Nanocarbon morphology

In general, the various synthesis strategies for nanocarbon hybrids can be categorized as ex situ and in situ techniques [3]. The ex situ ( building block ) approach involves the separate synthesis of the two components prior to their hybridization. One can rely on a plethora of scientific work to ensure good control of the component s dimensions (i.e. size, number of layers), morphology (i.e. spherical nanoparticles, nanowires) and functionalization. The components are then hybridized through covalent, noncovalent or electrostatic interactions. In contrast, the in situ approach is a one-step process that involves the synthesis of one of the components in the pres-... 

The greatest advantage of in situ methods over ex situ processes is the benefit of using the nanocarbon as a substrate, template and heat sink for stabilizing metastable phases and small particle sizes and creating hybrids with unusual morphologies [232]. This enables the synthesis of new hybrid materials that may offer new properties and unknown potential for future research and application. 

It is thus evident that the characteristics of nanocarbons (conductivity, local structure, presence of defects and functional groups, morphology, etc.) are critical to determining the properties of the hybrid nanomaterial with the semiconductor. However, most of the literature studies put emphasis on the analysis of semiconductor characteristics, while often nanocarbons are only described in generic terms (CNT, for example). Yet, it is well known how the properties of nanocarbons can be considerably different from case to case (depending on details in preparation), even if the structure is formally the same (MWCNT, for example). 

Liu and Zeng [88] showed that [001]-oriented petal-like Ti02 mesocrystals could be grown onto MWCNTs in aqueous solution (Fig. 16.6(c)). These examples show how in the presence of CNTs unusual morphologies for Ti02 nanocrystals could be prepared, with clear relevance for their photocatalytic and/or photoanode activity due to both different crystallographic faces exposed and different type of interface with nanocarbons on which they are supported. 

The morphology and structure of porous nanocarbons are very sensitive to the synthesis method [3]. Figure 8.2, for example, demonstrates the typical morphology of porous nanocarbon films made up of connected carbon nanoparticle aggregates obtained by a solution synthesis method. This structure is made up of closely packed carbon nanoparticles and differs considerably from the flame synthesized carbonaceous films. 

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