{"content":[{"text":"in alkaline media.[9], [10] Recently, we showed that nanoscale electroless Ir plating is possible as long as the choice of \n metal precursor, complexing agent and reducing agent is carefully considered.[7] In this case, either citrate or ethylene \n diamine (EDA) proved to be suitable stabilizers, when NaBH4 is used as reducer. Figure 1a shows SEM images of Ir- \n coated ion-track etched polycarbonate membranes, prepared using a citrate stabilized plating bath. The deposit is \n remarkably homogenous, consisting of crystallites multiple nanometers in size. XPS and XRD measurements on a \n similar deposit have confirmed that metallic Ir is deposited predominantly.[7] However, small amounts of surface oxides \n are to be expected, due to the comparatively high oxygen affinity of Ir. Interestingly, the presence of both Ir and IrOx \n has been linked to an increased catalytic activity of the material.[4]","bbox":{"left":0.05549,"top":0.141105,"width":0.8567940000000001,"height":0.130261}},{"text":"2.2. Application: Degradation of Methyl Orange \n The Ir coated membrane can then be used as a catalyst e.g. for various hydrogenation reactions such as the reduction \n of 4-NP or the degradation of organic dyes, such as methyl orange or rhodamine B. In our case, we assessed the activity \n of the deposit by utilizing it in the reduction of 4-NP[7] as well as the degradation of methyl orange (shown here). The \n coated membranes can be used in a flow-through configuration, in which the reaction solution is pumped through the \n membrane, as well as in a more conventional way, by simply submerging the catalyst in the solution under constant \n agitation. In the case of methyl orange, the reaction can be easily followed by UV-Vis spectroscopy, due to the strong \n and characteristic absorbance of the dye. Assuming Lambert-Beer’s law, the reduction in absorbance before and after \n reaction on the catalyst is proportional to the decrease in educt concentration. Figures 1b and c show schematics of the \n experimental setup as well as UV-Vis spectra before, during and after the reaction, for (b) the flow-catalysis and (c) the \n conventional method. Using the membrane as a flow-catalyst enables a remarkable conversion even at a comparatively \n high flow rate of 5 ml min-1. After one pass of the membrane, about 93% of the methyl orange has been converted. With \n the conventional method, a similar conversion requires much more time (Fig. 1c). This can be ascribed to the limited \n accessibility of the 400 nm diameter pores by diffusion. It can be concluded, that in order to unlock the full potential of \n the catalyst material, it is necessary to mechanically push the solution through the membrane. From the data shown in \n Fig. 1b, the apparent rate constant kapp of the reaction can be determined, which amounts to 0.059 min-1.[7]","bbox":{"left":0.05549,"top":0.284698,"width":0.8568,"height":0.25761500000000004}},{"text":"Figure 1: a) SEM images of Ir-coated ion-track etched polycarbonate membranes; b) characteristic absorbance of methyl orange \n after treatment with the catalyst for different times in stirred solution; c) absorbance of methyl orange/NaBH4 solution before and after \n passing the membrane in a flow reactor setup at 5 ml min-1 (adapted from [8]).","bbox":{"left":0.049804,"top":0.765823,"width":0.881241,"height":0.04571599999999998}},{"text":"ICNNFC 109-2","bbox":{"left":0.443807,"top":0.939079,"width":0.11218899999999993,"height":0.018595000000000028}}],"images_bbox":[],"images_bbox_not_text_overlap":[]}