Research On CNT/C Composite Spheres Prepared By Extrusion-Spheronization And Their Adsorption Properties

Carbon nanotubes?CNTs?are considered as promising adsorbents in many fields including water treatment,medical hemoperfusion and purification of traditional Chinese medicines for their unique pore structure and high adsorption capacity.However,as-produced CNTs in industry are mainly powdery aggregates,which limits their application as the adsorbents.Therefore,it is necessary to convert the powdery CNTs into bulk materials,especially in spherical shape.In this research,we proposed a scalable extrusion–spheronization method followed by carbonization to fabricate CNT/C composite spheres.A Freeze-casting and activation post-treatment by K₂CO₃ were adopted separately to further tailor the pore structure of the composite spheres.Composite spheres with hierarchical pore structure were synthesized in this approach and exhibited extraordinary adsorption properties for middle molecular toxins with different sizes.First,CNT/C composite spheres were prepared by extrusion-spheronization with the microcrystalline cellulose as the excipients and subsequent carbonization process.The effects of excipient ratio,amount of water and spheronization speed were investigated.Spheres with a homogeneous diameter of about 1.2 mm and a breakage force of 5.14 N were finally gained in this work.The pore structure of the composite spheres were modified by the freeze-casting method.Macropores with the diameter distribution from 100 nm to 1000 nm were obtained in the composite spheres by placing the half-wet spheres in liquid nitrogen and then making them lyophilized afterwards.The microporous structure of the composite spheres could be strengthened by post-treatment by K₂CO₃ activation.The effect of K₂CO₃ ratio and activation temperature were studied systematically.The adsorption properties of the CNT/C composite spheres were evaluated by examining their adsorption capacities for VB₁₂2 and lysozyme in 2 h.The composite spheres with modified pore structures exhibited higher adsorption capacities and significantly higher adsorption rates for both VB₁₂ and lysozyme compared to commercial sorbents of AC beads and MR beads used in hemoperfusion.This advantage in adsorbing middle molecular toxins of the composite spheres was attributed not only to the intrinsic adsorption ability of CNTs,but also to the hierarchical porous structure tailored by freeze-casting,particularly to the macropores which acted as diffusion throughways to promote the utilization of the CNTs in the inner zone of the composite spheres.The extraction of ginsenoside by the CNT/C composite spheres was explored in this work.With a higher adsorption capacity and a better elution efficiency,the extraction rate of the composite spheres was about 2.5 times that of the commonly used adsorbents,indicating their application prospect in the purification of traditional Chinese medicine.