The Preparation And Properties Of Carbon-based Nanocomposite Materials Through Precursors Control Strategy

Energy and environment issue is one of the most important problems that humans must face at present and in the future.Fossil fuels are main resources to meet the industrial needs for energy consumption,but a series of environmental problems were caused in the using process.The CO2,CH4 and N2 O emissions gave rise to air pollution and greenhouse effect.In order to realize sustainable development,new green energy technologies such as production-storage hydrogen system,rechargeable battery,supercapacitor,etc must be studied to meet the needs of industry and life.Porous carbon materials and related nanofunctional materials such as metal/metal oxide nanoparticles?M/Mx Oy NPs?and metal/metal oxide@carbon composite material?M/Mx Oy@C?could be used as a catalyst for hydrogen production and electrode materials for Li ion battery?LIBs?or supercapacitor.They have great potential applications in energy and environment field.In this paper,a series of carbon-based nanomaterials were prepared from different MOFs and core-shells@sheets precursors and used in catalytic hydrogen production system,LIBs and sewage disposal.The applications of carbon-based nanomaterials were explored through precursor method in energy and environmental issues.The main content consisted of four parts:Co-Co₃O₄@carbon composites were prepared by controllable pyrolysis of Co-MOF nanocrystals in confined space,and used as catalysts for Na BH4 hydrolysis.Firstly,Co-MOFs@glucose polymer?Co-MOFs@GP?displaying core-shell structures were synthesized by a hydrothermal reaction.Then the pyrolysis of Co-MOFs@GP in N2 generated a core-shell structure composed of carbon shells and Co NPs?Co@C-n?.The controlled partial oxidation of Co NPs formed Co-Co₃O₄ heterojunctions confined in carbon shells,and then a core-shell structure of Co-Co₃O₄@carbon-n?Co-Co₃O₄@C-n?were prepared.These composites were used as catalysts in Na BH4 hydrolysis with different catalytic activity.Compared with Co-MOFs@GP and Co@C-n,Co-Co₃O₄@C-n exhibited the highest catalytic activity toward Na BH4 hydrolysis.Co-Co₃O₄@C-? provided of a H₂ generation specific rate of 5360 m L·min-1·g Co-1 at 298 K and 13111 m L·min-1·g Co-1 at 318 K,respectively.The high catalytic activity and good stability of Co-Co₃O₄@C were ascribed to the synergistic effect between Co and Co₃O₄ NPs,and protection of carbon shell.This fabrication method for core-shell composite of MOFs and the pyrolysis of MOFs composites in confined space for construction of hierarchical core-shells with heterojunction may find their wide application in electro or chemical catalysis fields involving energy storage and conversion issues.Co-MOFs were synthesized via the solvothermal reaction.Then Co-MOFs were used as precursor and calcinated under controllable condition to prepare samples with different structures: nitrogen-doped porous carbon with Co NPs composites?Co@C-N?,bulk Co₃O₄?B-Co₃O₄?and hollow Co₃O₄?H-Co₃O₄?.The mixture of cobalt formate and glucose were calcinated under specific conditions to get carbon with Co NPs composites?Co@C?.The LIBs performances of above products were studied.The pyrolysis precursor and conditions had important effects on the properties of materials.As anode materials for LIBs,Co@C-N exhibited the best performances.After the 200 th charge–discharge cycle at a current density of 0.2A·g-1,a reversible capacity of 869 m A·h·g-1can be retained,which was 112 % of the second capacity and 2.3 times the theoretical capacity of commercial graphite?372m A·h·g-1?.The product Co@C-N still maintained a reversible capacity of about 300 m A·h·g-1at a large current of 5 A·g-1.Compared with other materials,Co@C-N presented a high reversible capacity and good cycle stability.It was rarely reported in literatures that the Co0-based N-doped porous carbon composites derived from MOFs precursors for LIBs anode.These results provided a new design idea for LIBs,and proved that MOFs pyrolysis is an effective method for construction of LIBs anode materials.Co-MOF@PVP-GO were synthesized via the solvothermal reaction of Co?NO₃?₂·6H₂O,1,3,5-benzenetricarboxylate?H3BTC?,PVP and GO.Then Co-MOF@PVP-GO was used as precursor and calcinated at 500 °C for 3 h under N2 to prepare nitrogen-doped porous carbon and r GO with Co NPs composites?Co@N-CG?.Under the same pyrolysis conditions,porous carbon with Co NPs composites?Co@C?were obtained by using Co-MOF as precursor;nitrogen-doped porous carbon with Co NPs composites?Co@N-C?were produced by using Co-MOF@PVP as precursor.In order to further comparison,the mixture of cobalt formate and glucose were calcinated under the same conditions to get carbon with Co NPs composites?Co-C?.As anode materials for LIBs,Co@N-CG exhibited the best performance.After the 500 th charge–discharge cycle at a current density of 0.2A·g-1,a reversible capacity of 532 m A·h·g-1 can be retained,which was 118% of the second capacity and 3.1 times the capacity of Co-C.The product Co@N-CG still maintained a reversiblecapacity of about 274 m A·h·g-1at a current of 3 A·g-1.Co@N-CG exhibited high reversible capacity and good cycle stability.The good performance was mainly due to the following reasons: the pyridinic and pyrrolic N in carbon framework can provide more active sites for Li ions and thus accelerate the transportation of electrons and Li ions in the electrode;the existence of r GO enhanced electron conductivity;large specific surface area was conducive to increase the contact area of the electrode and electrolyte,and increase active position that Li ion embedded;porous structure could shorten ion diffusion distance,relieved the impact of volume changes during the repeated discharge/charge process,and help Li ion occur reversible-embedded reaction;the size of Co NPs was relatively uniform and ensured steady electrochemical process;carbon shell not only prevented Co NPs gather during the process of charging-discharging cycle,but also improved the conductivity and cycle stability of electrode materials.MOF@PVP-GO is used as precursors to prepare cobalt-based nitrogen doped carbon materials for LIBs anode.The research offer new results for LIBs,PVP is not only the surface active agent,but also can be used as a nitrogen source to apply in MOFs pyrolysis;the existence of r GO play an important role for the improvement of the LIBs performance;MOFs pyrolysis is an effective method to construct LIBs anode material.Nanoporous carbons were prepared through a novel template-activation method by using core-shells@r GO sheet composites?Fe₃O₄-C@r GO?as precursors.The preparation procedures consist of synthesis of precursors,an acid-etching and thermal activation.The activation at different temperatures could provide materials with different specific surface areas.These nanoporous carbon materials were used as absorbents for rhodamine B?Rh-B?from aqueous solution.The unique nanoporous structures with large surface areas are ideal adsorbents,thus C@r GO-650 illustrated better adsorption performance than the other synthesized adsorbents.It displayed good recyclability,and its highest adsorption capacity reached up to 14.8 L·g-1.The remarkable adsorption properties make nanoporous carbon a useful candidate for waste water treatment.This template-activation method can also broaden the potential applications of core-shells@sheet structures for the construction of nanoporous carbon,which helps to resolve the related energy and environmental issues.