Flexible route to fabricate excellent adsorbents for vitamin B12 by specially designed oil-drop process

This work presented the preparation of an excellent adsorbent composed of carbon nanotubes (CNTs) and activated carbon (AC) with hierarchical porous structure by specially designed oil-drop process. In this process, CNTs were pre-dispersed in the ethanol diluted phenolic formaldehyde resin and subsequently, the uniform suspension was injected dropwise into the stratified liquids. These liquids were composed of paraffin, polydimethyl siloxane and poly(ethylene glycol) (PEG)-6000 aqueous solution with different densities. After being semi-cured in the three-layered liquids at 70 degrees C, the spheres were carbonised at 600 degrees C and further activated at 800 degrees C with steam. Scanning electron microscope observations indicated that compared with those prepared by two-layered oil bath in the authors' previous work, the CNTs/phenolic resin spheres acquired by the modified oil-drop method would absorb PEG-6000 instead of polydimethyl siloxane and hence no residue of silica spheres produced in the final CNTs/AC spheres. Meanwhile, pore structure analyses indicated that the average diameter of the pores in the CNTs/AC spheres increased from 8.1 to 23.3 nm, which could be ascribed to the pore forming effect of PEG-6000. The adsorption capacity for vitamin B-12 by the porous CNTs/AC spheres reached 52.98 mg/g, which was much higher than commercial AC beads and macroporous resin spheres. This implied that the CNTs/AC spheres could have potential applications in hemoperfusion.