Janus Carbon Nanotube Membranes by Selective Surface Plasmoxidation

DOI: 10.1002/admi.201600445 can be prepared accordingly. As descripted in experimental the plasma etcher parameters and condition were preselected and the etcher time was optimized at this condition. The selected CNT membrane was subjected to plasmoxidation using the surface plasma etcher and monitored by Raman spectroscopy to determine the minimum etcher time Scanning Electron Microscope (SEM) images of the used CNT membrane shown in Figure S8, Supporting Information). The correlation plot versus etch time as shown in Figure 2 a is typical of the CNT surface oxidation level which is meaningful when refl ected to the Raman bands (D-band and G-band) intensity change ( I D / I G ). The D-band is assigned to the presence of disorder in the graphitic material while G-band corresponds to the tangential vibration of the carbon atoms. Moreover, due to the possibilities of carbon impurities that can generated in the sample during the plasmoxidation, the G/D-band intensity ratio can be used to assess the CNT wall defects or oxidation disorder levels. [ 22–24 ] Results we obtained shows that the intensity of D-band (≈1350 cm −1 ) reaches its maximum relative to that of G-band (≈1590 cm −1 ) after being treated with plasma for 15 min, and no obvious change was observed further. Figure 2 b shows the correlation plot of the intensity ratio of I D / I G versus plasma etch time. This indicated 15 min is suffi cient time for complete oxidization of the membrane surface under the CO 2 plasma beam. Obviously a Gaussian peak at 1620 cm −1 (D′-band) apperas to be separated during the plasma treatment of the CNT membrane surface. CNT is a conductive material with conjugated π electronic fl ow. The conductivity studies on six membranes by varying the time of plasma treatment were measured (Figure 2 c). The membrane before plasmoxidation is highly conductive compared to those are subjected to plasma treatment. This indicate the plasma surface oxidation causes disturbance to these conjugated structure due to covalent functionlaization by σ-bond formation, which disrupts the sp 2 hybridization of the carbon atoms, [ 25,26 ] that typically cause the decrease in the conductance of the carbon nanotubes. The conductivity of these membranes decreased with the time of exposure of plasma and, interestingly, after 15 min it regains. A noticable increase in conductivity was observed with 30 min of etch time (Figure S7, Supporting Information). Therefore 15 min of plasma etching is the best to generate the thickest layer of the defected carbon on the membrane surface. Prolonged exposure of the surface can cause decrease in surface layer thickness due to plasma beam evaporation or slightly removing defective layer on the membrane surface. Considering this optimization, all the surfaces used in this study was subjected to 15 min of surface treatment. The change in surface texture is included as Figure 2 d which clearly demonstrates the difference before and after of this treatment. Carbon nanotubes (CNTs) are of great interest in the areas of material science because they have shown promising applications in catalyst support, supercapacitors, sensors, and separation materials. [ 1–5 ] This is due to the 3D network structures and outstanding mechanical, thermal, and electrical properties of CNTs. Recently, the application of CNT membranes as water desalination and as an oil/water separation material has attracted extensive attention because of their low density, high porosity, and hydrophobic properties. [ 6–9 ] However, from practical aspect, its surface wetting property can be further improved to match the desired application. For example, by modifying the surface to increase the fl ux, one can now be applied to multiple applications. Janus materials possess dissimilar properties within the same object and gained tremendous attention since being reported due to their remarkable diversity in surface structural properties. There are potential applications in electronics, biomedicine, and biological science as sensors, optical probes, surfactants, and imaging agents. [ 10–18 ]