In this paper, we report a facile ultrasonic method to synthesize well-dispersed CoO quantum dots (3-8 nm) on graphene nanosheets at room temperature by employing Co(4)(CO)(12) as cobalt precursor. The prepared CoO/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (1592 mAh g(-1) after 50 cycles), high Coulombic efficiency (over 95%), excellent cycling stability, and high rate capability (1008 mAh g(-1) with a total retention of 77.6% after 50 cycles at a current density of 1000 mA g(-1), dramatically increased from the initial 50 mA g(-1)). The extraordinary performance arises from the structure advantages of the composites: the nanosized CoO quantum dots with high dispersity on conductive graphene substrates supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions, which are beneficial for high capacity and rate capability. Meanwhile, the isolated CoO quantum dots anchored tightly on the graphene nanosheets can effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction during discharge/charge processes, which is good for high capacity as well as cycling stability. Moreover, regarding the anomalous behavior of capacity increase with cycles (activation effect) observed, we proposed a tentative hypothesis stressing the competition between the conductivity increase and the amorphorization of the composite electrodes during cycling in determining the trends of the capacity, in the hope to gain a fuller understanding of the inner working of the novel nanostructured electrode-based lithium-ion batteries.

The CO 2 desorption tests were conducted at 363-378 K for 5.0 mol/L blended monoethanolamine (MEA)-diethanolamine (DEA) solutions to develop the energy efficient solvents with high CO 2 production and low energy consumptions. These desorption tests were performed with a recirculation process for various preloaded, 5 mol/L (4.5 + 0.5 to 0.5 + 4.5) MEA-DEA solutions to find out the optimized solvents with minimum heat duty. Therefore, 1-4 mol/L and 0.5-0.45 mol/L MEA-DEA solvents have larger CO 2 production (nCO 2 ) and lower heat duties (H CO 2 ) than 5 mol/L DEA under similar operation conditions. They have lower heat duty (510 and 538 kJ/mol) than DEA (572 kJ/mol) due to increased CO 2 desorption rates, despite 10% higher heat input (Q Total ) than DEA. Moreover, the critical points were studied as research focus of amine regeneration curves, along with reaction energy calculation. Finally, secondary amines blending minor MEA (<20%) as promotor turned out to be an alternative approach of solvents improvement with low energy requirement.

Heat-duty reduction is the major challenge in CO 2 desorption and amine regeneration. The use of a combination of heterogeneous catalytic desorption with improved amine solvents is a novel approach to address this issue. We studied CO 2 -desorption tests of noncatalytic diethylamine (DEA) solvents as a benchmark and focused on five blended amines (DEA−monoethanolamine, MEA; 4.5:0.5 to 2.5:2.5 M) with three types of catalysts (γ-Al 2 O 3 , H-ZSM-5, and 2:1 blended γ-Al 2 O 3 −H-ZSM-5) to explore the synergy effects of DEA-based amine blends with solid catalysts. The heat duty and CO 2 production of each case scenario were tested for six sets of solutions with initial loading of 0.5 mol of CO 2 per mole of amine at 363−378 K and were compared with those of 5 M DEA solvents. The results showed that the three catalyst conditions (blended catalyst, H-ZSM-5, and γ-Al 2 O 3 ) followed different trends at rich and lean loadings. Finally, both 5 M DEA and 4.5:0.5 M DEA−MEA with blended catalysts exhibited very low heat duties of 151.2 and 168.0 kJ per mole of CO 2 at loadings of 0.50− 0.20 mol per mole of amine at 378 K among the six solutions. Both approaches proved to be the most-energy-efficient amine solutions whereas the blended amine with blended catalysts was the best strategy that was applicable in the CO 2 desorber.

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Utilizing and reducing carbon dioxide is a key target in the fight against global warming. The photocatalytic performance of bulk graphitic carbon nitride (g-C3N4) is usually limited by its low surface area and rapid charge carrier recombination. To develop g-C3N4 more suitable for photocatalysis, researchers have to enlarge its surface area and accelerate the charge carrier separation. In this work, novel hybrid graphitic carbon nitride and carbon (H-g-C3N4/C) composites with various carbon contents have been developed for the first time by a facile one-step pyrolysis method using melamine and natural soybean oil as precursors. The effect of carbon content on the structure of H-g-C3N4/C composites and the catalytic activity for the photoreduction of CO2 with H2O were investigated. The results indicated that the introduction of carbon component can effectively improve the textural properties and electronic conductivity of the composites, which exhibited imporved photocatalytic activity for the reduction of CO2 with H2O in comparison with bulk g-C3N4. The highest CO and CH4 yield of 22.60 μmol/g-cat. and 12.5 μmol/g-cat., respectively, were acquired on the H-g-C3N4/C-6 catalyst with the carbon content of 3.77 wt % under 9 h simulated solar irradiation, which were more than twice as high as that of bulk g-C3N4. The remarkably increased photocatalytic performance arises from the synergistic effect of hybrid carbon and g-C3N4.