• Energy Research
• chemical sciences close

In this work, plane tree seed-based activated carbons were characterized in detail for a variety of applications. The particularly important area of application would be in the artificial photosynthesis. After carbonization process of biomass precursor at 650°C, the resulting preliminary activated carbons were activated at various temperatures. The activated carbons were characterized by oxygen functionalities (a particularly important role has ester oxygen groups) which provide a unique microstructure. The chemical compositions of as-prepared activated carbons were analyzed through Fourier transform infrared and Raman spectra as well as gas chromatography–mass spectroscopy analysis, while morphology was observed by scanning electron microscopy analysis. Applied analysis showed that detected graphite mainly becomes uniformly nanocrystalline system. The current study also explored the applicability of carbon material obtained from plane tree seed as a potential gaseous adsorbent. The characterization showed that the tested material contains both mesopores and micropores, and this should be advantageous for the gas sorption process, since mesopores may provide low-resistant pathways for the diffusion of CO2 molecules, while the micropores are the most suitable for trapping of CO2. The sorption process analysis (including adsorption/desorption isotherms behavior) shows indication that the rate-limiting step of CO2 adsorption onto activated carbon is probably governed by diffusion-controlled process, especially at temperatures below 850°C.

The development of carbon materials with desirable textures and new aqueous electrolytes is the key strategy to improve the performance of supercapacitors. Herein, a deep eutectic solvent (DES) was used for in situ templating of a carbon material. A carbon material was characterized (XRD, N2-physisorption, FTIR, SEM and EDS) and used as an electrode material for the first time in multivalent-based supercapacitors. In situ templating of carbon was performed using a novel DES, which serves as a precursor for carbon and for in situ generation of MgO. The generation of MgO and its roles in templating of carbon were discussed. Templating of carbon with MgO lead to an increase in surface area and a microporous texture. The obtained carbon was tested in multivalent-ion (Al3+ and Mg2+) electrolytes and compared with H2SO4. The charge-storage mechanism was investigated and elaborated. The highest specific capacitance was obtained for the Al(NO3)3 electrolyte, while the operating voltage follows the order: Mg(NO3)2 > Al(NO3)3 > H2SO4. Electrical double-layer capacitance (versus pseudocapacitance) was dominant in all investigated electrolytes. The larger operating voltage in multivalent electrolytes is a consequence of the lower fraction of free water, which suppresses hydrogen evolution (when compared with H2SO4). The GCD was experimentally performed on the Al(NO3)3 electrolyte, which showed good cyclic stability, with an energy density of 22.3 Wh kg−1 at 65 W kg−1.

Rhyolite is an extrusive, igneous rock of aluminosilicate composition that upon rapid cooling forms obsidian. Obsidian is amorphous and contains limited water portions ( 5 mass%). In the current study, kinetics of hydrous rhyolite dehydration were investigated by thermogravimetry up to 1000 °C, at heating rates of 2.5, 5, 10 and 20 °C min−1 and under inert atmosphere. The mass loss is approx. 7.6 mass%, occurs along wide temperature range (100–800 °C) and is solely attributed to the release of molecular water ((H2O)m) and hydroxyl groups (OH). Rhyolite dehydration was considered as a solid-state reaction, and the apparent activation energy (Ea) of dehydration was calculated throughout the whole conversion range (a) by applying the isoconversional Friedman and advanced Vyazovkin methods. Both methods revealed inverse sigmoid trend in Ea values versus conversion degree, possessing almost stable value of 61 ± 5 kJ mol−1 for Friedman method and 59.44 kJ mol−1 for Vyazovkin method on conversion range between 0.25 and 0.75, and sharp increase at higher conversion degree. The intensive change in Ea during dehydration progression is attributed to the change in releasing species (from (H2O)m to OH). Raman and FT-IR spectroscopy analyses of raw and partially dehydrated samples at different stages revealed that up to 300 °C mainly (H2O)m is diffused out of the material causing sample enrichment in OH groups. OH release, which occurs at relatively higher temperature, is accompanied by increase in apparent Ea value of dehydration. Concerning microstructure of raw rhyolite, it exhibits a network of micro-fractures which serve as water release routes. Upon heating, more and wider fractures are created. At 600 °C, fractures merging occurs creating voids, which constitute forerunners of the expansion phenomenon. Further temperature increase causes material softening allowing local plastic deformation, which under the high pressure that is exerted by the releasing water species incites the formation of large cavities and fractures, initiating expansion.

Abstract Pyrolysis process of coffee paper cup samples was investigated in a flow stream of nitrogen at different heating rates (10, 20, 30 and 40 °C min−1), using thermo-analytical techniques. It was found that second pyrolysis stage can be described by Sestak–Berggren (SB) autocatalytic model, with mechanism function f(α) = α0.011(1 − α)1.459. Based on analysis of SB kinetic exponents (designated by M and N), it was found that second pyrolysis stage is mainly controlled by chemical process, involving reactions with reaction-order (n) higher than unity. Applying specific statistical analysis, in order to obtain precise distribution of reactivity, the discrete (binomial) distribution has shown that there are two important areas of current distribution for corresponding energy outcomes, within the apparent activation energy as random variable. The first “concentration” area of energy outcomes corresponds to start of chain end depolymerization reaction forming levoglucosan at high enough temperature region, while second “concentration” area of energy outcomes includes occurrence of macro-radicals in liquid phase propagate with radical addition on unsaturated C–C bonds, with cross-linking and formation of small chemical species. It was found that further elevating of temperature (above 340 °C), will leads to fact that rate of tar-forming reactions increases and formation of char decreases.