Because of the concave shape, the specific surface area increases and hence an increased photocatalytic activity is observed in porous materials compared to the nanoparticles. When the surface bends into a convex shape, it becomes a particle and when it bends into a concave shape, a pore is formed ( Wunderlich et al., 2006). Nanopores are differentiated from the nanoparticles by the bending of the surface ( Figure 4.2(b)). This is attributed to the fact that the structural diameter d of the pore or the particle becomes similar in size to the interaction distance between the atoms r ( Figure 4.2(a)). In terms of the band gap energy of titania nanoparticle and nano pores, it can be seen that when the diameter d of the particles or pores drops below a critical limit, the band gap energy increases for nanoparticles and decreases for nanopores. the bandgap or the surface energy) there is a change in the property depending on whether the structure consists of nanoparticles or nanopores. It can be seen from Figure 4.2 that for any physical property (e.g. Schematic illustration of the relationship between nanoparticles and nanopores. Further investigation and understanding of the characterization methods, as well as development of the testing methods and technology, not only boost the real application of porous materials but also drive the development of their preparation.įigure 4.2. The aim is to optimize the application of porous materials by controlling these elements. The pore characteristics determine the properties of these materials, and so the establishment of the relationship between the physical properties and the pore elements (like porosity, pore size and distribution, and pore wall thickness) is significant. Besides the porosity and pore size, the properties of porous materials also depend on the pore shape, pore strut/wall size and shape, surface roughness, and surface area. The establishment of the property modeling of porous materials highly depend on the material structures, and there are many challenges to measuring the structural characteristics due to the complex structures. The physical properties demonstrated by these materials are a reflection of the internal structure, so in order to improve them, their internal structures need to be understood correctly. Porous materials need to be characterized quantitatively with accuracy based on the prediction of the internal structural information. Chen, in Porous Materials, 2014 10.4 Concluding Remarks
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