1362 . Corni et al /Journal of the European Ceramic Society 28(2008)1353-136 over Wang et al. 8 have deposited uniformly CNT coatings on glass plates with a silver or a ITo film layer and they observed that the emission properties of these CNT films were as good as those of the coatings produced by other methods such as screen printing. EPD seems thus to be a low cost and favourable method to produce CNT films for field emitters. Moreover composites 彐 consisting of ceramic nanoparticles and MWCNT have been produced recently by sequential EPD and by electrophoretic co-deposition The results presented in the literature demonstrate that EPD is a very versatile method to manipulate CNTs, thus the tech- nique is likely to be a focus of research efforts in the near future. EPD is a potentially powerful method to produce CNt Mag- 59.02Kx based devices, particularly because few alternative techniques exist to deposit and align CNTs on the required surfaces. CNT Fig 9. SEM image of the electrophoretically deposited MWCNT coating on the films may be suitable for a wide range of applications: sugges- surface of a bioactive glass foam, which was placed in front of the anode durin tions to date include field emission devices. 183, 184 biomedical EPD(MWCNT were negatively charged ). 186 scaffolds, 86 catalyst supports, structural composites and coat ings, large surface area electrodes for fuel cells, photochemical The most effective method for dispersion of carbon nan- solar cells. 85 electrodes for electronic devices(si supercapacitors otubes in a liquid medium is to add a surfactant and to apply and battery manufacturing), 81, 82 capacitors and gas sensors ultrasonication 7A different method based on the application of Similarly, EPD of CNTs can be seen as a very effective process an electric field to the suspension has been recently developed by to create CNT membranes and nanofilters which are commonly Zhang et al. 79, 180 They applied an AC electric field to suspen- made by slow and tedious filtration of CNT suspensions sions of carbon nanotubes and compared the results with those obtained without applying an electric field; they noticed that the 3.3.3. Nanorods, nanowires, nanotubes and nanosheets dispersion status of carbon nanotubes in liquid media was con- There has been an increasing interest in the use of elec siderably improved by applying an electric field. Moreover they trophoretic deposition techniques for the fabrication of a variety observed that the dispersion results were strongly dependent on of nano-architectures, including nanorods, nanowires, nan- the magnitude and frequency of the applied electric field. Du tubes and nanosheets. This section presents the most recent and Pan81, 182 deposited MWCNT thin films by EPD to pro- research carried out in this field. duce supercapacitors with high specific power density and a Zinc oxide nanorods, nanowires and nanotubes have been very small equivalent series resistance. These thin films could synthesized andelectrophoretically deposited by Routet al 9to be applied as coating layers over ordinary current collectors to produce sensors for hydrogen and ethanol. The sensing charac considerably enhance the electrode performance teristics of these nanostructures were examined before and after Junget al. 83, 184 deposited a thin film of horizontally aligned impregnating them with 1% Pt The nanowires exhibited excel SWCNTs from an aqueous mixture of CNT and detergent. The lent hydrogen sensing characteristics at temperatures below coating was naturally dried and then pressed on the surface to 150C especially when impregnated with Pt. The nanorods make it smooth. The films strongly adhered to the substrate showed a satisfactory dependence of sensitivity on hydrogen and showed good field emission properties. Recently, Hasobe et concentration. Moreover nanorods and nanowires impregnated al.8 deposited SWCNTs and protonated porphyrin on nanos- with Pt demonstrated high sensitivity for ethanol at temperatures tructured SnOz electrodes for applications in photochemical below 150C, with short recovery and response times. Kim et solar cells al.converted commercial titania nanoparticles to nanotubes As mentioned above, beyond the fabrication of uniform, pla- using an hydrothermal method and then deposited nar, CNT-based coatings, EPD can be applied to deposit CNTs nanotube film on a Si substrate by EPD Porous nanosheet-stacked NiCo2O4/Ni composite electrode strates and fibrous bodies or textiles. Boccaccini et al. 86 have have been produced by a novel electrophoretic deposition deposited MWCNTs onto highly porous bioactive glass scaf- calcination method. These electrode films present a crys- folds with the intention of imparting a monotopography to the talline structure and they are composed of regular hexagonal pore wall surfaces. Fig 9 shows the surface of MWCnT depo- NiCo2O4 nanosheets with an average diameter of 200 nm. sition on the 3D pore network of the Bioglass foam, which Moreover these films exhibited good electrocatalytic proper- was placed in front of the anode (MWCNT were negatively ties for water electrolysis. 93, 94 Sugimoto et al. 9> prepared charged). There has been also recent development on the fabri- stable colloids of ruthenic acid nanosheets in acetonitrile or cation by EPD of CNT reinforced HA coatings for biomedical N, N-dimethylformamide. The nanosheets were subsequently applications. 87 The fabrication of more complex patterns of deposited by EPD on gold, indium-tin oxide coated glass and CNT deposits can be realized by using masks or by designing indium-tin oxide coated polyethylene terephthalate)electrodes combinations of conductive and non-conductive surfaces. More- which presented high energy density at room temperature1362 I. Corni et al. / Journal of the European Ceramic Society 28 (2008) 1353–1367 Fig. 9. SEM image of the electrophoretically deposited MWCNT coating on the surface of a bioactive glass foam, which was placed in front of the anode during EPD (MWCNT were negatively charged).186 The most effective method for dispersion of carbon nan￾otubes in a liquid medium is to add a surfactant and to apply ultrasonication.7 A different method based on the application of an electric field to the suspension has been recently developed by Zhang et al.179,180 They applied an AC electric field to suspen￾sions of carbon nanotubes and compared the results with those obtained without applying an electric field; they noticed that the dispersion status of carbon nanotubes in liquid media was con￾siderably improved by applying an electric field. Moreover they observed that the dispersion results were strongly dependent on the magnitude and frequency of the applied electric field. Du and Pan181,182 deposited MWCNT thin films by EPD to pro￾duce supercapacitors with high specific power density and a very small equivalent series resistance. These thin films could be applied as coating layers over ordinary current collectors to considerably enhance the electrode performance. Jung et al.183,184 deposited a thin film of horizontally aligned SWCNTs from an aqueous mixture of CNT and detergent. The coating was naturally dried and then pressed on the surface to make it smooth. The films strongly adhered to the substrate and showed good field emission properties. Recently, Hasobe et al.185 deposited SWCNTs and protonated porphyrin on nanos￾tructured SnO2 electrodes for applications in photochemical solar cells. As mentioned above, beyond the fabrication of uniform, pla￾nar, CNT-based coatings, EPD can be applied to deposit CNTs onto complicated structures, including microwires, porous sub￾strates and fibrous bodies or textiles.7 Boccaccini et al.186 have deposited MWCNTs onto highly porous bioactive glass scaf￾folds with the intention of imparting a monotopography to the pore wall surfaces. Fig. 9 shows the surface of MWCNT depo￾sition on the 3D pore network of the Bioglass® foam, which was placed in front of the anode (MWCNT were negatively charged). There has been also recent development on the fabri￾cation by EPD of CNT reinforced HA coatings for biomedical applications.187 The fabrication of more complex patterns of CNT deposits can be realized by using masks or by designing combinations of conductive and non-conductive surfaces. More￾over Wang et al.188 have deposited uniformly CNT coatings on glass plates with a silver or a ITO film layer and they observed that the emission properties of these CNT films were as good as those of the coatings produced by other methods such as screen printing. EPD seems thus to be a low cost and favourable method to produce CNT films for field emitters. Moreover composites consisting of ceramic nanoparticles and MWCNT have been produced recently by sequential EPD and by electrophoretic co-deposition.189,190 The results presented in the literature demonstrate that EPD is a very versatile method to manipulate CNTs, thus the tech￾nique is likely to be a focus of research efforts in the near future. EPD is a potentially powerful method to produce CNT￾based devices, particularly because few alternative techniques exist to deposit and align CNTs on the required surfaces. CNT films may be suitable for a wide range of applications; sugges￾tions to date include field emission devices,183,184 biomedical scaffolds,186 catalyst supports, structural composites and coat￾ings, large surface area electrodes for fuel cells, photochemical solar cells,185 electrodes for electronic devices (supercapacitors and battery manufacturing),181,182 capacitors and gas sensors. Similarly, EPD of CNTs can be seen as a very effective process to create CNT membranes and nanofilters which are commonly made by slow and tedious filtration of CNT suspensions. 3.3.3. Nanorods, nanowires, nanotubes and nanosheets There has been an increasing interest in the use of elec￾trophoretic deposition techniques for the fabrication of a variety of nano-architectures, including nanorods, nanowires, nan￾otubes and nanosheets. This section presents the most recent research carried out in this field. Zinc oxide nanorods, nanowires and nanotubes have been synthesized and electrophoretically deposited by Rout et al.191 to produce sensors for hydrogen and ethanol. The sensing charac￾teristics of these nanostructures were examined before and after impregnating them with 1% Pt. The nanowires exhibited excel￾lent hydrogen sensing characteristics at temperatures below 150 ◦C especially when impregnated with Pt. The nanorods showed a satisfactory dependence of sensitivity on hydrogen concentration. Moreover nanorods and nanowires impregnated with Pt demonstrated high sensitivity for ethanol at temperatures below 150 ◦C, with short recovery and response times. Kim et al.192 converted commercial titania nanoparticles to nanotubes using an hydrothermal method and then deposited a titanate nanotube film on a Si substrate by EPD. Porous nanosheet-stacked NiCo2O4/Ni composite electrodes have been produced by a novel electrophoretic deposition calcination method. These electrode films present a crys￾talline structure and they are composed of regular hexagonal NiCo2O4 nanosheets with an average diameter of 200 nm. Moreover these films exhibited good electrocatalytic proper￾ties for water electrolysis.193,194 Sugimoto et al.195 prepared stable colloids of ruthenic acid nanosheets in acetonitrile or N,N-dimethylformamide. The nanosheets were subsequently deposited by EPD on gold, indium-tin oxide coated glass and indium-tin oxide coated poly(ethylene terephthalate) electrodes which presented high energy density at room temperature