## 3 Nanocomposite Catalysts
### Cold Atmospheric Pressure Plasmas Ex Situ Approach  
Although the new heterogeneous catalysts turned out to be very efficient, the developed in situ approach requires more investigations on different functional groups and their ability to fabricate NPs of defined granulometric properties. Hence, the ex situ approach, as a more convenient one, was also tested. The ex situ approach allows for the fabrication of NPs outside the polymeric matrix, by applying methods assuring comprehensive control over the optical and granulometric properties thereof. As such, the cold atmospheric pressure plasmas (CAPPs) were applied by our research group. It is well known that, due to their unique properties, the CAPP-based technologies are widely applied in the industrial and in the know-how sectors. The properties of CAPP-based technologies are associated with the fact that CAPPs are plenteous sources of reactive oxygen species (ROS) and reactive nitrogen species (RNS) [57]. Due to the possibility of controlling the concentration of these ROS and RNS, as well as CAPP operating parameters by constructing and tailoring dedicated for that purpose reaction-discharges systems, it is possible to control the CAPP-liquid interactions of the generated CAPP. For that reason, the CAPP-based technologies find applications in nanotechnology [58], food industry [59], agriculture [60], and biomedicine [61]. A few years ago, a significant increase in the interest was observed for using CAPP-based technologies in nanotechnology due to the fact that the ROS and RNS of defined red-ox properties, generated during the CAPP operation, can be used for the synthesis of nanomaterials [58; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72]. Bearing in mind a wide range of possibilities for nanomaterials' applications and simplicity of their CAPP-based synthesis, recently our research group developed an innovative and efficient CAPP-based method for the continuous synthesis of nanomaterials, including AuNPs [73; 74; 75; 76], AgNPs [77; 78; 79; 80; 81], Au-Ag@NPs [82], and PtNPs [83]. In contrast to the CAPP-based methods suitable for stationary metallic nanostructures' synthesis that were developed and applied by other research groups [62; 63; 64; 65; 67; 68; 69; 70; 71; 72], in the proposed method, the metallic nanostructures are being continuously produced in a flow mode (Figure 8). This highly efficient production of metallic nanostructures is associated with the character of the developed reaction-discharge system, employing as a CAPP source either the direct current atmospheric pressure glow discharge (dc-APGD) [73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83] or pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD) [78; 84]. In our studies, the dc-APGD was generated between either the pin-type tungsten electrode [75; 76; 77; 78; 79; 80; 81; 83] or Ar nozzle [73; 74; 82] and the surface of flowing liquid electrode, being a NPs' precursor solution introduced to the designed reaction-discharge systems. On the other hand, the pm-rf-APGD was generated between the pin-type tungsten electrode and the surface of the flowing liquid electrode [78; 84]. Since dc-APGD operation led to emit the positive ions or electrons, depending on the polarity of applied electrodes [68], the surface of resulted nanostructures is charged [75], which might exclude the addition of capping agents to the NPs precursor solution [75]. In the case of pm-rf-APGD, the polarity of the electrodes is continuously changed, leading to the alternating production of electrons and positive ions [78]. Typically, the stabilizers are added to this solution in order to preclude the aggregation, agglomeration, and sedimentation of the further obtained nanostructures [74].