Facile Synthesis Of PAN Based Spherical Carbon With Hierarchically Macro-/microporous Structure And Its Application Exploration

Compared with conventional activated carbon,spherical carbon.materials with hierarchically porous structure have a series of advantages,such as uniform particle size and packing density,controllable pore size distribution,good sphericity,smooth surface,high mechanical strength,fast adsorption/desorption speed and good biological compatibility,which is expected to be wildly used in gas adsorption,catalysis,electrochemistry and other fields.However,the potential of hierarchically porous carbons is drastically limited by their high cost,intrinsic fragility and poor processability.In the present study,through a novel solvent-induced phase separation,we develop PAN based spherical carbon with hierarchically macro-/microporous structure?MMCBs?.The as-prepared MMCBs have spherical shape with millimeter size,which give the carbons many value-added physical properties such as regular geometry,high mechanical properties,low dust,and good liquidity.On this basis,we explored the potentially environmental applications of CO₂ adsorption and NO catalytic oxidation.The main conclusions are summarized as follows:?1?Preparation of millimeter-sized hierarchically macro-/microporous carbon beads?MMCBs?.The synthesis starts with an injection of N,N-Dimethylformamide?DMF?solution containing a polymeric PAN precursor into water/ethanol coagulation bath.Then,we systematically investigated a variety of technological parameters,including the mass fraction,molecular mass of PAN,the dropping height,the composition and temperature of coagulation bath and so on,which have important influence on final physical structure and properties of MMCBs.It is found the non-solvent with the water/ethanol volume ratio of 70/30,selecting polyacrylonitrile withr mass of 85000,PAN concentration of 15%wt,drop height of 20 cm could achieve relatively uniform and slender macrovoid channel,final MMCBs show the highest mechanical strength of 43 N for the carbonized beads.In addition,in order to improve the mechanical property of MMCBs,the CNTs is dispersed into PAN solution,result shows that introduction of of CNTs is beneficial for the improvement of mechanical strength.?2?Research on CO₂ adsorption capacity of MMCBs.Considering the multiple advantages of the MMCBs,such as regular spherical geometry,large particle size,high mechanical strength,hierarchical porosity,high surface area and rich surface chemistry,these materials are potentially promising for high performance adsorbents,catalyst supports and catalysts.Herein,we firstly exemplified these MMCBs as CO₂ adsorbents at 273 and 298 K under atmospheric pressure.The CO₂ adsorption capacity is generally increased with the increase of activation time,and shows a highest value of 4.1 mmol g-1 for MMCB-3.Compared to other porous carbon materials,the BET surface areas of MMCBs prepared here are not high;however,their CO₂ uptakes are very impressive,possibly due to the synergistic contributions of narrow micropores centred at 0.6-0.7 nm and appropriate nitrogen doping.?3?NO oxidation performance on MMCBs.The as-prepared MMCBs possess unique hierarchical porosity in which high accessible micropores should efficiently oxidize NO to NO₂ while the hierarchical macropores could do favor to the mass diffusion and provide large pore volume as storehouses for urea loading.The adsorption and oxidation of NO has steady-state conversion of?80%.Furthermore,we exemplified one sample with 50%urea supported onto MMCBs-3 for NO selective catalytic reduction at 30?,the resulting NO conversion reaches its stationary state after 18h,being same with the results of NO oxidation over MMCBs-3 without urea loading.No NO₂ is detected at the outlet of the reactor in the initial 46 h,suggesting that the formed NO₂ are quickly reduced by supported urea.After the start of NO₂ emission,the total NO_x conversion gradually decreases to 15%after 120 h.Compared to the urea-supported activated carbons with effective loading of less than 10%,the present catalyst exhibits prominent advantages,including higher urea loading,higher steady-state NO_x conversion and longer conversion time.