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International audience 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 curva-tures/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 E g 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.

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible. ; This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (NanoMOFdeli), ERC-2016-COG 726380, Innovate UK (104384) and EPSRC IAA (IAA/RG85685). N.R. acknowledges the support of the Cambridge International Scholarship and the Trinity-Henry Barlow Scholarship (Honorary). O.K.F. and R.Q.S. acknowledge funding from the U.S. Department of Energy (DE-FG02-08ER15967). R.S.F. and D.B. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (SCoTMOF), ERC-2015-StG 677289. Sandia National Laboratories is a multimission laboratory managed and operated by National ...

Funding: European Research Council. Grant Number: ERC-2016-COG 726380 Innovate UK. Grant Number: 104384 EPSRC. Grant Number: IAA/RG85685 U.S. Department of Energy. Grant Number: DE-FG02-08ER15967 European Research Council. Grant Number: ERC-2015-StG 677289 Sandia National Laboratories National Nuclear Security Administration. Grant Number: DE-NA-0003525 U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Hydrogen and Fuel Cell Technologies Office SERB. Grant Number: CRG/2019/000906 Active Co. Research European Research Council. Grant Number: ERC-2017-StG 756489 European Commission. Grant Number: 872102 Spanish MICINN AEI/FEDER. Grant Number: RTI2018-099504-B-C21 University of Alicante. Grant Number: UATALENTO17-05 Spanish MINECO. Grant Number: SEV-2017-0706 Fund for Scientific Research Flanders. Grant Numbers: 12T3519N, 11D2220N EPSRC Cambridge. Grant Number: EP/L015978/1 National Research Foundation of Korea. Grant Numbers: NRF-2017M3A7B4042140, NRF-2017M3A7B4042235 Basic Energy Sciences. Grant Number: DE-SC0010596 Indonesian Endowment Fund. Grant Number: 202002220216006 European Union's Horizon 2020 Research and Innovation Program. Grant Number: 639233 ; Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area ...