Tailoring the energy band gap and edges' potentials of g-C3N4/TiO2 composite photocatalysts for NOx removal

•Visible light active g-C3N4/TiO2 composites employed for NO oxidation.•Determination of CB edge of the composites by Mott-Schottky relation.•Tuning of composites' band gap and CV edge by variation of components' weight ratio.•Superior NO oxidation by 1:4 composite than pure g-C3N4 and TiO2 components.

Graphitic carbon nitride/titania (g-C3N4/TiO2) composite photocatalysts with different C3N4/TiO2 ratios were synthesised by a simple preparation route through annealing the mixtures of melamine and commercial TiO2 P25 powder at 550 °C for 3 h under Ar flow. The resulting composite photocatalysts were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical impedance spectroscopy. The photocatalytic activity of the composites was evaluated using NO as a target inorganic air pollutant. Variation of the initial weight ratio of melamine precursor/TiO2 (3:1, 1:1, 2:3, 1:3, 1:4 and 1:7) allowed tuning of the composites' band gap from 2.66 eV in pure g-C3N4 to 3.14 eV in pure P25 as revealed by UV-visible spectroscopy. The conduction band edges position determined by electrochemical measurements using Mott-Schottky relation varied from ∼−1.27 eV in pure g-C3N4 to ∼−0.67 eV in pure P25 (vs NHE, pH 7). Under visible light, the g-C3N4/TiO2 composite with initial ratio 1:4 exhibited superior photocatalytic activity in NO oxidation in comparison to the pure semiconductors g-C3N4 and TiO2. This finding was explained to be a result of a combination of the optical and electronic properties of the composites.

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