Abstract: Semiconductor photocatalytic technology is widely recognized as one of the most promising technologies to solve current energy and environmental crisis, due to its ability to make effective use of solar energy. In recent years, graphite carbon nitride (g-C₃N₄), a new type of non-metallic polymer semiconductor photocatalyst, has rapidly become the focus of intense research in the field of photocatalysis because of its suitable bandgap energy, unique structure, and excellent chemical stability. In order to improve its intrinsic shortages of small specific surface area, narrow visible light response range, high electron-hole pair recombination rate, and low photon quantum efficiency, a simple method was utilized to synthesize Br-doped g-C₃N₄ (CN-BrX, X=5, 10, 20, 30), where X is a percentage mole ratio of NH₄Br to melamine. Experimental results showed that Br atoms were doped into the g-C₃N₄ lattice by replacing the bonded N atoms in the form of C-N=C, while the derived material retained the original framework of g-C₃N₄. The interaction of Br element with the g-C₃N₄ skeleton not only broadened the visible-light response of g-C₃N₄ to 800 nm with an adjustable band gap, but also greatly promoted the separation efficiency of the photogenerated charge carrier and the surface area. The photocurrent intensity of bare CN and CN-BrX (X=5, 10, 20, 30) catalysts is calculated to be 1.5, 2.0, 3.1, 6.5, and 1.9 μA, respectively. And their specific surface area is measured to be 9.086, 9.326, 15.137, 13.397, and 6.932 m²/g. As a result, this Br-doped g-C₃N₄ gives significantly enhanced photocatalytic reduction of Cr(VI), achieving a twice enhancement over g-C₃N₄, with high stability during prolonged photocatalytic operation compared to bare g-C₃N₄ under visible light irradiation. Furthermore, an underlying photocatalytic reduction mechanism was proposed based on control experiments using radical scavengers.

Key words: Graphitic carbon nitride, Bromine, Doping, Cr(VI) reduction, Visible light