ELECTROSPUN NANOFIBERS FOR CATALYSTS

Heterogeneous catalysis is of vital importance to the world’s economy and the sustainable development of our society (Ertl, 2008; Schauermann et al., 2013). It has been estimated that 90% of all chemical processes take place on the surface of heterogeneous catalysts. This contributes approximately 35% of global GDP (Fechete et al., 2012). Nanostructured materials are attractive candidates as heterogeneous catalysts (Kung and Kung, 2004), and include nanoparticles, nanowires, nanotubes, and nanofifibers (Panthi et al., 2015b). Indeed, nanoparticles (e.g., platinum (Pt), palladium (Pd), and rhodium (Rh) supported on substrate surfaces (e.g., carbon and oxide) form the basis for the most widely used industrial catalysts (Norskov et al., 2008; Wegener et al., 2011). Recently, electrospinning has received great attention in catalysis research because of its versatility in the production of continuous one-dimensional nanofifibers (Rezaee et al., 2017). Furthermore, electrospinning offers an easy way to construct three-dimensional hierarchically porous nanostructures made of nanofifibers with diameters in the nanometer range (i.e., 1e1000 nm) (Lu and Xia, 2013a). Fibers on the nanoscale exhibit characteristically different physical and chemical properties that are not shown on a macro scale. For example, nanofifibers have a much larger specifific surface area than traditional textile fifibers, which leads to increased activity in catalytic applications because more active surface is available and accessible by reactants in a chemical process (Lu et al., 2015). Moreover, electrospinning is capable of generating nanofifibers from a wide range of organic and inorganic materials (e.g., polymers and oxides) to meet the needs of all kinds of applications.

The simplicity of recovery and reuse of catalysts based on electrospun nanofifibers makes them economically appealing and environmentally friendly (Astruc et al., 2005). As such, catalysts made of electrospun nanofifibers are characterized as a type of “green” catalysts (Shao et al., 2012b; Ren et al., 2012). For instance, recyclable biocatalysts (enzymes immobilized on nanofifibers) have been successfully employed in textile treatment, food processing, bioremediation, and protein digestion among other things (Li et al., 2012). When a reaction is carried out in harsh conditions, electrospun nanofifibers can provide a suitable microenvironment to minimize enzyme deactivation (Ge et al., 2009). In addition, the immobilized enzymes have a longer lifetime as compared to free enzymes because their chemical structure and conformation are stabilized by the supporting nanofifibers. Using traditional metal-based catalysts, metals leaching into the environment are a huge concern in many applications, especially in the large-scale production of pharmaceuticals (Shao et al., 2012a). Attaching metal catalysts to nanofifibers has proven to reduce the amount of leaching to an insignifificant level, resulting in less product contamination and environmental pollution. Further, recovering the expensive metal catalysts on nanofifibers can be as simple as fifiltering the reaction solution in most cases, or using a magnet for the separation of catalysts in other cases (Shao et al., 2012b; Ghasemi et al., 2015). Recovering and reusing these nanofifibrous catalysts have been shown to have little to no effect on their catalytic performance.

Nanofifibers for catalysts are one of the most important topics in electrospinning applications, and many works have been published in this fifield in recent years (Wang et al., 2009; Panthi et al., 2015a,b; Hao et al., 2015; Ma et al., 2016; Siqueira et al., 2015; Pei and Leung, 2015; Oktay et al., 2015; Moreno et al., 2015). However, a dedicated review of the recent development, characterization, and design of heterogeneous catalysts based on nanofifibers is still not available. This chapter does not attempt to give a comprehensive overview of the subject of nanofifibers for catalysts, but concentrates on heterogeneous catalysts based on electrospun nanofifibers with signifificant importance. Using this approach, the chapter begins with a brief introduction to methods for the preparation of nanofifibrous catalysts and gives some examples of directly utilizing electrospun nanofifibers as active catalysts. It further focuses on discussing catalysts supported on nanofifibers and illustrating recent efforts toward the development and design of nanofifibrous catalysts with greatly improved stability and activity. The chapter concludes with a personal perspective on the potential of nanofifibrous catalysts in various important applications.

Paper link：https://www.sciencedirect.com/book/9780323512701/electrospinning-nanofabrication-and-applications