Synthesis and characterization of a nanofiltration carbon membrane derived from phenol-formaldehyde resin

We have synthesized carbon membranes by carbonizing a phenol-formaldehyde (PF) resin in the absence of air, and evaluated their physical properties and separation performance. Carbonization of the PF resin at 500 degreesC for 30 min resulted in around 20% mass reduction and produced a membrane material which exhibited a moderate BET surface area of 29.6 m(2)/g, with the majority of its porous structure confined to pores <15 nm. As observed by visible Raman spectroscopy, the carbon membrane seems to consist of a crystalline structure imbedded in an amorphous carbon matrix. The average grain size was found to be around 9.18 nm, which matches closely the results of Raman studies. The crystal structure is based on a hexagonal structure with a = 7.8072 Angstrom and c = 7.066 Angstrom with the latter length matching that of graphite. The difference in the former parameter was attributed to a motif consisting of a seven-membered plane benzene ring (one ring surrounded by six others) due to internal strain which was determined to be 3.22% by an XRD technique. The molecular weight cut-off (MWCO) of this membrane was found to be about 7500 Daltons. The performance of the membrane was studied by separating hexavalent chromium ions from an aqueous chromic acid solution. The apparent and intrinsic rejection of Cr6+ ions was of the order of 70 and 90%, respectively, and was found to increase with an increase in applied pressure. (C) 2003 Elsevier Ltd. All rights reserved.