Study On The Synthesis Of Porous Carbon Materials Derived From Polymer Wastes And The Electrochemical Performance

Recycling of solid polymer waste is a serious problem, but also the current research focus. This dissertation aims to investigate the control synthesis of nanoporous carbon materials as well as the application in supercapacitors, mainly due to the advantages of high specific surface area, large pore volume, tunable porous structure, high thermal conductivity, good mechanical stability and mass productivity. A series of nanoporous carbon materials have been achieved by a template carbonization method, using different carbon sources and templates. XRD, FESEM, HRTEM, Raman, XPS and BET techniques have been implemented to characterize these carbon products and their capacitive behaviors have been measured by three-electrode system and/or two-electrode system. The brief research contents are summarized as follows:1. In this work, polytetrafluoroethene waste has been successfully converted into nanoporous carbon spheres by a simple template carbonization method, using CaCO3 as hard template. It is revealed that the carbonization temperature and the mass ratio of polytetrafluoroethene and CaCO3 play crucial roles in the determination of pore structures. The sample obtained with the ratio of polytetrafiuoroethene-to-CaCO3 as 2:1 at 700℃, the carbon-2:1 sample, exhibits BET surface area of 646.3 m2 g-1, and pore volume of 0.65 cm3 g-1. The resulting specific capacitance is 179.9 F g-1 when measured at 1 A g-1 in a three-electrode system, using 6 mol L-1 KOH as electrolyte. Next, to modify the pore structures as well as the resultant electrochemical behaviors, CO(NH2)2 has been added to make the carbon matrix nitrogen-containing. The sample produced with the mass ratio of polytetrafluoroethene, CaCO3 and CO(NH2)2 as 2:1:2 at 700℃, the carbon-2:1:2 sample, exhibits BET surface area of 1048.2 m2 g-1, and pore volume of 1.03 cm3 g-1. As a consequence, its specific capacitance has been improved to be 237.8 F g-1 at 1 A g-1. The present CaCO3-assisted template carbonization method is simple, reproducible and scalable and can be readily extended to treat with other halogen-containing plastic wastes.2. Using PET wastes as carbon source, and Ca(OAc)2-H2O as hard template, a template carbonization method has been implemented to produce nanoporous carbon materials, and also investigated the electrochemical performance. It is found out that the mass ratio of PET and Ca(OAC)2·H2O has a key impact upon the pore structures and electrochemical behaviors of carbon materials. The sample obtained with the ratio of PET-to- Ca(OAc)2·H2O as 3:1 at 800℃, the carbon-3:1 sample, exhibits good porosities, whose BET surface area is of 749.6 m2 g-1, and pore volume of 0.52 cm3 g-1.Its specific capacitance can reach up to 402.2 F g-1 at 1 A g-1, when electrochemical measurement is carried out in a three-electrode system, using 6 mol L-1 KOH aqueous solution as electrolyte; and it retains 172 F g-1 even at 40 A g-1. In addition, the carbon-3:1 sample can maintain up to 96.05% after 5000 cycles, indicating its superior cycling stability. The present Ca(OAc)2·H2O -assisted template carbonization method is expected to dispose other plastic wastes.3. Using Mg citrate as hard template, PTFE, PVC and PVDF wastes have been converted into nanoporous carbon materials by a simple and efficient template carbonization method, which are further implemented in the field of supercapacitors. PTFE-1:1-700, PVC-1:1-700 and PVDF-1:1-700 samples can be achieved by designating the mass ratio of PTFE (PVC or PVDF) and Mg citrate as 1:1 at the carbonization temperature of 700℃. In terms of XRD, Raman and FESEM results, it is clearly seen that the as-produced carbon materials take on typically nanoporous structures. According to N2 adsorption-desorption measurements, the order of BET surface area and total pore volume is as follows:PVDF-1:1-700> PVC-1:1-700> PTFE-1:1-700. Notably, the PVDF-1:1-700 sample indicates the largest BET surface area of 668.3 m2 g-1 and total pore volume of 0.60 cm3 g-1. The corresponding electrochemical measurements have been conducted in a three-electrode system, using 6 mol L-1 KOH as electrolyte. It is revealed that the PTFE-1:1-700, PVC-1:1-700 and PVDF-1:1-700 samples possess the specific capacitances of 33.5 F g-1,31.7 F g-1 and 89.6 F g-1 at a current density of 1 Ag-1. The template carbonization method herein has the green, environmental and scalable advantages, which are expected to dispose other kinds of plastics wastes.4. We demonstrate an efficient template carbonization method to produce nitrogen-containing nanoporous carbon materials at elevated temperatures, using ethylenediamine tetraacetate magnesium serving as carbon/nitrogen precursor, and Mg(OH)2 as hard template, and investigated the utilization in supercapacitors. It reveals that the addition of Mg(OH)2 can greatly adjust the porous structures and thereby improve the electrochemical performance of the carbon materials. As a result, the carbon-1:3-800 sample prepared by heating the mixture of ethylenediamine tetraacetate magnesium and Mg(OH)2 (the mass ratio of 1:3) at 800℃ exhibits large BET surface area 766.8 m2 g-1, high pore volume of 1.16 cm3 g-1, as well as high nitrogen content of 9.48%. Its specific capacitance can reach up to 367.5 F g-1 at a current density of 1 A g-1, and high rate capability of 47.3% also appears at high current density of 40 A g, when electrochemical measurement is carried out in a three-electrode system, using 6 mol L-1 KOH aqueous solution as electrolyte. It should be pointed out that the ethylenediamine tetraacetate magnesium commonly produced in the analysis process is always discarded as solid waste. Therefore, the present template carbonization method has opened a simple but efficient avenue to convert this kind of solid waste into nanoporous carbon materials, acting as superior supercapacitor electrode materials.