Synthesis of carbon nanotube on stainless steel microfibrous composite-Comparison of direct and indirect growth and its application in fixed bed m-cresol adsorption

Two types of novel carbon nanotube (CNT) integrated stainless steel microfibrous (SSMF) composites were prepared through a combined wet lay-up papermaking, sintering and thermal chemical vapor deposition (CVD) process. Preparation methods with (indirect growth) and without (direct growth) the pretreatment using Fe-Mo/Al2O3 catalysts were applied to grow CNTs on SSMF support (SSMF-CNT and SSMF-CCNT, respectively). The composites were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption-desorption, mercury porosimetry, X-ray photoelectron spectroscopy (XPS) and Raman spectra. Results show that CNTs are successfully synthesized onto the support by both methods. In SSMF-CNT, CNTs grow on the surface of stainless steel microfibers while in SSMF-CCNT, CNTs grow on the surface of microfibers as well as in the network structure. The textures of CNTs in two composites are also quite different. CNTs on SSMF-CNT show better degree of graphitization than CNTs on SSMF-CCNT. Finally, fixed bed adsorption experiments of m-cresol were carried out to compare the adsorption efficiency of fixed bed filled with individual CNT particles and structured fixed bed filled with both CNT particles and CNT-microfibrous composites. Results have shown that the structured fixed beds with CNT-microfibrous composite show a smaller m-cresol adsorption capacity but lower pressure drop and enhanced mass transfer efficiency compared with the individual CNT particle bed. Comparison between SSMF-CNT and SSMF-CCNT shows that SSMF-CNT shows a higher mass transfer efficiency and utilization efficiency than SSMF-CCNT due to different growth forms and texture properties, indicating that direct method is more suitable for the preparation of CNT-microfibrous composites for pollutant removal in waste water.