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Graphitic carbon nitride (g-C 3 N 4) modified with bromine and iodine was synthesized by a novel two-stage technique that included hydrothermal pre-treatment of melamine and its calcination in a mixture with ammonium halide. Prepared photocatalysts were tested by a set of methods including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal gravimetric analysis (TGA), low temperature nitrogen adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CVA), impedance spectroscopy, and the Mott – Schottky method. All the photocatalysts were studied in the photocatalytic hydrogen production from triethanolamine (TEOA) under visible light irradiation (λ = 428 nm). The most active photocatalyst was prepared from a mixture of 50% NH 4 I and 50% melamine. Its catalytic activity (2120 μmol g−1 h−1) was 35 times higher than that of the catalyst synthesized by the simple calcination of melamine. The highest short-circuit current density of 2.7 mA/cm2 was obtained with a sample synthesized from the mixture of 80% NH 4 Br and 20% melamine. [Display omitted] • Halide-modified g-C 3 N 4 was prepared by a novel two-stage technique. • High catalytic activity was assigned to changes in S BET and electronic structure. • I-doped samples were more active in H 2 production than Br-doped ones. • The highest catalytic activity was 2120 μmol Н 2 g−1 h−1. • Br-doped samples demonstrated higher J sc than I-doped samples. [ABSTRACT FROM AUTHOR]