest adsorption capacities at 273 K and 0.95 bar were achieved for materials containing the alkali metals in the following order K < Na < Li, respectively, 4.54, 5.55 and 5.94 mmol/g. It was found that it is associated with the porous parameters of the ion-exchanged samples. The Li0.61Na0.39X form of zeolite exhibited the highest specific surface area of 624 m2/g and micropore volume of 0.35 cm3/g compared to sodium form 569 m2/g and 0.30 cm3/g, respectively. The increase of CO2 uptake is not related with deterioration of CO2 selectivity. At room temperature, the CO2 vs. N2 selectivity remains at a very high stable level prior and after ion exchange in co-adsorption process (XCO2 during adsorption 0.15; XCO2 during desorption 0.95) within measurement uncertainty. Additionally, the Li0.61Na0.39X sample was proven to be stable in the aging adsorption-desorption tests (200 sorption-desorption cycles; circa 11 days of continuous process) exhibiting the CO2 uptake decrease of about 6%. The exchange with alkaline earth metals (Mg, Ca) led to a significant decrease of SSA and micropore volume which correlated with lower CO2 adsorption capacities. Interestingly, the divalent cations cause formation of mesopores, due to the relaxation of lattice strains.