Effect of biochar on the photocatalytic activity of nitrogen-doped titanium dioxide nanocomposite in the removal of aqueous organic pollutants under visible light illumination

Biochar, as a low-cost carbon obtained from barley straw, was used for the simple sol–gel synthesis of visible-light photocatalysts comprising N-doped TiO2/biochar nanocomposite (N-TiO2/C) and thermally treated N-TiO2/C. The nanocomposites were characterized by SEM, EDX, TEM, XRD, BET, FTIR, DRS UV-vis, and PL measurements. The doped TiO2 catalyzed the photodegradation of rhodamine B (RhB) in aqueous dispersion under visible-light illumination where the N-TiO2/C nanocomposite with a band-gap of 2.96 eV and large surface area (206 m^2 g^-1) demonstrated the highest photocatalytic activity and degrading 99% of RhB under visible light of a 40-Watt white LED lamp within 105 min. Photoluminescence (PL) spectroscopy experiments revealed the effective separation of charge carriers by the N-doped TiO2 materials. The presence of carbon enhances the photocatalytic activity of N-TiO2 material by decreasing the band gap, enhancing the visible light absorption, reducing the reflection of light, enhancing the adsorption of RhB and intermediates on the N-TiO2 surface, thus prolonging the separation electrons (e-) and valence band hole (h^+).