Isr 603 integrating sphere

The light absorption, transmittance, and reflection of the carbonized chitin and cellulose nanopapers were evaluated using an ultraviolet−visible−near-infrared (UV–vis–NIR) spectrometer (UV-3600i Plus, Shimadzu Corp., Kyoto, Japan) equipped with an ISR-603 integrating sphere (Shimadzu Corp., Kyoto, Japan). More than five samples were prepared and evaluated under each condition. Light absorption was calculated from the total light transmittance and reflection spectra. Solar absorption was calculated using Equation (1) [26 (link)] as follows: $$\overline{\alpha } \left(\%\right)=\frac{{{\displaystyle \int }}_{{\lambda }_{min}}^{{\lambda }_{max}}{I}_{solar}\left(\lambda \right)·{\alpha }_{solar}\left(\lambda \right)d\lambda }{{{\displaystyle \int }}_{{\lambda }_{min}}^{{\lambda }_{max}}{I}_{solar}\left(\lambda \right)d\lambda }\times 100,$$
where $\overline{\alpha }$ is the solar absorption (%); λ is the wavelength (nm); λ_min and λ_max are 300 and 2500 nm, respectively; I_solar(λ) is the solar spectral irradiance (AM1.5G) at λ; and α_solar(λ) is the light absorption (%) at λ. The optical bandgap values were also calculated from the UV–vis–NIR absorption spectra according to a previously reported method [15 (link)] and Tauc’s equation [27 (link)] (Equation (2)):
where α, hν, A, and E_g are the absorbance, photon energy, constant, and optical band gap, respectively. The optical bandgap was estimated by plotting (αhν)^1/n vs. photon energy (hν) and extrapolating the linear region of the curve to the X-axis (Figure S1). The parameter n was set to 2 for the indirect transition of the carbonized nanopapers because of their amorphous carbon structures.

UV–vis absorbance spectroscopy was measured on thin film and powder samples by using Shimadzu (Tokyo, Japan) UV-3600 Plus spectrophotometer equipped with ISR-603 integrating sphere at room temperature, respectively. BaSO₄ was used as a 100% reflectance reference. The thin film was detected in transmission mode, and the powder sample was detected in diffuse reflection mode.

Diffuse reflectance UV/VIS spectra were recorded on a Shimadzu UV-3600 Plus spectrophotometer equipped with an ISR-603 integrating sphere (Shimadzu, Kyoto, Japan). The spectra were recorded in the wavelength range of 200–800 nm at room temperature, using BaSO₄ as a standard and a diluent. The obtained spectra were processed using the UVProbe software (Shimadzu, Kyoto, Japan).