Abstract
Even though, owing to the complexity of nanoporous carbons' structure and chemistry, the origin of their photoactivity is not yet fully understood, the recent works addressed here clearly show the ability of these materials to absorb light and convert the photogenerated charge carriers into chemical reactions. In many aspects, nanoporous carbons are similar to graphene; their pores are built of distorted graphene layers and defects that arise from their amorphicity and reactivity. As in graphene, the photoactivity of nanoporous carbons is linked to their semiconducting, optical, and electronic properties, defined by the composition and structural defects in the distorted graphene layers that facilitate the exciton splitting and charge separation, minimizing surface recombination. The tight confinement in the nanopores is critical to avoid surface charge recombination and to obtain high photochemical quantum yields. The results obtained so far, although the field is still in its infancy, leave no doubts on the possibilities of applying photochemistry in the confined space of carbon pores in various strategic disciplines such as degradation of pollutants, solar water splitting, or CO2 mitigation. Perhaps the future of photovoltaics and smart‐self‐cleaning or photocorrosion coatings is in exploring the use of nanoporous carbons.
Highlights
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In many photoactivity studies of nanoporous carbon materials reported in this review, an inspiration was in their semiconducting nature and in similarity to graphene, whose distorted and full of defects units are, the building blocks of their pore walls
Their unique and important aspect is a high porosity for which extent only metal organic framework (MOF) of covalent organic framework (COF) can be considered as being competitive
Summary
Amorphous carbons can be considered as semiconducting materials, and some theoretical attempts have been published to explain their optical properties, there is still some. Theye and Paret[38] discussed the applicability of this method to hydrogenated amorphous carbon films, inferring that the Tauc gap must be considered as a phenomenological parameter to be used to compare different samples Another method recently used to estimate the position of the energy bandgap and a type of charge carries in nanoporous carbons is based on impedance spectroscopy measurements and the Mott–Schottky approach.[56] The studies on S-, N-, and O-containing nanoporous carbons placed the bandgap between 1.4 and 2.9 eV.[57,58,59] The positions of CB and VB were indicated depending on the microstructure and chemistry of the carbon materials (Figure 5). It should be mentioned that the nature of this behavior remains unclear, since the validity of the Mott–Schottky approach and the optimal frequency region for nanoporous carbons—with large double-layer capacitances—is under debate
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