Abstract
This study provides a critical analysis on the use of diffuse reflectance spectroscopy and Tauc equation to estimate the optical energy bandgap of semiconductor/carbon composites and amorphous porous carbons. Determination of the energy gap from diffuse reflectance is strongly dependent on the analyst’s experience, due to uncertainties related to establish the adequate range to fit the experimental data to Tauc equation, and to identify the type of electronic transitions. Furthermore, its application to strong light absorbing or multiphase materials with several absorbing components is not straightforward, due to the appearance of various curvatures/linear ranges. For such, reporting the linear fitting range used in the diffuse reflectance spectra is recommended to avoid miscalculation of a gap value. For materials absorbing in the visible range (e.g., displaced onset in Tauc representation), a double-linear fitting must be used in the extrapolation of [F(R∞)hv]1/n to avoid underestimation of Eg values. For amorphous porous carbons, different optical responses were obtained from the diffuse reflectance spectra recorded upon dilution with a non-absorbing matrix. The application of Tauc equation (indirect transitions) to data rendered bandgap values ranging between 1.5–2.3 eV for fourteen carbons, which are in agreement with those reported for these materials.
Highlights
The use of carbon materials in heterogeneous photocatalysis, either in their role of additives in semiconductor/carbon mixtures or as photocatalysts themselves, has become a largely investigated topic over recent decades [1,2,3]
While the origin of the optical features of such unconventional semiconductors still remains unclear, researchers have soon adopted the application of diffuse reflectance spectroscopy and Tauc method to calculate energy bandgap values
Its extension to semiconductor/carbon composites and amorphous carbon materials suffers from similar limitations, aggravated by the fact that these materials are strong light absorbing and often multiphase ones
Summary
The use of carbon materials in heterogeneous photocatalysis, either in their role of additives in semiconductor/carbon mixtures or as photocatalysts themselves, has become a largely investigated topic over recent decades [1,2,3]. Motivated by the low efficiency of most semiconductors under solar light (due to low absorption under visible light, high recombination rates, or photocorrosion issues), the incorporation of a variety of carbons as additives to TiO2 and other semiconductors has appeared as an effective and simple method to enhance the performance of resulting photocatalyst [1,4,5,6]. Carbon materials would act as effective photosensitizers due to the high density of C]C double bonds [7,8,9], which with an adequate functionalization would trigger the harvesting of light in the visible range [10,11,12]. Carbon nanotubes and nanoporous carbons display self-photoactivity, and are capable of generating reactive oxygen species upon illumination in aqueous suspensions [15,16,17]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Journal of Photochemistry and Photobiology A: Chemistry
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
