The reduction of CO 2 emissions and its elimination from the atmosphere has become one of the major problems worldwide, since CO 2 is the main cause of the greenhouse effect and climate change. In recent years, a great number of carbonaceous materials that can be used as CO 2 adsorbents have been synthesized. The strategy is usually to synthesize the materials and determine their adsorption capacity without studying previously the factors that influence this capacity. In this work, different properties of the adsorbents are analyzed to study their influence on the CO 2 adsorption capacity. For this purpose, 10 adsorbents have been synthesized using different strategies and characterized with X-ray photoelectron spectroscopy, X-ray diffraction, and micro-Raman spectroscopy. The percentage of sp 2 carbons, the position of the D + D′ peak of the second-order Raman spectrum, the micropore volume, and the grain size of the C sp 2 domains have been related to the amount of CO 2 adsorbed by the adsorbents. The results confirm a linear relationship between the volume of the micropores and the CO 2 uptake and it proves that CO 2 retention is favored in those materials that, in addition to having a high volume of micropores, also have low grain size of C.

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The quantum Fisher information can be different with the Bures metric and becomes discontinuous at the parameter points where the rank of the parametric density operator changes. We show that the invalidation of the QCRB at such parameter points is due to the fact that the symmetric logarithmic derivative operator tends to be unbounded when the value of parameter approaches these singular parameter points. We give an alternative derivation of the QCRB through the Bures distance and show that this form of the QCRB still holds even when the parametric density operator changes its rank.