Preparation Of Micro-Mesoporous Materials From Hollow Carbon Spheres Filled With Carbon Microspheres And Its Adsorption Performance For Toluene

Volatile organic compounds（VOCs）are important precursors for the formation of fine particulate matter(PM_2.5)and ozone（O₃）,which further lead to air pollution problems such as haze,greenhouse effect,photochemical pollution and ozone layer depletion,as well as pose a threat to human health.Adsorption technology is considered as an economic and efficient treatment strategy due to the advantages of high removal efficiency and reuse of adsorbents,and is currently recognized as one of the most widely used technologies for treating low concentration VOCs,therefore the research on adsorption technology and adsorbents has a broad prospect.Hollow carbon spheres（HCS）are a novel adsorbent applied in VOCs adsorption due to its porous hollow structure and high pore volume,but the drawback of few microporous structures in hollow carbon spheres hinders its practical application.Therefore,in this study,we designed and synthesized composites filled with microporous carbon microspheres in hollow carbon spheres,which can achieve an increase in the microporosity of the adsorbent and thus enhance the adsorption performance of hollow carbon sphere adsorbents.A series of micro-mesoporous carbon material adsorbents C_X@HCS were prepared by using ultrasonic-hydrothermal method by filling hollow carbon spheres with glucose carbon microspheres,and the effects of glucose solution concentration,activation temperature,time and activation gas flow rate on the structure and surface chemistry of the adsorbents were investigated by using BET,SEM and FTIR techniques.The results showed that filling the hollow carbon spheres with porous carbon microspheres could significantly enhance the microporous structure of the adsorbent,and the porous carbon C_0.1@HCS prepared under the conditions of glucose solution concentration of 0.1mol/L,activation temperature of 950°C,activation time of 120min and CO₂gas flow rate of60m L/min possessed the best specific surface area（1945m²/g）and pore volume（1.627cm³/g）,and the microporous specific surface area was increased from 281m²/g to1134m²/g.The dynamic adsorption capacity of toluene was 813mg/g at 25°C and the initial concentration of toluene was 1000 ppm,and the adsorption efficiency was maintained above 90%after 8 regeneration experiments,which has good regeneration performance.To further enhance the toluene adsorption capacity,nitrogen-doped micro mesoporous carbon materials were prepared by impregnation method using urea as the nitrogen source,and the effect of urea impregnation ratio on the pore structure and surface properties of the adsorbent was investigated.It was found that urea would release gas such as NH₃at high temperature decomposition to play a synergistic activation role with CO₂and promote the development of the pore structure of the material,while the introduction of nitrogen-containing groups N-5 and N-6 enhances the chemisorption of the adsorbent,thus improving the adsorption performance of the adsorbent.When the mass ratio of urea impregnation was 1:1,C_0.1@HCS-11N had the best pore structure and adsorption capacity,with specific surface area and pore volume of 2056m²/g and 1.663cm³/g,respectively,and the toluene adsorption capacity was enhanced to 896mg/g.To obtain the process and mechanism of toluene adsorption by C_X@HCS adsorbent and nitrogen-doped modified adsorbent,adsorption kinetics study were conducted.The results showed that the adsorption behavior of C_X@HCS and nitrogen-doped C_X@HCS on toluene was mainly due to their pore channel effects,and the adsorption process could be described as three stages:adsorbent surface diffusion,intraparticle diffusion,and adsorption equilibrium,in which the intraparticle diffusion stage was the key stage affecting the adsorption rate.