By employing particle-swarm optimization (PSO) and first-principles computations, we theoretically predicted five stable phases of graphene-like borocarbonitrides (g-BCN) with the stoichiometric ratio of 1:1:1 and uniformly distributed B, C, N atoms, which are the isoelectronic analogues of graphene. These g-BCN monolayers are effectively stabilized by their relatively high proportion of robust C-C or B-N bonds and strong partial ionic-covalent B-C and C-N bonds within them, leading to pronounced thermal and kinetic stability. The visible-light absorption and high carrier mobility of the investigated g-BCN monolayers indicate their possible applications in high-efficiency photochemical processes and electronic devices. Our computations could provide some guidance for designing the graphene-like materials with earth-abundant elements, as well as some clues for the experimental synthesis and practical applications of ternary BCN nanosheets.
The urgent desire for Halon substitution has propelled the exploration of potential alternatives because of the severe damage of Halon to the stratospheric ozone layer. As a perfluoroketone substance, C 5 F 10 O has a similar chemical structure and comparable environmental friendliness to that of the widely utilized Novec-1230 (C 6 F 12 O) extinguishant. Both theoretical calculations and experimental measurements are utilized to unveil the thermal decomposition and fireextinguishing mechanisms of C 5 F 10 O in this study. It was found that the C 5 F 10 O pyrolysis generates perfluoroolefins, perfluoroalkanes, and highly active free radicals that can efficiently capture H• and OH• radicals in the flame to interrupt the chain reactions of combustion. Apart from the chemical exhaustion of radicals, the endothermic pyrolysis of C 5 F 10 O imposes a prominent cooling effect upon high-temperature fires. Moreover, the release of incombustible CO 2 and perfluoroalkanes effectively dilutes the combustible fuel−air mixture in the combustion region. The synergistic chemical and physical suppression effects endow C 5 F 10 O with desirable fire-extinguishing effectiveness (6.83 and 6.04 vol % for suppressing methane-air and propane-air flames, respectively). Notably, compared with C 6 F 12 O, the less poisonous (CF 3 ) 2 CCF 2 is emitted at high temperatures (700−800 °C) by C 5 F 10 O decomposition, indicating the biosafety of C 5 F 10 O in confined and human-exposed regions. These findings suggest the promising applicability of C 5 F 10 O in practical Halon replacement and the necessity of its further evaluation.
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